Contact

Dr. René Heller

Head Ion Beam Analysis
r.hellerAthzdr.de
Phone: +49 351 260 3617

Publications - Ion Beam Analysis

Here you are finding current publications that have emerged from user experiments and collaborations with our group.

Year from 2021
"Online First" included
First HDZR Author OU: Ion Beam Analysis (FWIZ-A)

Beyond Cation Disorder: Site Symmetry-Tuned Optoelectronic Properties of the Ternary Nitride Photoabsorber ZrTaN₃

Sirotti, E.; Wagner, L. I.; Jiang, C.-M.; Eichhorn, J.; Munnik, F.; Streibel, V.; Schilcher, M. J.; März, B.; Hegner, F. S.; Kuhl, M.; Höldrich, T.; Müller-Caspary, K.; Egger, D. A.; Sharp, I. D.

Abstract

Ternary nitrides are rapidly emerging as promising compounds for optoelectronic and energy conversion applications, yet comparatively little of this vast composition space has been explored. Furthermore, the crystal structures of these compounds can exhibit a significant amount of disorder, the consequences of which are not yet well understood. Here, the deposition of bixbyite-type ZrTaN3 thin films is demonstrated by reactive magnetron co-sputtering and observed semiconducting character, with a strong optical absorption onset at 1.8 eV and significant photoactivity, with prospective application as functional photoanodes. It is found that Wyckoff-site occupancy of cations is a critical factor in determining these beneficial optoelectronic properties. First-principles calculations show that cation disorder leads to minor deviations in the total energy but modulates the bandgap by 0.5 eV, changing orbital hybridization of valence and conduction band states. In addition to demonstrating that ZrTaN3 is a promising visible light-absorbing semiconductor and active photoanode material, the findings provide important insights regarding the role of cation ordering on the electronic structure of ternary semiconductors. In particular, it is shown that not only cation order, but also the cationic Wyckoff site occupancy has a substantial impact on key optoelectronic properties, which can guide future design and synthesis of advanced semiconductors.

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Permalink: https://www.hzdr.de/publications/Publ-39372


Impact of Defects and Disorder on the Stability of Ta3N5 Photoanodes

Wolz, L. M.; Grötzner, G.; Rieth, T.; Wagner, L. I.; Kuhl, M.; Dittloff, J.; Zhou, G.; Santra, S.; Streibel, V.; Munnik, F.; Sharp, I. D.; Eichhorn, J.

Abstract

The photoelectrochemical performance of Ta₃N₅ photoanodes is strongly impacted by the presence of shallow and deep defects within the bandgap. However, the role of such states in defining the stability under operational conditions is not well understood. Here, we use a highly controllable synthesis approach to create homogenous Ta₃N₅ thin films with tailored defect concentrations to establish the relationship between atomic-scale point defects and macroscale stability. Reduced oxygen contents increase long-range structural order but lead to high concentrations of deep-level states, while higher oxygen contents result in reduced structural order but beneficially passivate deep-level defects. Despite the different defect properties, the synthesized photoelectrodes degrade similarly under water oxidation conditions due to formation of a surface oxide layer that blocks interfacial hole injection and accelerates charge recombination. In contrast, under ferrocyanide oxidation conditions, we find that Ta₃N₅ films with high oxygen concentrations exhibit long-term stability, whereas those possessing lower oxygen contents and higher deep-level defect concentrations rapidly degrade. These results indicate that deep-level defects result in rapid trapping of photocarriers and surface oxidation but that shallow oxygen donors can be introduced into Ta₃N₅ to enable kinetic stabilization of the interface.

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Permalink: https://www.hzdr.de/publications/Publ-39286


Zirconium Oxynitride Thin Films for Photoelectrochemical Water Splitting

Streibel, V.; Schönecker, J. L.; Wagner, L. I.; Sirotti, E.; Munnik, F.; Kuhl, M.; Jiang, C.-M.; Eichhorn, J.; Santra, S.; Sharp, I. D.

Abstract

Transition metal oxynitrides are a promising class of functional materials for photoelectrochemical (PEC) applications. Although these compounds are most commonly synthesized via ammonolysis of oxide precursors, such synthetic routes often lead to poorly controlled oxygen-to-nitrogen anion ratios, and the harsh nitridation conditions are incompatible with many substrates, including transparent conductive oxides. Here, we report direct reactive sputter deposition of a family of zirconium oxynitride thin films and the comprehensive characterization of their tunable structural, optical, and functional PEC properties. Systematic increases of the oxygen content in the reactive sputter gas mixture enable access to different crystalline structures within the zirconium oxynitride family. Increasing oxygen contents lead to a transition from metallic to semiconducting to insulating phases. In particular, crystalline Zr2ON2-like films have band gaps in the UV−visible range and are n-type semiconductors. These properties, together with a valence band maximum position located favorably relative to the water oxidation potential, make them viable photoanode candidates. Using chopped linear sweep voltammetry, we indeed confirm that our Zr2ON2 films are PEC-active for the oxygen evolution reaction in alkaline electrolytes. We further show that high-vacuum annealing boosts their PEC performance characteristics. Although the observed photocurrents are low compared to state-of-the-art photoanodes, these dense and planar thin films can offer a valuable platform for studying oxynitride photoelectrodes, as well as for future nanostructuring, band gap engineering, and defect engineering efforts.

Keywords: zirconium oxynitride; reactive sputtering; thin film photoanodes; photoelectrochemical water splitting; oxygen evolution reaction; water oxidation

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Permalink: https://www.hzdr.de/publications/Publ-39149


Comparison of three titanium-precursors for atomic-layer-deposited TiO2 for passivating contacts on silicon

Hiller, D.; Munnik, F.; López-Vidrier, J.; Solonenko, D.; Reif, J.; Knaut, M.; Thimm, O.; Grant, N. E.

Abstract

Atomic layer-deposited (ALD) TiO2 thin films on silicon were deposited using titanium tetrachloride (TiCl4), titanium tetraisopropoxide (TTIP), and tetrakis(dimethylamino)titanium (TDMAT) together with water vapor as the oxidant at temperatures ranging between 75 and 250 °C. The Si surface passivation quality of as-deposited and isothermally annealed samples was compared using photoconductance lifetime measurements in order to calculate their effective surface recombination velocities Seff. A low Seff of 3.9 cm/s (J0s = 24 fA/cm2) is achieved for as-deposited TiCl4-TiO2 at 75 °C when a chemically grown (i.e., from RCA cleaning) SiOx interface layer is present. Depositing TTIP-TiO2 at 200 °C on a chemically grown SiOx interface layer yields equivalent Seff values; however, in this case, TTIP-TiO2 requires a 5–15 min postdeposition forming gas anneal at 250 °C. In contrast, TDMAT-TiO2 was not found to provide a similar level of passivation with/without a chemically grown SiOx interface layer and postdeposition anneal. Modeling of the effective lifetime curves was used to determine the magnitude of the effective charge densities Qf in the TiO2 films. In all cases, Qf was found to be of the order of ∼10^11 q cm−2, meaning field-effect passivation arising from ALD TiO2 is relatively weak. By comparing the material properties of the various TiO2 films using ellipsometry, photothermal deflection spectroscopy, Raman spectroscopy, elastic recoil detection analysis, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, we find experimental support for the role of Cl (in conjunction with hydrogen) playing a beneficial role in passivating dangling bond defects at the Si surface. It is concluded that low deposition temperature TiCl4 processes are advantageous, by providing the lowest Seff without any postanneal and a comparatively high growth per cycle (GPC).

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Permalink: https://www.hzdr.de/publications/Publ-39016


Sputter deposited silver niobate thin films: pathway towards phase purity

Kölbl, L.; Kobald, A.; Griesser, T.; Munnik, F.; Mitterer, C.

Abstract

Among the lead-free alternatives currently under research, silver niobate (AgNbO3) is a promising candidate to replace lead-based ceramics in dielectric capacitors for energy storage. Homogeneity and phase-purity of the used thin films are vital for optimal performance of these devices. In this study, a systematic variation of oxygen partial pressure and bias voltage during reactive d.c. magnetron co-sputtering from metallic targets is employed to synthesise AgNbO3 thin films. Structural and chemical composition of the films are investigated using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, elastic recoil detection analysis, and Rutherford backscattering spectrometry. The findings emphasise the necessity of precise parameter control during deposition to avoid the presence of undesirable secondary phases like Ag and Ag2Nb4O11 and to ensure the formation of homogeneous and phase-pure AgNbO3 thin films. The gained insights demonstrate the potential of reactive d.c. magnetron sputtering for the deposition of lead-free AgNbO3 thin films, offering pathways for enhanced environmental compatibility of future dielectric capacitors.

Keywords: AgNbO3; silver niobate; thin film; magnetron sputtering; energy storage

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Permalink: https://www.hzdr.de/publications/Publ-39013


High-Performance Thermochromic VO2-Based Coatings Deposited by Roll-to-Roll High-Power Impulse Magnetron Sputtering

Szelwicka, J.; Fahland, M.; Rezek, J.; Kaufman, M.; Munnik, F.; Vlcek, J.; von Hauff, E.

Abstract

Thermochromic vanadium dioxide (VO2) undergoes a metal-to-semiconductor (MST) transition, a property that can be exploited for energy reduction in buildings in smart windows. We present thermochromic VO2-based films prepared in a roll-to-roll process on ultra-thin glass (0.1 mm) with High Power Impulse Magnetron Sputtering (HiPIMS) without any post annealing. We characterized the film structure with X-ray diffraction, the stoichiometry by Rutherford Backscattering Spectrometry, and the optical properties with spectrophotometry. The selected films (over 2.6 m x 0.3 m), sputtered from a V-metallic tube target doped with 1.2 at.% of W (V-W target), show a transition temperature of 28 °C and 34 °C, a luminous transmittance over 50% and a modulation of the solar energy transmittance of about 7 and 10%. We monitor the deposition control parameters in the roll-to-roll process with optical emission spectroscopy, and show that both the process parameters and target history impact the thermochromic properties. Finally, we extract the charge carrier concentration and mobility by modelling the transmittance and reflectance spectra, which indicates that the VO2-coating has a slight sub-stoichiometric character.

