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41396 Publications

Tellurium hyperdoped Si

Zhou, S.

Tellurium is one of the deep-level impurities in Si, leading to states of 200-400 meV below the conduction band. Non-equilibrium methods allow for doping deep-level impurities in Si well above the solubility limit, referred as hyperdoping, that can result in exotic properties, such as extrinsic photo-absorption well below the Si bandgap [1]. In this talk, we will present an overview about Te hyperdoped Si. The hyperdoping is realized by ion implantation and pulsed laser melting. We will present the resulting optical, electrical properties and the perspective applications as infrared photodetectors. With increasing the Te concentration, the samples undergo an insulator to metal transition [2, 3]. Surprisingly, the electron concentration obtained in Te-hyperdoped Si is approaching 1021 cm-3 and does not show saturation [4]. It is even high than that of P or As doped Si and potentially meets the criteria of source/drain applications in future nanoelectronics. The infrared optical absorptance is found to increase with increasing dopant concentration [2]. We demonstrate the room-temperature operation of a mid-infrared photodetector based on Te-hyperdoped Si. The key parameters, such as the detectivity, the bandwidth and the rise/fall time, show competitiveness with the commercial products [5]. To understand the microscopic picture, we have performed Rutherford backscattering angular scans and first-principles calculations [4]. The Te-dimer complex sitting on adjacent Si lattice sites has the smallest formation energy and is thus the preferred configuration at high doping concentration. Those substitutional Te-dimers are effective donors, leading to the insulator-to-metal transition, the non-saturating carrier concentration as well as the sub-band photoresponse. Moreover, the Te-hyperdoped Si layers exhibit thermal stability up to 400 °C with a duration of at least 10 minutes [6]. Therefore, Te-hyperdoped Si presents a test-bed for electrical and optical applications utilizing deep-level impurities.
[1] J. M. Warrender, Laser hyperdoping silicon for enhanced infrared optoelectronic properties, Appl. Phys. Rev. 3, 031104 (2016).
[2] M. Wang, et al., Extended Infrared Photoresponse in Te-Hyperdoped Si at Room Temperature, Phys. Rev. Appl. 10, 024054 (2018).
[3] M. Wang, et al., Critical behavior of the insulator-to-metal transition in Te-hyperdoped Si, Phys. Rev. B 102, 085204 (2020).
[4] M. Wang, et al., Breaking the doping limit in silicon by deep impurities, Phys. Rev. Appl. 11, 054039 (2019).
[5] M. Wang, et al., Silicon-Based Intermediate-Band Infrared Photodetector Realized by Te Hyperdoping, Adv. Opt. Mater. 9, 2001546, (2020).
[6] M. Wang, et al., Thermal stability of Te-hyperdoped Si: Atomic-scale correlation of the structural, electrical, and optical properties, Phys. Rev. Mater. 3, 044606 (2019).

Related publications

  • Lecture (others)
    Colloquium at TU-Brandenburg, 07.02.2023, Cottbus, Germany

Permalink: https://www.hzdr.de/publications/Publ-38307
Publ.-Id: 38307


Defect engineering for oxide thin films by ion irradiation

Zhou, S.

Complex oxides host a multitude of novel phenomena in condensed matter physics, such as various forms of multiferroicity, colossal magnetoresistance, quantum magnetism, and superconductivity. This is largely due to the strong correlation between charge, spin, orbital, and lattice parameters. Specifically, tilting the delicate energy balance in lattice interactions and kinetics, achieved by temperature, strain, or chemical doping, can result in significant modifications in these materials. In this context, defect engineering by ion irradiation, which can introduce strain and electronic disorder, has emerged as a powerful technique to fine-tune complex phases of oxide thin films. The induced uniaxial strain, manifested as the elongation of the out-of-plane lattice spacing, is not limited to available substrates, the conventional and well-known strain engineering approach. In this contribution, we will introduce the tailoring of oxide thin films by ion irradiation, with examples including the modification of magnetic and magneto-transport properties of NiCo2O4 [1] and SrRuO3 [2,3], and ferroelectric properties of BiFeO3, KTN (KTaNbO3), and PbZrO3 [4-6]. The irradiated SrRuO3 films exhibit a pronounced topological Hall effect in a wide temperature range from 5 to 80 K, which can be attributed to the emergence of Dzyaloshinskii–Moriya interaction resulting from artificial inversion symmetry breaking associated with lattice defect engineering. In BiFeO3, we have obtained a super-tetragonal phase with the largest c/a ratio (~1.3) ever experimentally achieved [2]. For both KTN and PbZrO3, ion irradiation induces the formation of polar nanoregions [5, 7]. In PbZrO3, both the energy storage density and the breakdown strength are effectively increased. We show that ion irradiation is a very versatile pathway for tailoring oxide functionalities, analogous to ion-implantation doping for conventional semiconductors. It is worth noting that ion beam technology has been well-developed for microelectronics. Once the principle of concept is approved, the approach can be easily scaled up and integrated into the industry production line.
References:
[1] P. Pandey, et al., APL Materials 6 (2018) 066109.
[2] C. Wang, et al., ACS Appl. Mater. Interfaces 10 (2018) 27472.
[3] C. Wang, et al., Adv. Electron. Mater. 6 (2020) 2000184.
[4] C. Chen, et al., Nanoscale 11 (2019) 8110.
[5] Q. Yang, et al., Acta Mater. 221 (2021) 117376.
[6] Y. Luo, et al, Appl. Phys. Rev. 10 (2023) 011403.

Related publications

  • Invited lecture (Conferences)
    E-MRS 2023 Fall Meeting, 18.-21.09.2023, Warsaw, Poland
  • Lecture (Conference)
    21st International Conference on Radiation Effects in Insulators, 03.-08.09.2023, Fukuoka, Japan

Permalink: https://www.hzdr.de/publications/Publ-38306
Publ.-Id: 38306


Employee attrition prediction for imbalanced data using genetic algorithm-based parameter optimization of XGB Classifier

Das, S.

Attrition of employees is vital for any organization as it significantly influences productivity and hampers the long-term growth strategies of the organization. Since employee attrition leads to loss of skills and experiences any organization always try to find a way to retain their employees to reduce training and recruiting cost as well as to achieve their business goal smoothly. Machine learning approaches, which predict the possibility of attrition based on the employee attributes avoid the tedious, and biased manual prediction, and help the organization take preventive measures. This paper presents a framework for attrition prediction that emphasizes imbalance classification and the adoption of genetic algorithms to optimize the model. First, we have adopted different oversampling methods like Synthetic Minority Over-sampling Technique (SMOTE), Adaptive Synthetic (ADASYN), and Borderline Synthetic Minority Over-sampling Technique to balance our data set. We have used XGBoost classifiers for classification with the data that are obtained from different over-sampling techniques. As the XGBoost classifier has many hyperparameter a genetic algorithm is used to optimize our model where the accuracy is chosen as the fitness function. The comparative performance analysis of different over-sampling methods as well as hyper-parameter tuning (Amongst Genetic algorithm, GridSearchCV, and with the default value of different hyper-parameter) on the real dataset suggests that SMOTE for oversampling techniques and genetic algorithm for optimization attains improved performance.

Keywords: Machine learning; Imbalanced Classification; XGBoost; Genetic Algorithm

  • Contribution to proceedings
    2023 International Conference on Computer, Electrical & Communication Engineering (ICCECE), 20.-21.01.2023, Kolkata, India
    2023 International Conference on Computer, Electrical & Communication Engineering (ICCECE), Kolkata, India: IEEE, 978-1-6654-5251-9, 1-6
    DOI: 10.1109/ICCECE51049.2023.10085402
    Cited 2 times in Scopus

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Permalink: https://www.hzdr.de/publications/Publ-38305
Publ.-Id: 38305


Hyperspectral Unmixing by Convolutional Auto-encoder with Deep Subspace Clustering and Candidate Pixel Selection

Das, S.

The hyperspectral unmixing process is central to identifying the objects in a ground scene and quantifying their fractional abundance in each pixel. However, the high spatial resolution and the intrinsic interactions pose a challenge in object identification from hyperspectral images by non-linear unmixing. Typically the data points are generated due to non-linear, intimate mixing from non-linear subspaces. In this work, we propose a deep subspace clustering framework to identify the underlying non-linear subspaces in the initial stage and perform non-linear unmixing on the local clusters. To this aim, we proposed a deep auto-encoder network with additional total variation and spatial consistency regularization to determine the underlying non-linear mixing process from each cluster separately. Next, we identify the pixels which contain a dominant source from the latent representation obtained after the encoding stage. Subsequently, we carried out unmixing on local clusters using a linear algebraic based on the low-rank structure of the data. A detailed comparative analysis of the unmixing algorithms on three real hyperspectral images exhibits that our proposed algorithm achieves improved performance.

Keywords: Nonlinear Unmixing; Local Unmixing; Subspace Clustering; Auto-encoder; Hyperspectral Unmixing

  • Contribution to proceedings
    2023 14th International Conference on Computing Communication and Networking Technologies (ICCCNT), 06.-08.07.2023, Delhi, India
    2023 14th International Conference on Computing Communication and Networking Technologies (ICCCNT), Delhi: IEEE, 979-8-3503-3509-5
    DOI: 10.1109/ICCCNT56998.2023.10307721

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Permalink: https://www.hzdr.de/publications/Publ-38303
Publ.-Id: 38303


Application of Deep Learning for standardized delineation of healthy reference regions in O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET

Nikulin, P.; Lohmann, P.; Maus, J.; Lerche, C.; van den Hoff, J.

FET PET is a valuable tool for managing brain tumors. Quantitative image analysis is of obvious relevance in this context. One clinically useful image derived measure is the maximal tumor-to-background SUV ratio which can be used for therapy response assessment as well
as for discrimination between tumor recurrence and treatment-related changes. Computation of this ratio requires determination of the background SUV (bSUV) from a suitable ROI defined within healthy brain tissue. Currently, the standard procedure requires manual definition of the background ROI by an experienced human observer while adhering to a set of somewhat loosely defined rules. This process is time consuming and prone to inter- and intra-observer variability. The goal of this study, therefore, was development of a reliable automated method for bSUV derivation in FET PET of brain tumor patients.

Automated delineation of the healthy brain regions was performed with a residual 3D U-Net convolutional neural network (CNN). 561 FET PET scans were used for network training (N=448) and testing (N=113). In these data, reference brain regions were manually delineated by an experienced observer. The network was trained to reproduce the corresponding manual bSUVs by identifying a suitable brain ROI (rather than aiming at reproducing the manual ROI delineation). Performance of the trained network model was assessed in the test data using the fractional difference between automatically and manually derived bSUVs.

The trained U-Net was able to accurately reproduce the manually derived bSUVs in the test data: the fractional bSUV difference was (mean +/- SD)=(-0.9 +/- 5.3)% with a 95% confidence interval of [-10.9, 8.4]%.

The achieved concordance of the network's results with the given ground truth bSUV is in line with typical achievable levels of inter- and intra-observer concordance for this task. It thus might be considered for supervised routine use to reduce user workload and improve reproducibility.

Keywords: FET PET; CNN; Deep learning; Brain PET

Permalink: https://www.hzdr.de/publications/Publ-38302
Publ.-Id: 38302


Unmixing aware compression of hyperspectral image by rank aware orthogonal parallel factorization decomposition

Das, S.; Ghosal, S.

Efficient compression is pertinent for the convenient storage, transmission, and processing of modern high-resolution hyperspectral images (HSI). This paper proposes a new high-performance HSI compression method using library-based spectral unmixing and tensor decomposition. Unlike the existing approaches, our proposed work incorporates unmixing in the compression framework and achieves significantly higher compression performance with negligible loss. The proposed library-based unmixing method includes a new index for accurate endmember number estimation, followed by exact library pruning and a novel sparsity regularized formulation with norm-smoothing to compute the abundance maps. As the spectral library is available at the reconstruction (decoder) side also; compressing the abundance maps is as good as compressing the original HSI data. Since the abundance constraints used for the unmixing indicate the correlation of the abundance maps, compressing all abundance maps seems to cause redundant computation. A metric using the image smoothness and information measures is used here to identify the abundance map hardest to compress and the remaining part is left uncompressed. Subsequently, the work compresses the abundance map tensor using orthogonal Parallel Factorisation (PARAFAC) decomposition with optimal rank determination. The orthogonalization process ensures that the factors span independent subspaces and reduces redundancy, while the rank selection prevents noisy or insignificant components. Extensive experiments are carried out to demonstrate that the unmixing workflow leads to negligible loss due to accurate endmember number estimation, exact library pruning, and accurate physically meaningful sparse inversion. Comparative assessments of compression efficacy suggest that the proposed work corresponds to better compression performance and higher classification accuracy.

Keywords: Hyperspectral Image Processing; Data Compression; Hyperspectral Unmixing; Tensor Decomposition; Dictionary Learning; Rank Selection

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Permalink: https://www.hzdr.de/publications/Publ-38299
Publ.-Id: 38299


Certification of major and trace elements in a Leucomonzogranite, GMN-1, using the GeoPT proficiency testing certification protocol

Gowing, C. J. B.; Potts, P. J.; Webb, P. C.; Renno, A.; Cook, J. M.

In the past, many geochemical reference materials have been characterised either by the compilation of data published in the research literature, or by relatively informal ‘round-robin’ type of collaborative analysis programme. Neither approach complies with the most recent recommendations in ISO-REMCO Guide 35:2017. In order to develop a more rigorous approach that would lead to the full certification of such materials, Potts et al. (2019) published a certification protocol based on the well established GeoPT proficiency testing programme designed for laboratories that routinely analyse silicate rocks and related materials. In developing this certification protocol, a full assessment of compliance with the most recent version of ISO-REMCO Guide 35 was undertaken.
This protocol has now been applied to the certification of a leucomonzogranite (GMN-1), based on round 51 of the GeoPT programme that included participation by 112 laboratories from 43 countries. This exercise has led to the certification of 9 major and 39 trace elements.
In the development of this protocol, a number of issues remain that are not fully resolved in Guide 35. One is the potential clash between the requirements of proficiency testing in relation to procedures recommended for certification, perhaps the most important being the way in which well characterized consensus values derived from an assessment of data contributed to the proficiency testing programme effectively demonstrate the property of traceability.

Potts P J, Webb P C and Thompson M (2019). The GeoPT proficiency testing programme as a scheme for the certification of geological reference materials. Geostandards and Geoanalytical Research, 43, 409-418, doi: 10.1111/ggr.12261.

Keywords: Reference Material; Certification; GeoPT; Proficiency Testing

  • Poster
    Eurachem PT 2023, 25.-28.09.2023, Windsor, UK

Permalink: https://www.hzdr.de/publications/Publ-38297
Publ.-Id: 38297


Editorial: Complex Flow and Heat Transfer in Advanced Nuclear Energy Systems

Chen, D.; Ding, W.; Chen, L.

Nuclear energy is a crucial source of energy supply worldwide and is essential for achieving carbon neutrality. This is particularly true for advanced nuclear energy systems. In these systems, the complexity of flow and the efficiency and stability of heat transfer present ongoing challenges that necessitate further research efforts. In this specialized issue entitled "Complex Flow and Heat Transfer in Advanced Nuclear Energy Systems", a collection of related research works, including experimental research and numerical simulation works were gathered.Li Yong and colleagues conducted research focusing on condensation and acoustic characteristics of steam condensation. They experimentally studied the complex twophase flow regimes and acoustic characteristics of direct contact condensation when steam is injected into water.Mengmeng Liu, et al. carried out numerical simulations on heat transfer of supercritical pressure water in a helical tube. This process occurs in a supercritical steam generator, which may potentially be used for future high-temperature gas-cooled reactors.In the research carried out by Ji Wang, et al., an intriguing method was intruded to study

Keywords: Complex Flow; Heat Transfer; Advanced Nuclear Energy Systems

Permalink: https://www.hzdr.de/publications/Publ-38296
Publ.-Id: 38296


Curvilinear micromagnetism

Makarov, D.

Curvilinear magnetism is a framework, which helps understanding the impact of geometrical curvature on complex magnetic responses of curved 1D wires and 2D shells [1,2]. In this talk, we will address fundamentals of curvature-induced effects in magnetism and review current application scenarios. In particular, we will demonstrate that curvature allows tailoring fundamental anisotropic and chiral magnetic interactions and enables fundamentally new nonlocal chiral symmetry breaking effect [3], which is responsible for the coexistence and coupling of multiple magnetochiral properties within the same magnetic object [4]. We will discuss the application potential of geometrically curved magnetic thin films as mechanically reshapeable magnetic field sensors for automotive applications, memory, spin-wave filters, high-speed racetrack memory devices, magnetic soft robotics as well as on-skin interactive electronics.
[1] D. Makarov et al., Curvilinear micromagnetism: from fundamentals to applications (Springer, Zurich, 2022).
[2] D. Makarov et al., New dimension in magnetism and superconductivity: 3D and curvilinear nanoarchitectures. Adv. Mat. 34, 2101758 (2022).
[3] D. D. Sheka et al., Nonlocal chiral symmetry breaking in curvilinear magnetic shells. Comm. Phys. 3, 128 (2020).
[4] O. M. Volkov et al., Chirality coupling in topological magnetic textures with multiple magnetochiral parameters. Nat. Comm. 14, 1491 (2023).

Keywords: curvilinear magnetism; shapeable magnetoelectronics

Related publications

  • Invited lecture (Conferences)
    DPG Meeting of the Condensed Matter Section, 18.-22.03.2024, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-38294
Publ.-Id: 38294


Data publication: Revealing Non-equilibrium and Relaxation in Warm Dense Matter

Vorberger, J.; Preston, T. R.; Medvedev, N.; Böhme, M.; Moldabekov, Z.; Kraus, D.; Dornheim, T.

All data as needed to generate the figures in the manuscript.

Keywords: plasma; warm dense matter; x-ray scattering; non-equilibrium; dynamic structure; imaginary time correlation function; detailed balance

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Permalink: https://www.hzdr.de/publications/Publ-38292
Publ.-Id: 38292


DALI Control System Considerations

Zenker, K.; Justus, M.; Steinbrück, R.

The Dresden Advanced Light Infrastructure is a future infrastructure under consideration at the Helmholtz-Zentrum Dresden-Rossendorf. In the current conceptional design phase, we are surveying different control system options. To benefit as much as possible from community experiences with different control systems, in 2023 a survey was conducted and participants from accelerator and light source facilities world-wide were invited. The results of that survey are presented and conclusions for our center are drawn.

Keywords: ELBE; Control System; EPICS; TANGO

Related publications

  • Open Access Logo Poster
    ICALEPCS 2023, 09.-13.10.2023, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-38291
Publ.-Id: 38291


Data publication: Characterization of Magnetic and Mineralogical Properties of Slag Particles from WEEE Processing

Siddique, A.; Boelens, P.; Long, F.; Zhou, S.; Cnudde, V.; Leißner, T.

This dataset includes the modal mineralogy and the SQUID-VSM measurements. The latter were conducted at the HZDR.

Keywords: magnetic characterization; magnetic susceptibility classes; WEEE slag; vibrating-sample magnetometer (VSM)

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Permalink: https://www.hzdr.de/publications/Publ-38290
Publ.-Id: 38290


The beauty of curved momentum space

Franchino-Vinas, S.; Mignemi, S.; Relancio, J. J.

In this manuscript, we will discuss the notion of curved momentum space, as it arises in the discussion of noncommutative or doubly special relativity theories.We will illustrate it with two simple examples, the Casimir effect in anti-Snyder space and the introduction of fermions in doubly special relativity.We will point out the existence of intriguing results, which suggest nontrivial connections with spectral geometry and Hopf algebras.

Keywords: Quantum gravity; Noncommutative spacetimes; Snyder model; Doubly Special Relativity; Curved momentum space; Hopf algebras

  • Open Access Logo Contribution to proceedings
    22th Hellenic School and Workshops on Elementary Particle Physics and Gravity, 18.-25.09.2022, Corfu, Greece
    CORFU2022
    DOI: 10.22323/1.436.0340
    arXiv: 2303.08220 [hep-th]

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Permalink: https://www.hzdr.de/publications/Publ-38289
Publ.-Id: 38289


Trace anomalies for Weyl fermions: too odd to be true?

Abdallah, S.; Franchino-Vinas, S.; Frob, M. B.

We review recent discussions regarding the parity-odd contribution to the trace anomaly of a chiral fermion. We pay special attention to the perturbative approach in terms of Feynman diagrams, comparing in detail the results obtained using dimensional regularization and the Breitenlohner–Maison prescription with other approaches.

Keywords: Trace anomaly; Weyl fermions; Pontryagin density; Parity-odd contribution

  • Open Access Logo Contribution to proceedings
    Avenues of Quantum Field Theory in Curved Spacetime, 14.-16.09.2022, Genova, Italy
    Journal of Physics: Conference Series 2531 (2023) 012004: IOP Publishing
    DOI: 10.1088/1742-6596/2531/1/012004
    arXiv: 2304.08939 [hep-th]
    Cited 3 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-38288
Publ.-Id: 38288


Universal definition of the non-conformal trace anomaly

Ferrero, R.; Franchino-Vinas, S.; Frob, M. B.; Lima, W. C. C.

