Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

35836 Publications

PORTAF–postoperative radiotherapy of non-small cell lung cancer: accelerated versus conventional fractionation–study protocol for a randomized controlled trial

Bütof, R.; Simon, M.; Löck, S.; Troost, E.; Appold, S.; Krause, M.; Baumann, M.

BACKGROUND:

In early-stage non-small cell lung cancer (NSCLC) without affected lymph nodes detected at staging, surgical resection is still the mainstay of treatment. However, in patients with metastatic mediastinal lymph nodes (pN2) or non-radically resected primary tumors (R1/R2), postoperative radiotherapy (possibly combined with chemotherapy) is indicated. So far, investigations about time factors affecting postoperative radiotherapy have only examined the waiting time defined as interval between surgery and start of radiotherapy, but not the overall treatment time (OTT) itself. Conversely, results from trials on primary radio(chemo)therapy in NSCLC show that longer OTT correlates with significantly worse local tumor control and overall survival rates. This time factor of primary radio(chemo)therapy is thought to mainly be based on repopulation of surviving tumor cells between irradiation fractions. It remains to be elucidated if such an effect also occurs when patients with NSCLC are treated with postoperative radiotherapy after surgery (and chemotherapy). Our own retrospective data suggest an advantage of shorter OTT also for postoperative radiotherapy in this patient group.
METHODS/DESIGN:

This is a multicenter, prospective randomized trial investigating whether an accelerated course of postoperative radiotherapy with photons or protons (7 fractions per week, 2 Gy fractions) improves locoregional tumor control in NSCLC patients in comparison to conventional fractionation (5 fractions per week, 2 Gy fractions). Target volumes and total radiation doses will be stratified in both treatment arms based on individual risk factors.
DISCUSSION:

For the primary endpoint of the study we postulate an increase in local tumor control from 70% to 85% after 36 months. Secondary endpoints are overall survival of patients; local recurrence-free and distant metastases-free survival after 36 months; acute and late toxicity and quality of life for both treatment methods.

Permalink: https://www.hzdr.de/publications/Publ-26999
Publ.-Id: 26999


PO-0616: HPV, CSC marker expression and tumor hypoxia as prognosticators for LRC in patients with HNSCC

Linge, A.; Löck, S.; Krenn, C.; Appold, S.; Lohaus, F.; Schneider, M.; Nowak, A.; Gudziol, V.; Baretton, G. B.; Buchholz, F.; Baumann, M.; Krause, M.

PO-0616: HPV, CSC marker expression and tumor hypoxia as prognosticators for LRC in patients with HNSCC

Permalink: https://www.hzdr.de/publications/Publ-26997
Publ.-Id: 26997


PO-0968: The Role of epithelial to mesenchymal transition (EMT) as Biomarker for Radioresistance in HNSCC

Kurth, I.; Digomann, M.; Hein, L.; Linge, A.; Koi, L.; Loeck, S.; Maebert, K.; Stephan, H.; Peitzsch, C.; Krause, M.; Baumann, M.; Dubrovska, A.

PO-0968: The Role of epithelial to mesenchymal transition (EMT) as Biomarker for Radioresistance in HNSCC

Permalink: https://www.hzdr.de/publications/Publ-26996
Publ.-Id: 26996


Optimisation and stabilisation of cathepsin B-endopeptidase substrates: Towards a Cathepsin B-activated cell-penetrating peptide

Kuhne, K.; Behring, L.; Belter, B.; Neuber, C.; Wodtke, R.; Pietzsch, J.; Löser, R.

Cathepsin B (CTB), whose expression in tumours correlates with increased metastasis, therapy resistance, and generally poor prognosis, represents an excellent target for molecular imaging using radiotracers [1]. It is our aim to develop a CTB-specifc, substrate-based radiotracer based on activatable, poly-D-arginine-derived cell pentrating peptides [2]. Central prerequisite for such a probe is an endopeptidase substrate for CTB used as an activator sequence that shows efficient cleavage kinetics towards CTB and is stable in circulation and against other relevant cathepsins. After newly identifying the P4' position as major determinant of CTB endopeptidase specificity, we determined Val (kcat/KM=245 mM-1s-1, 16xGly) as the ideal amino acid at this position. In terms of stabilisation, we were able to increase serum half-life from 3.6 min to >1440 min by amino acid exchange at P1 and N2-methylation of a secondary cleavage site, while still retaining good cleavability by CTB. Analysis of cleavage by other relevant ctahepsins is currently ongoing.