Keywords: vanadium dioxide; thermochromic; roll-to-roll; HiPIMS; ultrathin glass

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Permalink: https://www.hzdr.de/publications/Publ-38989


A comparative compositional study of Egyptian glass from Amarna with regard to cobalt sources and other colourants

Hodgkinson, A. K.; Lemasson, Q.; Mäder, M.; Munnik, F.; Pichon, L.; Röhrs, S.; Reiche, I.

Abstract

A selection of Late Bronze Age glass objects from the site of Amarna (Egypt) was analysed for their overall chemical composition, colourants and transition metals associated with the sources of cobalt ore. The objects were analysed by means of Particle Induced X-Ray and Gamma-ray Emission and Rutherford Backscattering Spectrometry at the IBC, HZDR, Dresden and the New AGLAE facility, C2RMF, Paris. The data was subsequently compared with further measurements obtained by portable X-Ray Fluorescence (and by Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry) in order to sound the potential of these non-destructive methods to obtain new insights into the production process of glass from Amarna and its provenancing.

Keywords: Glass; Amarna; Egypt; PIXE; PIGE; RBS; microPIXE-imaging; Trace elements; Cobalt sources; Colourants

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Permalink: https://www.hzdr.de/publications/Publ-38780


Ion Beam Microprobe analysis for friction-induced material transfer processes in ta-C/steel and ta-C/brass pairs

Munnik, F.; Lorenz, L.; Härtwig, F.; Makowski, S.; Krause, M.

Abstract

A ion beam microprobe is applied for the analysis of friction-induced material transfer processes for ta-C/100Cr6 steel and ta-C/brass friction pairs. Using the appropriate combination of He and H ion beam Rutherford backscattering spectrometry and particle-induced X-ray emission spectrometry, detailed laterally- and depth-resolved information about the element composition of the friction pairs and formation of a tribo layer are obtained. The study shows the formation of a heterogeneously distributed, up to few nm thick surface layer of Fe on the surface of the ta-C coating, and the absence of a carbon transfer layer on the 100Cr6 counter body contact area after the friction treatment in high vacuum. This material combination is responsible for a high coefficient of friction of the order of 0.8. In contrast to that, a homogeneous, sub-nm thick brass transfer layer on the ta-C coating and a C- and O-rich tribolayer were formed in the central contact area of the brass counter body under ambient conditions, resulting in a low friction coefficient of 0.13.

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Permalink: https://www.hzdr.de/publications/Publ-38773


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.

Abstract

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


Supporting microscope images: The Impact of Al2O3 Particles from Grit-Blasted Ti6Al7Nb (Alloy) Implant Surfaces on Biocompatibility, Aseptic Loosening, and Infection

Kocjančič, B.; Avsec, K.; Šetina Batič, B.; Feizpour, D.; Godec, M.; Kralj Iglič, V.; Podlipec, R.; Cor, A.; Debeljak, M.; Grant T., J.; Jenko, M.; Dolinar, D.

Abstract

Supporting confocal fluorescence microscope images of live cells grown on different implant surfaces

Keywords: Ti6Al7Nb implant alloy cementless hip endoprostheses; roughness; Al2O3 grit blasting; surface and subsurface implant contamination; cytotoxicity; aseptic loosening; infection; osteointegration

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Permalink: https://www.hzdr.de/publications/Publ-37728


The Impact of Al2O3 Particles from Grit-Blasted Ti6Al7Nb (Alloy) Implant Surfaces on Biocompatibility, Aseptic Loosening, and Infection

Kocjančič, B.; Avsec, K.; Šetina Batič, B.; Feizpour, D.; Godec, M.; Kralj-Iglič, V.; Podlipec, R.; Cör, A.; Debeljak, M.; Grant, T. J.; Jenko, M.; Dolinar, D.

Abstract

For the improvement of surface roughness, titanium joint arthroplasty (TJA) components are grit-blasted with Al2O3 (corundum) particles during manufacturing. There is an acute concern, particularly with uncemented implants, about polymeric, metallic, and corundum debris generation and accumulation in TJA, and its association with osteolysis and implant loosening. The surface morphology, chemistry, phase analysis, and surface chemistry of retrieved and new Al2O3 grit-blasted titanium alloy were determined with scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and confocal laser fluorescence microscopy, respectively. Peri-prosthetic soft tissue was studied with histopathology. Blasted retrieved and new stems were exposed to human mesenchymal stromal stem cells (BMSCs) for 7 days to test biocompatibility and cytotoxicity. We found metallic particles in the peri-prosthetic soft tissue. Ti6Al7Nb with the residual Al2O3 particles exhibited a low cytotoxic effect while polished titanium and ceramic disks exhibited no cytotoxic effect. None of the tested materials caused cell death or even a zone of inhibition. Our results indicate a possible biological effect of the blasting debris; however, we found no significant toxicity with these materials. Further studies on the optimal size and properties of the blasting particles are indicated for minimizing their adverse biological effects.

Keywords: Ti6Al7Nb implant alloy cementless hip endoprostheses; roughness; Al2O3 grit blasting; surface and subsurface implant contamination; cytotoxicity; aseptic loosening; infection; osteointegration

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Permalink: https://www.hzdr.de/publications/Publ-37725


New high-resolution microscopy approaches for understanding biocompatibility of hip implants

Podlipec, R.; Štrancar, J.; Barlič, A.; Dolinar, D.; Jenko, M.

Abstract

Ensuring the biocompatibility of hip implants is essential for the safety, effectiveness, and longevity of these medical devices [1]. The material-induced tissue inflammation and immune reaction must be negligible while promoting tissue integration. However, the major unresolved issue in joint replacement is the occurrence of adverse biological reactions to wear debris, leading to severe inflammation [2] which has been observed at the subcellular level [3]. To gain a deeper understanding of the biocompatibility related to material chemistry and surface topography and to better predict the material functionality and clinical use, it is crucial to investigate the properties of cell adhesion, proliferation, and migration on the implant's surface. In this study, we demonstrate how Al2O3-coated titanium alloys with varying surface topographies and roughness affect the growth and morphology of human bone marrow mesenchymal stromal cells (BM-MSCs). This subcellular-level investigation was conducted on live cells using novel high-resolution 3D confocal fluorescence and backscatter microscopy.

1. Hu CY, Yoon TR. Biomaterials Research, 2018, 22, 33.
2. Cobelli N, Scharf B, Crisi GM, Hardin J, Santambrogio L. Nat Rev Rheumatol. 2011, 7, 600–608.
3. Podlipec R, Punzón-Quijorna E, Pirker L, Kelemen M, Vavpetič P, Kavalar R, Hlawacek G, Štrancar J, Pelicon P, Fokter SK, Materials, 2021, 14, 3048.

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  • Invited lecture (Conferences)
    5th International Symposium on Biomaterials (5ISB), 13.10.2023, Portorož, Slovenia

Permalink: https://www.hzdr.de/publications/Publ-37723


Supporting Data: Particulate matter triggers the formation of extracellular amyloid β and tau -containing plaques and neurite shortening in vitro

Sebastijanovič, A.; Podlipec, R.; Gianoncelli, A.; Hlawacek, G.; Bonanni, V.; Camassa, L. M. A.; Malmborg, V.; Kralj, S.; Pagels, J.; Vogel, U.; Zienolddiny-Narui, S.; Urbančič, I.; Koklič, T.; Štrancar, J.

Abstract

Supplementary material including sample preparation, microscope setup, correlative microscopy analysis and supporting images.

Keywords: neurite shortening; neuronal degeneration; amyloid beta (Aβ); microtubule-associated protein (tau); air pollution; particulate matter; TiO2 nanotubes; diesel exhaust; CeO2 nanoparticles; iron oxide

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Permalink: https://www.hzdr.de/publications/Publ-37722


Defect Engineering of Ta3N5 Photoanodes: Enhancing Charge Transport and Photoconversion Efficiencies via Ti Doping

Wagner, L. I.; Sirotti, E.; Brune, O.; Grötzner, G.; Eichhorn, J.; Santra, S.; Munnik, F.; Olivi, L.; Pollastri, S.; Streibel, V.; Sharp, I. D.

Abstract

Ta3N5 shows great potential as a semiconductor photoanode for solar water splitting. However, its performance is hindered by poor charge carrier transport and trapping due to a high density of defects that introduce electronic states deep within its bandgap. Here, we demonstrate that controlled Ti doping of Ta3N5 can dramatically reduce the concentration of deep-level defects and enhance its photoelectrochemical performance, yielding a sevenfold increase in photocurrent density and a 300 mV cathodic shift in photocurrent onset potential compared to undoped material. Comprehensive characterization reveals that Ti+4 ions substitute Ta+5 lattice sites, thereby introducing compensating acceptor states, reducing concentrations of nitrogen vacancies and reduced Ta+3 states, and thereby suppressing trapping and recombination. Importantly, Ti doping offers distinct advantages compared to Zr, an intensively investigated dopant of Ta3N5 in the same group of the periodic table. Specifically, Ti+4 and Ta+5 have more similar atomic radii, allowing for substitution without introducing lattice strain, and Ti exhibits a lower affinity for oxygen than Zr, enabling its incorporation without increasing the oxygen donor content. Consequently, we demonstrate that the electrical conductivity can be tuned by over seven orders of magnitude. Thus, Ti doping in Ta3N5 provides a powerful basis for precisely engineering the optoelectronic characteristics of Ta3N5 and to substantially improve its functional characteristics as an advanced photoelectrode for solar fuels applications.

Keywords: solar water splitting; tantalum nitride (Ta3N5); doping; defect engineering; charge carrier engineer

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Permalink: https://www.hzdr.de/publications/Publ-37651


The study of silver diffusion in hard coatings by means of Ion Beam Analysis techniques

Munnik, F.; Krause, M.; Cavaleiro, D.; Fernandes, F.