We show that there exists a generalized, universal notion of the trace anomaly for theories which are not conformally invariant at the classical level. The definition is suitable for any regularization scheme and clearly states to what extent the classical equations of motion should be used, thus resolving existing controversies surrounding previous proposals. Additionally, we exhibit the link between our definition of the anomaly and the functional Jacobian arising from a Weyl transformation.

Keywords: Conformal anomaly; Trace anomaly; Nonconformal theory; Conformal theory

Permalink: https://www.hzdr.de/publications/Publ-38287
Publ.-Id: 38287


Deportment study of critical elements – The Ruwai Pb-Zn-Ag skarn deposit in Central Kalimantan, Indonesia, as a case study

Faizy, S. M.; Kontonikas-Charos, A.; Burisch-Hassel, M.; Idrus, A.; Frenzel, M.

The Ruwai Pb-Zn-Ag skarn deposit is located within the Schwaner Mountain Complex in Central Kalimantan, Indonesia. It is the largest polymetallic skarn deposit in Kalimantan with the resources is estimated up to 14.43 Mt. at 4.94 wt.% Zn, 3.28 wt.% Pb, 108.11 g/t Ag which hosted by Jurassic limestones of the Ketapang Complex and Cretaceous granitoids of Sukadana Complex. In order to study the complex mineralogy and deportment of critical-elements (Ag, Bi, Sb, In, Te, Cd) pulp samples from the main stages of the processing plant (Ball mill/feed, Pb concentrate, Zn concentrate, Pb scavenger, Zn scavenger, Fe screw, and tailings) as well as 66 core samples of Pb-Zn-Ag mineralization were obtained.
Preliminary results on the pulp samples from X-ray diffraction (XRD), X-ray fluorescence (XRF) and mineral liberation analysis (MLA) agree within analytical uncertainties. The data allows a preliminary assessment of the deportment and distribution of Ag and Bi in the skarn ores and processing products. Particularly, acanthite (Ag2S) and freibergite ((Ag,Cu,Fe)12(Sb,As)4S13) are likely to be important hosts of Ag, while Bi occurs within bismuthinite (Bi2S3) and native bismuth (Bi). For the core samples, µ-XRF measurements of slabs have so far provided a broad overview of elemental distribution within the samples, while XRD results indicate more complex mineralogical compositions than the pulp samples.
Further analytical work including electron probe microanalysis (EPMA) and laser ablation ICP-MS are planned for all samples to be also able to evaluate the resource potential of other critical elements of interest such as Sb, In, Te, Cd.

Keywords: Skarn; Deportment; Ruwai

  • Open Access Logo Contribution to proceedings
    GeoBerlin 2023 – Geosciences Beyond Boundaries - Research, Society, Future, 03.-07.09.2023, Berlin, Germany
    DOI: 10.48380/ndg6-xh54

Permalink: https://www.hzdr.de/publications/Publ-38285
Publ.-Id: 38285


Reversal of the transverse force on a spherical bubble rising close to a vertical wall at moderate-to-high Reynolds numbers

Shi, P.

The flow past a clean spherical bubble translating steadily parallel to a no-slip wall in a stagnant fluid is studied numerically over a wide range of moderate to high Reynolds numbers. We focus on situations where the distance separating the bubble from the wall is smaller than the size of the bubble in order to explore the competition between viscous and inertial effects in the gap. More precisely, the range of the wall distance considered is $1.1\leq \LR \leq 2$ ($\LR$ being the distance from the bubble center to the wall normalized by the bubble radius), and that of the Reynolds number is $50\leq \Rey \leq 1000$ ($\Rey$ being based on the bubble diameter and the slip velocity). In contrast to predictions based on potential flow theory, the numerical results reveal that, when the gap is smaller than a critical value that depends on the Reynolds number, the transverse force starts to decrease with decreasing separation and may finally reverse, changing from attractive to repulsive. This effect is found to be due to the strong shear generated in the gap, which, combined with the local transverse gradient of the streamwise velocity, results in a system of two counter-rotating streamwise vortices and, consequently, a shear-induced lift pointing away from the wall. Computational results together with available high-Reynolds-number theory provide empirical expressions for the drag and transverse forces in the steady-state limit. Then the competition between the various transverse forces on a bubble bouncing close to the wall is examined, based on previously measured data for bubble trajectory. The central role of the history effects due to the misalignment between the wake and the instantaneous angle of the bubble path is confirmed. Computational results also reveal that, depending on the initial separation, a freely moving bubble may either reach a stable equilibrium position close to the wall or depart from the wall up to infinity.

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  • Secondary publication expected from 06.02.2025

Permalink: https://www.hzdr.de/publications/Publ-38284
Publ.-Id: 38284


Geometallurgical Characterisation of Sediment-Hosted Cu-(Ag) Ore from the Spremberg-Graustein-Schleife Kupferschiefer Deposit, Germany

Nourizenouz, Z.; Guy, B. M.; Möckel, R.; Ebert, D.; Frenzel, M.

The Spremberg-Graustein-Schleife Kupferschiefer deposit is a sediment-hosted stratabound copper (SSC) deposit located in eastern Germany. The Cu mineralization occurs at depths of 980 to 1,580 m below surface, predominantly in a Permian carbon-rich black shale unit, commonly known as the Kupferschiefer. Mineralization is not only restricted to this unit and can extend into the overlying Zechstein carbonates, as well as the underlying Redbed sandstones. Recent studies have confirmed 91.7 Mt of inferred mineral resource at an average grade of 1.5% Cu and 24.0 g/t Ag.

In addition to Cu and Ag, elevated levels of Co, Ni, and Re are also found in Kupferschiefer ores. This contribution provides the first detailed evaluation of the mineralogy of the complete mineralization interval of the Spremberg-Graustein-Schleife deposit, including the mineralogical deportment of Cu. Mineral chemistry work constraining the deportments of Ag and Re is planned.

Fifty-three individual samples were collected from three drill cores. The samples were crushed, milled, and composited into 19 composite samples. These were then subjected to multi-element analytical methods (XRF, ICP-OES, ICP-MS) for bulk-ore geochemistry, X-ray diffractometry (XRD), and mineral liberation analysis (MLA) for mineralogy. Electron probe micro-analysis (EPMA) and laser ablation ICP-MS (LA-ICP-MS) for trace element geochemistry are currently planned. Mineralogical results reveal that major Cu-bearing minerals vary both spatially between the three different drill cores and vertically between lithological units. For example, chalcocite and covellite (and to a lesser extent bornite) are the dominant carriers of Cu in the most mineralized core (80% of contained Cu), whereas chalcopyrite is the most prominent carrier of Cu in the Pb-Zn Kupferschiefer facies (75% of contained Cu). By combining different analytical results, we aim to develop a quantitative predictive model to describe the mineralogical distribution of the copper and potential by-products that will be usable for mineral processing and mine-planning purposes

  • Contribution to proceedings
    SEG 2023 Conference: Resourcing the Green, 26.-29.08.2023, London, UK

Permalink: https://www.hzdr.de/publications/Publ-38282
Publ.-Id: 38282


Minor and trace elements in the Spremberg-Graustein-Schleife Kupferschiefer deposit: A deportment study

Nourizenouz, Z.; Guy, B. M.; Möckel, R.; Ebert, D.; Frenzel, M.

The sediment-hosted Spremberg-Graustein-Schleife deposit is located in Lusatia, eastern Germany. Mineralization occurs in the lower Zechstein units, extending from the Grauliegend conglomerates and sandstones into the overlying organic-rich Kupferschiefer black shales and Zechstein carbonates. Around 100 Mt of Cu-Ag ore is present within the deposit. The ore is also enriched in Pb, Zn, Co, Ni, Au, Bi, Se, Re, and Ge (in addition to Cu and Ag). Despite the metal endowment, detailed quantitative metal deportment studies have not been carried out for this deposit, or indeed any other Kupferschiefer deposit. This study aims to bridge the gap. Core samples representing the complete mineralization interval (31 m in total) at three different sites within the deposit were mineralogically and geochemically analyzed. To ensure a comprehensive, high-quality and internally consistent dataset, various analytical methods including X-ray fluorescence (XRF), ICP-OES, ICP-MS, X-ray diffraction (XRD), Mineral Liberation Analysis (MLA), electron probe micro-analysis (EPMA) and laser ablation ICP-MS (LA-ICP-MS) were performed. The results reveal that the concentration and main hosts of copper and potential by-products vary vertically between the stratigraphical units, and spatially at different locations of the deposit. Such information will eventually help to predict deportments across the deposit, track each element within the minerals processing plants and also to get an idea of expected recoveries and thus optimizing the procedure.

  • Open Access Logo Contribution to proceedings
    GeoBerlin 2023 – Geosciences Beyond Boundaries - Research, Society, Future, 03.-07.09.2023, Berlin, Germany
    DOI: 10.48380/9fdk-7x45

Permalink: https://www.hzdr.de/publications/Publ-38281
Publ.-Id: 38281


Imposing correct jellium response is key to predict the density response by orbital-free DFT

Moldabekov, Z.; Shao, X.; Pavanello, M.; Vorberger, J.; Graziani, F.; Dornheim, T.

Orbital-free density functional theory constitutes a computationally highly effective tool for modeling electronic structures of systems ranging from room-temperature materials to warm dense matter. Its accuracy critically depends on the employed kinetic energy (KE) density functional, which has to be supplied as an external input. In this work we consider several nonlocal and Laplacian-level KE functionals and use an external harmonic perturbation to compute the static density response at T=0 K in the linear and beyond-linear response regimes. We test for the satisfaction of exact conditions in the limit of uniform densities and for how approximate KE functionals reproduce the density response of realistic materials (e.g., Al and Si) against the Kohn-Sham DFT reference, which employs the exact KE. The results illustrate that several functionals violate exact conditions in the uniform electron gas (UEG) limit. We find a strong correlation between the accuracy of the KE functionals in the UEG limit and in the strongly inhomogeneous case. This empirically demonstrates the importance of imposing the limit of UEG response for uniform densities and validates the use of the Lindhard function in the formulation of kernels for nonlocal functionals. This conclusion is substantiated by additional calculations for bulk aluminum (Al) with a face-centered cubic (fcc) lattice and silicon (Si) with an fcc lattice, body-centered cubic (bcc) lattice, and semiconducting crystal diamond state. The analysis of fcc Al, and fcc as well as bcc Si data follows closely the conclusions drawn for the UEG, allowing us to extend our conclusions to realistic systems that are subject to density inhomogeneities induced by ions.

Keywords: Density functional theory; Condensed Matte; Electronic structure

Permalink: https://www.hzdr.de/publications/Publ-38280
Publ.-Id: 38280


Unlocking the potential of GaAs nanowires for telecom photonics

Sun, X.; Hilliard, D.; Chatzopoulou, P.; Vasileiadis, I.; Florini, N.; Dimitrakopulos, G.; Komninou, P.; Lymperakis, L.; Devulapalli, V.; Liebscher, C.; Pashkin, O.; Winnerl, S.; Helm, M.; Dimakis, E.

Strain engineering is a powerful tool for designing nanowires with tailored properties for a variety of applications. By carefully controlling the built-in strain in nanowires, it is possible to tune their bandgap to the near-infrared region, making them ideal for applications in telecommunication and imaging. In our previous work, we demonstrated that in GaAs/In x Al 1-x As core/shell nanowires, the bandgap of the core can be narrowed by up to 40%, for x up to 0.54, via strain due to the lattice mismatch between the shell [1]. Here, we explored the upper end of the lattice mismatch regime, extending the same concept to the contents of the shell towards x = 1, achieving unusually high strain values. The strain in the core and its effect on band structure are studied by a combination of spectroscopic methods and high-resolution transmission and scanning-transmission electron microscopy (HR(S)TEM). Raman spectroscopy showed that the tensile strain in the GaAs core increased linearly with increasing the In content in the shell (Fig. 1a), following the trend we reported in the past for lower values of x [1]. This behavior suggests the absence of plastic relaxation despite the very large lattice mismatch between the core and the shell. Using cross-sectional and longitudinal HR(S)TEM observations, we assessed the strain distribution normal and along the nanowire axis (Figs. 1b to 1d), which was found to be in good agreement with finite element and molecular dynamics simulations. Above a critical x value, plastic relaxation sets in via dislocations (Fig. 1b). We also correlated the photoluminescence emission properties with the strain distribution in the core and the shell, and the corresponding band alignment via band structure simulations. All in all, our results identified the limits of a coherent core and shell heterostructures and the potential application of tensile-strained GaAs nanowires for C- and O-band telecom photonics.

Keywords: nanowire; photonics; strain engineering; GaAs

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Publ.-Id: 38279


Recent advances in the improvement of the measurement accuracy of capacitance wire-mesh sensors

de Assis Dias, F.; Wiedemann, P.; Schleicher, E.; Marco José, D. S.; Hampel, U.

In this paper, we report recent advances in the improvement of the measurement accuracy of capacitance wire-mesh sensors. We review the principles of the wire-mesh sensor and discuss the problem of inherent energy losses. An advanced model that combines finite element analysis and an electronic circuit model capable of predicting such losses is also introduced. Then, we discuss different procedures and methods, which improve the measurement accuracy of capacitance wire-mesh sensors by suppressing or correcting loss effects. First, limitations of a threshold method are discussed, in particular, for water-oil-gas three-phase mixtures. Next, we discuss a procedure based on the optimization of the electronic circuit of the sensor to suppress losses and crosstalk. This improves the measurement accuracy, but only for fluids with narrow dynamic range in their electrical impedance. Finally, we discuss a method based on a modified wire-mesh sensor with extra transmitter electrode embedded in the dielectric construction material, which allows predicting nonlinear behaviors in sensor readings and compensating for them in later post-processing. In contrast to the threshold method and the optimization circuit procedure, the latter allows improved measurement accuracy, reducing local phase fraction deviations from more than 30% to less than 5% for a much wider impedance range.

Keywords: wire-mesh sensor; multiphase flow; impedance measurement; three-phase flow

  • Lecture (Conference)
    11th World Congress on Industrial Process Tomography, 06.-08.09.2023, Mexico City, Mexico

Permalink: https://www.hzdr.de/publications/Publ-38278
Publ.-Id: 38278


The colliding planar shocks platform to study warm dense matter at the National Ignition Facility

Macdonald, M. J.; Di Stefano, C. A.; Döppner, T.; Fletcher, L. B.; Flippo, K. A.; Kalantar, D.; Merritt, E. C.; Ali, S. J.; Celliers, P. M.; Heredia, R.; Vonhof, S.; Collins, G. W.; Gaffney, J. A.; Gericke, D. O.; Glenzer, S. H.; Kraus, D.; Saunders, A. M.; Schmidt, D. W.; Wilson, C. T.; Zacharias, R.; Falcone, R. W.

We have developed an experimental platform at the National Ignition Facility that employs colliding planar shocks to produce warm dense matter with uniform conditions and enable high-precision equation of state measurements. The platform uses simultaneous x-ray Thomson scattering and x-ray radiography to measure the density, electron temperature, and ionization state in warm dense matter. The experimental platform is designed to create a large volume of uniform plasma (approximately 700 x 700 x 150 μm3) at pressures approaching 100 Mbar and minimize the distribution of plasma conditions in the x-ray scattering volume, significantly improving the precision of the measurements. Here, we present the experimental design of the platform and compare hydrodynamic simulations to x-ray radiography data from initial experiments studying hydrocarbons, producing uniform densities within ±25% of the average probed condition. We show that the platform creates a homogeneous plasma that can be characterized using x-ray Thomson scattering. Thus, the new platform enables accurate measurements of plasma conditions necessary to test models for the equation of state and ionization potential depression in the warm dense matter regime.

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  • Secondary publication expected from 01.06.2024

Permalink: https://www.hzdr.de/publications/Publ-38277
Publ.-Id: 38277


X-ray Thomson scattering spectra from density functional theory molecular dynamics simulations based on a modified Chihara formula

Schörner, M.; Bethkenhagen, M.; Döppner, T.; Kraus, D.; Fletcher, L. B.; Glenzer, S. H.; Redmer, R.

We study ab initio approaches for calculating x-ray Thomson scattering spectra from density functional theory molecular dynamics simulations based on a modified Chihara formula that expresses the inelastic contribution in terms of the dielectric function. We study the electronic dynamic structure factor computed from the Mermin dielectric function using an ab initio electron-ion collision frequency in comparison to computations using a linear-response time-dependent density functional theory (LR-TDDFT) framework for hydrogen and beryllium and investigate the dispersion of free-free and bound-free contributions to the scattering signal. A separate treatment of these contributions, where only the free-free part follows the Mermin dispersion, shows good agreement with LR-TDDFT results for ambient-density beryllium, but breaks down for highly compressed matter where the bound states become pressure ionized. LR-TDDFT is used to reanalyze x-ray Thomson scattering experiments on beryllium demonstrating strong deviations from the plasma conditions inferred with traditional analytic models at small scattering angles.

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Publ.-Id: 38276


Nanoscale 3D Strain Mapping and Structural Features of GaAs/In(Al,Ga)As Core-Shell Nanowires

Chatzopoulou, P.; Hilliard, D.; Vasileiadis, I. G.; Florini, N.; Devulapalli, V.; Liebscher, C. H.; Lymperakis, L.; Komninou, P.; Dimakis, E.; Dimitrakopulos, G. P.

Elastic accommodation of the high lattice mismatch in GaAs/In(Al,Ga)As core-shell nanowires holds great potential for applications in high-frequency electronics and optoelectronics. The unique core-shell geometry offers several advantages over planar systems. The reduced dimensionality of the core enables strain relaxation along the lateral dimension and strain partitioning, ultimately reducing the overall strain energy and expanding the limits of coherency [1]. Consequently, the GaAs core can undergo extreme elastic stretching, particularly along the nanowire axis, without the onset of plastic relaxation.

Growing thick Inx(Al,Ga)1-xAs shells with high In-contents on narrow [111]-oriented GaAs cores leads to extreme elastic dilatation of the core that promotes a 40% bandgap reduction [2] as well as a 30-50% boost in electron mobility [3]. In order to elucidate the intricate 3D strain fields of such nanowires, we have employed transmission and scanning-transmission electron microscopy ((S)TEM) methods to study a series of nanowires featuring narrow cores (25 nm diameter) and thick shells (80 nm thickness) with composition x ranging from 0.20 up to 1. To enable the nanoscale investigation of all strain components, we developed elaborate sample preparation methods to facilitate observation along three zone axes, i.e. [111], <1-10> and <11-2>, as shown in Fig.1. For (S)TEM and high-resolution TEM (HRTEM) observations, a 200 kV JEOL JEM F200 CFEG microscope was used. High resolution STEM (HRSTEM) was performed in a 300 kV probe-corrected Thermo Fisher Scientific Titan Themis 60/300 microscope. In an integrated approach, experimental strain fields were compared with finite element (FE) calculations, performed using thermal expansivity to model the lattice mismatch, and with energetic calculations by molecular dynamics (MD) using the Tersoff interatomic potential [4].

(S)TEM observations revealed that for indium contents up to x≈50%, the shells were coherent and dislocation-free (Fig.1), exhibiting only occasional (111) ortho-twins and stacking faults. These are typically associated with similar faults originating in the core and are unrelated to strain relaxation. The experimental strain fields were in good agreement with the FE and MD simulations. In the core, all strain components were tensile. The axial (ezz) strain was uniform, whereas the radial (err) and azimuthal (eθθ) strains were position-dependent and saturated at the same value, in the region where the shell was completely relaxed. Upon reaching a critical composition, threading dislocations emerged in the shell, spreading radially from the core towards the {1-10} free surfaces of the shell. Their Burgers vectors were analysed using weak-beam dark-field TEM and were found to lie on the (111) plane. In the defected nanowires, Moiré fringes observed in the core region normal to [111], revealed axial relaxation, attributed to the introduction of misfit dislocations. By measuring the spacing of the Moiré fringes, the residual elastic strain in the cores was calculated.

Figure 1. (a) Bright field STEM image showing an unrelaxed, coherent GaAs/In0.56Al0.44As core-shell NW observed along <11-2>. (b) Z-contrast STEM image showing a NW cross-section, observed along [111] (top) and the corresponding strain map from the GaAs core (bottom). The nominal In-composition in b is again ≈50%.

Acknowledgements
This work was supported by the program for the promotion of the exchange and scientific cooperation between Greece and Germany (IKYDA 2020), project title: Strain tuning of iii-v semiconductor nanowires (TUNE).

References
1. Th. E. Trammell, X. Zhang, Y. Li, L-Q. Chen and E. C. Dickey, Journal of Crystal Growth 310 (2008), 3084-3092.
2. L. Balaghi, G. Bussone, R. Grifone, R. Hübner, J. Grenzer, M. Ghorbani-Asl, A. V. Krasheninnikov, H. Schneider, M. Helm and E. Dimakis, Nature Communications 10 (2019), 2793.
3. L. Balaghi1, S. Shan, I. Fotev, F. Moebus, R. Rana, T. Venanzi, R. Hübner, Th. Mikolajick, H. Schneider, M. Helm, A. Pashkin and E. Dimakis, Nature Communications 12 (2021), 6642.
4. H. Detz and G. Strasser, Semicond. Sci. Technol. 28 (2013), 085011.

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  • Lecture (Conference)
    XXXVII Panhellenic Conference on Solid State Physics and Materials Science, 17.09.2023, Thessaloniki, Greece

Permalink: https://www.hzdr.de/publications/Publ-38275
Publ.-Id: 38275


Monte-Carlo event generation for the interaction of x-ray laser fields and hot electrons

Hernandez Acosta, U.