Literature
[1] Löser & Pietzsch Front. Chem. 2015, 3, 37
[2] Jang et al. PNAS 2004, 101, 17867

  • Poster
    International Sympsosium on Bioorganic Chemistry (ISBOC-11), 27.-29.09.2017, Konstanz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26995
Publ.-Id: 26995


Neutron imaging of particle laden Foam

Heitkam, S.; Lappan, T.; Eckert, S.; Eckert, K.

This presentation reports on the simultaneous measurement of foam structure and attached particles employing neutron imaging. An aqueous foam sample is placed in the NEUTRA beamline at PSI, enables for achieving a spatial resolution of less than 200 μm at a frame rate of more than 1 Hz. A forced drainage setup allows to control the liquid content of the foam. The averaged attenuation of the neutrons is demonstrated to yield the liquid fraction of the foam. Hydrophobized gadolinium particles of 200 μm diameter are added to the foam. Using two surfactants different levels of hydrophobicity are achieved. Depending on the drainage flow and the hydrophobicity, the particles are washed out of the foam with different rates. An avalanche-like motion of particle clusters is observed. The neutron radiography is demonstrated to yield unique insights into the unsteady froth flotation process.

Keywords: Neutron Imaging; Froth; Foam

  • Lecture (others)
    Seminarvortrag, 24.10.2017, Strasbourg, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26994
Publ.-Id: 26994


Using Lorentz forces to control the distribution of bubbles in a vertical tube filled with liquid metal

Heitkam, S.; Tschisgale, S.; Krull, B.; Wetzel, T.; Baake, E.; Fröhlich, J.

In this work, a method to increase the residence time of bubbles in tubes or pipes filled with liquid metal is investigated. Imposing a horizontal electric current and a perpendicular horizontal magnetic field generates an upward-directed Lorentz force. This force can counteract gravity and cause floating of bubbles. Even with homogeneous electric fields these float in the mean but fluctuate randomly within the swarm due to mutual interactions.
In the present case the cylindrical shape of the container furthermore creates inhomogeneous electric currents and an inhomogeneous force distribution resulting in a macroscopic convection pattern stirring the bubbles and further homogenising the spatial distribution of the bubbles.

Keywords: Magnetohydrodynamics; Bubbles; Flow

Permalink: https://www.hzdr.de/publications/Publ-26993
Publ.-Id: 26993


The Role of epithelial to mesenchymal transition (EMT) as Biomarker for Radioresistance in HNSCC

Kurth, I.; Digomann, D.; Hein, L.; Linge, A.; Koi, L.; Loeck, S.; Maebert, K.; Stephan, H.; Peitzsch, C.; Krause, M.; Baumann, M.; Dubrovska, A.

Purpose or Objective
It is described that epithelial – to -mesenchymal transition (EMT) plays an important role in head and neck squamous carcinomas (HNSCC) progression and resistance to therapy. Recent studies suggest that for instance the expression of EMT related microRNAs may cause intrinsic radioresistance in HNSCC. During the process of EMT epithelial cancer cells obtain a more mesenchymal –like motile and invasive phenotype, which has been argued to sustain survival and therapy resistance of those tumor cells and facilitate cancer progression. Radiotherapy is one of the main approaches to treat HNSCC. However, tumor radioresistance often impedes the success of radiotherapy and has been found to drive tumor aggressiveness and expansion. In this study we asked the question, if radioresistant HNSCC populations display EMT features on a molecular as well as on a functional level and whether we can correlate those characteristics to treatment outcome.
Material and Methods
We used multiple irradiated HNSCC lines (IR) as an established model to investigate the traits of radioresistance. Global gene expression analysis in vitro and on xenograft models and functional radiobiological analyis was applied.
Results
Interestingly, global gene expression analysis revealed a negative correlation of genes associated with cell motility and migration in the IR derivatives of two HNSCC cell lines, namely Cal33, FaDu. We functionally validated those findings and screened for known EMT marks from literature by functional migration assays and EMT-related protein expression in several HNSCC model cell lines and established xenografts as well as in their IR derivatives in order to correlate the acquired findings to radiotherapy outcome. The only positive correlation was found for the initial before therapy protein expression in vitro and in vivo for Slug, a zinc - finger protein encoded by the SNAI2 gene and c-Met, a receptor tyrosine kinase encoded by the MET gene. Functional knockdown of Slug or c-Met expression let to radiosensitization in 3-D clonogenic survival assays of several HNSCC cell lines.
Conclusion
Currently the expression of these molecules is scored for clinical outcome to better understand the context of EMT biomarkers for HNSCC progression and the development of a potential well-directed combinational radiochemotherapy.