Abstract

Hard coatings of a few micrometre thickness are often used to extend the lifespan of machining tools and components for, e.g., automotive and aerospace applications [1]. A further increase of the lifespan of these tools and components can be achieved by making so-called self-lubricant coatings. They make use of self-adaptive mechanisms that can lead to a protective tribolayer as a solid lubricant [2]. Self-lubrication can be achieved by the incorporation of noble metals like silver in hard matrices. When applied in this way, silver can diffuse to the surface and act as a solid lubricant. However, these benefits are limited in time as the silver is released and is quickly depleted from the coating.
The fast depletion of silver can be reduced by encapsulating it in a dense barrier sandwich layer [3]. In this presentation, the diffusion of silver in two hard matrices (TiN and TiSiN) is studied during annealing by in-situ Rutherford Backscattering Spectrometry (RBS) using the cluster tool at HZDR [4]. Samples were annealed at 600°C and 800°C for two hours with continuous monitoring by RBS measurements. These show changes in the elemental distribution during and after annealing as a function of sandwich type and microstructure. The results are part of a larger study to understand the effect of microstructure of hard coatings on the diffusion behaviour of silver, which also includes Transmission Election Microscopy measurements [5].

References
[1] P.H. Mayrhofer, C. Mitterer, L. Hultman, H. Clemens, Microstructural design of hard coatings, Progress in Materials Science 51 (2006) 1032-1114, 10.1016/j.pmatsci.2006.02.002
[2] A.A. Voevodin, C. Muratore, S.M. Aouadi, Hard coatings with high temperature adaptive lubrication and contact thermal management: review, Surf. Coat. Technol. 257 (2014) 247–265, 10.1016/j.surfcoat.2014.04.046
[3] D. Cavaleiro, D. Figueiredo, C.W. Moura, A. Cavaleiro, S. Carvalho, F. Fernandes, Machining performance of TiSiN(Ag) coated tools during dry turning of TiAl6V4 aerospace alloy, Ceram. Int. 47 (2021) 11799–11806, 10.1016/j.ceramint.2021.01.021
[4] R. Wenisch et al., Cluster Tool for In Situ Processing and Comprehensive Characterization of Thin Films at High Temperatures, Anal. Chem. 90 (2018) 7837-7842, 10.1021/acs.analchem.8b00923
[5] D. Cavaleiro, F. Munnik, M. Krause, E. Carbo-Argibay, P.J. Ferreira, A. Cavaleiro, F. Fernandes, The role of interfaces and morphology on silver diffusion in hard coatings, Surfaces and Interfaces 41 (2023) 103182, 10.1016/j.surfin.2023.103182

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  • Lecture (Conference)
    Nationaler Ionenstrahlworkshop, 30.09.-02.10.2024, Duisburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-37548


Towards decoupling the effects of kinetic and potential ion energies: Ion flux dependent structural properties of thin (V,Al)N films deposited by pulsed filtered cathodic arc

Unutulmazsoy, Y.; Kalanov, D.; Oh, K.; Karimi Aghda, S.; Gerlach, J. W.; Braun, N.; Munnik, F.; Lotnyk, A.; Schneider, J. M.; Anders, A.

Abstract

Pulsed filtered cathodic arc deposition involves formation of energetic multiply charged metal ions, which help to form dense, adherent, and macroparticle-free thin films. Ions possess not only significant kinetic energy, but also potential energy primarily due to their charge, which for cathodic arc plasmas is usually greater than one. While the effects of kinetic ion energy on the growing film are well investigated, the effects of the ions’ potential energy are less known. In the present work, we make a step towards decoupling the contributions of kinetic and potential energies of ions on thin film formation. The potential energy is changed by enhancing the ion charge states via using an external magnetic field at the plasma source. The kinetic energy is adjusted by biasing the arc source (“plasma bias”), which allows us to approximately compensate the differences in kinetic energy while the substrate and ion energy detector remain at ground. However, application of an external magnetic field also leads to an enhancement of the ion flux and hence the desired complete decoupling of the potential and kinetic energy effects will require further steps. Charge-state-resolved energy distribution functions of ions are measured at the substrate position for different arc source configurations, and thin films are deposited using exactly those configurations. Detailed characterization of the deposited thin films is performed to reveal the correlations of changes in structure with kinetic and potential energies of multiply charged ions. It is
observed that the cathode composition (Al:V ratio) strongly affects the formation of the thermodynamically stable wurtzite or the metastable cubic phase. The external magnetic field applied at the arc source is found to greatly alter the plasma and therefore to be the primary, easily accessible
“tuning knob” to enhance film crystallinity. The effect of “atomic scale heating” provided by the ions’ kinetic and potential energies on the film crystallinity is investigated, and the possibility to deposit crystalline (V,Al)N films without substrate heating is demonstrated. This study shows an approach towards
distinguishing the contributions stemming from kinetic and potential energies of ions on the film growth, however, further research is needed to assess and distinguish the additional effect of ion flux intensity (current).

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Permalink: https://www.hzdr.de/publications/Publ-37538


Lithium-induced reorientation of few-layer MoS2 films

Sojková, M.; Píš, I.; Hrdá, J.; Vojteková, T.; Pribusová Slušná, L.; Vegso, K.; Siffalovic, P.; Nadazdy, P.; Dobročka, E.; Krbal, M.; Fons, P. J.; Munnik, F.; Magnano, E.; Hulman, M.; Bondino, F.

Abstract

Molybdenum disulfide (MoS2) few-layer films have gained considerable attention for their possible applications in electronics, optics, and also as a promising material for energy conversion and storage. Intercalating alkali metals, like lithium, offers the opportunity to engineer the electronic properties of MoS2. However, the influence of lithium on the growth of MoS2 layers has not been fully explored. Here, we have studied how lithium affects the structural and optical properties of the MoS2 few-layer films prepared using a new method based on one-zone sulfurization with Li2S as a source of the lithium. This method enables incorporation of Li into octahedral and tetrahedral sites of the already prepared MoS2 films or during the MoS2 formation. Our results discover an important effect of lithium promoting the epitaxial growth and horizontal alignment of the films. Moreover, we have observed a vertical-to-horizontal reorientation in vertically aligned MoS2 films upon lithiation. The measurements show long-term stability and preserved chemical composition of the horizontally aligned Li-doped MoS2.

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Permalink: https://www.hzdr.de/publications/Publ-37278


Supplementary file: Intracellular biocompatible hexagonal boron nitride quantum emitters as single-photon sources and barcodes

Kavčič, A.; Podlipec, R.; Vella, D.; Humar, M.

Abstract

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Permalink: https://www.hzdr.de/publications/Publ-37102


Intracellular biocompatible hexagonal boron nitride quantum emitters as single-photon sources and barcodes

Kavčič, A.; Podlipec, R.; Vella, D.; Humar, M.

Abstract

Color centers in hexagonal boron nitride (hBN) have been emerging as a multifunctional platform for various optical applications including quantum information processing, quantum computing and imaging. Simultaneously, due to its biocompatibility and biodegradability hBN is a promising material for biomedical applications. In this work, we demonstrate single-photon emission from hBN color centers embedded inside live cells and their application to cellular barcoding. The generation and internalization of multiple color centers into cells was performed via simple and scalable procedure while keeping the cells unharmed. The emission from live cells was observed as multiple diffraction-limited spots, which exhibited excellent single-photon characteristics with high single-photon purity of 0.1 and superb mission stability without photobleaching or spectral shifts over several hours. Due to different emission wavelengths and peak widths of the color centers, they were employed as barcodes. Each color center can exist in one out of 470 possible distinguishable states and a combination of a few color centers per cell can be used to uniquely tag virtually an unlimited number of cells. This barcoding technique is superior to others in almost all respects, including ease of production by a single-step procedure, biocompatibility and biodegradability, emission stability, no photobleaching, small size and a huge number of unique barcodes. This work provides a basis for the use of hBN color centers for robust barcoding of cells and due to the single photon emission, presented concepts could in future be extended to quantum-limited sensing and super-resolution imaging.

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Different effect of anatase TiO2 nanotubes and nanocubes on microtubule fragmentation, mitotic arrest and aneuploidy indicating plausible carcinogenicity

Podlipec, R.; Hlawacek, G.

Abstract

Ultra-high resolution Helium Ion Microscopy (HIM) images of lung epithelial cells exposed to titanium dioxide (TiO2) nanotubes. Images reveal cell nuclear envelope with nuclear pores and cytoskeleton structure showing local damage at the site with the presence of single TiO2 nanotubes. 

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Permalink: https://www.hzdr.de/publications/Publ-36913


15-N NRA Data for article: Tracer diffusion in proton-exchanged congruent LiNbO3 crystals as a function of hydrogen content

Dörrer, L.; Heller, R.; Schmidt, H.

Abstract

Raw data from 15N NRA measurements including data evaluation.

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Permalink: https://www.hzdr.de/publications/Publ-36244


Tracer diffusion in proton-exchanged congruent LiNbO3 crystals as a function of hydrogen content

Dörrer, L.; Heller, R.; Schmidt, H.

Abstract

The proton-exchange process is an effective method of fabricating low-loss waveguides based on LiNbO3 crystals. During proton-exchange, lithium is replaced by hydrogen and Li1 xHxNbO3 is formed.
Currently, mechanisms and kinetics of the proton-exchange process are unclear, primarily due to a lack in reliable tracer diffusion data. We studied lithium and hydrogen tracer diffusion in proton-exchanged congruent LiNbO3 single crystals in the temperature range between 130–230 1C. Proton-exchange was done in benzoic acid with 0, 1, 2, or 3.6 mol% lithium benzoate added, resulting in micrometre thick surface layers where Li is substituted by H with relative fractions between x = 0.45 and 0.85 as determined by Nuclear Reaction Analysis. For the diffusion experiments, ion-beam sputtered isotope enriched 6LiNbO3 was used as a Li tracer source and deuterated benzoic acid as a H tracer source.
Isotope depth profile analysis was carried out by secondary ion mass spectrometry. From the experimental results, effective diffusivities governing the lithium/hydrogen exchange as well as individual hydrogen and lithium tracer diffusivities are extracted. All three types of diffusivities can be described by the Arrhenius law with an activation enthalpy of about 1.0–1.2 eV and increase as a function of hydrogen content nearly independent of temperature. The effective diffusivities and the lithium tracer diffusivities are identical within a factor of two to five, while the hydrogen diffusivities are higher by three orders of magnitude. The results show that the diffusion of Li is the rate determining step governing the protonexchange process. Exponential dependencies between diffusivities and hydrogen concentrations are determined. The observed increase of Li tracer diffusivities and effective diffusivities as a function of hydrogen concentration is attributed to a continuous reduction of the migration enthalpy of diffusion by a maximum factor of about 0.2 eV. Simulations based on the determined diffusivities can reproduce the step-like profile of hydrogen penetration during proton-exchange.