With the advent of advanced laser systems producing high-frequency X-ray beams, e.g. the Euro- peanXFEL as a prominent example, a regime of laser-plasma interaction is reached, where all-optical methods, as used in particle-in-cell simulations, are no longer applicable. Instead, the interaction of hot electrons and the X-ray laser pulse must be modeled with a QED-driven approach. Furthermore, future experiments taking place at HED-HIBEF, LCLS, and other facilities targeting this regime, will encounter processes in x-ray scattering from (laser-driven) relativistic electrons, where the effects of the energy spectrum of the x-ray laser field as well as multi-photon interactions can not be neglected anymore. To explore this regime, where strong fields meet high frequencies, we present a novel approach for a numerical modeling tool, QED.jl, which inherently uses exact strong-field QED descriptions. This brings, for the first time, the technique of Monte-Carlo event generation to X-ray laser physics experiments.

Keywords: Strong-field QED; Laser-Matter Interaction; Monte-Carlo Simulation

  • Open Access Logo Lecture (Conference)
    Many-particle systems under extreme conditions - Polish-German WE-Heraeus Seminar & Max Born Symposium, 04.-06.12.2023, Görlitz, Germany

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Unveiling the Characteristics of Monolayer-thick InGaN/GaN Quantum Wells: An Integrated Analysis

Vasileiadis, I. G.; Chatzopoulou, P.; Lymperakis, L.; Adikimenakis, A.; Gkotinakos, A.; Devulapalli, V.; Liebscher, C. H.; Androulidaki, M.; Hübner, R.; Georgakilas, A.; Pontikis, V.; Karakostas, T.; Komninou, P.; Dimakis, E.; Dimitrakopulos, G. P.

Short period superlattices comprising ultra-thin InGaN/GaN quantum wells (QWs) with thickness of a few (0002) monolayers (MLs) have gained significant attention in the field of advanced optoelectronics. These nano-heterostructures offer the ability to tune the band gap by precisely controlling the thickness of both the QW and the GaN barrier [1]. Moreover, their potential applications in quantum computing and spintronics have sparked interest due to their possible topological insulator behaviour [2,3]. These properties are intricately linked to the indium content as well as the thicknesses of the QWs and GaN barriers. Growth efforts aim at high quality heterostructures with ML-thick QWs and high indium content. Previous theoretical and experimental studies have indicated that the highest indium content in such ultra-thin QWs is kinetically limited to a maximum of ~33% for growth under nitrogen-rich conditions. Meanwhile, strained substrates offer a solution to surpass the limits of indium incorporation in InGaN QWs [4]. The aim of this work was to determine the impact of growth temperature on the incorporation of indium atoms in GaN, to develop a growth model of such ultra-thin QWs and investigate the influence of strained GaN barriers on band-gap variation in this material system.

An integrated methodology combining quantitative high resolution scanning transmission electron microscopy (HRSTEM), empirical potential and density functional theory (DFT) calculations, image simulations, and strain analysis was developed and employed [5,6,7]. A series of multi-QW heterostructures were fabricated by plasma-assisted molecular beam epitaxy (PAMBE) under metal-rich conditions, varying the growth temperatures of the QWs and GaN barriers. Our STEM-based analysis verified the formation of ultra-thin QWs with self-limited thickness up to 2 MLs along with the formation of ML-thick QWs with the highest known composition (~45%) (see Fig. 1(a)) under specific growth conditions [6]. The interplay between growth temperatures and incorporation of indium atoms in GaN was determined and this led to the development of a substitutional synthesis mechanism, involving the exchange between indium and gallium atoms at surface sites during the growth process. The proposed model presents promising routes for achieving higher indium contents in such QWs. DFT calculations were also utilized to address the impact of strained GaN barriers on the band gap of such heterostructures by considering that the deployment of tensile-strained barriers is an alternative option to further increase the indium incorporation limits. The changes in the band-gap energy were explored considering pseudomorphic QWs with thickness of only one ML grown on equibiaxially strained GaN barriers. The introduction of elastic strain into these heterostructures leads to modifications in their optoelectronic behaviour. The results indicated a reduction in the band gap for lower indium contents. However, for indium compositions above the mid-range, the trend is reversed, and the band gap increases with the indium content instead of reducing it (see Fig. 1 (b)) [7]. In general, while tensile-strained GaN can assist in the incorporation of indium, our calculations indicate that this strategy for reducing the band gap is only effective for lower indium concentrations.

Figure 1: (a) Pseudocolor HRSTEM image of a 1 ML InGaN/GaN QW with indium content ~45%. Inset illustrates the structural model of an InN/GaN QW. (b) Diagram of band-gap energy of 1ML-thick InGaN/GaN heterostructure with respect to the indium content of its QW. 0%, 1.5% and 3% in-plane strain of the GaN barriers are indicated by different colors. The vertical gray line shows the highest indium content experimentally achieved so far.

Acknowledgements
Work supported by the project “INNOVATION-EL” (MIS 5002772). I.G.V. acknowledges support by the State Scholarships Foundation (IKY) project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432). We would like to thank the Aristotle University of Thessaloniki HPC infrastructure for the provision of computing resources.

References
1. I. Gorczyca, T. Suski, N. E. Christensen et. al, J. Phys. Condens. Matter 30 (2018) 063001.
2. M. S. Miao, Q. Yan, C. G. Van de Walle et. al, Phys. Rev. Lett. 109 (2012) 186803.
3. W. Pan, E. Dimakis, G. T. Wang et. al, Appl. Phys. Lett. 105 (2014), 213503.
4. T. Schulz, L. Lymperakis, M. Anikeeva et. al, Phys. Rev. Materials 4 (2020) 073404.
5. G. P. Dimitrakopulos, I. G. Vasileiadis, C. Bazioti et. al, Appl. Phys. 123 (2018) 024304.
6. I. G. Vasileiadis, L. Lymperakis, A. Adikimenakis et. al, Scientific Reports 11 (2021) 20606
7. P. Chatzopoulou, I. G. Vasileiadis, Ph. Komninou et. al, Crystals 13 (2023) 700.

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    XXXVII Panhellenic Conference on Solid State Physics and Materials Science, 17.09.2023, Thessaloniki, Greece

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III-V semiconductor nanowires with unique heterostructure possibilities

Hilliard, D.; Balaghi, L.; Tauchnitz, T.; Hübner, R.; Fotev, I.; Rana, R.; Pashkin, O.; Vasileiadis, I.; Chatzopoulou, P.; Florini, N.; Dimitrakopulos, G. P.; Komninou, P.; Winnerl, S.; Schneider, H.; Helm, M.; Dimakis, E.

III-V semiconductor heterostructures have contributed to a wealth of studies in solid state physics, as well as to applied research and technology in electronics and photonics. More recently, the nanowire geometry introduced new possibilities, such as one-dimensional quantum transport, formation of Majorana modes, enhanced light-matter coupling, photon entanglement, as well as monolithic integration in Si-CMOS platforms for the realization of more-than-Moore hybrid systems. This talk will be focusing on the bottom-up fabrication and the structural and electronic properties of III-As nanowire heterostructures.

The first type of heterostructures will be radial ones, comprising a GaAs core and a lattice-mismatched InxAl1-xAs or InxGa1-xAs shell. Molecular beam epitaxy and a combination of vapor-liquid-solid and vapor-solid growth modes are employed to grow free-standing nanowires on Si substrates [1, 2]. Owing to its high surface-to-volume ratio and the peculiar geometry, the thin core can be hydrostatically tensile strained to extremely high levels, depending on the In content x and the thickness of the shell. As a welcome effect, the bandgap of GaAs can be tuned to be anywhere between the strain-free value of 1.4 and 0.8 eV, allowing for potential applications in telecom photonics [3]. Furthermore, the electron mobility in the GaAs core is increased with increasing the tensile strain, as a result of a corresponding decrease in electron effective mass [4]. This is of major importance for the realization of transistors with high speed and low-power consumption.

The second type of heterostructures will be axial ones, where the composition is modulated from GaAs to AlxGa1-x¬As and back to GaAs along the nanowire axis. Here, we develop a pulsed-growth technique [5], which grants precise control over the axial growth rate and droplet composition. Using advanced transmission electron microscopy methods and a thermodynamic equilibrium model, it becomes possible to quantitatively describe the compositional grading of Al across the heterostructure interfaces and to identify the control parameters. In the end, symmetric GaAs to AlxGa1-x¬As and AlxGa1-x-As to GaAs interfaces with widths of only 2 – 3 monolayers (comparable to, or better than, state-of-the-art thin film heterostructures) are achieved for the full range of x [6]. This is particularly important for quantum heterostructures and nano-devices, where the compositional grading at interfaces can critically affect the electronic properties and the device characteristics.

Acknowledgements
Part of this work was supported by the program for the promotion of the exchange and scientific cooperation between Greece and Germany (IKYDA 2020), project title: Strain tuning of III-V semiconductor nanowires (TUNE).

References
1. T. Tauchnitz et al., Cryst. Growth Des. 17 (2017) 5276.
2. T. Tauchnitz et al., Nanotechnology 29 (2018) 504004.
3. L. Balaghi et al., Nat. Commun. 10 (2019) 2793.
4. L. Balaghi et al., Nat. Commun. 12 (2021) 6642.
5. L. Balaghi et al., Nano Lett. 16 (2016) 4032.
6. D. Hilliard et al., in preparation (2023).

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    XXXVII Panhellenic Conference on Solid State Physics and Materials Science, 17.09.2023, Thessaloniki, Greece

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Concepts of strong-field QED in momentum space: gauge invariance and soft-photon theorems

Hernandez Acosta, U.

Usually, quantum electrodynamics acts as the prime example, when it comes to a well-understood and outstandingly precise description of elementary particle processes. However, modern laser facilities provide highly intense light with a non-trivial temporal structure, where an arbitrary number of ‘photons’ from the light source may interact with the colliding particles. In this case, the standard perturbative treatment known from quantum electrodynamics becomes cumbersome and impractical. Accordingly, there are, among others, wide theoretical investigations w.r.t. scattering processes of particles impinging these extreme light sources. This has been done by applying the strong-field quantum electrodynamics, a theory of electromagnetic interactions within coherent highly intense light treated as a classical background field. Here, the distinction between a classical background field and a quantized photon field revealed a vast amount of novel non-linear structures and non-perturbative phenomena. In this seminar, we introduce the basic concepts of strong-field QED and derive the Feynman rules for the theory in momentum space. Then, we explore their general structure and implications from fundamental principles, namely gauge invariance.

Keywords: Strong-Field QED; Quantum Field Theory

  • Invited lecture (Conferences) (Online presentation)
    Worldline Seminars, 27.11.2023, Plymouth, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-38271
Publ.-Id: 38271


Transient nanowire bending during the growth of core/shell heterostructures with large lattice mismatch

Hilliard, D.; Hübner, R.; Chatzopoulou, P.; Dimitrakopulos, G.; Komninou, P.; Winnerl, S.; Helm, M.; Dimakis, E.

The elastic accommodation of lattice mismatch in core/shell nanowires presents unique features because both the shell and the core can be strained depending on their volume ratio. This allows the realization of heterostructure combinations with large lattice mismatch, as well as the extensive strain-mediated tailoring of their electronic properties [1]. Owing to the large stresses involved, any shell thickness asymmetry around the core may cause the bending of the nanowires, forming shapes like circular arcs, which can be a desired effect or not, depending on the targeted application.
Here, we monitor the asymmetric shell growth, the asymmetric strain, and the resulting bending during the growth of GaAs/In0.4Al0.6As core/shell nanowires [2]. We show how the profile of the elemental beams in a conventional MBE system accounts for the asymmetric growth rate of the shell around the core, in spite of the substrate rotation during growth. The resulting asymmetric stresses around the core cause the bending of the nanowires to the side of the thinner shell, which, in turn, enhances further the growth rate and stress asymmetry, and thus the bending itself, in a self-feeding circle. Nevertheless, after a critical minimum shell thickness on all core sides has been reached, the bending is reversed and the nanowires straighten up. Analyzing cross sections normal to the axis of such straightened up nanowires by STEM, we developed a method to reconstruct, for the first time, the evolution of the shell thickness on every core side and the corresponding bending angle during growth. Furthermore, geometric phase analysis revealed the spatial distribution of strain in the core and the shell with respect to the uneven shell thicknesses around the core. Our results shine a light on the growth of lattice-mismatched core/shell nanowires and could serve as a guide to design deliberate curved structures or, instead, strategies to suppress the bending.

Figure 1. (a) Side-view SEM image of as-grown core/shell nanowires on a Si substrate. Inset: HAADF-STEM image of a cross-sectional TEM lamella. (b) Evolution of the shell thickness on two opposite core sides (thinnest vs. thickest shell) during growth and the corresponding bending angle. (c) Schematic representation of the transient nanowire bending.

[1] L. Balaghi et al., Nature Commun 10, 2793 (2019); Nature Commun 12, 6642 (2021).
[2] D. Hilliard et al., in preparation.

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    Nanowire Week 2023, 09.10.2023, Atlanta, Georgia, USA

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Axial heterostructures in vapor-liquid-solid grown nanowires: at the limit of interface sharpness

Hilliard, D.; Tauchnitz, T.; Hübner, R.; Vasileiadis, I.; Dimitrakopulos, G.; Komninou, P.; Winnerl, S.; Schneider, H.; Helm, M.; Dimakis, E.

When lowering the dimensions of semiconductor heterostructures, controlled compositional changes become paramount owing to the increasing role of the heterointerfaces in the electronic properties of the heterostructures. A common issue faced in fabricating axial heterostructures in vapor-liquid-solid (VLS)-grown nanowires is the compositional grading, which is caused by the involved growth mechanisms and broadens the interfaces.
Here, our previously developed nanowire growth technique called droplet-confined alternate pulsed-epitaxy (DCAPE) [1] (an adaptation of conventional molecular beam epitaxy), which grants precise control over the axial growth rate and droplet composition, is employed to grow AlxGa1-xAs axial insertions in self-catalyzed GaAs nanowires. Some examples showcasing the capability of DCAPE in growing systems of complex, abrupt heterostructures are shown in Fig. 1a, where AlxGa1-xAs is revealed as horizontal dark grey lines. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and a semi-empirical growth model [2] are utilized to gain an understanding of the compositional grading mechanism and its dependence on the growth temperature (TG), the nanowire radius (RNW), and the total Al content [2]. We show that pre-filling the Ga droplet with Al before the growth of an insertion is enough to sharpen the GaAs-to-AlxGa1-xAs interface at any TG. On the other hand, though, sharper AlxGa1-xAs-to-GaAs interfaces are obtained only at lower TG and/or smaller RNW, where the so-called reservoir effect is markedly reduced. In the best case, symmetric AlxGa1-xAs insertions with interface widths of only 2– 3 monolayers (comparable to, or better than, state-of-the-art thin film heterostructures) are achieved for the full range of x (Fig. 1b), proving the strength of VLS in the fabrication of sharp axial heterostructures.

Figure 1: (a) HAADF-STEM images with 5 examples of GaAs/AlxGa1-xAs heterostructures grown in self-catalyzed GaAs nanowires. Dark contrast denotes Al-containing regions. (b) Symmetric AlxGa1-xAs profiles obtained after optimization of all growth parameters.

[1] L. Balaghi et al., Nano Lett. 16, 4032 (2016).
[2] D. Hilliard et al., in preparation.

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    Nanowire Week 2023, 09.10.2023, Atlanta, Georgia, USA

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Publ.-Id: 38269


Towards GaAs/AlxGa1-xAs axial heterostructures with atomically sharp interfaces in self-catalyzed nanowires

Hilliard, D.; Tauchnitz, T.; Hübner, R.; Vasileiadis, I.; Dimitrakopulos, G.; Komninou, P.; Winnerl, S.; Helm, M.; Dimakis, E.

Axial heterostructures have diverse functionality in electronic and optoelectronic devices. Implementing such systems in freestanding semiconducting nanowires further broadens the scope of potential applications, for example: distributed Bragg reflectors, high-efficiency light-emitting diodes, and quantum dot heterostructures. Although, as the physical dimensions of such devices approach the atomic scale, managing the compositional grading effect of the constituent materials at the heterointerface becomes critical and can be particularly challenging in nanowires grown in vapor-liquid-solid mode.
We grow self-catalyzed GaAs nanowires with AlxGa1-xAs axial insertions on Si substrates using our previously developed nanowire growth technique called droplet-confined alternate pulsed-epitaxy (DCAPE) [1]. Here, nanowires are grown using alternating short beam pulses as opposed to the conventional molecular beam epitaxy analog where material is continuously supplied. With this approach, precise control over the axial growth rate, droplet composition and contact angle is granted along with the unique opportunity to grow nanowire heterostructures at CMOS compatible temperatures. To examine the compositional grading mechanism of Al in our AlxGa1-xAs axial insertions we employ high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Quantitative AlxGa1-xAs profiles are extracted from atomically resolved images to study in detail the profile’s interface sharpness and symmetry in relation to the profiles total Al content, heterostructure growth temperature and nanowire diameter. Additionally, building on a previously existing heterostructure growth model that describes the AlxGa1-xAs-to-GaAs interface while considering the solid-liquid thermodynamics and the so-called reservoir effect [2], we derive our own semi-empirical model that describes remarkably well the AlxGa1-xAs profile as a whole and allows for a rigorous analysis of both the profile’s leading and trailing interfaces.
We show the AlxGa1-xAs profile’s leading interface sharpness can be maximized in thin nanowires, largely due to the Al prefilling possibilities provided by DCAPE [3]. Furthermore, we demonstrate increases in trailing interface sharpness by decreasing the nanowire radius and, considerably more so, by decreasing the heterostructure growth temperature [3]. In the best case, practically symmetrical insertions with interface lengths of only 1 – 3 monolayers are achieved for a wide range of peak Al contents, accordingly approaching the absolute limit of atomically sharp interfaces [3].

References

[1] Balaghi et al., Nano Lett. 16, 4032 (2016)
[2] Priante et al., Nano Lett. 16, 1917 (2016)
[3] Hilliard et al., unpublished results

Related publications

  • Lecture (Conference)
    21 st European Workshop on Molecular Beam Epitaxy (EuroMBE 2023), 16.04.2023, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-38268
Publ.-Id: 38268


Characterization of the Inter-grain Coupling in Uniaxial Antiferromagnets via Domain Wall Patterns

Pylypovskyi, O.; Hedrich, N.; Tomilo, A.; Kosub, T.; Wagner, K.; Hübner, R.; Shields, B.; Sheka, D.; Faßbender, J.; Maletinsky, P.; Makarov, D.

Antiferromagnets (AFMs) as materials with a high degree of magnetic compensation and complex dynamics attract attention for fundamental research and use in high-speed and low-energy-cosuming electronics. Technologically relevant AFM thin films usually possess a granular crystal structure, which alters the properties of domain walls and skyrmions [1,2]. Here, we provide a material model of a granular AFM and describe domain wall pinning at grain boundaries [3]. The model is applied to Cr2O3 films with a maze-like domain pattern visualized using nitrogen vacancy magnetometry. Using the statistical analysis of domain size and measuring the self-similarity parameters of the domain wall pattern, we estimate the material parameters characterizing the inter-grain coupling. Namely, for the films with a grain size of about 50 nm, the distribution of exchange bonds between grains is characterized by an average of 10% from the bulk value and a wide standard deviation, including a small amount of ferromagnetic bonds. The presented approach is compatible with machine learning techniques. Based on the material model, we provide design rules for the granular AFM recording media.

[1] Jing et al, Phys. Rev. B 103, 174430 (2021)
[2] Veremchuk et al, ACS Appl. El. Mat. 4, 2943 (2022); Erickson et al, RCS Adv. 13, 178 (2023)
[3] Pylypovskyi et al, Phys. Rev. Appl. 20, 014020 (2023)

Keywords: antiferromagnetism; Cr2O3; grains

  • Lecture (Conference) (Online presentation)
    APS March Meeting, 03.-08.03.2024, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-38267
Publ.-Id: 38267


A Web-Based COVID-19 Tool for Testing Residents in Retirement Homes: Development Study

Davoodi Monfared, M.; Batista, A.; Mertel, A.; Senapati, A.; Abdussalam, W.; Vyskocil, J.; Barbieri, G.; Fan, K.; Schlechte-Welnicz, W.; Calabrese, J.

Long-term care facilities have been widely affected by the COVID-19 pandemic. Empirical evidence demonstrated that older people are the most impacted and are at higher risk of mortality after being infected. Regularly testing care facility residents is a practical approach to detecting infections proactively. In many cases, the care staff must perform the tests on the residents while also providing essential care, which in turn causes imbalances in their working time. Once an outbreak occurs, suppressing the spread of the virus in retirement homes (RHs) is challenging because the residents are in contact with each other, and isolation measures cannot be widely enforced. Regular testing strategies, on the other hand, have been shown to effectively prevent outbreaks in RHs. However, high-frequency testing may consume substantial staff working time, which results in a trade-off between the time invested in testing and the time spent providing essential care to residents.