Keywords: EMT; radiotherapy; HNSCC; migration

Permalink: https://www.hzdr.de/publications/Publ-26992
Publ.-Id: 26992


Cytokine-dependent regulation of prostate cancer stem cells maintenance in response to radiotherapy

Peitzsch, C.; Baumbach, M.; Cojoc, M.; Hein, L.; Kurth, I.; Baumann, M.; Krause, M.; Dubrovska, A.

Purpose: According to the cancer stem cell hypothesis prostate cancer is driven by a malignant subpopulation with stem-like properties. These cancer stem cells (CSC) contribute to tumor-initiation, metastasis, therapy-resistance and tumor relapse. In parallel, genetic mutations accumulate over time and CSC subclones evolve. Therapeutic interventions like radiotherapy provide selective pressure for the expansion of resistant subclones with genetic diversification. We hypothesize that the determination of CSC-related biomarker in prostate cancer biopsies is correlating with clinical parameter and can be used for patient stratification and treatment selection to improve personalized radiotherapy.
Methodology: We generated isogenic radioresistant prostate cancer cell lines with a high expression of CSC marker, a epithelial-to-mesenchymal transition (EMT) phenotype, higher self-renewal properties, higher tumorigenicity and enhanced DNA repair capacity. We applied comparative genomic, proteomic, metabolomic, epigenomic and secretome analysis to identify novel biomarker for prostate cancer radioresistance and to unravel contributing molecular mechanisms.
Results: Within our first proof-of-principle study, we could show that ALDH-positive CSCs are radioresistant and maintained directly by the Wnt/β-catenin signaling pathway (1). In addition, we found that irradiation is inducing CSC marker and CSC properties in a dose- and time-dependent manner. This irradiation-induced CSC-plasticity was attributed to the modulation of the histone methylation code (2). Within the present study we analyzed a panel of secreted cytokines and their corresponding cytokine receptors in the radioresistant prostate cancer sublines, in a s.c. xenotransplantation model, in ex vivo irradiated primary prostate cancer biopsies and in blood samples of prostate cancer patients during the course of radiotherapy and found, for example, the CXCR4-CXCL12 signaling to be involved in the CSC maintenance and the induction of prostate cancer radioresistance.

References:

(1) Peitzsch C, Cojoc M, Hein L, Kurth I, Mäbert K, Trautmann F, Klink B, Schrock E, Wirth MP, Krause M et al: An epigenetic reprogramming strategy to re-sensitize radioresistant prostate cancer cells. Cancer research 2016, 76; 2637.

(2) Cojoc M*, Peitzsch C*, Kurth I, Trautmann F, Kunz-Schughart LA, Telegeev GD, Stakhovsky EA, Walker JR, Simin K, Lyle S et al: Aldehyde Dehydrogenase Is Regulated by beta-Catenin/TCF and Promotes Radioresistance in Prostate Cancer Progenitor Cells. Cancer research 2015, 75(7):1482-1494.

Keywords: Cytokines; prostate cancer; radioresistance

Permalink: https://www.hzdr.de/publications/Publ-26991
Publ.-Id: 26991


Synthesis and 18F-Radiolabelling of Novel Benzoimidazotriazines for Imaging of Phosphodiesterase 2A (PDE2A)

Ritawidya, R.; Wenzel, B.; Teodoro, R.; Scheunemann, M.; Deuther-Conrad, W.; Brust, P.

1. Introduction
Cyclic nucleotide phosphodiesterases (PDEs) are a class of intracellular enzymes that inactivate the secondary messenger molecules cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Thus, PDEs regulate the signaling cascades mediated by these cyclic nucleotides and affect fundamental cellular processes, such as proliferation, differentiation, migration, survival, and apoptosis. Accordingly, they are promising therapeutic targets. Since PDE2A was found to be related to a variety of tumors, it is our aim to synthesize novel PDE2A inhibitors based on the benzoimidazotriazine (BIT) moiety that might be a prospective lead compound for the development of an F-18 labelled ligand for PDE2A imaging with PET.