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RBS Raw Data for publication: Investigation of matrix independent calibration of oxygen in glow discharge optical emission spectrometry

Hoffmann, V.; Gebel, B.; Heller, R.; Gemming, T.

Abstract

Raw RBS data for article Investigation of matrix independent calibration of oxygen in glow discharge optical emission spectrometry. All raw data as well as simulation files (SIMNRA) are included.

Keywords: glow discharge; optical emission spectroscopy; material science

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Investigation of matrix independent calibration of oxygen in glow discharge optical emission spectrometry

Hoffmann, V.; Gebel, B.; Heller, R.; Gemming, T.

Abstract

The performance of glow discharge optical emission spectrometry for matrix independent oxygen determination was
investigated using the spectral lines of atomic oxygen at 130 nm and 777 nm and standard conditions for dc discharge with a
4 mm anode (700 V, 20 mA). Using hot-pressed calibration samples of Cu-, Al- and Mg-powder mixed with their oxides, at
130 nm the dependence of the emission yield on these matrices was confirmed. However, at 777 nm oxygen has the same
emission yield in these matrices. In order to compare the emission yield of oxygen with the emission yield in iron a thick 43
μm FeO-layer was prepared and characterized by Rutherford backscattering spectrometry, X-ray diffraction and glow
discharge optical emission spectrometry. At 130 nm, the emission yield of oxygen in FeO is most similar to that in an Almatrix.
At 777 nm, the calibration revealed a higher emission yield of oxygen in FeO in comparison to the common emission
yield of oxygen in Cu-, Al- and Mg-matrices. © 2022 The Royal Society of Chemistry

Keywords: glow discharge; optical emission spectroscopy; material science

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In situ stability study of WAlSiN based selective absorber under heating and cooling cycles in vacuum up to 800°C

Lungwitz, F.; Niranjan, K.; Munnik, F.; Hübner, R.; Garcia Valenzuela, A.; Escobar Galindo, R.; Krause, M.; Barshilia, H.

Abstract

In situ measurements using RBS, ERD, and SE are less explored in characterizing solar absorber materials at high temperatures [1, 2]. In the present work, we report the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating with excellent optical, compositional and structural properties at high temperatures [3, 4]. We have carried out in situ Rutherford backscattering spectrometry, elastic recoil detection and spectroscopic ellipsometry measurements at three different temperatures at 450°C, 650°C, and 800°C. An optical model describing perfectly the reflectance and ellipsometric data was developed. Further, the microstructural properties of the solar absorber coating are evaluated using cross-sectional transmission electron microscopy before and after annealing. Our data obtained before and after the heating experiments demonstrate excellent compositional, optical and structural stability of the coatings under the applied conditions. Furthermore, in situ ellipsometry showed the conservation of the optical properties of the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber up to 800 °C, which is crucial for high-temperature applications.
[1] Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021).
[2] Lungwitz, F. et al. Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 196, 84-93, doi:10.1016/j.solmat.2019.03.012 (2019).
[3] K. Niranjan, A. Soum-Glaude, A. Carling-Plaza, S. Bysakh, S. John, H.C. Barshilia, Extremely high temperature stable nanometric scale multilayer spectrally selective absorber coating: Emissivity measurements at elevated temperatures and a comprehensive study on ageing mechanism, Solar Energy Mater. Sol. Cells 221 (2021) 110905, doi:10.1016/j.solmat.2020.110905.
[4] K. Niranjan, A.C. Plaza, T. Grifo, M. Bordas, A. Soum-Glaude, H.C. Barshilia, Performance evaluation and durability studies of W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing, Solar Energy 227 (2021) 457–467, doi:10.1016/j.solener.2021.09.026.

Keywords: Concentrated solar power; high-temperature solar-selective coatings; nanolaminates; in situ analysis; ion beam analysis; STEM-EDXS imaging

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  • Poster
    PSE 2022 - 18th International Conference on Plasma Surface Engineering, 12.-15.09.2022, Erfurt, Deutschland

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Contrast modes in transmission experiments using broad and focussed keV ion beams

Lohmann, S.; Hlawacek, G.; Holeňák, R.; Klingner, N.; Primetzhofer, D.; Serralta, E.

Abstract

The helium ion microscope (HIM) is an instrument for high-resolution imaging, composition analysis, and materials modification at the nanoscale. Ion transmission experiments could further improve the analytical capabilities of this technique, and multiple contrast modes are possible. We explore the latter at keV ion energies using a HIM in a scanning transmission approach as well as a broad beam in combination with a time-of-flight (ToF) set-up. Both systems employ positionsensitive detectors allowing for analysis of angular distributions.
In the ToF-system, we find a strong trajectory-dependence of the measured specific energy loss attributed to charge-exchange events in close collisions. Channelling and blocking of transmitted ions allows for mapping of intensity as well as different energy loss moments. In the HIM we demonstrate different contrasts, e.g., due to orientation of nanocrystals, channelling in single-crystalline membranes and material contrast for layered films.

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  • Lecture (Conference)
    DPG-Tagung der Sektion Kondensierte Materie (SKM), 04.-09.09.2022, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-35654


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

Lohmann, S.; Goodall, R.; Hlawacek, G.; Hübner, R.; Ma, L.; Gandy, A. S.

Abstract

High-entropy alloys (HEAs) are a relatively new class of metal alloys composed of several principal elements, usually at (near) equiatomic ratios. It has previously been reported that some HEAs dis-play superior radiation damage resistance, with composition and microstructure being cited as con-tributing factors, though the precise mechanism is still unknown. To study the influence of the crys-tal structure on the response to radiation, we have chosen FeCoCrNiV as a model system. While FeCoCrNi has a face-centred cubic (fcc) structure, adding V leads to a structural transformation to-wards a body-centred tetragonal (bct) structure with both phases present at near-stochiometric composition.
The as-cast sample was characterised by energy-dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM) confirming the presence of both phases. Irradiations were performed with a focussed He beam provided by a helium ion mi-croscope (HIM) at temperatures between room temperature and 500°C. The irradiation fluence was varied between 6x10^17 ions/cm² and 1x10^20 ions/cm². High-resolution images of the irradiated areas were taken with the same HIM, and an example is shown in Fig. 1a. Selected irradiated areas were additionally studied by transmission electron microscopy (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 as exemplary shown for the bct phase in Fig. 1a forms in both phases. We have 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 as shown in Fig. 1b for the bct phase. Scanning TEM-based EDXS of these structures indicates a He-induced change in composition.

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  • Lecture (Conference)
    FIT4NANO Workshop, 11.-13.07.2022, Krakow, Poland

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Helium-induced nano-structuring in an FeCoCrNiV high-entropy alloy

Lohmann, S.; Goodall, R.; Hlawacek, G.; Hübner, R.; Ma, L.; Gandy, A. S.

Abstract

High-entropy alloys (HEAs) are a relatively new class of metal alloys composed of several principal elements, usually at (near) equiatomic ratios. It has previously been reported that some HEAs display superior radiation damage resistance, with composition and microstructure being cited as contributing factors, though the precise mechanism is still unknown. To study the influence of the crystal structure on the response to radiation, we have chosen FeCoCrNiV as a model system. While FeCoCrNi has a face-centred cubic (fcc) structure, adding V leads to a structural transformation towards a body-centred tetragonal (bct) structure with both phases present at near-stochiometric composition.
The as-cast sample was characterised by energy-dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction in a scanning electron microscope confirming the presence of both phases. Irradiations were performed with a focussed He beam provided by a helium ion microscope (HIM) at temperatures between 20°C and 500°C. The fluence was varied between 6×10^17 ions/cm² and 1×10^20 ions/cm². High-resolution images of the irradiated areas were taken with the same HIM as shown in Fig. 1a. Selected irradiated areas were additionally
studied by transmission electron microscopy (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 as exemplary shown for the bct phase in Fig. 1a forms in both phases. TEM images reveal that these tendrils span the whole depth of the irradiated area (Fig. 1b) and are accompanied by bubbles of various sizes. Scanning TEM-based EDXS of these structures indicates a He-induced change in composition.

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  • Lecture (Conference)
    29th International conference on atomic collisions in solids & 11th International symposium on swift heavy ions in matter, 19.-24.06.2022, Helsinki, Finnland

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Data publication: Examining different regimes of ionization-induced damage in GaN through atomistic simulations

Sequeira, M.; Djurabekova, F.; Nordlund, K.; Mattei, J.-G.; Monnet, I.; Grygiel, C.; Alves, E.; Lorenz, K.

Abstract

Two Temperature Model - Molecular Dynamics (TTM-MD) simulations describing the interaction of Swift Heavy Ions (0.35-0.54 MeV/amu Xe, 0.6 and 5.8 MeV/amu Pb, and 3.8 MeV/amu U ions. The simulations are discussed in:

Sequeira, M. C., Djurabekova, F., Nordlund, K., Mattei, J.-G., Monnet, I., Grygiel, C., Alves, E., Lorenz, K., Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations. Small 2022, 2102235. https://doi.org/10.1002/smll.202102235

Each zip file contains the input and output corresponding to each ion simulation. The input and output files are those used and generated by PARCAS 5.22 (https://gitlab.com/acclab/parcas). The radial energy profile deposited by the ion, as calculated within the TTM, can be found in the in/track.in file. The file contains two columns: one with the distance to the ion trajectory (in Angstrom) and another with the energy per atom (in eV/atom). For additional information on the simulations (e.g. bulk vs surface), please refer to the methods section of the reference above.