Keywords: application; COVID-19; optimized testing; pandemic; retirement home; web

  • Open Access Logo JMIR Formative Research 7(2023), e45874
    Online First (2023) DOI: 10.2196/45875

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Permalink: https://www.hzdr.de/publications/Publ-38266
Publ.-Id: 38266


Tinto: Multisensor Benchmark for 3-D Hyperspectral Point Cloud Segmentation in the Geosciences

Afifi, A. J. M.; Thiele, S. T.; Rizaldy, A.; Lorenz, S.; Ghamisi, P.; Tolosana Delgado, R.; Kirsch, M.; Gloaguen, R.; Heizmann, M.

The increasing use of deep learning techniques has reduced interpretation time and, ideally, reduced interpreter bias by automatically deriving geological maps from digital outcrop models. However, accurate validation of these automated mapping approaches is a significant challenge due to the subjective nature of geological mapping and the difficulty in collecting quantitative validation data. Additionally, many state-of-the-art deep learning methods are limited to 2-D image data, which is insufficient for 3-D digital outcrops, such as hyperclouds. To address these challenges, we present Tinto, a multisensor benchmark digital outcrop dataset designed to facilitate the development and validation of deep learning approaches for geological mapping, especially for nonstructured 3-D data like point clouds. Tinto comprises two complementary sets: 1) a real digital outcrop model from Corta Atalaya (Spain), with spectral attributes and ground-truth data and 2) a synthetic twin that uses latent features in the original datasets to reconstruct realistic spectral data (including sensor noise and processing artifacts) from the ground truth. The point cloud is dense and contains 3242964 labeled points. We used these datasets to explore the abilities of different deep learning approaches for automated geological mapping. By making Tinto publicly available, we hope to foster the development and adaptation of new deep learning tools for 3-D applications in Earth sciences. The dataset can be accessed through this link: https://doi.org/10.14278/rodare.2256 .

Keywords: Deep learning; digital outcrop; hypercloud; hyperspectral; point cloud; point cloud segmentation; remote sensing; synthetic data

Related publications

  • Open Access Logo IEEE Transactions on Geoscience and Remote Sensing 62(2024), 5501015
    Online First (2023) DOI: 10.1109/TGRS.2023.3340293
    EISSN: 1558-0644
    PISSN: 0196-2892

Permalink: https://www.hzdr.de/publications/Publ-38265
Publ.-Id: 38265


Compositionally relevant post hoc tests of compositional linear models

Pospiech, S.; van den Boogaart, K. G.

The geochemistry of surficial Earth materials, e.g. (weathered) rocks, soils, plants, peatlands, waterbodies or snow, is influenced by many processes and environmental parameters. Often, however, it is unknown which of the observed environmental variables, like soil pH, precipitation, slope, underlying bedrock type, to name but a few, have a significant influence on the geochemical pattern of the respective material. For this purpose, one can test hypotheses about the influence of variables on the (ilr or alr transformed) composition, e.g. by means of linear regression. These tests can either be rejected or accepted. If the result of the statistical analysis shows that the variable(s) tested could have an influence on the overall composition of the surficial material, the question immediately arises for geochemists as to which of the elements or element groups change in relation to this variable. In the case of non-compositional and univariate data, there are the classical post-hoc tests, e.g. tests according to Scheffé or Bonferroni, that allow to check which of certain interpretable subhypothesis are responsible for significant result. However, as far as the authors are aware, there are no such tests developed for multivariate situations and geochemically or compositionally relevant sub-hypotheses, such as those that consider sub-compositions or balances of specific elements.
The contribution provides a systematic compilation of compositionally and geochemically potentially relevant subhypotheses and corresponding post-hoc tests. A particular challenge is that the number of compositional hypotheses is much larger than the number of subhypotheses (all subcompositions and balances) than in a contrast’s situation (all pairs). A Bonferroni approach is therefore impractical. We thus extend Scheffé’s principle of post-hoc testing to the situation where any number of additional subhypotheses can be tested simultaneously without the need for additional p-value corrections. Geochemists in this system of post-hoc tests can then either test geochemically interpretable relevant sub-hypotheses or test the model for the least explanatory sub-hypotheses and interpret these results based on a hierarchy of implied hypotheses.
The application of the method will be demonstrated on a snow data set, which was collected for exploration purposes on a Co-Au deposit.

Keywords: Scheffee test; post-hoc test; linear model; statistics; geochemistry; exploration; compostional data

  • Lecture (Conference)
    22st Annual Conference of the International Association for Mathematical Geosciences, 05.-12.08.2023, Trondheim, Norwegen

Permalink: https://www.hzdr.de/publications/Publ-38264
Publ.-Id: 38264


Behavioral responses of terrestrial mammals to COVID-19 lockdowns

Tucker, M.; Schipper, A.; Adams, T.; Attias, N.; Avgar, T.; Babic, N.; Barker, K.; Bastille-Rousseau, G.; Behr, D.; Belant, J.; Beyer Jr, D.; Blaum, N.; Blount, D.; Bockmühl, D.; Pires Boulhosa, R. L.; Brown, M.; Buuveibaatar, B.; Cagnacci, F.; Calabrese, J.; Černe, R.; Chamaillé-Jammes, S.; Chan, A. N.; Chase, M.; Chaval, Y.; Chenaux-Ibrahim, Y.; Cherry, S.; Ćirović, D.; Çoban, E.; Cole, E.; Conlee, L.; Courtemanch, A.; Cozzi, G.; Davidson, S.; Debloois, D.; Dejid, N.; Denicola, V.; Desbiez, A.; Douglas-Hamilton, I.; Drake, D.; Egan, M.; Eikelboom, J.; Fagan, W.; Farmer, M.; Fennessy, J.; Finnegan, S.; Fleming, C.; Fournier, B.; Fowler, N.; Gantchoff, M.; Garnier, A.; Gehr, B.; Geremia, C.; Goheen, J.; Hauptfleisch, M.; Hebblewhite, M.; Heim, M.; Hertel, A.; Heurich, M.; Hewison, M.; Hodson, J.; Hoffman, N.; Hopcraft, G.; Huber, D.; Isaac, E.; Janik, K.; Ježek, M.; Johansson, Ö.; Jordan, N.; Kaczensky, P.; Kamaru, D.; Kauffman, M.; Kautz, T.; Kays, R.; Kelly, A.; Kindberg, J.; Krofel, M.; Kusak, J.; Lamb, C.; Lasharr, T.; Leimgruber, P.; Leitner, H.; Lierz, M.; Linnell, J.; Lkhagvaja, P.; Long, R.; López-Bao, J.; Loretto, M.-C.; Marchand, P.; Martin, H.; Martinez, L.; Mcbride Jr, R.; Mclaren, A.; Meisingset, E.; Melzheimer, J.; Merrill, E.; Middleton, A.; Monteith, K.; Moore, S.; Moorter, B. V.; Morellet, N.; Morrison, T.; Müller, R.; Mysterud, A.; Noonan, M.; O’Connor, D.; Olson, D.; Olson, K.; Ortega, A.; Ossi, F.; Panzacchi, M.; Patchett, R.; Patterson, B.; Paula, R. C. D.; Payne, J.; Peters, W.; Petroelje, T.; Pitcher, B.; Pokorny, B.; Poole, K.; Potočnik, H.; Poulin, M.-P.; Pringle, R.; Prins, H.; Ranc, N.; Reljić, S.; Robb, B.; Röder, R.; Rolandsen, C.; Rutz, C.; Salemgareyev, A.; Samelius, G.; Sayine-Crawford, H.; Schooler, S.; Şekercioğlu, Ç.; Selva, N.; Semenzato, P.; Sergiel, A.; Sharma, K.; Shawler, A.; Signer, J.; Silovský, V.; Silva, J.; Simon, R.; Smiley, R.; Smith, D.; Solberg, E.; Soto, D.; Spiegel, O.; Stabach, J.; Stacy-Dawes, J.; Stahler, D.; Stephenson, J.; Stewart, C.; Strand, O.; Sunde, P.; Svoboda, N.; Swart, J.; Thompson, J.; Toal, K.; Uiseb, K.; Vanacker, M.; Velilla, M.; Verzuh, T.; Wachter, B.; Wagler, B.; Whittington, J.; Wikelski, M.; Wilmers, C.; Wittemyer, G.; Young, J.; Zięba, F.; Zwijacz-Kozica, T.; Huijbregts, M.; Mueller, T.

COVID-19 lockdowns in early 2020 reduced human mobility, providing an opportunity to disentangle its effects on animals from those of landscape modifications. Using GPS data, we compared movements and road avoidance of 2300 terrestrial mammals (43 species) during the lockdowns to the same period in 2019. Individual responses were variable with no change in average movements or road avoidance behavior, likely due to variable lockdown conditions. However, under strict lockdowns 10-day 95th percentile displacements increased by 73%, suggesting increased landscape permeability. Animals’ 1-hour 95th percentile displacements declined by 12% and animals were 36% closer to roads in areas of high human footprint, indicating reduced avoidance during lockdowns. Overall, lockdowns rapidly altered some spatial behaviors, highlighting variable but substantial impacts of human mobility on wildlife worldwide.

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Permalink: https://www.hzdr.de/publications/Publ-38263
Publ.-Id: 38263


Modeling radionuclide sorption for crystalline rocks using real samples: Challenges and sources of uncertainty

Pospiech, S.; Bok, F.; Brendler, V.

In a deep geological repository for nuclear waste, the host rock forms the outermost shell of the multi-barrier system designed to prevent toxic radionuclides from reaching the biosphere and subsequently the food chain. As a natural material, this host rock is characterized by heterogeneities, anisotropies, and different types of fluid pathways. Accordingly, the prediction of radionuclide (RN) migration through the host rock is complex and subject to large uncertainties. Besides salt and clay rocks, crystalline or granitoid rocks can also be considered as host rocks. There, joints and fracture network are very important parameters for the estimation of RN migration. However, microcracks or spatial veriability in the mineral composition, especially with respect to exposed mineral surfaces along fluid migration paths, can also significantly increase the uncertainties of the sorption capacity of the host rock. Another important uncertainty component is the scarcity of RN sorption data, namely for mafic minerals like the Biotite group or Amphiboles. Often one has to resort to analogues. Thus, for the calculation of distribution coefficients (Kd values, see the Smart Kd concept [1]) for a given combination of RN and rock formation, the results depend both on the knowledge of which mineral phases are actually exposed to pore water (as opposed to average rock compositions) and on the sorption models used. In our contribution, we present a workflow to use geologic samples to capture the heterogeneity of mineral composition along pathways using an approach from graph theory. Data of these spatially variable mineral compositions obtained from real
samples are then used as input parameters for the calculation of Kd values of uranium. The geochemical modelling was based on background data from sorption and surface complexation models. Furthermore, we show the uncertainties that can arise from measurement artifacts or (incomplete or missing) sorption data for certain mineral phases, especially at different pH levels. This, in turn, paves the way for corresponding sensitivity analyses indicating which input parameters deserve highest priority in future research efforts.

Keywords: kd value; sorption; nuclear waste repository; crystalline rock; uncertainty; geostatistics

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Permalink: https://www.hzdr.de/publications/Publ-38262
Publ.-Id: 38262


Tunable Crystallinity and Electron Conduction in Wavy 2D Conjugated Metal-Organic Frameworks via Halogen Substitution

Jastrzembski, K.; Zhang, Y.; Lu, Y.; Sporrer, L.; Pohl, D.; Rellinghaus, B.; Waentig, A. L.; Zhang, H.; Mücke, D.; Fu, S.; Polozij, M.; Li, X.; Zhang, J.; Wang, M.; Morag, A.; Yu, M.; Mateo-Alonso, A.; Wang, H. I.; Bonn, M.; Kaiser, U.; Heine, T.; Dong, R.; Feng, X.

Currently, most reported 2D conjugated metal-organic frameworks (2D c-MOFs) are based on planar polycyclic aromatic hydrocarbons (PAHs) with symmetrical functional groups, limiting the possibility of introducing additional substituents to fine-tune the crystallinity and electrical properties. Herein, a novel class of wavy 2D c-MOFs with highly substituted, core-twisted hexahydroxy-hexa-cata-benzocoronenes (HH-cHBCs) as ligands is reported. By tailoring the substitution of the c-HBC ligands with electron-withdrawing groups (EWGs), such as fluorine, chlorine, and bromine, it is demonstrated that the crystallinity and electrical conductivity at the molecular level can be tuned. The theoretical calculations demonstrate that F-substitution leads to a more reversible coordination bonding between HH-cHBCs and copper metal center, due to smaller atomic size and stronger electron-withdrawing effect. As a result, the achieved F-substituted 2D c-MOF exhibits superior crystallinity, comprising ribbon-like single crystals up to tens of micrometers in length. Moreover, the F-substituted 2D c-MOF displays higher electrical conductivity (two orders of magnitude) and higher charge carrier mobility (almost three times) than the Cl-substituted one. This work provides a new molecular design strategy for the development of wavy 2D c-MOFs and opens a new route for tailoring the coordination reversibility by ligand substitution toward increased crystallinity and superior electric conductivity.

Keywords: 2D conjugated MOFs; conductive MOFs; halogen substitution; tunable crystallinity; wavy structure

Related publications

Permalink: https://www.hzdr.de/publications/Publ-38260
Publ.-Id: 38260


Structural changes in Salophen versus Pyrophen actinide complexes –a case study

Duckworth, T.; Köhler, L.; Schmidt, M.; Gericke, R.; Patzschke, M.; Kaden, P.; Stumpf, T.; März, J.

Understanding how structural changes of the ligand scaffold influence the coordination chemistry of early actinides is indispensable for the development of selective ligands for e.g. decontamination purposes. To obtain a profound insight into the electronic und bonding properties of early actinides, Schiff base ligands based on the salen type, have been extensively used in our group and others.[1–4] Schiff bases have shown to be excellent model ligands due to their accessible synthesis and easy functionalization and their ability to coordinate to the 5f-elements. In this respect, we have been exploring the coordination chemistry of the early actinides (Th – Pu) with pyrophen, a pure nitrogen donor ligand formed by a condensation reaction of 2-formylpyrrole with o-phenylendiamine.[5,6] A series of homoleptic 2:1 complexes has been synthesized, allowing the comparison of the hard oxygen donor of the phenolate group in the salophen system versus the soft nitrogen donor of the pyrrolide group in pyrophen. Quantum chemical calculations along with spectroscopic studies by nuclear magnetic resonance (NMR) and single crystal x-ray diffraction (SC-XRD) have been performed to elucidate the influence of hard and soft donors on the bonding strength. In solution, as confirmed by NMR, we encountered just one set of signals corresponding to a 2:1 homoleptic complex in the pyrophen system compared to two sets of signals corresponding to 2:1 homoleptic isomers present in the salophen case. In the solid state, crystallographic analysis shows that the salophen ligand adopts a sandwich like structure whereas in the pyrophen system a pincer like arrangement is preferred (see figure below).

Figure 1 Uranium(IV) complexes of salophen (left) and pyrophen (right)
References
[1] T. Radoske et al., Dalton Transactions 2020, 49, 17559–17570.
[2] R. Kloditz et al., Inorg. Chem. 2021, 60, 2514–2525.
[3] L. Köhler et al., Chemistry – A European Journal 2021, 27, 18058–18065.
[4] B. E. Klamm et al., Inorg. Chem. 2018, 57, 15389–15398.
[5] C.D. Bérubé et al., Organometallics 2003, 22, 434–439.
[6] T. Duckworth et al. manuscript in preparation.

Acknowledgment
This work was supported by the German Federal Ministry of Education and Research (BMBF) under project number 02NUK059 (f-char).

  • Poster
    ICFE-11 Strasbourg 2023, 22.-26.08.2023, Strasbourg, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-38259
Publ.-Id: 38259


A tripodal pyrrol imine schiff base ligand: synthesis and coordination chemistry with early actinides

Duckworth, T.; März, J.; Patzschke, M.; Schmidt, M.; März, J.; Stumpf, T.

Our laboratory has been actively engaged in exploring the fundamental behavior of the early 5f elements in solution and solid state, for instance with tetradentate coordinating Schiff base ligands.[1–4] Schiff base ligands are of special interest since they can easily be prepared by a condensation reaction and are known to coordinate to different metal centers in various oxidation states. To study the reactivity and complexation differences from the tetradentate to a hexadentate binding motif, with regards to bonding trends and electronic properties, we recently extended our palette of Schiff base chelators to the hexadentate pure N-donor (tris-((1H-pyrrol-2-ylmethyl-ene)ethane)-amine (trenpy) and began to explore its coordination chemistry with the early tetravalent actinides.
Applying a salt metathesis reaction of one equivalent of AnCl4(dme)2 (An = Th, U, Np, and Pu) and one equivalent of the trianionic trenpy ligand led to the formation of the respective complexes. SC-XRD measurements confirmed the coordination of three imine and three pyrrolide nitrogens of one trenpy ligand to the metal center in the predicted hexadentate fashion. In addition, a chloro ligand binds to the An(IV), forming a 7-coordinate distorted monocapped octahedron. Analysis of SC-XRD data and quantum chemical calculations revealed different bond lengths and strengths for the different nitrogen donors (Npyrrolide and Nimine) which are slightly longer for the first and slightly shorter for the later case compared to the reported homoleptic bispyren complexes.[3] Remarkably, quantum chemical calculations for Pa(IV)-N revealed no exceptional backbonding effects as seen in [Pa(pyren)2]. We can speculate that the chloride atom indicating an influence of the chlorine atom contributes to the suppression of this effect.

Acknowledgement: This work is supported by the German Federal Ministry of Education and Research (BMBF) under project number 02NUK059B (f-Char).

[1] T. Radoske et al., Chemistry – A European Journal 2020, 26, 16853–16859.
[2] T. Radoske et al., Dalton Transactions 2020, 49, 17559–17570.
[3] L. Köhler et al., Chemistry – A European Journal 2021, 27, 18058–18065.
[4] R. Kloditz et al., Inorganic Chemistry 2021, 60, 2514–2525.

  • Poster
    Actinides 2023, 05.-08.06.2023, Golden, USA

Permalink: https://www.hzdr.de/publications/Publ-38258
Publ.-Id: 38258


Optical measurement of the shear stress and velocity distribution in an idealized deglutition process

Skrypnik, A.; Heitkam, S.; Gerstenberg, C.; Morelle, E.; McHardy, C.; Rauh, C.

The paper and dataset on the modelling of foam deglutition in a replica of a human mouth cavity.
It includes the optical measurement of elastic stresses and bubble flows of the foam flow furing the deglutition.

Each data folder includes:

Laborbuch.xls labbook
Fluessigkeitsgehalt--data on liquid fraction

1. masking2.mlx script --- script to create the mask for the tongue and palete plates
2.025 --- original data folder
3.025_pre --- cutted (to ROI) image data folder
4.025_pre_predict --- folder with the ANN processed data, with enhanced bubble positions
5.masked2--- masked images
6.SCRIPTS--- folder with the matlab scripts
6.* some video for the visualisation
7. Calculate_new-- folder with the scripts used for the calculation. Including:
common_mod.msx --- common matlab file for the stress data at the right wall
left_common_mod.msx --- common matlab file for the stress data at the left wall
tau_loc_left.m -- to plot the graph
all_script.msx --- run the common file for all the images

bub_parts -- folder with the files to define bubble velocity:

full_bub-- velocity of full bubble

Keywords: foam; deglutition; shear stress; bubble tracking

Permalink: https://www.hzdr.de/publications/Publ-38256
Publ.-Id: 38256


A novel bioleaching approach for metal(loid) mobilisation from mine waste by halophilic sulfur-oxidising bacteria

Opara, C. B.

Mining industries in the European Union (EU) have been disposing of waste from mining activities for over a century, accounting for 29% of the EU-28's current waste output. These mine wastes usually contain elevated amounts of valuable and hazardous metal(loid)s, which may pose environmental risks but can also provide opportunities for resource recovery. Reprocessing of mine waste can benefit the economy by meeting some of the increasing global demand for raw materials, while also providing environmental benefits by mitigating the environmental risks associated with mine waste. Bioleaching is considered a more sustainable and cost-effective technology for the extractive metallurgy of refractory and low-grade ores (including waste materials), in comparison to other methods such as pyrometallurgy. Despite its acceptance, bioleaching has remained limited in its use in the mining industry and has only found application as a niche technology. Bioleaching operations are hindered by the presence of chloride ions, which affect the growth and activities of conventional acidophilic bioleaching prokaryotes. This vulnerability restricts the application of bioleaching, especially in areas such as Chile and Western Australia, where soil and water sources have high chloride content and obtaining fresh water for mineral processing is scarce and becoming a financial burden. This has generated significant interest in discovering halotolerant microorganisms capable of bioleaching in seawater media. Furthermore, bioleaching with acidophilic organisms is performed at a pH of ≤ 2 and can therefore lead to the acidification of the environment. Therefore, it is worthwhile to investigate the bioleaching of mine waste at circumneutral pH, as it may be beneficial to the environment.
In order to reduce the environmental risks associated with mine wastes, as well as economically recover valuable metals while contributing to the ongoing search for halotolerant organisms for saline water bioleaching, this thesis aimed to develop an alternative bioleaching approach for the bioprocessing of mine wastes in the presence of chloride ions and/or at circumneutral pH. Initially, three mine waste samples originating from the active Neves Corvo mine in Portugal and the closed Freiberg mine in Germany were assessed for their potential environmental risks (Chapter 2). The metal(loid)s in the waste samples were partitioned into seven operationally defined geochemical fractions using the Zeien and Brummer sequential extraction scheme (Zeien and Brummer, 1989) along with chemical and mineralogical analysis. This study revealed that certain elements, particularly Pb and Zn, were highly mobile in the three mine waste samples and could therefore be easily released into the environment, potentially contaminating important human resources such as surface water, soil, and plants, and may be incorporated into the food chain. The possibility to simultaneously generate economic value and reduce environmental risks via the bioprocessing of mine waste was demonstrated in Chapter 3. In this study, a novel acidophilic consortium mainly dominated by the iron-oxidizing Leptospirillum genus and Acidiphilium sp. simultaneously recovered both valuable and hazardous metal(loid)s from the Neves Corvo mine’s waste rock (NC_01) and tailings (NC_02) samples. Over 70% of the total Zn, Co, In, As and Cd contents of the two waste samples were solubilised, as well as 55 - 65% of Mn. However, the recovery of Cu was refractory (21 – 33%) and Pb was not solubilised, as they were mainly co-precipitated with biogenic jarosite. Scanning electron microscope-based automated image analyses (SEM/MLA-GXMAP) and X-ray diffraction (XRD) detected a reduction in the pyrite and silicate contents of both NC_01 and NC_02 after bioleaching by the acidophilic consortium, as well as the formation of secondary minerals, mainly jarosite.
The screening of new organisms for bioleaching potential is presented in Chapters 4, 5 and 6. Four halophilic neutrophile sulfur-oxidising bacteria (Thiomicrospira cyclica, Thiohalobacter thiocyanaticus, Thioclava electrotropha, and Thioclava pacifica) (Chapter 4) and two heterotrophic bacteria (Alicyclobacillus acidiphilus and Brevundimonas sp.) (Chapter 6) were screened for bioleaching potential by evaluating their rates of metal(loid) mobilisation from NC_01 into solution. Bioleaching results revealed T. electrotropha and T. pacifica as the most promising for bioleaching as they both leached about 30% of the total Co content of NC_01, as well as between 8 – 17% of other metal(loid)s (Cu, Pb, Zn, K, Cd, and Mn). The study also showed that roasting the waste rock in a microwave at 400 and 500 °C improved the bioleaching efficiency of T. electrotropha for Pb (13.7% to 45.7%), Ag (5.3% to 36%), and In (0% to 27.4%). In Chapter 5, the two promising organisms were assessed for their capacity to also mobilise metal(loid)s from NC_02. The maximum recoveries for Cu, Pb, Zn, Co, As, Cd, K, Sb, Ag & Mn from NC_02 were between 2 – 24%, slightly lower than the recoveries from NC_01. SEM/MLA-GXMAP did not detect any difference in the mineralogy of both NC_01 and NC_02 before and after bioleaching by the two promising halophilic bacteria.

  • Doctoral thesis
    TU BA Freiberg, 2023
    Mentor: Kutschke, Sabine
    178 Seiten

Permalink: https://www.hzdr.de/publications/Publ-38253
Publ.-Id: 38253


Fabrication and characterization of heavily doped n-type GaAs for mid-infrared plasmonics

Duan, J.; Liedke, M. O.; Dawidowski, W.; Li, R.; Butterling, M.; Hirschmann, E.; Wagner, A.; Wang, M.; Boyu Young, L.; Glen Lin, Y.-H.; Hong, M.; Helm, M.; Zhou, S.; Prucnal, S.

N-type doping in GaAs is a self-limited process, rarely exceeding a carrier concentration level of 10^19 cm−3. Here, we investigated the effect of intense pulsed light melting on defect distribution and activation efficiency in chalcogenide-implanted GaAs by means of positron annihilation spectroscopy and electrochemical capacitance–voltage techniques. In chalcogenide-doped GaAs, donor–vacancy clusters are mainly responsible for donor deactivation. Using positrons as a probe of atomic scale open volumes and DFT calculations, we have shown that after nanosecond pulsed light melting the main defects in heavily doped GaAs are gallium vacancies decorated with chalcogenide atoms substituting As, like VGa–nTeAs or VGa–nSAs. The distribution of defects and carriers in annealed GaAs follows the depth distribution of implanted elements before annealing and depends on the change in the solidification velocity during recrystallization.

Keywords: GaAs; hyperdoping; plasmonics

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  • Secondary publication expected from 06.09.2024

Permalink: https://www.hzdr.de/publications/Publ-38251
Publ.-Id: 38251


Sharp MIR plasmonic modes in gratings made of heavily doped pulsed laser-melted Ge1-xSnx

Berkmann, F.; Steuer, O.; Ganss, F.; Prucnal, S.; Schwarz, D.; Fischer, I. A.; Schulze, J.

Plasmonic structures made out of highly doped group-IV semiconductor materials are of large interest for the realization of fully integrated mid-infrared (MIR) devices. Utilizing highly doped Ge1−xSnx alloys grown on Si substrates is one promising route to enable device operation at near-infrared (NIR) wavelengths. Due to the lower effective mass of electrons in Sn compared to Ge, the incorporation of Sn can potentially lower the plasma wavelength of Ge1−xSnx alloys compared to that of pure Ge. However, defects introduced by the large lattice mismatch to Si substrates as well as the introduction of alloy scattering limit device applications in practice. Here, we investigate pulsed laser melting as one strategy to increase material quality in highly doped Ge1−xSnx alloys. We show that a pulsed laser melting treatment of our Ge1−xSnx films not only serves to lower the material’s plasma frequency but also leads to an increase in active dopant concentration. We demonstrate the application of this material in plasmonic gratings with sharp optical extinction peaks at MIR wavelengths.

Keywords: Plasmonics; group-IV semiconductors; GeSn alloys; PLM

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Permalink: https://www.hzdr.de/publications/Publ-38250
Publ.-Id: 38250


Highly Efficient Near-Infrared Light-Emitting Diode Based on CdHgSe/ZnCdS Core/Shell Nanoplatelets

Roshan, H.; Prudnikau, A.; Paulus, F.; Martín-García, B.; Hübner, R.; Jalali, H. B.; de Franco, M.; Prato, M.; Di Stasio, F.; Lesnyak, V.

Luminescent Quantum dots (QDs) have gathered significant attention over the past decade. Their distinct chemical and optical properties, including size-adjustable light emission, remarkable photostability, and a range of fluorescence colors, have motivated extensive investigations. In recent years, near-infrared (NIR) quantum dots have emerged as a promising avenue for a new generation of optoelectronic devices including infrared detectors and light sources. This study presents the fabrication of NIR-LEDs operating at the o-band optical telecommunication wavelength (1300 nm) using novel CdHgSe/ZnCdS core/shell nanoplatelets with a photoluminescence quantum yield of 70%. The nanoplatelets achieve a remarkable external quantum efficiency (EQE) of 7% in the final device. Notably, the resulting EQE of the fabricated NIR-LED sets a new benchmark for mercury-based QD LEDs.

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  • Poster
    2023 MRS Fall Meeting & Exhibit, 26.11.-01.12.2023, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-38249
Publ.-Id: 38249


Enhanced Luminescence of Yb3+ Ions Implanted to ZnO through the Selection of Optimal Implantation and Annealing Conditions

Ratajczak, R.; Guziewicz, E.; Prucnal, S.; Mieszczynski, C.; Jozwik, P.; Barlak, M.; Romaniuk, S.; Gieraltowska, S.; Wozniak, W.; Heller, R.; Kentsch, U.; Facsko, S.

Rare earth-doped zinc oxide (ZnO:RE) systems are attractive for future optoelectronic devices such as phosphors, displays, and LEDs with emission in the visible spectral range, working even in a radiation-intense environment. The technology of these systems is currently under development, opening up new fields of application due to the low-cost production. Ion implantation is a very promising technique to incorporate rare-earth dopants into ZnO. However, the ballistic nature of this process makes the use of annealing essential. The selection of implantation parameters, as well as post-implantation annealing, turns out to be non-trivial because they determine the luminous efficiency of the ZnO:RE system. This paper presents a comprehensive study of the optimal implantation and annealing conditions, ensuring the most efficient luminescence of RE3+ ions in the ZnO matrix. Deep and shallow implantations, implantations performed at high and room temperature with various fluencies, as well as a range of post-RT implantation annealing processes are tested:

rapid thermal annealing (minute duration) under different temperatures, times, and atmospheres (O2, N2, and Ar), flash lamp annealing (millisecond duration) and pulse plasma annealing (microsecond duration). It is shown that the highest luminescence efficiency of RE3+ is obtained for the shallow
implantation at RT with the optimal fluence of 1.0 × 10^15 RE ions/cm2 followed by a 10 min annealing in oxygen at 800 ◦C, and the light emission from such a ZnO:RE system is so bright that can be observed with the naked eye.

Keywords: wide bandgap oxides; zinc oxide; rare earth; ion implantation

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Permalink: https://www.hzdr.de/publications/Publ-38248
Publ.-Id: 38248


Alpha-emitting Radionuclides: Current Status and Future Perspectives

Miederer, M.; Benešová-Schäfer, M.; Mamat, C.; Kästner, D.; Pretze, M.; Michler, E.; Brogsitter, C.; Kotzerke, J.; Kopka, K.; Scheinberg, D.; McDevitt, M.

The use of radionuclides for targeted endoradiotherapy is a rapidly growing field in oncology. In particular, the focus on the biological effects of different radiation qualities is an important factor in understanding and implementing new therapies. Together with the combined approach of imaging and therapy, therapeutic nuclear medicine has made great progress recently. A par-ticular area of research is the use of alpha-emitting radionuclides, which have unique physical properties associated with outstanding advantages, e.g. for single tumor cell targeting. Here, recent results and open questions regarding the production of alpha-emitting isotopes, their chemical combination with carrier molecules and clinical experience from compassionate use reports and clinical trials are discussed.

Keywords: Alpha emitter; targeted alpha therapy; actinium-225; high LET; theranostic

Permalink: https://www.hzdr.de/publications/Publ-38247
Publ.-Id: 38247


The deep underground Bellotti Ion Beam Facility - status and perspectives

Junker, M.; Imbriani, G.; Best, A.; Boeltzig, A.; Compagnucci, A.; Di Leva, A.; Ferraro, F.; Rapagnani, D.; Rigato, V.

For more than three decades, accelerators are in use in the underground laboratories of the Laboratori Nazionali del Gran Sasso (LNGS), located in central Italy. The LUNA Collaboration has exploited the potential of the site’s low cosmic ray background to achieve important and often groundbreaking results in the field of nuclear astrophysics. This long success story stimulated the installation of accelerators in deep underground laboratories also in other countries, including the USA and China. Recently, LNGS took a major step forward with the activation of the Bellotti Ion Beam Facility, which will provide ion beams to the scientific community for research not only in nuclear astrophysics, but in all fields that can benefit from the low cosmic ray background conditions of the underground site.

Keywords: ion beam accelerator; underground laboratory; nuclear astrophysics; applied sciences; ion beam analysis

Permalink: https://www.hzdr.de/publications/Publ-38245
Publ.-Id: 38245


Solar thermal energy applications - state of the art and current challenges

Krause, M.; Niranjan, K.; Barshilia, H.; Escobar-Galindo, R.

Solar thermal energy is the only form of renewable energy with an intrinsic storage capacity in the form of heat. Based on flat plate and evacuated tube collectors, approx. 520 GW power have been installed worldwide for domestic hot water supply boiling and heating so far. For concentrated solar power (CSP), the solar flux from solar concentrators is transformed into heat at a solar receiver, and either immediately converted into electricity by a downstream turbine power generator unit or stored as disposable heat energy in storage tanks. Starting from its today’s 7 GW installed peak power, CSP has a huge growth potential in the next decades for electricity generation, industrial heat production, decentralized district heating and thermal building management. Its further progress depends mainly on two crucial factors: i) the increase of energy conversion efficiency and ii) the reduction of installation and service costs.

In this talk, an overview of the state of the art and the current challenges for solar thermal energy applications will be given. It will start with few remarks about recent approaches to improve the performance and stability of flat plate and tube collectors. The main part of the talk will focus on recent materials science efforts devoted to increase the CSP plant efficiency by implementing higher operation temperatures and reducing the levelized costs of electricity. An overview about current and ongoing plant installations as well as on results for conventional absorber paints is provided. Based on the identified limitations of these approaches, the concept of solar selective coatings (SSCs) is introduced. Using realistic operational parameters of CSP plants, its potential and its limitations are discussed and graphically illustrated [1]. Examples from our own research on design, characterization and thermal testing of SSCs will be given with emphasis on their optical efficiency and thermal stability up to temperatures of 800 °C [2, 3]. Finally, volumetric receivers are introduced as another alternative concept to advance CSP technology. These solar absorbers consist of regular, porous metal or dielectric frameworks. The porous structure mutually affects radiation, convection, and conductive transport of thermal energy. At high temperature, the porous absorber matrix is expected to have a higher efficiency than a "standard" tubular receiver, because the volumetric effect leads to a low temperature at the front of the absorber, reducing the radiative emission losses.
[1] R. Escobar-Galindo, M. Krause, K. Niranjan and H. Barshilia, Solar selective coatings and materials for high-temperature solar thermal applications, Chapter 13 in "Sustainable Material Solutions for Solar Energy Technologies", Elsevier, 2021
[2] F. Lungwitz et al., Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Materials and Solar Cells 196, 84-93 (2019)
[3] K. Niranjan et al., WAlSiN-based solar-selective coating stability-study under heating and cooling cycles in vacuum up to 800 °C using in situ Rutherford backscattering spectrometry and spectroscopic ellipsometry, Solar Energy Materials and Solar Cells 255, 112305 (2023)

Keywords: Solar thermal energy; Concentrated solar power; Energy materials; High temperature materials; Solar selective coatings

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  • Invited lecture (Conferences)
    V2023 - International conference and Exhibition, 18.-21.09.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38244
Publ.-Id: 38244


In situ depth-resolved compositional, structural and optical characterization of functional thin films at high temperatures

Escobar Galindo, R.; Janke, D.; Lungwitz, F.; Munnik, F.; Hübner, R.; Niranjan, K.; Fernandes, F.; Barshilia, H. C.; Krause, M.

In addition to classical studies comparing composition, structure and functional properties of thin films before and after high-temperature treatments, new approaches towards the correlation of optical properties, composition and structural changes upon annealing are necessary by using in situ techniques. In situ measurements allow the investigation of the materials in real-time under conditions simulating the intended applications, e.g. high temperatures and defined atmospheres. Intra- and interlayer phase transitions, defect generation and annealing, degradation processes, such as element redistribution and interface mixing, as well as material exchange with the environment can have substantial effects on the material’s structure, properties and functionality. All these processes can be studied employing in situ techniques.
In this work, various applications of a cluster tool for depth-resolved compositional, structural and optical characterization of layered materials with thicknesses ranging from sub-nm to 1 μm and for temperatures of -100 to 800 °C are described. [1] The techniques implemented in this setup include Rutherford backscattering spectrometry (RBS), Elastic Recoil Detection (ERD), Raman spectroscopy, Spectroscopic Ellipsometry (SE) and UV-Vis-NIR spectrometry. These in situ techniques allow to identify and to quantify element redistributions, material losses and gains, and the conservation or changes of the optical material properties. Intermixing of the sharp interlayers could also appear at temperatures of up to 800 °C. The onset-temperature of those effects, corresponding to the stability limit, are identified by the in situ measurements. Results of different material systems and processes will be presented including: i) metal-induced crystallization of amorphous carbon in a layer stack of SiO2/ a-C/ Ni; ii) high-temperature stability tests of a SnO2:Ta transparent conductive oxide coating [2] and of a WAlSiN-based solar-selective coating [3] as well as iii) diffusion monitoring of an solid-lubricant Ag-rich layer sandwiched between two layers of either TiN or TiSiN.

References

[1] R. Wenisch, F. Lungwitz, D. Hanf, R. Heller, J. Zscharschuch, R. Hübner, J. von Borany, G. Abrasonis, S. Gemming, R. Escobar-Galindo, M. Krause. Anal. Chem. 90 (2018) 7837–7842.
[2] F. Lungwitz, R. Escobar-Galindo, D. Janke, E. Schumann, R. Wenisch, S. Gemming, M. Krause. Sol. Energy Mater. Sol. Cells. 196 (2019) 84–93.
[3] K. Niranjan, M. Krause, F. Lungwitz, F. Munnik, R. Hübner, S. Pramod Pemmasani, R. Escobar Galindo, H. C. Barshilia. Sol. Energy Mater. Sol. Cells. 255 (2023) 112305.

Keywords: In situ analysis; functional thin films; solar coatings; high temperature materials; energy materials

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  • Lecture (Conference)
    19th International Conference on Thin Films, 26.-29.09.2023, Burgos, Espana

Permalink: https://www.hzdr.de/publications/Publ-38243
Publ.-Id: 38243


X-ray absorption spectroscopy reveals the transient oxidation state during microbial uranium(VI) reduction by a sulfate-reducing microorganism

Hilpmann, S.; Roßberg, A.; Steudtner, R.; Drobot, B.; Hübner, R.; Bok, F.; Prieur, D.; Bauters, S.; Kvashnina, K.; Stumpf, T.; Cherkouk, A.

High-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy was used to investigate the reduction of U(VI) by the sulfate-reducing bacterium Desulfosporosinus hippei DSM 8344T, confirming the partial reduction of U(VI) and the presence of U(V).

Keywords: uranium(VI) reduction; sulfate-reducing bacteria; HERFD-XANES

  • Open Access Logo Contribution to external collection
    in: ESRF Highlights 2023, Grenoble: European Synchrotron Radiation Facility, 2024

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Permalink: https://www.hzdr.de/publications/Publ-38242
Publ.-Id: 38242


Resonance-Based Sensing of Magnetic Nanoparticles Using Microfluidic Devices with Ferromagnetic Antidot Nanostructures

Dowling, R.; Narkovic, R.; Lenz, K.; Oelschlägel, A.; Lindner, J.; Kostylev, M.

We demonstrated resonance-based detection of magnetic nanoparticles employing novel designs based upon planar (on-chip) microresonators that may serve as alternatives to conventional magnetoresistive magnetic nanoparticle detectors. We detected 130 nm sized magnetic nanoparticle clusters immobilized on sensor surfaces after flowing through PDMS microfluidic channels molded using a 3D printed mold. Two detection schemes were investigated: (i) indirect detection incorporating ferromagnetic antidot nanostructures within microresonators, and (ii) direct detection of nanoparticles without an antidot lattice. Using scheme (i), magnetic nanoparticles noticeably downshifted the resonance fields of an antidot nanostructure by up to 207 G. In a similar antidot device in which nanoparticles were introduced via droplets rather than a microfluidic channel, the largest shift was only 44 G with a sensitivity of 7.57 G/ng. This indicated that introduction of the nanoparticles via microfluidics results in stronger responses from the ferromagnetic resonances. The results for both devices demonstrated that ferromagnetic antidot nanostructures incorporated within planar microresonators can detect nanoparticles captured from dispersions. Using detection scheme (ii), without the antidot array, we observed a strong resonance within the nanoparticles. The resonance’s strength suggests that direct detection is more sensitive to magnetic nanoparticles than indirect detection using a nanostructure, in addition to being much simpler.

Keywords: nanoparticles; sensors; fluids; ferromagnetic resonance; magnetism; microfluidics

Permalink: https://www.hzdr.de/publications/Publ-38241
Publ.-Id: 38241


Graphene and Other 2D Materials: Basics and Light-Matter interaction

Winnerl, S.

We discuss basic physical properties of graphene and other 2D materials, in particular TMDCs and their heterostructures with a focus on light-matter interaction.

Keywords: graphene; 2D materials; light-matter interaction

  • Lecture (others)
    Summer school CRC 1242, 21.-25.08.2023, Selb, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38240
Publ.-Id: 38240


Auger scattering in Landau-quantized graphene and Hg0.83Cd0.17Te

Winnerl, S.

We explore the carrier dynamics in graphene and gapless bulk Hg0.83Cd0.17Te under Landau quantization. To this end, individual levels of the non-equidistant Landau ladders are pumped and probed by circularly polarized mid-infrared radiation pulses. While Auger scattering is very efficient in graphene, resulting in carrier redistribution on a ps timescale, this process is strongly suppressed in Hg0.83Cd0.17Te, yielding two orders of magnitude longer lifetimes.

Keywords: graphene; HgCdTe; Landau quantization

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  • Invited lecture (Conferences)
    24th Conference on onApplied Electromagnetics and Communication (ICECOM 2023), 27.-29.09.2023, Dubrovnik, Kroatien

Permalink: https://www.hzdr.de/publications/Publ-38239
Publ.-Id: 38239


Low energy carrier dynamics in Landau quantized graphene and HgCdTe - Perspectives for optical gain?

Winnerl, S.; Seidl, A.; But, D.; Orlita, M.; Helm, M.