Keywords: Defects; GaN; Molecular Dynamics; Radiation; Recrystallization; Two-Temperature Model

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Permalink: https://www.hzdr.de/publications/Publ-35645


Advancements in the fabrication and characterization of actinide targets for superheavy element production

Düllmann, C. E.; Artes, E.; Dragoun, A.; Haas, R.; Jäger, E.; Kindler, B.; Lommel, B.; Mangold, K. M.; Meyer, C. C.; Mokry, C.; Munnik, F.; Rapps, M.; Renisch, D.; Runke, J.; Seibert, A.; Stöckl, M.; Thörle‑Pospiech, P.; Trautmann, C.; Trautmann, N.; Yakushev, A.

Abstract

The heaviest elements can exclusively be produced in actinide-target based nuclear fusion reactions with intense heavy-ion beams. Ever more powerful accelerators deliver beams of continuously increasing intensity, which brings targets of current technology to their limits and beyond. We motivate efforts to produce targets with improved properties, which calls for a better understanding of targets produced by molecular plating, the current standard method. Complementary analytical methods will help shedding more light on their chemical and physical changes in the beam. Special emphasis is devoted to the aspect of the optimum target thickness and the choice of the backing material.

Keywords: Superheavy elements; Actinide targets; Heavy-ion beam; Target backing; Molecular plating; Thin film analytics

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Permalink: https://www.hzdr.de/publications/Publ-35486


Sensitive multi-element profiling with high depth resolution enabled by time-of-flight recoil detection in transmission using pulsed keV ion beams

Holeňák, R.; Lohmann, S.; Primetzhofer, D.

Abstract

The potential of time-of-flight recoil detection for sensitive multi-element profiling of thin membranes and quasi-2D systems in transmission geometry using pulsed keV ion beams is assessed. While the time-of-flight approach allows for simultaneous detection of multiple elements, to the largest extent irrespective of recoil charge states, the keV projectile energies guarantee high recoil-cross sections yielding high sensitivity at low dose. We demonstrate the capabilities of the approach using 22Ne and 40Ar as projectiles transmitted through thin carbon foils featuring optional LiF-coatings and single-crystalline silicon membranes for different sample preparation routines and crystal orientations.
Using a large position-sensitive detector (0.13 sr), a depth resolution below 6 nm and sensitivity below 1014 atoms/cm2 was achieved for H in a 50 nm thick silicon membrane. For crystalline targets, we show how the probability of creation and detection of recoils and their observed angular distribution depend on sample orientation.

Keywords: Recoils; keV ions; Self-supporting films; Time-of-flight

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Examining different regimes of ionization-induced damage in GaN through atomistic simulations

Sequeira, M.; Djurabekova, F.; Nordlund, K.; Mattei, J.-G.; Monnet, I.; Grygiel, C.; Alves, E.; Lorenz, K.

Abstract

The widespread adoption of gallium nitride (GaN) in radiation-hard semiconductor devices relies on a comprehensive understanding of its response to strongly ionizing radiation. Despite being widely acclaimed for its high radiation resistance, the exact effects induced by ionization are still hard to predict due to the complex phase-transition diagrams and defect creation-annihilation dynamics associated with group-III nitrides. Here, Two-Temperature Model, Molecular Dynamics simulations and Transmission Electron Microscopy, are employed to study the interaction of Swift Heavy Ions with GaN at the atomic level. The simulations reveal a high propensity of GaN to recrystallize the region melted by the impinging ion leading to high thresholds for permanent track formation. Although the effect exists in all studied electronic energy loss regimes, its efficiency is reduced with increasing electronic energy loss, in particular when there is dissociation of the material and subsequent formation of N 2 bubbles. The recrystallization is also hampered near the surface where voids and pits are prominent. The exceptional agreement between the simulated and experimental results establishes the applicability of the model to examine the entire electronic energy loss spectrum. Furthermore, the model supports an empirical relation between the interaction cross sections (namely for melting and amorphization) and the electronic energy loss.

Keywords: Defects; GaN; Molecular Dynamics; Radiation; Recrystallization

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Permalink: https://www.hzdr.de/publications/Publ-35270


Data publication: Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Nichterwitz, M.; Duschek, K.; Zehner, J.; Oswald, S.; Heller, R.; Leistner, K.

Abstract

All RBS Data from measurements with both standard RBS as well as liquid cell RBS, including Simulation files in SIMNRA data format

Keywords: Electrodeposition; sulfate electrolyte; electro chemistry; Rutherford backscattering; iron oxide; nano structures; magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-35230


Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Nichterwitz, M.; Duschek, K.; Zehner, J.; Oswald, S.; Heller, R.; Leistner, K.

Abstract

Iron and iron oxide nanostructures are of broad interest for numerous applications, such as in the fields of magnetic data
storage, spintronics, biosensing and catalysis. In all of these cases, defined deposition on nanometer scale is essential for
functionality. For conventional electrodeposition of transition metals, precise thickness control and layer stability at the
nanoscale are difficult due to dissolution tendencies in acidic electrolytes after the voltage is switched off. In contrast to
previous studies that focused on self-termination of Ni and Ni-based alloys, we investigate the thickness control of nanoscale
iron oxide/iron layers using self-terminated electrodeposition from sulfate electrolytes. Electrochemical quartz crystal
microbalance measurements show that self-terminated thickness can be controlled by both deposition potential and iron ion
concentration. Comparison of experimental results with model calculations based on diffusion theory reveal two different
growth modes for self-termination. At low iron ion concentration, self-termination of iron proceeds via the formation of an
ultrathin iron hydroxide layer. At larger iron ion concentration, precipitation of bulk Fe(OH)2 dominates the film growth and
self-termination is shifted to more negative potentials. All self-terminated layers exhibit enhanced stability in the electrolyte
after the voltage is switched off compared to those deposited in the conventional deposition regime. With in situ Rutherford
backscattering spectrometry measurements, we can follow the self-terminating deposition and the stability after voltage
switch-off for longer times online. Surface analytical and morphological analyses show that the self-terminated layers exhibit
a higher iron oxide/iron ratio and are smoother than layers obtained by conventional electrodeposition.

Keywords: Electrodeposition; sulfate electrolyte; electro chemistry; Rutherford backscattering; iron oxide; nano structures; magnetic properties

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Permalink: https://www.hzdr.de/publications/Publ-35228


Ion-Induced Surface Charge Dynamics in Freestanding Monolayers of Graphene and MoS2 Probed by the Emission of Electrons

Niggas, A.; Schwestka, J.; Balzer, K.; Weichselbaum, D.; Schlünzen, N.; Heller, R.; Sascha, C.; Inani, H.; Tripathi, M.; Speckmann, C.; McEvoy, N.; Susi, T.; Kotakoski, J.; Gan, Z.; George, A.; Turchanin, A.; Bonitz, M.; Aumayr, F.; Wilhelm, R. A.

Abstract

We compare the ion-induced electron emission from freestanding monolayers of graphene and MoS2 to find a sixfold higher number of emitted electrons for graphene even though both materials have similar work functions. An effective single-band Hubbard model explains this finding by a charge-up in MoS2 that prevents low energy electrons from escaping the surface within a period of a few femtoseconds after ion impact. We support these results by measuring the electron energy distribution for correlated pairs of electrons and transmitted ions. The majority of emitted primary electrons have an energy below 10 eVand are therefore subject to the dynamic charge-up effects at surfaces.

Keywords: Highly charged ions; 2D materials; Graphene; MoS2; Electron Emission; Surface Charge; Ion induced surface modifications

Permalink: https://www.hzdr.de/publications/Publ-35226


Trajectory dependence of electronic energy-loss straggling at keV ion energies

Lohmann, S.; Holeňák, R.; Grande, P. L.; Primetzhofer, D.

Abstract

We measured the electronic energy-loss straggling of protons, helium, boron and silicon ions in silicon using a time-of-flight approach. Ions with velocities 0.25 - 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channelling or random geometry to study the trajectory dependence of energy-loss straggling. Nuclear and path length contributions were determined with the help of Monte Carlo simulations. Our results exhibit an increase in straggling with increasing ion velocity for channelled trajectories for all projectiles as well as for protons and helium in random geometry. For heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. A satisfying agreement between experiment and transport cross section calculations for helium shows that energy deposition of light ions is dominated by electron-hole pair excitations. No agreement is found for boron and silicon indicating that local electron-promotion and charge-exchange events significantly contribute to energy loss at low velocities.

Permalink: https://www.hzdr.de/publications/Publ-35200


Ion Microprobe analysis of wear processes in ta-C coatings and contact areas on the counter bodies

Munnik, F.; Lorenz, L.; Härtwig, F.; Krause, M.

Abstract

Solid lubricants, like ta-C (hydrogen-free tetrahedral amorphous carbon) coatings, are an active area of research to replace liquid lubricants. This substitution is important because of the negative environmental impact and high material consumption of liquid lubricants. The influence of soft metal counter bodies on the unlubricated friction behaviour of hydrogen-free carbon coatings has mostly been studied for doped a-C coatings so far. All these studies show that low friction and wear can only be achieved if a tribolayer is formed to protect the contact. Even with a formed tribolayer, its composition is crucial for the frictional behaviour, making the investigation of this composition essential. A study currently underway aims to identify friction-induced surface changes like material loss of the coating, material transfer between the counter body and the coating, or the formation of a tribolayer.
The current work presents Ion Beam Analysis methods to deliver laterally and depth-resolved element analysis of the wear track on the coating and the contact area of the counter bodies (CB). In a first test, a ta-C coating has been subjected to pin-on-disk tests with various metallic and ceramic CBs. He and H ion microbeams have been used to scan over the tracks and the contact areas of the CBs. Both RBS and PIXE have been used and first results are presented. It is shown that, in this case, RBS yields the more useful information. Both, a 2 MeV He ion beam and a 3 MeV H ion beam provide valuable results. The advantages of each type of ion beam depend on the sample and the information needed. As shown in this work, RBS with a 2 MeV He ion beam is useful to determine the transfer layer of a (soft) metal CB to the ta-C coating, whereas 3 MeV H RBS can be used to determine the presence of C and O on the CB because of the increased non-Rutherford cross-sections for these elements.

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    18th International Conference on Nuclear Microprobe Technology and Applications, 11.-16.09.2022, Ljubljana, Slovenia

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New correlative microscopy approaches for toxicology studies of nanomaterials

Podlipec, R.; Kriselj, A.; Pirker, L.; Hlawacek, G.; Kelemen, M.; Strancar, J.

Abstract

A comprehensive understanding of the mechanisms leading to chronic inflammation of tissues after exposure to different types of nanomaterials is greatly lacking. In the case of lung tissue, repeating events of exposure to metal-oxide or carbon nanomaterials can eventually lead to persistent inflammation and further cardiovascular diseases [1,2]. A similar outcome can occur in periprosthetic tissues suffering severe inflammation from the constant influx of metal wear debris from nearby implant materials [3].
To better understand these adverse outcomes, one needs to dig into the initial events that are formed on a molecular, nanoscale, thus requiring an advanced combination of microscopy techniques. Lately, more and more studies in live science are tackled by correlative microscopy (CM) which implements an optimal combination of complementary and advanced techniques on the same sample to be able to reveal new phenomena.
In our recent studies related to both lung and periprosthetic tissue inflammation, we show the new workflow of advanced microscopies and spectroscopies from which we have gained new structural as well as functional insights (Figure 1) [4,5]. With the combination of super-resolution optical microscopy (STED), hyperspectral and fluorescence lifetime imaging (sp-FLIM), Helium Ion Microscopy (HIM), Scanning electron microscopy (SEM-EDS), and Proton Induced X-ray Emission (PIXE) we reveal/present the new mechanisms and impact of nanomaterial interaction with lung epithelium and periprosthetic tissue, which leads to better knowledge and causal relations of the nanotoxicity on such small scales.

References:

1. X. Li, L. Jin, H. Kan, Nature 2019, 570, 437-439.
2. E. Underwood, Science 2017, 355, 342–345.
3. S.B. Goodman, J. Gallo, E. Gibon, M. Takagi, Expert Rev Med Devices 2020, 17, 41–56.
4. H. Kokot, et. al, Advanced Materials, 2020, 32, 2003913-1-15.
5. R. Podlipec, et. al, Materials, 2021, 14, 3048.

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    4th SLOVENE MICROSCOPY SYMPOSIUM, 12.-13.05.2022, Ankaran, Slovenia

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Differential evolution optimization of Rutherford back-scattering spectra

Heller, R.; Klingner, N.; Claessens, N.; Merckling, C.; Meersschaut, J.

Abstract

We investigate differential evolution optimization to fit Rutherford back-scattering data. The algorithm helps to find, with very high precision, the sample composition profile that best fits the experimental spectra. The capabilities of the algorithm are first demonstrated with the analysis of synthetic Rutherford back-scattering spectra. The use of synthetic spectra highlights the achievable precision, through which it becomes possible to differentiate between the counting statistical uncertainty of the spectra and the fitting error. Finally, the capability of the algorithm to analyze large sets of experimental spectra is demonstrated with the analysis of the position-dependent composition of a SrxTiyOz layer on a 200 mm silicon wafer. It is shown that the counting statistical uncertainty as well as the fitting error can be determined, and the reported total analysis uncertainty must cover both.

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Permalink: https://www.hzdr.de/publications/Publ-34563


Syntetic Spectra Data used in publication "Differential evolution optimization of Rutherford back-scattering spectra"

Heller, R.; Meersschaut, J.; Claessens, N.; Merckling, C.; Klingner, N.

Abstract

The zip-file contains all synthetic spectra as used for and  described in the publication "Differential evolution optimization of Rutherford back-scattering spectra" and all simulation input files for the code RUTHELDE presented therein. Naming according to the text in the paper. All files are in human readable ASCII format. The simulation input files can be best viewed with any kind of JSON file editor.

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Permalink: https://www.hzdr.de/publications/Publ-34545


Dataset: spatially resolved temperature distribution in a rare-earth-doped transparent glass-ceramic

Podlipec, R.; Sedmak, I.

Abstract

Dataset of glass-ceramic temperature-dependent fluorescence emission used for the calibration of the time measurements of spatially resolved temperature distribution in rare-earth-doped glass-ceramic materials for the studies of thermal processes within optically transparent materials.   

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Permalink: https://www.hzdr.de/publications/Publ-34411


Spatially resolved temperature distribution in a rare-earth-doped transparent glass-ceramic

Sedmak, I.; Podlipec, R.; Urbancic, I.; Strancar, J.; Mortier, M.; Golobic, I.

Abstract

Knowing the temperature distribution within the conducting walls of various multilayer-type materials is crucial for a better understanding of heat-transfer processes. This applies to many engineering fields, good examples being photovoltaics and microelectronics. In this work, we present a novel fluorescence technique that makes possible the non-invasive imaging of local temperature distributions within a transparent, temperature-sensitive, co-doped Er:GPF1Yb0.5Er glass-ceramic with micrometer spatial resolution. The thermal imaging was performed with a high-resolution, fluorescence microscopy system, measuring different focal planes along the z-axis. This ultimately enabled a precise axial reconstruction of the temperature distribution across a 500-µm-thick glass-ceramic sample. The experimental measurements showed excellent agreement with computer-modeled heat simulations and suggest that the technique could be adopted for the spatial analyses of local thermal processes within optically transparent materials. For instance, the technique could be used to measure the temperature distribution of intermediate, transparent layers of novel ultra-high-efficiency solar cells at the micron and sub-micron levels.

Keywords: Temperature-dependent fluorescence; co-doped glass-ceramic; axial temperature distribution; micro-scale temperature measurements

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Permalink: https://www.hzdr.de/publications/Publ-34222


Trajectory-dependent electronic excitations at keV ion energies

Lohmann, S.; Holeňák, R.; Primetzhofer, D.

Abstract

We present experiments directly demonstrating the significance of charge-state dynamics in close collisions at ion velocities below the Bohr velocity resulting in a drastic trajectory dependence of the specific energy loss.
Experiments were performed with the time-of-flight medium energy ion scattering set-up at Uppsala University [1]. In our 3D-transmission approach [2], pulsed beams of singly charged ions are transmitted through self-supporting Si(100) nanomembranes and detected behind the sample. We record ion energy together with the angular distributions of deflected particles and can additionally insert a deflector to measure exit charge states [3].
We specifically studied the difference in energy loss between channelled (ΔEch) and random trajectories (ΔEr) for ions with masses ranging from 1 (protons) to 40 u (Ar+) as shown in Fig. 1 [4,5]. For protons, the observed effect can be explained with increasing contributions of core-electron excitations in close collisions only attainable in random geometry. For He and heavier ions we observe a reverse trend – a decrease of the ratio ΔEch/ ΔEr with decreasing ion velocity. Due to the inefficiency of core-electron excitations at these velocities, we explain this behaviour by contributions of collision-induced charge-exchange events along random trajectories. The resulting higher mean charge state leads to higher electronic stopping along random trajectories. For heavier ions, local losses due to electron promotion, also including several electrons, are expected to contribute strongly to the energy deposition in random geometry. By studying the trajectory dependence of the statistical distribution of electronic excitations (electronic energy straggling), we present evidence that for heavier ions, individual events with large energy transfer indeed significantly contribute to the energy loss. Finally, we show that our experimental approach leads to results that can serve to benchmark dynamic theories such as time-dependent density functional theory [5].

References
[1] M. A. Sortica et al., Nucl. Instrum. Methods Phys. Res. B 463 (2020) 16-20.
[2] R. Holeňák, S. Lohmann and D. Primetzhofer, Ultramicroscopy 217 (2020) 113051.
[3] R. Holeňák et al., Vacuum 185 (2021) 109988.
[4] S. Lohmann and D. Primetzhofer, Phys. Rev. Lett. 124 (2020) 096601.
[5] S. Lohmann, R. Holeňák and D. Primetzhofer, Phys. Rev. A 102 (2020) 062803.

  • Invited lecture (Conferences) (Online presentation)
    25th International Conference on Ion Beam Analysis & 17th International Conference on Particle Induce X-ray Emission & International Conference on Secondary Ion Mass Spectrometry, 11.-15.10.2021, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-34019


Trajectory-dependent electronic excitations of keV ions

Lohmann, S.; Holeňák, R.; Primetzhofer, D.

Abstract

We present experiments directly demonstrating the significance of charge-exchange events for the energy deposition of ions with velocities below the Bohr velocity. The observed effects lead to a drastic trajectory-dependence of the specific energy loss.
Experiments were performed with the time-of-flight medium energy ion scattering set-up at Uppsala University [1]. We employed pulsed beams of singly charged ions with masses ranging from 1 (H+) to 40 u (Ar+) and energies between 20 and 350 keV. Ions were transmitted through self-supporting Si(100) nanomembranes and detected behind the sample. We assessed the energy and angular distributions of deflected particles for different alignments of the initial beam direction with the crystal axes and planes. A set-up for measuring the exit charge state was constructed to support the analysis [2].
For all ions we observe lower electronic stopping for channelled trajectories as compared to random ones as shown in Fig. 1 [3]. For protons, this difference is explained by increasing contributions of core-electron excitations more likely to happen at small impact parameters accessible only in random geometry. For heavier ions, core-electron excitations at employed ion velocities are inefficient and we, therefore, explain these results by reionisation events occurring in close collisions of ions with target atoms [4]. These events in turn result in trajectory-dependent mean charge states, which heavily affects the energy loss, and could be confirmed by first qualitative measurements of the trajectory dependence of exit charge states. The simplicity of our experimental geometry leads to results that can serve as excellent benchmark systems for calculations using time-dependent density functional theory.

References
[1] M. A. Sortica et al., Nucl. Instrum. Methods Phys. Res. B, 463 (2020) 16-20.
[2] R. Holeňák et al., Vacuum, 185 (2021) 109988.
[3] S. Lohmann et al., Phys. Rev. A, 102 (2020) 062803.
[4] S. Lohmann and D. Primetzhofer, Phys. Rev. Lett., 124 (2020) 096601.

  • Lecture (Conference)
    Applied Nuclear Physics Conference, 12.-16.09.2021, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-33961


Ion-electron dynamics studied in a 3D-transmission approach

Lohmann, S.; Holeňák, R.; Grande, P. L.; Primetzhofer, D.