Over six decades ago, the potential of relativistic electrons to emit electromagnetic radiation was initially reported [1]. The discovery of graphene with a band structure resembling massless Dirac fer-mions revitalized the search for Landau-level lasing schemes [2, 3] that started earlier on non-parabolic semiconductors. The realization of a maser based on this concept, with tuning through changes in magnetic field, holds significant appeal, especially for applications within the terahertz frequency range.
The initial steps towards reaching optical gain are selective pumping of individual Landau levels (LLs) and characterizing the lifetimes in these levels. The carrier dynamics in the three-level system LL-1, LL0 and LL1 of the non-equidistant Landau ladder in graphene was investigated by pump-probe ex-periments. Circularly polarized radiation was utilized to selectively pump and probe the energetically degenerate transitions LL-1 → LL0 and LL0 → LL1 [4]. The experiments were carried out at a photon energy of 75 meV (wavelength 16.5 µm) using the free-electron laser FELBE as a source for intense ps pulses [5]. Our findings indicate, fast Auger scattering rapidly redistributes the carriers [4]. Since several Landau laser schemes [2, 3] involve the levels LL1 and LL2, we performed pump-probe experiments on the transitions LL-1 → LL2 and LL-2 → LL1.
Pumping and probing with co-polarized radiation results in higher pump-probe signals as compared to counter-polarized configurations (cf. Fig. 1). Note that in the absence of scattering, the coun-ter-polarized configuration would provide no signal as it probes levels that are not directly affected by optical pumping. The results show that within the temporal resolution of the experiment, a non-equilibrium distribution is achieved. However, it rapidly thermalizes as indicated by the induced transmission in counter-polarized configurations that reaches a maximum a few ps later than the signals in co-polarized configuration. In summary, while the linear band structure is ideal for selective optical pumping, our experiments indicate that rapid Coulomb scattering severely limits potential to achieve population inversion in Landau-quantized graphene. For comparison, we have explored the dynamics in HgCdTe. Materials with a Cd concentration of 17 % feature (three dimensional) linear dispersion along with flat bands. The main difference to graphene is the strong spin-orbit coupling in this material. As a consequence, the energy Eigenvalues are modified to a non-equidistant ladder that does not comprise pairs of levels that match energetically for Auger scattering. Pump-probe experiments on the lowest levels reveal lifetimes of 0.5 ns, i.e. two orders of magnitude longer than in graphene, indicating that indeed Auger scattering is strongly suppressed. In this material, tunable classical cyclotron emission in the THz range has been realized upon electrical excitation.
References:
[1] J. Schneider, Phys. Rev. Lett. 2, 504 (1959).
[2] Y. R. Wang, M. Tokman, A. Belyanin, Phys. Rev. A 91, 033821 (2015).
[3] S. Brem, F. Wendler, S. Winnerl, E. Malic, Phys. Rev. Mater. 2, 034002 (2018)
[4] M. Mittendorff et al. Nature Phys. 11, 75 (2015).
[5] M. Helm et al., Eur. Phys. J. Plus 138, 158 (2023).
[6] D.B. But et al., Nat. Photonics 13, 783 (2019).

Keywords: Landau quantization; graphene; HgCdTe; Landau level gain

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  • Invited lecture (Conferences)
    22nd International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 22), 14.-18.08.2023, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38238
Publ.-Id: 38238


Terahertz radiation from a large-area photoconductive emitter via high average power Yb-oscillator

Khalili, M.; Vogel, T.; Mansourzadeh, S.; Winnerl, S.; Saraceno, C.

Photoconductive emitters excited by fs-lasers are the most commonly used emitters in THz-TDS systems, enabling record high dynamic range and wide bandwidths [1,2]. So far, these emitters have mostly optimized for operation with low average power, low-cost fs-laser systems and have a typical dimension of a few µm^2 for the photoconductive gap [3]. In parallel, large-area emitters with mm^2 size have been explored for scaling fluence and obtaining high fields [4]. However, so far, no attempts have been made of using high average power laser systems as excitation sources, as a possible path to increase the THz source average power and reach even higher dynamic range than current reported records. In this work, we present our first results in this direction and show THz emission from a large area photoconductive emitter (LAE) based on SI-GaAs with a 1×1 cm^2 active area, excited by a frequency-doubled home-built high average power ultrafast oscillator, capable of 92 fs at a centre frequency 515 nm with 90 MHz repetition rate and 17 W of average power. We show here preliminary results exciting the LAE with 1 W from this laser system, which is to the best of our knowledge the highest average power applied to such an emitter, without any apparent sign of thermal saturation.
1. R. B. Kohlhaas, S. Breuer, L. Liebermeister, S. Nellen, M. Deumer, M. Schell, M. P. Semtsiv, W. T. Masselink, and B. Globisch, Appl. Phys. Lett. 117, 131105 (2020).
2. U. Nandi, K. Dutzi, A. Deninger, H. Lu, J. Norman, A. C. Gossard, N. Vieweg, and S. Preu, Opt. Lett. 45, 2812 (2020).
3. S. Winnerl, J Infrared Milli Terahz Waves 33, 431 (2012).
4. M. Beck, H. Schäfer, G. Klatt, J. Demsar, S. Winnerl, M. Helm, and T. Dekorsy, Opt. Express 18, 9251 (2010).

Keywords: terahertz; photoconductive emitter; large-area emitter

  • Poster
    CLEO Europe/EQEC, 26.-30.06.2023, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38237
Publ.-Id: 38237


Low-energy population inversion in graphene evidenced in a three-pulse pump-probe experiment

Mavridou, K.; Seidl, A.; Pashkin, O.; Helm, M.; Winnerl, S.

Population inversion and optical gain are often difficult to measure in systems that do not exhibit lasing. For example, two-color pump-probe experiments targeting gain require precise reference measurements in order to distinguish gain from simple absorption bleaching due to Pauli blocking. In the mid-infrared (MIR) and far-infrared (FIR) spectral range such experiments are even more difficult as free-carrier absorption complicates the analysis. Here we utilize a three-pulse technique [1], which has been employed to find evidence for gain and spectral hole burning in the near-infrared (NIR), to study the dynamics of the MIR population inversion in optically pumped intrinsic graphene. Graphene is an interesting material to apply this technique since there are on one hand many reports on ultrafast thermalization, excluding inversion, but on the other hand many suggestions to realize gain, in particular in the THz range.

The principle of the technique is sketched in Fig. 1a. A strong NIR “gain” pulse (photon energy 1.55 eV) excites interband transitions in an epitaxial multilayer graphene sample on SiC. The majority of graphene layers is almost intrinsic. The low-energy carrier dynamics is monitored by measuring the differential transmission change in a degenerate MIR (photon energy 250 meV) pump-probe experiment. This differential transmission generally is positive, corresponding to bleaching via Pauli blocking by carriers that are photoexcited by the MIR pump pulse. If, however, the gain pulse is strong enough to induce an inverted population at 250 meV, the situation is qualitatively different: Now the mid-infrared pulse causes stimulated emission from the inverted population, thus decreasing the number of carriers in the conduction band at the probed energy. Consequently, the differential transmission with regard to the MIR pump pulse changes from positive to negative (cf. Fig.1b)

In addition to the NIR fluence dependence shown in Fig. 1b we also present for the gain dynamics varying the time delay between gain pulse and mid-infrared pump pulse. The observed transient gain is a consequence of a bottleneck of carrier relaxation via optical phonons and the decreasing density of states in the vicinity of the Dirac point. NIR transient gain has been observed previously in doped graphene [2], where a bottleneck appears above the Fermi level.
References
[1] K. Kim, J. Urayama, T. B. Norris, J. Singh, J. Phillips, and P. Bhattacharya, "Gain dynamics and ultrafast spectral hole burning in In(Ga)As self-organized quantum dots," Appl. Rev. Lett. 81, 670 (2002).
[1] T. Li, L. Luo, M. Hupalo, J. Zhang, M. C. Tringides, J. Schmalian, and J. Wang, "Femtosecond population inversion and stimulated emission of dense Dirac fermions in graphene," Phys. Rev. Lett. 108, 167401 (2012).

Keywords: gain; population inversion; ultrafast dynamics; graphene

  • Poster
    CLEO Europe/EQEC, 26.-30.06.2023, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38236
Publ.-Id: 38236


All-silicon single photon sources based on deterministic defect engineering in photonic diodes

Schmitt, S. W.; Ritter, S.; Arslan, D.; Klingner, N.; Hlawacek, G.; Eilenberger, F.

In this study, we propose the development of a purely silicon-based photonic enhanced single photon emitter that can be optically or electrically pumped. Its design is based on an introduction of near-infrared (NIR) single photon emitting color centers in silicon photonic resonators and diodes by focused ion beams and high energy ion implantation. Color centers will deterministically be implanted in positions of guided high-Q modes to ensure an efficient optical coupling and to enhance the single photon purity, photon indistinguishability and brightness of the device. Implanted species to be tested in the experiments are C and Si that create various NIR single photon emitting centers in silicon.

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  • Lecture (Conference)
    SPIE Nanoscience + Engineering, 23.08.2023, San Diego, USA
    DOI: 10.1117/12.2677738

Permalink: https://www.hzdr.de/publications/Publ-38234
Publ.-Id: 38234


Nonlinear dynamics and time-resolved spectroscopy in graphene investigated at the free-electron laser FELBE

Winnerl, S.

The FELBE free-electron laser delivers intense THz and mid infrared pulses that are ideal to excite various low-energy quasipartcles in solids and to study their ultrafast dynamics [1]. We present the capabilities in the FELBE laboratories for degenerate and two-color pump-probe experiments, four-wave mixing and time-resolved near-field experiments. As an example, we show how nonlinear intraband transport in bilayer graphene manifests itself in polarization resolved pump-probe experiments [2]. Polarization resolved pump-probe experiments furthermore shed light into the microscopic scattering mechanisms, allowing us to disentangle Coulomb and phonon-related scattering processes [3].
[1] M. Helm, S. Winnerl, A. Pashkin, J. M. Klopf, J.-C. Deinert, S. Kovalev, P. Evtushenko, U. Lehnert, R. Xiang, A. Arnold, A. Wagner, S. M. Schmidt, U. Schramm, T. Cowan & P. Michel, Eur. Phys. J. Plus 138, 158 (2023).
[2] A. Seidl, R. Anvari, M. M. Dignam, P. Richter, T. Seyller, H. Schneider, M. Helm, and S. Winnerl Phys. Rev. B 105, 085404 (2022).
[3] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).

Keywords: FELBE; pump-probe spectroscopy; ultrafast dynamics

Related publications

  • Poster
    Dynamical Control of Quantum Materials, 22.-26.05.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38232
Publ.-Id: 38232


Generation and detection of THz radiation with photoconductive devices

Winnerl, S.

We discuss the basics and modern developements regarding generation and detection of pulsed and cw THz radiation with photoconductive antennas.

Keywords: terahertz; photoconductive antenna

  • Lecture (others)
    Winter College on Optics: Terahertz Optics and Photonics, 06.-17.02.2023, Trieste, Italia

Permalink: https://www.hzdr.de/publications/Publ-38231
Publ.-Id: 38231


RBS HEDGEHOG – New 680 msr RBS Setup for fastest channeling experiments and ultra-high sensitivity measurements

Klingner, N.; Heller, R.; Bektas, U.; Hlawacek, G.

RBS as one of the most widely used IBA methods requires a rather high beam fluence due to the small backscattering cross-section. Although the lack of measurement statistics can be compensated by a longer measurement time, this can only be applied to macroscopic beam spots and is not possible for sensitive samples or in a micro beam setup.

Larger detectors are an easy means to increase the covered solid angle, however this is limited in terms of kinematic broadening and decreasing energy resolution due to increasing detector capacitance [1]. Multi-detector setups overcome this limitation and are attracting increasing interest in various laboratories. Geometric constraints, mechanical robustness, the cost of multiple MCA systems, as well as the difficulty of simultaneously analyzing data from the individual detectors make this a difficult but worthwhile endeavor.

In this contribution, we report on our recently commissioned setup - namely, the "RBS hedgehog" located at the 3 MV tandem accelerator of the HZDR’ Ion Beam Center. The setup is equipped with 78 independent RBS detectors arranged in 5 concentric rings with backscattering angles from 165° to 105° covering a total solid angle of 680 msr - equivalent to 34% of the total backscatter angle. The 78 independent MCA systems can handle up to 8 Mega counts per second.

The presentation will start with an introduction to RBS technique, it’s advantages and disadvantages. It will be followed by a theoretical design study of the influence of different detector configurations on the kinematic broadening for different energies and ion species. We then introduction the used in-house designed and fabricated PIPS detectors and MCA systems and present initial experimental results for various projectiles and energies. Finally, we will illustrate its power at a future application of ion beam induced phase transformation in Ga2O3 [2].

[1] Klingner, N., et al. (2013), Optimizing the Rutherford Backscattering Spectrometry setup in a nuclear microprobe, NIMB, 306, 44-48. DOI: 10.1016/j.nimb.2012.12.062
[2] Azarov A., et al. (2023), Universal radiation tolerant semiconductor. Nat Commun. 2023 DOI: 10.1038/s41467-023-40588-0

Related publications

  • Lecture (Conference)
    WG1 FIT4NANO Meeting, 09.10.2023, Belval, Luxembourg

Permalink: https://www.hzdr.de/publications/Publ-38230
Publ.-Id: 38230


On demand spatially, controlled fabrication of single photon emitters in Silicon by liquid metal alloy ion source focused ion beam implantation

Klingner, N.; Hollenbach, M.; Bischoff, L.; Hlawacek, G.; Astakhov, G.

Single photon emitters (SPE) are fundamental building blocks for future quantum technology applications. However, many approaches lack the required spatial placement accuracy and Si technology compatibility required for many of the envisioned applications. Here, we present a method to place single or few SPEs emitting in the telecom O-band1. The successful integration of these telecom quantum emitters into photonic structures such as micro-resonators, nanopillars and photonic crystals with sub-micrometer precision paves the way toward a monolithic, all-silicon-based semiconductor-superconductor quantum circuit for which this work lays the foundations.
To achieve our goal, we employ home built AuSi liquid metal alloy ion sources (LMAIS) and an Orsay Physics CANION M31Z+ focused ion beam (FIB). Silicon-on-insulator substrates from different fabrication methods have been irradiated with Si++ 40 keV ions in a spot pattern of 6 to 500 ions per spot.
For the analysis and confirmation of the fabrication of true SPEs a home build photo luminescence setup has been used. G-centers formed by the combination of two carbon atoms and a silicon atom with a zero phonon lines (ZPL) at 1278 nm have been created in carbon rich SOI wafers. In ultra clean SOI wafers W-centers, a tri-interstitial Si complex has been created with a ZPL at 1218 nm. The achieved lateral SPE placement accuracy is below 50 nm in both cases and the success rate of SPE formation is more than 50%.
Finally, we give an overview on possible other applications and give an outlook on future projects and instrumentation developments.
1Hollenbach, M., Klingner, N., Jagtap, N.S. et al. Wafer-scale nanofabrication of telecom single-photon emitters in silicon. Nature Communications 13, 7683 (2022). https://doi.org/10.1038/s41467-022-35051-5

Related publications

  • Lecture (Conference)
    ICMAT 2023, 26.06.2023, Singapore, Singapore
  • Lecture (Conference)
    3rd FIT4NANO Workshop, 19.07.2023, Lissabon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-38229
Publ.-Id: 38229


TIBUSSII - the first triple beam single ion implantation setup for quantum applications

Klingner, N.; Hlawacek, G.; Facsko, S.; Wedel, G.; Grunze, S.; Kirschke, T.; Lange, B.; Findeisen, S.; Silvent, J.; Delobbe, A.

The ongoing miniaturization has reached a point where dopants, impurities or active impurities reach the quantum limit, making deterministic single ion implantation (SII) indispensable. Moreover, applications in quantum computing, spintronics, and magnonics require at the same time, a very precise spatial placement of these implants. Other requirements for such an implantation system would be a wide range of available ion species, the ability to implant at extremely low fluence as well as low voltage operation.
Our new system, named Tibussii, is expected to address all of these requirements. It will be the first UHV system to include a liquid metal alloy ion source (LMAIS) focused ion beam (FIB) column, a plasma FIB, and a scanning electron microscope (SEM). The 4-nm SEM will be used for damage-free navigation, orientation and inspection. Both FIB columns are mass-separated columns with three Einzellenses, a chicane for neutral particles, and additional blankers and features optimized for single ion implantation.
We will show the current status of the system, which is currently being installed and further developed by HZDR and Orsay Physics. To verify the implantation of single ions, we are currently developing a secondary electron (SE) detection system with a sensitivity close to unity. It will be based on a semiconductor detector and is expected to surpass the detection efficiency of existing systems based on electron multiplication, such as channeltrons or microchannel plates.

Related publications

  • Poster
    6th EUFN Workshop 2023, 08.06.2023, Zürich, Schweiz
  • Invited lecture (Conferences)
    AVS 69, 09.11.2023, Portland, USA
  • Lecture (others) (Online presentation)
    Sino-German Symposium Defect Engineering in SiC and Other Wide Bandgap Semiconductor, 23.10.2023, Shenzhen, China

Permalink: https://www.hzdr.de/publications/Publ-38228
Publ.-Id: 38228


Influence of crystal structure on helium-induced tendril formation in an FeCoCrNiV high-entropy alloy

Klingner, N.; Svenja, L.; Hlawacek, G.; Hübner, R.; Amy, S. G.; Russell, G.; Le, M.

High-entropy alloys (HEAs) are a relatively new class of metal alloys composed of several principal elements, usually at (near) equiatomic ratios. Our goal is to understand how such a multicomponent alloy behaves under irradiation. The FeCoCrNiV HEA exhibits both a face-centred cubic (fcc) and a body-centred tetragonal (bct) phase, thus allowing us to specifically study the influence of crystalline structure at very similar chemical composition. We irradiated both phases with a focussed He beam provided by a helium ion microscope (HIM) at temperatures between room temperature and 500∘C. The irradiation fluence was varied between 6× 1017 ions/cm2 and 1× 1020 ions/cm2. High-resolution images of the irradiated areas were taken with the same HIM. Selected irradiated areas were additionally studied by TEM in combination with EDXS. Under irradiation, pores start to be generated in the material with pore sizes differing significantly between the two phases. At higher fluences and above a critical temperature, a tendril structure forms in both phases. We found that the critical temperature depends on the phase and is lower for fcc. TEM images reveal that the tendrils span the whole depth of the irradiated area, and are accompanied by bubbles of various sizes. Scanning TEM-based EDXS of these structures indicates a He-induced change in composition.

Related publications

  • Lecture (Conference)
    MML Workshop Jülich, 20.04.2023, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38227
Publ.-Id: 38227


Fabrication of 2D magnets by ion implantation of phyllosilicates

Zubair Khan, M.; Klingner, N.; Hlawacek, G.; Matković, A.; Teichert, C.

Since the first reports on intrinsically magnetic two-dimensional (2D) materials in 2017 [1,2], the price-to-pay for accessing their monolayers is still the lack of ambient stability. Recently, we demonstrated weak ferromagnetism in 2D Fe:talc at room temperature and proposed iron-rich phyllosilicates as a promising platform for air-stable magnetic monolayers [3]. Since these minerals are rather rare and since phyllosilicates are hard to synthesize, we suggest here as an alternative ion implantation to tailor the magnetic properties of the phyllosilicates. Nonmagnetic, single-crystalline bulk talc crystals [4] were implanted with 50 keV iron and cobalt ion beams at different substrate temperatures. In all cases, ultra-thin layers could be exfoliated indicating that the layered crystal structure is maintained after ion irradiation. For both ion species, the Mg-OH Raman peak showed a triplet formation implying a successful substitution of Mg by Fe or Co in the talc layers.
[1] Gong, C., et al., Nature 546, 265 (2017).
[2] Huang, B., et al., Nature 546, 270 (2017).
[3] A. Matković, et al., npj 2D Mat. Appl. 5, 94 (2021).
[4] B. Vasić, et al., Nanotechnology 32, 265701 (2021).

Related publications

  • Lecture (Conference)
    DPG Frühjahrstagung, 20.03.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38226
Publ.-Id: 38226


Spatially controlled fabrication of telecom single-photon emitters in Si by focused ion beam implantation

Klingner, N.; Hollenbach, M.; Jagtap, N.; Bischoff, L.; Fowley, C.; Kentsch, U.; Hlawacek, G.; Erbe, A.; Abrosimov, N. V.; Helm, M.; Berencen, Y.; Astakhov, G.

Single photon emitters (SPE) are the starting point and foundation for future photonic quantum technologies. We present the laterally
controlled fabrication of single G and W centers in silicon that emit in the telecom O-band. We utilized home built gold-silicon liquid metal
alloy ion sources (LMAIS) in a focused ion beam (FIB) system to perform mask-free implantation of 40 keV Si ions from 6 to 500 ions per
spot. Analysis and confirmation of SPEs has been done in a home-build cryo-photoluminescence setup. We will demonstrate a success rate of
more than 50% and upscaling to wafer-scale. We will also provide an insight and overview on the LMAIS technology and an outlook on
other potential applications of FIB implantation.

Related publications

  • Lecture (Conference)
    DPG Frühjahrstagung, 20.03.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38225
Publ.-Id: 38225


Applying thallium isotopic compositions as novel and sensitive proxy for Tl(I)/Tl(III) transformation and source apportionment

Liu, J.; Wang, L.; Lin, J.; Yuan, W.; Li, L.; Peng, Y.-K.; Xiong, X.; Cao, H.; Wei, X.; Ouyang, Q.; Lippold, H.; Wang, J.; Lin, K.

Thallium is a rare metal known for its highly toxic nature. Recent research has indicated that the precise determination of Tl isotopic compositions using Multi Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP MS) provides new opportunities for understanding Tl geochemical behavior. While isotopic fractionation of Tl derived from anthropogenic activities (e.g., mining, smelting) have been reported, there is limited information regarding Tl influenced by both natural weathering processes and anthropogenic origins. Herein, we investigated, for the first time, the Tl isotopic compositions in soils across a representative Tl-rich depth profile from the Lanmuchang (LMC) quicksilver mine (southwest China) in the low-temperature metallogenesis zone. The results showed significant variations in Tl isotope signatures (ε205Tl) among different soil layers, ranging from –0.23 to 3.79, with heavier isotope 205Tl enrichment observed in the bottom layers of the profile (ε205Tl = 2.18–3.79). This enrichment of 205Tl was not solely correlated with the degree of soil weathering but was also partially associated with oxidation of Tl(I) by Fe (hydr)oxide minerals. Quantitative calculations using ε205Tl vs. 1/Tl data further indicated that the Tl enrichment across the soil depth profile was predominantly derived from anthropogenic origins. All these findings highlight the robustness and reliability of Tl isotopes as a proxy for identifying both anthropogenic and geogenic sources, as well as tracing chemical alterations and redox-controlled mineralogical processes of Tl in soils. The nascent application of Tl isotopes herein not only offers valuable insights into the behavior of Tl in surface environments, but also establishes a framework for source apportionment in soils under similar circumstances.

Keywords: Soil profile; Thallium contamination; Isotope fractionation; Geochemical fractionation; Environmental pollution tracer

Permalink: https://www.hzdr.de/publications/Publ-38224
Publ.-Id: 38224


Magnetically aware actuating composites: Sensing features as inspiration for the next step in advanced magnetic soft robotics

Oliveros Mata, E. S.; Xu, R.; Guo, L.; Makarov, D.

In this perspective, we explore the convergence of sensing and actuation in magnetic composites and its potential applications in various fields. There is a need for multifunctional mechanically flexible materials that can be easily processed into functional devices that respond to a wide range of physical stimuli, including magnetic fields. These characteristics aim for lightweight and mechanically imperceptible systems that help us to interact with technology and with each other without the need for a bulky gadget. Typically, magnetically responsive devices are constructed using materials that do not necessarily possess flexible properties, so magnetosensitive composites with tailored magnetic, conductive, and flexible properties arising from the combination of their constituents have been proposed. Such property tunability is, in turn, beneficial for achieving functional convergence. This perspective aims to address several of the challenges associated with magnetoresponsive soft composites while highlighting the synergistic Q2 convergence that will take further the applications of magnetically aware actuating composites.

Permalink: https://www.hzdr.de/publications/Publ-38223
Publ.-Id: 38223


Design and Development of Transient Sensing Devices for Healthcare Applications

Janićijević, Ž.; Huang, T.; Sandoval Bojorquez, D. I.; Tonmoy, T. H.; Pané, S.; Makarov, D.; Baraban, L.

With the ever-growing requirements in the healthcare sector aimed at personalized diagnostics and treatment, continuous and real-time monitoring of relevant parameters is gaining significant traction. In many applications, health status monitoring should be carried out by dedicated wearable or implantable sensing devices only within a defined period and followed by sensor removal without additional risks for the patient. At the same time, disposal of the increasing number of conventional portable electronic devices with short life cycles raises serious environmental concerns due to the dangerous accumulation of electronic and chemical waste. An attractive solution to address these complex and contradictory demands is offered by biodegradable sensing devices. Such devices should be able to perform required tests within a programmed period and then disappear by safe resorption in the body or harmless degradation in the environment. This review critically assesses the design and development concepts related to biodegradable and bioresorbable sensors for healthcare applications. We comprehensively address different aspects, from fundamental material properties and sensing principles to application-tailored designs, fabrication techniques, and device implementations. We emphasize the emerging approaches spanning the last 5 years and provide a broad insight into the most important challenges and future perspectives of biodegradable sensors in healthcare.

Keywords: biodegradable electronics; biosensors; healthcare applications; biomedical devices; point-of-care diagnostics; clinical diagnostics; wearable electronics

Permalink: https://www.hzdr.de/publications/Publ-38221
Publ.-Id: 38221


Advances in biomedical device engineering: From polymeric biomaterials for electrically controlled drug delivery systems to cost-effective electrochemical biosensors

Janićijević, Ž.

The engineering of biomedical devices necessitates comprehensive and multidisciplinary approaches to tackle specific problems in the biomedical field. These devices must also be designed to operate effectively in real-world applications, which demand scalability and cost-efficiency. The complexity of encountered challenges often sparks creative approaches, innovative designs, and sometimes unexpected collaborations, making the research journeys in the biomedical field truly exciting.

This seminar provides illustrative examples of how a seamless blending of knowledge and methodologies from electronics design, chemical engineering, biomaterials engineering, and biophysics can yield innovative devices or their components in two distinct yet complementary areas: controlled drug delivery and in vitro diagnostics. In the first part of the seminar, we delve into the development of polymeric biomaterials serving as compact reservoirs for active and passive controlled drug delivery, driven by non-specific electrical interactions. In the second part, we explore the development of cost-effective potentiometric field-effect transistor-based biosensing platforms and impedimetric biosensors tailored for advanced point-of-care applications. To conclude, the seminar provides a concise overview of the ongoing research endeavors within the Department of Nano-Microsystems for Life Sciences at the Institute of Radiopharmaceutical Cancer Research at Helmholtz-Zentrum Dresden-Rossendorf in Germany. This overview aims to highlight critical research challenges and interesting opportunities for future collaborations.

  • Invited lecture (Conferences)
    Seminar at the Department of Physics and Astronomy "Augusto Righi“, University of Bologna, 28.11.2023, Bologna, Italy

Permalink: https://www.hzdr.de/publications/Publ-38220
Publ.-Id: 38220


Deep underground measurement of ¹¹B(α,n)¹⁴N

Borgwardt, T. C.; Deboer, R. J.; Boeltzig, A.; Couder, M.; Görres, J.; Gula, A.; Hanhardt, M.; Manukyan, K. V.; Kadlecek, T.; Robertson, D.; Strieder, F.; Wiescher, M.

The primordial elemental abundance composition of the first stars leads to questions about their modes of energy production and nucleosynthesis. The formation of 12C has been thought to occur primarily through the 3α process, however, alternative reaction chains may contribute significantly, such as 7Li(α,γ)11B(α,n)14N. This reaction sequence cannot only bypass the mass A=8 stability gap, but could also be a source of neutrons in the first star environment. However, the efficiency of this reaction chain depends on the possible enhancement of its low energy cross section by α-cluster resonances near the reaction threshold. A new study of the reaction 11B(α,n) 14N has been undertaken at the CASPAR underground facility at beam energies from 300–700keV. A 4π neutron detector in combination with pulse shape discrimination at low background conditions resulted in the ability to probe energies lower than previously measured. Resonance strengths were determined for both the resonance at a laboratory energy of 411keV, which was measured for the second time, and for a new resonance at 337keV that has been measured for the first time. This resonance, found to be significantly weaker than previous estimates, dominates the reaction rate at lower temperatures (T<0.2KG) and reduces the reaction rate in first star environments.

Keywords: Nuclear Astrophysics; Sanford Underground Laboratory; CASPAR; Neutron Detection

Permalink: https://www.hzdr.de/publications/Publ-38219
Publ.-Id: 38219


CLYC as a neutron detector in low background conditions

Plaza, J.; Bécares, V.; Cano-Ott, D.; Gómez, C.; Martínez, T.; Mendoza, E.; Pérez De Rada, A.; Pesudo, V.; Sáez-Vergara, J. C.; Santorelli, R.; Villamarín, D.; Ianni, A.; Peña, C.; Balibrea-Correa, J.; Boeltzig, A.; Imbriani, G.

We report on the thermal neutron flux measurements carried out at the Laboratorio Subterráneo de Canfranc (LSC) with two commercial 2"x2" CLYC detectors. The measurements were performed as part of an experimental campaign at LSC with He detectors, for establishing the sensitivity limits and use of CLYCs in low background conditions. A careful characterization of the intrinsic α and γ-ray background in the detectors was required and done with dedicated measurements. It was found that the activities in the two CLYC crystals differ by a factor of three, and the use of Monte Carlo simulations and a Bayesian unfolding method allowed us to determine the specific activities from the 238U and 232Th decay chains. The simulations and unfolding also revealed that the γ-ray background registered in the detectors is dominated by the intrinsic activity of the components of the detector such as the aluminum housing and photo-multiplier and that the activity within the crystal is low in comparison. The data from the neutron flux measurements with the two detectors were analyzed with different methodologies: one based on an innovative α/neutron pulse shape discrimination method and one based on the subtraction of the intrinsic α background that masks the neutron signals in the region of interest. The neutron sensitivity of the CLYCs was calculated by Monte Carlo simulations with MCNP6 and GEANT4. The resulting thermal neutron fluxes are in good agreement with complementary flux measurement performed with 3He detectors, but close to the detection limit imposed by the intrinsic α activity.

Keywords: Neutron Detection; Scintillator; CLYC; Underground Laboratory; Backgrounds

Permalink: https://www.hzdr.de/publications/Publ-38218
Publ.-Id: 38218


Innovative UniCAR/RevCAR-engineered T-cell therapy

Feldmann, A.

Innovative UniCAR/RevCAR-engineered T-cell therapy

  • Invited lecture (Conferences)
    B-specific Kick Off Meeting, 23.10.2023, Leiden, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-38217
Publ.-Id: 38217


TheraSTAR – Project Overview

Feldmann, A.; Schmitz, M.; Bachmann, M.

TheraSTAR – Project Overview

  • Lecture (Conference)
    SaxoCell Konsortium und SAB Meeting, 11.-12.09.2023, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38216
Publ.-Id: 38216


Robust reconstruction of the bubble distribution from noisy magnetic flux density data using invertible neural networks

Kumar, N.; Krause, L.; Wondrak, T.; Eckert, S.; Eckert, K.; Gumhold, S.

Electrolysis stands as a pivotal method for environmentally sustainable hydrogen production. However, the formation of gas bubbles during the electrolysis process poses significant challenges by impeding reactions, diminishing cell efficiency, and dramatically increasing energy consumption. Furthermore, the inherent difficulty in detecting these bubbles arises from the non-transparency of the wall of electrolysis cells. Fortunately, these gas bubbles induce alterations in the cell’s conductivity, leading to corresponding fluctuations in the surrounding magnetic flux density. In this context, we can leverage external magnetic sensors to measure the magnetic flux density fluctuations induced by gas bubbles. Next, by solving the inverse problem of the Biot-Savart Law, we can estimate the conductivity, bubble size, and location within the cell. Nevertheless, reconstructing a high-resolution conductivity map from limited induced magnetic flux density measurements poses a formidable challenge as an ill-posed inverse problem. To overcome this challenge, we employ Invertible Neural Networks (INNs) to reconstruct the conductivity field. The inherent property of INNs, characterized by a bijective mapping between the input and output space, makes them exceptionally well-suited for resolving ill-posed inverse problems. We conducted extensive qualitative and quantitative evaluations to compare the performance of INNs with traditional approaches such as Tikhonov regularization. Our experiments demonstrate that, particularly in the presence of noise in the magnetic sensor data, our INN-based approach outperforms Tikhonov regularization in accurately reconstructing bubble distributions and conductivity fields. We hope that, given the efficacy of INNs shown in this work, they will become an indispensable deep-learning based approach for addressing inverse problems not only in Process Tomography but across various other domains.

Keywords: Machine Learning; Invertible Neural Networks; Normalizing Flows; Water Electrolysis; Biot-Savart Law; Inverse Problems; Current Tomography; Random Error Diffusion

Permalink: https://www.hzdr.de/publications/Publ-38215
Publ.-Id: 38215


Data publication: Learning from nature: recovery of rare earth elements by the extremophilic bacterium Methylacidiphilum fumariolicum

Singer, H.; Steudtner, R.; Sottorff, I.; Drobot, B.; Pol, A.; Op Den Camp, H. J. M.; Daumann, L. J.

Rohdaten aus denen Ergebnisse und Grafiken erstellt wurden um die benötigten Erkenntnisse für diese Publikation zu generieren

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Permalink: https://www.hzdr.de/publications/Publ-38214
Publ.-Id: 38214


Development of UniCAR TM for targeting of FAP positive cells

Feldmann, A.; Rodrigues Loureiro, L. R.; Robinson, A.

Development of UniCAR TM for targeting of FAP positive cells

  • Lecture (Conference)
    Monash-Helmholtz Laboratory for Radio-Immuno-Theranostics (MHELTHERA) Research Symposium, 16.-17.03.2023, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-38213
Publ.-Id: 38213


Wie Dresdner Forschende Immunzellen gegen Krebs nutzen.

Feldmann, A.

Wie Dresdner Forschende Immunzellen gegen Krebs nutzen.

  • Invited lecture (Conferences)
    SaxoCell lecture, 10.02.2023, CRTD, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38212
Publ.-Id: 38212


Retention of trivalent actinides (Am, Cm) and lanthanides (Eu) by Ca feldspars

Lessing, J.; Neumann, J.; Bok, F.; Lützenkirchen, J.; Brendler, V.; Schmidt, M.; Stumpf, T.

Abstract. The transport of radionuclides in the environment is a major problem for the safety assessment of radioactive waste repositories. Storage in deep geological repositories is considered a safe disposal strategy because of their ability to isolate hazardous components from the biosphere for hundreds of thousands of years. Minor actinides (i.e. Am, Cm and Np) dominate the radiotoxicity of spent nuclear fuel over geological time scales. In underground repositories, reducing conditions are expected and therefore the trivalent oxidation state is dominant for Am and Cm, as well as possibly for Pu. For investigations of the mobility of the trivalent actinides Am3+ and Cm3+, the less toxic trivalent rare earth elements, in particular Eu3+, are commonly used.
Besides clay and salt, crystalline rock is considered as a possible host rock for deep geological repositories. Crystalline rock (e.g. granite), consists mainly of quartz, mica, and feldspar. The latter are common alumino silicates making up ~60 Vol-% of the earth’s crust, but their sorption behaviour is not well understood, especially for the Ca-bearing members of the group.
Here, we study the sorption of trivalent actinides and their rare earth element homologues on plagioclase, Ca-bearing feldspars, quantitatively and mechanistically. Zeta potential of various Ca-feldspars show an unexpected increase at pH 4-7, which becomes more pronounced as the amount of Ca in the crystal lattice increases. This can be interpreted by assuming uptake of Al3+ and/or the precipitation of an Al phase, where Al originates from feldspar dissolution at different pH values.
Nevertheless, only minor differences were found in the retention and surface speciation of Cm3+ on Ca and K-feldspar (Neumann et al., 2021). Ca-feldspar has a slightly higher potential to retain trivalent metal ions compared to K feldspar. An inner sphere (IS) complex and its two hydrolysis forms have been identified on both minerals, but the hydrolysis of the IS complex is stronger in the Ca-rich mineral.
A surface complexation model for Ca-feldspar was developed by combining the batch sorption data and the spectroscopically identified surface complexes to describe the experimental data. These data will be the basis for the improvement of transport simulations for a reliable safety assessment of potential radioactive waste repositories in crystalline rock.
References
Neumann, J. et al.: Sorption of trivalent actinides (Cm, Am) and their rare earth analogues (Lu, Y, Eu, Nd, La) onto orthoclase: Batch experiments, Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) and Surface Complexation Modeling (SCM), J. Colloid Interface Sci. 591, 490-499, https://doi.org/10.1016/j.jcis.2020.11.041, 2021.

Keywords: Ca-Feldspar; Anorthite; Sorption; Trivalent Actinides; Lanthanides

  • Poster
    safeND 2023: Forschungssymposium des BASE, 13.-15.09.2023, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-38211
Publ.-Id: 38211


Influence of the Competition of Al on the Retention of Trivalent Actinides and their Homologues in Feldspar

Lessing, J.; Neumann, J.; Bok, F.; Lützenkirchen, J.; Brendler, V.; Schmidt, M.; Stumpf, T.

Crystalline rock is one possible host rock for the final disposal of nuclear waste in a deep geological formation. For a proper safety assessment, it is of utmost importance to understand retention mechanisms of radionuclides at the water-mineral interface. The retention of trivalent actinides by K-feldspars, a main component of crystalline rock, was recently investigated by our group [1]. However, no sorption data of minor actinides is available for the series of Ca-feldspars (plagioclases) with different Al:Si ratios in the crystal lattice, which most likely causes differences in surface charge, dissolution, and sorption behavior.
Here, we study the sorption of trivalent actinides and their rare earth element homologues on Ca-feldspars quantitatively and mechanistically. We find that plagioclases show a stronger sorption affinity to actinides than K-feldspars (alkali feldspars). A possible explanation might be an increased concentration of Al³⁺ in the aqueous phase due to enhanced dissolution of the Ca-feldspars. The dissolved Al3+ may affect surface charge and sorption processes onto mineral surfaces, and in such case the underlying molecular mechanisms are expected to be complex and are clearly not well understood.
Therefore, we study the impact of Al3+ on the surface charge of K-feldspar and the concomitant effects on the retention of trivalent actinides and lanthanides. Zeta potential investigations reveal a strong impact of Al3+ on the surface charge of K-feldspar. The zeta potential increases for pH 4.5–7.5, and this increase is enhanced by higher added Al3+ concentration. Results from batch sorption experiments of Eu onto K-feldspar show a steeper sorption edge upon addition of Al3+, which can be interpreted as a slightly stronger sorption affinity. Indeed, in the presence of Al3+, K-feldspar behaves much like Ca-feldspar. To gain information about the formed surface complexes time resolved laser-induced fluorescence spectroscopy is applied. Potentially formed secondary phases of Al are evaluated by a combination of microscopy (SEM, TEM, Raman, AFM) and diffractometry (CTR/RAXR, high resolution PXRD). Ultimately, this will provide a better understanding of the fundamental mechanisms of sorption process of the minor actinides on naturally occurring mineral phases.

References
[1] Neumann, J. et al. (2021) J. Colloid Interface Sci. 591, 490-499.

Keywords: Feldspar; Actinide; Sorption; Charge Revearsal

  • Lecture (Conference)
    Goldschmidt Conference2023, 09.-14.07.2023, Lyon, France
  • Poster
    18th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (Migration Conference), 24.-29.09.2023, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-38210
Publ.-Id: 38210


Vorhersage der Abszessbildung bei Patienten mit chirurgisch bestätigter infektiöser Endokarditis anhand FDG-PET/CT-basierter Biomarke

Grosse, J.; Sag, S.; Menhart, K.; Hitzenbichler, F.; Schmid, C.; Hofheinz, F.; van den Hoff, J.; Maier, L.; Sag, C.; Hellwig, D.

Ziel/Aim Die Leitlinien der Europäischen Gesellschaft für Kardiologie (ESC) aus dem Jahr 2015 definieren eine pathologische F-18-FDG-Anreicherung in der PET/CT als Hauptkriterium der modifizierten Duke-Kriterien zur Diagnose einer infektiösen Endokarditis (IE) bei Klappenprothesen. Ziel der Studie ist die Untersuchung der Bedeutung quantitativer F-18-FDG-PET/CT-Parameter in unserer realen Kohorte von Patienten mit chirurgisch bestätigter IE.

Methodik/Methods Die retrospektive Analyse umfasst alle Patienten (n=27), die in unserem Universitätsklinikum von 01/2014 bis 10/2018 mit chirurgisch bestätigter IE hospitalisiert waren und präoperativ eine F-18-FDG-PET/CT erhalten hatten. In der F-18-FDG-PET/CT wurden die bildbasierten Biomarker Maximum Standard Uptake Ratio (SURmax), metabolisch aktives Volumen (MTV) und Total Lesion Glycolysis (TLG) gemessen.

Ergebnisse/Results Bei der Dichotomisierung in Patienten mit (n=10) und ohne chirurgisch bestätigte Abszessbildung (n=17) stellten wir fest, dass bei Patienten mit chirurgisch gesicherter Abszessbildung MTV (etwa 5-fach) und TLG (etwa 7-fach) signifikant erhöht waren. Receiver-Operation-Characteristics (ROC)-Analysen zeigten, dass in unserer Studienkohorte TLG (berechnet als MTV x SURmean, d. h. TLG(SUR)) die größte Fläche unter der ROC-Kurve für die Vorhersage einer IE-bedingten Abszessbildung aufwies (0,841, 95%-Konfidenzintervall: 0,659-1) bei einer Sensitivität von 80% und Spezifität von 88% für TLG(SUR)>14,14 ml.

Schlussfolgerungen/Conclusions Die F-18-FDG-PET/CT-basierte quantitative Bewertung der TLG(SUR) könnte ein neuer Parameter für die Vorhersage der Endokarditis-assoziierten Abszessbildung und somit für die Planung der herzchirurgischen Klappensanierung von besonderer Relevanz sein.

  • Lecture (Conference)
    Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 19.-22.04.2023, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38209
Publ.-Id: 38209


Validation of the prognostic value of tumor asphericity and an extracellular matrix-related prognostic gene signature in non-small cell lung cancer patients

Hofheinz, F.; Klinger, B.; Amthauer, H.; Apostolova, I.; Blüthgen, N.; Cegla, P.; Cholewinski, W.; Kreißl, M.; Zips, D.; van den Hoff, J.; Zschaeck, S.