Abstract

We present experiments demonstrating trajectory-dependent electronic excitations at low ion velocities attributed to charge-exchange events. Experiments were performed with the time-of-flight medium energy ion scattering set-up at Uppsala University [1]. We employed pulsed beams of singly charged ions with masses from 1 (H+) to 40 u (Ar+) and energies between 20 and 300 keV. Ions are transmitted through self-supporting Si(100) nanomembranes and detected behind the sample. Fig. 1 demonstrates our experimental approach, in which ion energy loss is measured together with angular distributions for different beam-crystal alignments. We have analysed both trajectory-dependent electronic stopping and electronic energy-loss straggling. Our results show higher electronic stopping for random than for channelled trajectories for all studied ions [2]. For ions heavier than protons, direct core-electron excitations at employed ion velocities are inefficient. We, therefore, explain our observation by reionisation events occurring in close collisions of ions with target atoms mainly accessible in random geometry [3]. These events result in trajectory-dependent mean charge states, which heavily affects the energy loss. The electronic energy-loss straggling likewise exhibits a strong dependence on ion type, velocity and trajectory. For all ions, straggling in random geometry is higher than in channelling orientation. While for He straggling increases with ion velocity, for B travelling along random trajectories a minimum is observed in the studied velocity range. We compare experimental results for these two ions with predictions by the Chu model and transport cross section calculations (Penn-TCS model). We provide strong evidence that electron-hole pair creation alone cannot explain electronic excitations by slow ions other than protons. Especially for heavy ions, additional energy-loss processes such as charge exchange and autoionisation including possible alterations of the scattering potential [4] have to be taken into account.
References
[1] M. A. Sortica et al., Nucl. Instrum. Methods Phys. Res. B, 463 (2020) 16-20.
[2] S. Lohmann et al., Phys. Rev. A, 102 (2020) 062803.
[3] S. Lohmann and D. Primetzhofer, Phys. Rev. Lett., 124, (2020) 096601.
[4] R. A. Wilhelm and P. L. Grande, Communications Physics, 2 (2019) 89.

  • Invited lecture (Conferences) (Online presentation)
    27th International Symposium on Ion-Atom Collisions (ISIAC), 14.-16.07.2021, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-33960


Sputter Deposited Magnetostrictive Layers for SAW Magnetic Field Sensors

Thormählen, L.; Seidler, D.; Schell, V.; Munnik, F.; McCord, J.; Meyners, D.

Abstract

For the best possible limit of detection of any thin film‐based magnetic field sensor, the functional magnetic film properties are an essential parameter. For sensors based on magnetostrictive layers, the chemical composition, morphology and intrinsic stresses of the layer have to be controlled during film deposition to further control magnetic influences such as crystallographic effects, pinning effects and stress anisotropies. For the application in magnetic surface acoustic wave sensors, the magnetostrictive layers are deposited on rotated piezoelectric single crystal substrates. The thermomechanical properties of quartz can lead to undesirable layer stresses and associated magnetic anisotropies if the temperature increases during deposition. With this in mind, we compare amorphous, magnetostrictive FeCoSiB films prepared by RF and DC magnetron sputter deposition. The chemical, structural and magnetic properties determined by elastic recoil detection, X‐ray diffraction, and magneto‐optical magnetometry and magnetic domain analysis are correlated with the resulting surface acoustic wave sensor properties such as phase noise level and limit of detection. To confirm the material properties, SAW sensors with magnetostrictive layers deposited with RF and DC deposition have been prepared and characterized, showing comparable detection limits below 200 pT/Hz(^1/2) at 10 Hz. The main benefit of the DC deposition is achieving higher deposition rates while maintaining similar low substrate temperatures.

Keywords: Magnetron Sputter Deposition; FeCoSiB; ERDA; XRD; film stress; magnetic field sensor; magnetic prop

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Permalink: https://www.hzdr.de/publications/Publ-33696


Determination of high-time resolution mineral dust concentration in real-time by optical absorption measurements

Ivančič, M.; Ježek, I.; Rigler, M.; Gregorič, A.; Alföldy, B.; Podlipec, R.; Drinovec, L.; Pikridas, M.; Unga, F.; Sciare, J.; Yus-Díez, J.; Pandolfi, M.; Griša, M.

Abstract

Mineral dust is an important natural source of aerosols and significantly influences air quality (Querol et al.,
Environ. Int., 2019) and the global radiation budget (Schepanski, Geosci., 2018). Frequent dust intrusions are
observed in the Mediterranean region (Ealo et al., Atmos. Chem. Phys., 2016; Pikridas et al., Atmos. Environ.,
2018) and Central Europe (Collaud Coen et al., Atmos. Chem. Phys., 2004; Schauer et al., Aerosol Air Qual.
Res., 2016), with high potential to cause exceedances of daily PM10 levels. To separate the influence of
anthropogenic and natural contribution to the PM10 levels, the new method was developed within the DNAAP
project (Detection of non-anthropogenic air pollution – http://www.aerosol.si/dnaap/).
Dust weakly absorbs light in the near ultra-violet and short wavelengths of the visible range, while the light
absorption of dust in longer wavelengths from the visible and near infra-red range is negligible. We used
filter-based photometer Aethalometer AE33 (Drinovec et al., Atmos. Meas. Tech., 2015) to measure the light
absorption at seven wavelengths, from 370 to 950 nm. The mineral dust is not the only light-absorbing aerosol
in the air. Black carbon (BC), a unique primary tracer for combustion emissions, strongly absorbs light across
the entire visual, near infra-red and near ultra-violet spectral range. Since optical absorption of mineral dust is
weaker than the optical absorption of black carbon, the coarse mode mineral particles have to be concentrated
using the high-volume virtual impactor (VI). The method is based on the optical absorption measurements of
the two sample streams, sampling particle size below 1 µm and sample stream with the concentrated coarse
mode particles, where mineral dust contribution is substantial. Experimental configuration includes two
Aethalometers AE33 with different size selective inlets: VI inlet for sampling coarse aerosol mode (mostly
mineral dust) and PM1 inlet for sampling fine mode of aerosols (mainly BC). The optical absorption of mineral
dust can be determined by subtracting the absorption of fine aerosol fraction (PM1) from the absorption of
aerosol sampled by the VI, taking into account the enhancement factor of VI setup (Drinovec et al., Atmos.
Meas. Tech., 2020). The mineral dust mass concentration is then calculated using mass absorption cross-section
(MAC) for dust which could be site and source-region specific.
The results from the measurement campaigns performed at six locations in the Mediterranean region will be
presented. The measurements took place in NE Spain (Barcelona – BCN, Montseny – MSY, Montsec – MSA),
on Cyprus (Nicosia – NI, Agia Marina Xyliatou – AMX), and in Slovenia (Ljubljana – LJ). Two year-long
datasets will be presented, focusing on the analyses of aerosol optical properties of PM1 and VI fractions. The
results were validated using low time resolution chemical specification of offline filters and a statistical
approach where dust was extracted from PM10 measurements for dust intrusions periods determined by models
and back-trajectory studies. For better understanding, helium ion microscopy (HIM) was applied to study the
microscopic differences between mineral dust and black carbon captured on the AE33 filter tapes.
This work was supported by SPIRIT Slovenia – Public Agency for Entrepreneurship, Internationalization,
Foreign Investments and Technology, project DNAAP.

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  • Lecture (Conference)
    DUST 2021, 04.-07.10.2021, Torre Cintola Conference Centre, MONOPOLI, Italy

Permalink: https://www.hzdr.de/publications/Publ-33623


On the correlation of angular distributions of keV ions and trajectory-dependent electronic excitations in transmission channelling geometry

Holeňák, R.; Lohmann, S.; Komander, K.; Primetzhofer, D.

Abstract

We use energy discrimination of keV ions transmitted through a thin, single-crystalline silicon membrane to correlate specific angular distribution patterns formed in channelling geometry with trajectory-dependent electronic energy loss. The integral energy and intensity distribution of transmitted ions can thus be dissected into on one side axially channelled projectiles travelling along rather straight trajectories and on the other side dechannelled projectiles predominantly experiencing blocking. Angular distributions of transmitted ions are further simulated with two different Monte-Carlo codes.

Keywords: Channelling; keV ions; Monte-Carlo; Time-of-flight

  • Open Access Logo Contribution to proceedings
    25th International Conference on Ion Beam Analysis & 17th International Conference on Particle Induce X-ray Emission & International Conference on Secondary Ion Mass Spectrometry, 11.10.2021, Online, Online
    Journal of Physics: Conference Series, Volume 2326, 012008
    DOI: 10.1088/1742-6596/2326/1/012008
    arXiv: arXiv:2111.06809
    Cited 3 times in Scopus

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Indirect bandgap, optoelectronic properties, and photoelectrochemical characteristics of high-purity Ta₃N₅ photoelectrodes

Eichhorn, J.; Lechner, S. P.; Jiang, C.-M.; Folchi, G.; Munnik, F.; Sharp, I. D.

Abstract

The (opto)electronic properties of Ta3N5 photoelectrodes are often dominated by defects, such as oxygen impurities, nitrogen vacancies, and reduced tantalum centers, impeding fundamental studies of its electronic structure, chemical stability, and photocarrier transport. Here, we synthesize high quality Ta3N5 thin films by reactive magnetron sputtering and subsequent NH3 annealing at varying temperatures. The resulting films are characterized by nearly-ideal N/Ta stoichiometry, low O content, and small Urbach energies. Both the crystallinity and material quality improve with increasing annealing temperatures up to 940 °C, while higher annealing temperatures introduce additional disorder within the Ta3N5 lattice, leading to reduced photoelectrochemical performance. These changes are also reflected in the surface and bulk composition, showing the elimination of oxygen impurities at moderate annealing temperatures and the loss of nitrogen at high annealing temperatures. As a consequence, defect-related sub-gap optical absorption initially decreases due to reduced oxygen impurity concentration, and subsequently increases due to increased formation of nitrogen vacancies. The high material quality enables us to unambiguously identify the nature of the Ta3N5 band gap as indirect, thereby resolving a long-standing controversy regarding the most fundamental characteristic of this material as a semiconductor. The assignment of Ta3N5 as indirect semiconductor is further supported by the suppression of disorder-induced band-edge photoluminescence with improved structural order within the Ta3N5 films.

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Correlated effects of fluorine and hydrogen in fluorinated tin oxide (FTO) transparent electrodes deposited by sputtering at room temperature

Morán-Pedroso, M.; Gago, R.; Julin, J. A.; Salas-Colera, E.; Jimenez, I.; de Andrés, A.; Prieto, C.

Abstract

The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering have been investigated varying the fluorine content and the hydrogen atmosphere. The complex behavior of the obtained films is disclosed using a wide set of characterization techniques that reveals the combined effects of these two parameters on the generated defects. These defects control the electrical transport (carrier density, mobility and conductivity), the optical properties (band gap and defects-related absorption and photoluminescence) and finally promote the amorphization of the samples. H₂ in the sputtering gas does not modify the H content in the films but induces the partial reduction of tin (from Sn4+ to Sn2+) and the consequent generation of oxygen vacancies with shallow energy levels close to the valence band. A variation of up to four orders of magnitude in electrical conductivity is reported in samples with the appropriate fluorine doping and hydrogen fraction in the sputtering gas, maintaining excellent optical transparency. Optimized room temperature grown electrodes reach sheet resistance ~20 Ω/□ and transparency >90%. This room temperature deposition process enables film preparation on flexible organic substrates, such as polyethylene terephthalate (PET), with identical performance of doubtless interest in flexible and large scale electronics.

Keywords: Transparent conductive materials; Fluorinated tin oxide; Room temperature film preparation

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Impact of Si on the high-temperature oxidation of AlCr(Si)N coatings

Jager, N.; Meindlhumer, M.; Zitek, M.; Spor, S.; Hruby, H.; Nahif, F.; Julin, J.; Keckes, J.; Mitterer, C.; Daniel, R.

Abstract

The resistance of wear protective coatings against oxidation is crucial for their use at high temperatures. Here, three nanocomposite AlCr(Si)N coatings with a fixed Al/Cr atomic ratio of 70/30 and a varying Si-content of 0 at.%, 2.5 at.% and 5 at.% were analyzed by differential scanning calorimetry, thermogravimetric analysis and X-ray in order to understand the oxidation behavior depending on their Si-content. Additionally, a partially oxidized AlCrSiN coating with 5 at.% Si on a sapphire substrate was studied across the coating thickness by depth-resolved cross-sectional X-ray nanodiffraction and scanning trans-mission electron microscopy to investigate the elemental composition, morphology, phases and residual stress evolution of the oxide scale and the non-oxidized coating underneath. The results reveal enhanced oxidation properties of the AlCr(Si)N coatings with increasing Si-content, as demonstrated by a retarded onset of oxidation to higher temperatures from 1100 °C for AlCrN to 1260 °C for the Si containing coatings and a simultaneous deceleration of the oxidation process. After annealing of the AlCrSiN sample with 5 at.% Si at an extraordinary high temperature of 1400 °C for 60 min in ambient air, three zones developed throughout the coating strongly differing in their composition and structure: (i) a dense oxide layer comprising an Al-rich and a Cr-rich zone formed at the very top, followed by (ii) a fine-grained transition zone with incomplete oxidation and (iii) a non-oxidized zone with a porous structure. The varying elemental composition of these zones is furthermore accompanied by micro-structural variations and a complex residual stress development revealed by cross-sectional X-ray nanodiffraction. The results provide a deeper understanding of the oxidation behavior of AlCr(Si)N coatings depending on their Sicontent and the associated elemental, microstructural and residual stress evolution during high-temperature oxidation.

Keywords: AlCrSiN; Nanocomposite; Cathodic arc; Oxidation behaviour; Cross-sectional X-ray nanodiffraction

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Ion Microprobe analysis of wear processes in tribological ta-C coatings.

Munnik, F.; Habenicht, C.; Lorenz, L.; Krause, M.

Abstract

Solid lubricants are an active research topic due to many factors, an important one being the elimination of current liquid lubrication because of its environmental impact. The tribological behaviour of different solid lubricants depends on the gas en¬vironment while testing. The most often-used solid lubricant coating is MoS2. A newer one still under research is ta-C (hydrogen-free, tetra-edic, amorphous carbon) that behaves like a polar opposite to MoS2. ta-C relies on free hydrogen and hydroxide ions to passivate free bonds resulting from the wear testing.
In a first test, a ta-C coating has been subjected to tribological tests with counter bodies made of various materials. The aim is to study tribological surface changes like material loss of the coating or material transfer from the counter body, processes which aren’t fully understood yet. Both the wear tracks on the ta-C coating and the counter bodies have been subjected to Ion Beam Analysis using a high energy ion microprobe. Both PIXE (Particle Induced X-ray Emission) and RBS (Rutherford Backscattering Spectrometry) measurements have been performed using a 2 MeV He ion beam and a 3 MeV H ion beam. Results for the wear tracks obtained with a brass and a Al2O3 counter body are presented as well as results on the counter bodies themselves. The advantages and drawbacks of the results obtained with different ions and different methods are presented. These results show that it is important to combine the measurements in order to obtain a complete picture of the damage caused by the wear tests.

Keywords: Tribilogy; Ion beam analysis

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  • Lecture (Conference) (Online presentation)
    Ion beam workshop 2021 - virtual meeting, 24.-25.03.2021, online, Deutschland

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Experimental electronic stopping cross section of tungsten for light ions in a large energy interval

Moro, M. V.; Wolf, P. M.; Bruckner, B.; Munnik, F.; Heller, R.; Bauer, P.; Primetzhofer, D.

Abstract

Electronic stopping cross section of tungsten for light ions was experimentally measured in a wide energy interval (20 to 6000 keV for protons and 50 to 9000 keV for helium) in backscattering and transmission geometries. The measurements were carried out in three laboratories (Austria, Germany and Sweden) using five different set-ups, the stopping data deduced from different data sets showed excellent agreement amongst each other, with total uncertainty varying within 1.5–3.8% for protons and 2.2–5.5% for helium, averaged over the respective energy range of each data set. The final data is compared to available data and to widely adopted semi-empirical and theoretical approaches, and found to be in good agreement with most adopted models at energies around and above the stopping maximum. Most importantly, our results extend the energy regime towards lower energies, and are thus of high technological relevance, e.g., in fusion research. At these low energies, our findings also revealed that tungsten – featured with fully and partially occupied f- and d-subshells, respectively – can be modeled as an electron gas for the energy loss process.

Keywords: Stopping power; Tungsten; Free electron gas; Bragg peak; Protons; Helium; Fusion

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Permalink: https://www.hzdr.de/publications/Publ-32543


Influence of precursor thin-film quality on the structural properties of large-area MoS2 films grown by sulfurization of MoO3 on c-sapphire

Spanková, M.; Sojková, M.; Dobrocka, E.; Hutár, P.; Bodík, M.; Munnik, F.; Hulman, M.; Chromik, S.

Abstract

In recent years, molybdenum disulfide (MoS2) has been investigated due to its unique electronic, optical, and mechanical properties with a variety of applications. Sulfurization of pre-deposited MoO3 layers is one of the methods of the preparation of large-area MoS2 thin films. The MoO3 layers have been grown on c-sapphire substrates, using two different techniques (rf sputtering, pulsed laser deposition). The films were subsequently annealed in vapors of sulfur at high temperatures what converted them to MoS2 films. The quality of MoS2 is strongly influenced by the properties of the precursor MoO3 layers. The pre-deposited MoO3, as well as the sulfurized MoS2, have been characterized by several techniques including Raman, Rutherford backscattering spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray diffraction. Here we compare two types of MoS2 films prepared from different MoO3 layers to determine the most suitable MoO3 layer properties providing good quality MoS2 films for future applications.

Keywords: Molybdenum disulfide; Sulfurization; Sputtering; Pulsed laser deposition; Structural properties

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Permalink: https://www.hzdr.de/publications/Publ-31693


Nanoparticle emission by electronic sputtering of CaF2 single crystals

Alencar, I.; Hatori, M.; Marmitt, G. G.; Trombini, H.; Grande, P. L.; Dias, J. F.; Papaléo, R. M.; Mücklich, A.; Assmann, W.; Toulemonde, M.; Trautmann, C.

Abstract

Material sputtered from CaF2 single crystals by 180 MeV Au ions impinging at different incidence angles were collected on high-purity amorphous C-coated Cu grids and Si100 wafer catcher surfaces over a broad angular range. These catcher surfaces were characterized complementary by transmission electron microscopy, atomic force microscopy and medium energy ion scattering, revealing the presence of a distribution of partially buried CaF2 nanoparticles in conjunction to a thin layer of deposited CaF2 material. Particle size distributions do not follow simple power laws and depend on the angles of ion incidence and particle detection. It is shown that the particle ejection is directly related to the jet-like component of sputtering, previously observed in ionic crystals, contributing significantly to the total yield. This contribution enhances as the impinging ions approach grazing incidence. Possible scenarios for the emission of particles are discussed in light of these observations.

Keywords: Atomic force microscopyCatcher technique; Nanoparticle; Medium energy ion scattering; Electronic sputtering; Swift heavy ions; Transmission electron microscopy

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Permalink: https://www.hzdr.de/publications/Publ-31682


High carrier mobility epitaxially aligned PtSe2 films grown by one-zone selenization

Sojkova, M.; Dobročka, E.; Hutár, P.; Tašková, V.; Pribusová-Slušná, L.; Stoklas, R.; Píš, I.; Bondino, F.; Munnik, F.; Hulman, M.

Abstract

Few-layer PtSe2 films are promising candidates for applications in high-speed electronics, spintronics and photodetectors. Reproducible fabrication of large-area highly crystalline films is, however, still a challenge. Here, we report the fabrication of epitaxially aligned PtSe2 films using one-zone selenization of pre-sputtered platinum layers. We have studied the influence of growth conditions onstructural and electrical properties of the films prepared from Pt layers with different initial thickness. The best results were obtained for the PtSe2 layers grown at elevated temperatures (600 °C). The films exhibit signatures for a long-range in-plane ordering resembling an epitaxial growth. The charge carrier mobility determined by Hall-effect measurements is up to 24 cm²/V.s

Keywords: PtSe2; epitaxial films; Laue oscillations; Raman spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-31532