Ziel/Aim The aim of the study was an independent evaluation of the prognostic value of a gene expression signature (EPPI) and the PET-derived tumor asphericity (ASP) in non-small cell lung cancer (NSCLC) patients.

Methodik/Methods This was a retrospective evaluation of PET imaging and gene expression data from three public databases and two institutional datasets. Altogether 253 NSCLC patients were included, all treated with curative intent surgery. Clinical parameters, standard PET parameters and ASP were evaluated in all patients. Additional gene expression data was available for 120 patients. Univariate and multivariate Cox regression and Kaplan-Meier analysis were calculated for the primary endpoint progression-free survival (PFS) and additional endpoints.

Ergebnisse/Results In the whole cohort a significant association with PFS was observed for ASP (p<0.001) and EPPI (p=0.012). On multivariate testing, EPPI remained significantly associated with PFS (p=0.018) in the subgroup of patients with additional gene expression data, while ASP was significantly associated with PFS in the whole cohort (p=0.012). In stage II patients, ASP was significantly associated with PFS (p=0.009) and a previously published cutoff value for ASP (19.5%) was successfully validated (p=0.008). In patients with additional gene expression data, EPPI showed a significant association with PFS, too (p=0.033). Exploratory combination of ASP and EPPI showed that the combinatory approach has potential to further improve patient stratification compared to the use of only one parameter.

Schlussfolgerungen/Conclusions The combination of EPPI and ASP seems to be a very promising approach for improvement of risk stratification in a group of patients with urgent need for a more personalized treatment approach.

  • Poster
    Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 19.-22.04.2023, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38208
Publ.-Id: 38208


Recovery of gallium (and indium) from spent LEDs: strong acids leaching versus selective leaching by siderophore desferrioxamine E

Zheng, K.; Benedetti, M. F.; Jain, R.; Pollmann, K.; van Hullebusch, E.

This study aimed to carry out the adapted pre-treatment and subsequent characterization of spent surface mounted device (SMD) light emitting diodes (LEDs) as well as strong acids leaching and selective leaching of gallium (Ga) and indium (In) using desferrioxamine E (DFOE). The results show that the pre-treated spent SMD LED powder fraction (< 500 μm) contained the highest concentration of Ga and In, 290.4 ± 21.2 mg/kg and 64.9 ± 20.2 mg/kg, respectively. The use of strong acid 3 M HCl and 30% H2O2 was found to the highly effective in achieving a high leaching yield for Ga and In, 97 ± 6 % and 98 ± 4 %, respectively. However, the associated leaching of highly concentrated non-targeted elements (i.e. Cu, Pb, Al, and Fe) was found to be significantly higher than the targeted metals (Ga and In). Therefore, selective leaching could offer a promising approach to recover targeted metals from waste streams. It is the first attempt to test DFOE for the selective leaching of Ga and In from spent LEDs by adjusting the pH, solid/liquid (S/L) ratio, molar concentration ratio of DFOE and Ga (n = n(DFOE)/n(Ga)), and temperature to investigate the behavior of metal-DFOE complexation. The highest Ga leaching efficiency (12%) was found to be at pH 4, with a S/L ratio of 5 g/L and n = 20 at 40 °C. However, the competing elements (Al and Fe), can have a significant effect on the efficiency of the Ga leaching process. Concerning In recovery, selective leaching could achieve maximum In recovery yield (24%) within 24 hours at pH 7.3. This study provides deep knowledge to better understand the development of sustainable processes for the selective recovery of critical metals from spent SMD LEDs by DFOE.

Keywords: Characterization; pre-treatment; acids leaching; selective leaching; operational conditions; competition

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  • Secondary publication expected from 27.01.2025

Permalink: https://www.hzdr.de/publications/Publ-38207
Publ.-Id: 38207


Blood-brain barrier permeability measured with arterial spin labeling as potential cerebrovascular biomarker over the lifespan

Padrela, B. E.; Tee, M.; Markus, S. H.; Geier, O.; Mahroo, A.; Grydeland, H.; Fladby, T.; Eickel, K.; Günther, M.; Barkhof, F.; Hilal, S.; Mutsaerts, H.-J.; Petr, J.

Blood-brain barrier (BBB) dysfunction is considered a hallmark of Alzheimer’s disease
(AD), making non-invasive imaging of BBB with arterial spin labeling (ASL) MRI a potential imaging
biomarker (BBB-ASL). However, the normal BBB development over the lifespan is unknown. Here, we
created population-based BBB-ASL permeability reference maps, and aimed to investigate associations
between BBB-ASL, chronological age, and biological cerebrovascular age – expressed as white matter
hyperintensities (WMH) volume

  • Contribution to proceedings
    Alzheimer's Association International Conference, 15.07.2023, Amsterdam, The Netherlands
  • Poster
    Alzheimer's Association International Conference, 15.07.2023, Amsterdam, The Netherlands
  • Contribution to proceedings
    OHBM '23: Proceedings of the Organization for Human Brain Mapping Annual Meeting, 22.07.2023, Montreal, Canada
  • Poster
    OHBM '23: Proceedings of the Organization for Human Brain Mapping Annual Meeting, 22.07.2023, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-38206
Publ.-Id: 38206


Intrinsic magnetic properties of the layered antiferromagnet CrSBr

Long, F.; Mosina, K.; Hübner, R.; Sofer, Z.; Klein, J.; Prucnal, S.; Helm, M.; Dirnberger, F.; Zhou, S.

van der Waals magnetic materials are an ideal platform to study low-dimensional magnetism. Opposed to other members of this family, the magnetic semiconductor CrSBr is highly resistant to degradation in air, which, in addition to its exceptional optical, electronic, and magnetic properties, is the reason the compound is receiving considerable attention at the moment. For many years, its magnetic phase diagram seemed to be well-understood. Recently, however, several groups observed a magnetic transition in magnetometry measurements at temperatures of around 40 K that is not expected from theoretical considerations, causing a debate about the intrinsic magnetic properties of the material. In this Letter, we report the absence of this particular transition in magnetization measurements conducted on high-quality CrSBr crystals, attesting to the extrinsic nature of the low-temperature magnetic phase observed in other works. Our magnetometry results obtained from large bulk crystals are in very good agreement with the magnetic phase diagram of CrSBr previously predicted by the mean-field theory; A-type antiferromagnetic order is the only phase observed below the Néel temperature at TN = 131 K. Moreover, numerical fits based on the Curie–Weiss law confirm that strong ferromagnetic correlations are present within individual layers even at temperatures much larger than TN.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-38205
Publ.-Id: 38205


Associations Between Cardiovascular Risk Factors and Arterial Spin Labelling Derived Perfusion Parameters

Tee, M.; Padrela, B. E.; Konstandin, S.; Eickel, K.; Günther, M.; Petr, J.; Mutsaerts, H.-J.; Hilal, S.

Decreased cerebral blood flow (CBF) and deterioration of blood-brain barrier (BBB) are suggested to be
precursor conditions of cognitive impairment. Using a novel multi-echo-time arterial spin labelling (ASL)
protocol, we examined the time of exchange (Tex) of water across the BBB as a measurement of BBB
permeability. We further examined the association of cardiovascular risk factors with Tex in an ongoing cohort
study.

  • Open Access Logo Poster
    Alzheimer's Association International Conference, 15.07.2023, Amsterdam, The Netherlands
  • Open Access Logo Contribution to proceedings
    Alzheimer's Association International Conference, 15.07.2023, Amsterdam, The Netherlands
    Alzheimer's & Dementia

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Permalink: https://www.hzdr.de/publications/Publ-38204
Publ.-Id: 38204


An unsupervised deep learning framework for respiratory motion correction in PET

Rosin, B.; Nikulin, P.; Hofheinz, F.; Maus, J.; Braune, A.; Kotzerke, J.; van den Hoff, J.

Breathing related patient motion is a serious source of image blurring in oncological whole body PET. Respiratory gating allows to subdivide the aquisition data into temporal bins ("gates") depending on the breathing cycle which are basically motion-free but exhhibit increased noise levels. Image registration of all gates to a reference gate and subsequent averaging is possible but traditional registration algorithms are frequently slow or of limited accuracy.
Deep learning methods have recently attracted much interest and have been successfully applied to image registration tasks. Their flexibility and execution speed are especially attractive in the present context. We have therefore implemented and evaluated an unsupervised deep learning framework for the registration of gated PET images.

Image volume pairs consisting of a fixed gate and a second moving gate serve as input to a convolutional neural network
which predicts a deformation vector field (DVF) mapping the moving image to the fixed image. The network is trained unsupervised by optimizing a similarity
metric between the registered image pairs as well as an additional regularization loss.
Fifty-two gated PET/CT scans (8 gates) were available for training (N=42; 2352 gate pairs) and testing (N=10).
Normalized cross correlation (NCC) was used as a measure of registration accuracy.
The motion corrected images were compared to the respective ungated image, single reference gate
and a commercially available motion correction method ("OncoFreeze", Siemens). Lesion SUVmax and noise levels in the liver were determined.

Our method achieved visually very satisfactory motion compensation and consequently improved NCC for all test scans. Motion artifacts were substantially reduced while maintaining the noise level of the ungated images. The detailed numerical results will be reported.

The proposed framework is suitable for efficient reduction of motion artifacts in PET and is competitive to the OncoFreeze method.

Keywords: motion correction; CNN; unsupervised; registration; PET; gates

  • Lecture (Conference)
    61. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 19.-22.04.2023, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38203
Publ.-Id: 38203


Associations between ASL-derived cerebrovascular health and cognitive performance: results from the Insight 46 study

Dijsselhof, M. B.; Lu, K.; Lorenzini, L.; Collij, L. E.; James, S.-N.; Thomas, D. L.; Scott, C. J.; Manning, E. N.; Cash, D. M.; Hughes, A. D.; Richard, M.; Barkhof, F.; Schott, J. M.; Petr, J.; Mutsaerts, H. J. M. M.

Cardiovascular and cerebrovascular pathology may accelerate brain aging and cognitive
decline. Structural cerebrovascular imaging biomarkers, such as white matter
hyperintensities, reflect mostly irreversible accumulated damage. In contrast, cerebral blood
flow (CBF), measured with arterial spin labelling (ASL) perfusion MRI, is a potential early
haemodynamic biomarker of cognitive impairment. However, our understanding of
physiological CBF variability and its relation with cognition is limited.

  • Poster
    Alzheimer's Association International Conference, 15.07.2023, Amsterdam, The Netherlands
  • Open Access Logo Contribution to proceedings
    Alzheimer's Association International Conference, 15.07.2023, Amsterdam, Alzheimer's & Dementia
    Alzheimer's & Dementia
    DOI: 10.1002/alz.081945

Permalink: https://www.hzdr.de/publications/Publ-38202
Publ.-Id: 38202


Ten years of VASARI features: A systematic review and meta-analysis of its impact and performance in glioma imaging

Azizova, A.; Prysiazhniuk, Y.; Wamelink, I. J. H. G.; Petr, J.; Barkhof, F.; Keil, V. C.

VASARI feature are a controlled vocabulary aiming to create reproducible terminology for glioma interpretation

  • Lecture (Conference)
    46th ESNR Annual meeting, 23.09.2023, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-38201
Publ.-Id: 38201


Recycling von Seltenen Erden

Lederer, F.

Welche Materielien können heute schon gut recycelt werden und wie sieht das für die Seltenen Erden aus. Beim Parlamentarischen Abend Sustainability der mathematisch-naturwissenschaftlichen Gesellschaften stehen Wissenschaftler den Abgeordneten des Bundestages Rede und Antwort.

  • Invited lecture (Conferences)
    SUSTAINABILITY - Parlmentarischer Abend der mathematisch-naturwissenschaftlichen Gesellschaften, 14.11.2023, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38200
Publ.-Id: 38200


Potentiale von Biomolekülen zur Trennung von Mikroschadstoffen und zur Rückgewinnung von Metallen aus Industriewasser

Lederer, F.

Vorstellung von Arbeiten die am Helmholtz Institut Freiberg für Ressourcentechnologie rund um das Thema Wasserausbereitung laufen.

  • Invited lecture (Conferences)
    Wissenstag "Sauberes Wasser", 3.11.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38199
Publ.-Id: 38199


[¹⁸F]Fluspidine – a PET tracer for imaging of σ1 receptors in the central nervous system

Ludwig, F.-A.; Laurini, E.; Schmidt, J.; Pricl, S.; Deuther-Conrad, W.; Wünsch, B.

σ1 Receptors play a crucial role in various neurological and neurodegenerative diseases including pain, psychosis, Alzheimer’s disease, and depression. Spirocyclic piperidines represent a promising class of potent σ1 receptor ligands. The relationship between structural modifications and σ1 receptor affinity and selectivity over σ2 receptors led to the 2-fluoroethyl derivative fluspidine (2, Ki = 0.59 nM). Enantiomerically pure (S)-configured fluspidine ((S)-2) was prepared by enantioselective reduction of the α,β-unsaturated ester 23 with NaBH4 and the enantiomerically pure Co-catalyst (S,S)-24. The pharmacokinetic properties of both fluspidine enantiomers (R)-2 and (S)-2 were an-alyzed in vitro. Molecular dynamics simulations revealed very similar interactions of both fluspidine enantiomers with the σ1 receptor protein with a strong ionic interaction between the protonated amino moiety of the piperidine ring and the COO- moiety of glutamate 172. The ¹⁸F-labeled radiotracers (S)-[¹⁸F]2 and (R)-[¹⁸F]2 were synthesized in automated syntheses using a TRACERlab FX FN synthesis module. High radiochemical yields and radiochemical purity were achieved. Radiometabolites were not found in the brains of mice, piglets, and rhesus monkeys. While both enantiomers revealed similar initial brain uptake, the slow washout of (R)-[¹⁸F]2 indicated a kind of irreversible binding. In a first clinical trial, (S)-[¹⁸F]2 was used to visualize σ1 receptors in the brain of patients with major depressive disorder (MDD). This study revealed an in-creased density of σ1 receptors in cortico-striato-(para)limbic brain regions of MDD patients. The increased density of σ1 receptors correlated with the severity of the depressive symptoms. In an occupancy study with the PET tracer (S)-[¹⁸F]2, the selective binding of pridopidine at σ1 receptors in the brain of healthy volunteers and HD patients was shown.

Keywords: σ1 receptor ligands; σ1:σ2 selectivity; structure-affinity-relationships; enantioselective synthes

Permalink: https://www.hzdr.de/publications/Publ-38198
Publ.-Id: 38198


Added value from residuals: Potentials and relevance for circular economy

Lederer, F.

The talk focusses on metal resources, their applications and their recovery from end-of-life products.

Keywords: metal resources; recycling; biological recycling tools

  • Invited lecture (Conferences)
    Internationales Dresdner Leichtbausymposium, 22.-23.06.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38197
Publ.-Id: 38197


Wie Biologie beim Recycling hilft

Lederer, F.

Neuste biotechnologische Methoden nutzen Biolaugung, Biosorption und Bioflotation, um die eher klassisch ausgerichteten Industriezweige Bergbau und Mülltrennung zu ergänzen. In der Abteilung Biotechnologie am Helmholtz Institut Freiberg für Ressourcentechnologie werden durch die Kombination von Biotechnologie mit verschiedenen klassischen Wissenschaften neue Lösungen für bisher ungelöste Probleme und neue Abfallströme gefunden.

Keywords: Biolaugung; Biosorption; Bioflotation

  • Invited lecture (Conferences)
    Tag der Wissenschaft, 25.05.2023, Radebeul, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38196
Publ.-Id: 38196


Bio-based microplastic detection and separation

Lederer, F.

Identification of microplastic binding peptides and their application in Microplastic detection assays.

Keywords: microplastics; peptides; biodegradation; detection assay

  • Lecture (others)
    PRIORITY Training School, 22.-26.05.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38195
Publ.-Id: 38195


How Biology helps in Recycling of Metals for Renewables

Lederer, F.

Presentation of novel recycling tools developed at HIF Biotechnology to recover valuables for renewables.

Keywords: metal resources; recycling; biotechnology; BioKollekt

  • Invited lecture (Conferences)
    Building Bridges for the next Generations, 16.-17.05.2023, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-38194
Publ.-Id: 38194


A convolutional neural network for respiratory motion correction in PET

Rosin, B.; Nikulin, P.; Hofheinz, F.; Maus, J.; Braune, A.; Kotzerke, J.; van den Hoff, J.

Breathing related patient motion is a serious source of image blurring in oncological PET. Respiratory gating allows to subdivide the acquisition data into temporal bins ("gates") depending on the breathing cycle which are basically motion-free but exhibit increased noise levels. Image registration of all gates to a reference gate and subsequent averaging is possible but traditional registration algorithms are frequently slow or of limited accuracy. Deep learning methods have recently attracted much interest and have been successfully applied to image registration tasks. Their flexibility and execution speed are especially attractive in the present context. We have therefore implemented and evaluated an unsupervised deep learning framework for the registration of gated PET images.

Image volume pairs consisting of a fixed gate and a second moving gate serve as input to a U-Net convolutional neural network which predicts a deformation vector field (DVF) mapping the moving image to the fixed image. The network is trained unsupervised by optimizing a similarity metric between the registered image pairs as well as an additional regularization loss. Fifty-two gated PET scans (8 gates) were available for training (N=42; 2352 gate pairs) and testing (N=10). Normalized cross correlation (NCC) was used as a measure of registration accuracy. The motion corrected images were compared to the respective ungated image, single reference gate and a commercially available motion correction method (OncoFreeze, Siemens). Lesion SUVmax and noise
levels in the liver were determined.

Our method achieved visually very satisfactory motion compensation and consequently improved NCC for all test scans (by 4.9% on average). Motion artifacts were substantially reduced while maintaining the noise level of the
ungated images.

The proposed framework is suitable for efficient reduction of motion artifacts in PET and is competitive to the OncoFreeze method.

Keywords: CNN; gates; motion correction; PET; registration; unsupervised

  • Lecture (Conference)
    2023 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room Temperature Semiconductor Detector Conference, 04.-11.11.2023, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-38193
Publ.-Id: 38193


Identification of yttrium oxide-specific peptides for future recycling of rare earth elements from electronic scrap

Maass, D.; Boelens, P.; Bloß, C.; Claus, G.; Harter, S. D.; Günther, D.; Pollmann, K.; Lederer, F.

Yttrium is a heavy rare earth element that acquires remarkable characteristics when it is in oxide form and doped with other rare earth elements. Owing to these characteristics Y2O3 can be used in the manufacture of several products. However, a supply deficit of this mineral is expected in the coming years, contributing to its price fluctuation. Thus, developing an efficient, cost-effective, and eco-friendly process to recover Y2O3 from secondary sources has become necessary. In this study, we used phage surface display to screen peptides with high specificity for Y2O3 particles. After three rounds of enrichment, a phage expressing the peptide TRTGCHVPRCNTLS (DM39) from the random pVIII phage peptide library Cys4 was found to bind specifically to Y2O3, being 531.6-fold more efficient than the wild-type phage. The phage DM39 contains two arginines in the polar side chains, which may have contributed to the interaction between the mineral targets. Immunofluorescence assays identified that the peptide’s affinity was strong for Y2O3 and negligible to LaPO4:Ce3+,Tb3+. The identification of a peptide with high specificity and affinity for Y2O3 provides a potentially new strategic approach to recycle this type of material from secondary sources, especially from electronic scrap.

Keywords: e-waste; mineral binding peptides; next-generation sequencing; phage surface display; waste of electrical and electronic equipment

Related publications

  • Biotechnology and Bioengineering 2024(2024), 1-10
    Online First (2024) DOI: 10.1002/bit.28629

Downloads

  • Secondary publication expected from 02.01.2025

Permalink: https://www.hzdr.de/publications/Publ-38192
Publ.-Id: 38192


A first-principles study on the CdS-Te van der Waals heterostructure for Photocatalytic Hydrogen Production

Tejaswini, G.; Sudheer, A. E.; Devaraj, M.; Posselt, M.

Two dimensional (2D) materials are showing advantageous electronic and optical properties compared to their bulk counterparts. Recently 2D heterostructures attracted much attention in catalysis. Here, we demonstrate novel chalcogen based 2D-2D heterostructure CdS-Te with improved efficiency for the water splitting hydrogen production. We analysed the structural, electronic and optical properties of this CdS-Te heterostructure using first principles DFT calculations. Compared with the pristine monolayers of Te and CdS, we noticed significant improvement in the solar visible light absorption, and charge transfer properties in the material after heterostructure construction. This is due to the electric field created at the interface of CdS and Te monolayers. To attain the favorable band alignment for the water redox reaction, we applied the biaxial strain and electric field on the CdS-Te heterostructure. The Gibbs free energy calculations also exhibit less energy barrier for the CdS-Te heterostructure. From the obtained results, it is observed that the applied biaxial strain followed by the heterostructure construction improved the photocatalytic water splitting capacity of the material proficiently.

Keywords: 2D materials; van der Waals heterostructures; CdS-Te; DFT calculations

  • Poster
    "Recent Progress in Graphene and 2D materials Research” (RPGR) 2023, 20.-23.11.2023, Bengaluru, India

Permalink: https://www.hzdr.de/publications/Publ-38191
Publ.-Id: 38191


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