Fig A. BIT key intermediates, B. Radiosynthesis of [18F]BIT1

2. Materials & Methods
Based on BIT key intermediates (Fig. A), a small series of novel fluorinated BIT derivatives was successfully prepared (overall in 7-10 steps) and the affinities towards PDE2A and other PDE subtypes were estimated. The most promising compound, BIT1, was radiolabelled by using the corresponding nitro precursor. The reaction was optimized by choosing different solvents, amounts of precursor, modes of heating (conventional or microwave), temperatures, and reaction times. Afterwards, best conditions (Fig. B) were transferred to an automated synthesis module (TracerLab FX2 N, GE Healthcare). The radiotracer was isolated by semi-preparative HPLC (Reprosil-Pur AQ column, 25010mm, 46 % ACN/aqu. 20 mM NH4OAc, flow 5.5 ml/min) followed by purification with a Sep-Pak C18 Plus light cartridge and formulation in isotonic saline containing 10% ethanol.

3. Results
BIT1 showed a high affinity towards PDE2A (IC50 PDE2A3 = 3.33 nM) and selectivity over other PDE subtypes. [18F]BIT1 was successfully synthesized with a radiochemical yield of 51.9 ± 1.3 % (n=3), molar activities between 46 – 100 GBq/µmol and radiochemical purities of ≥ 99%.

4. Discussion & Conclusion
Radiofluorination of a novel PDE2A ligand [18F]BIT1 was obtained with appropriate radiochemical yield and molar activity. First biological investigations are planned to estimate the potential of [18F]BIT1 as imaging agent for PDE2A.

Acknowledgement
1. Deutsche Forschungsgemeinschaft (German Research Foundation, Project Number: SCHE 1825/3-1).
2. Scholarship Program for Research and Innovation in Science and Technology Project (RISET-PRO)-Indonesia Ministry of Research, Technology and Higher Education.

Keywords: benzoimidazotriazines; PDE2A; radiolabelling; imaging

  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals, 05.-08.04.2018, Groningen, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-26990
Publ.-Id: 26990


High temperature reactions of UO2, ZrO2, B4C, CaO, and SiO2 under reducing and oxidizing atmospheres

Uehara, A.; Akiyama, D.; Numako, C.; Takeda-Homma, S.; Ikeda-Ohno, A.; Terada, Y.; Ina, T.; Nitta, K.; Kirishima, A.; Sato, N.

Uranium and several other radioactive materials reacted with zircaloy (Zry) and/or its oxide, ZrO2, presented in the fuel cladding, to form fuel debris at the Fukushima Daiichi Nuclear Power Station in 2011. Under very high temperature conditions, the melt core, mainly consisting of the control rods (stainless steel rod filled with B4C) and fuel assembly (UO2 and Zry) materials, was solidified at the lower head of the pressure vessel. In addition, the melt core was also solidified at the lower head of the pedestal reacted with cement materials (CaO and SiO2). In order to forward a safe and controlled decommissioning process, structural and thermodynamic estimations of the fuel debris under various atmospheric conditions such as reducing and oxidizing atmospheres have been conducted. In the present study, the local structure of basic uranium/zirconium compounds has been characterized under different treatment conditions in the presence of B4C, CaO and SiO2 in atmospheric conditions with different temperatures ranging from 1473 to 1873 K. These reactions are of specific interest to the interaction between nuclear fuel and cladding tube materials.

Keywords: Nuclear debris; uranium; zirconium; solid-solution; synchrotron; X-ray absorption spectroscopy; powder X-ray diffraction

  • Lecture (Conference)
    17th international conference on X-ray absorption fine structure (XAFS 2018), 22.-27.07.2018, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-26989
Publ.-Id: 26989


Epigenetic and metabolic reprogramming as a target for prostate tumor radiosensitization

Dubrovska, A.; Peitzsch, C.; Tyutyunnykova, A.; Cojoc, M.

Purpose or Objective
Radiotherapy remains one of the main modalities to treat solid cancers and is one of the mainstays of curative prostate cancer treatment. Nevertheless, the risk of recurrence after radiotherapy still remains substantial in locally advanced disease. Tumor relapse after radiotherapy is attributed to the population of cancer stem cells (CSCs) which survived the treatment. Therefore, analysis of the CSC populations might be an important predictive tool of radiotherapy outcome and individualized treatment selection. However, compelling evidence suggests a high plasticity of CSCs imposed by tumor treatment. This study is aiming to investigate the interconnection of the glutamine metabolism and cancer cell plasticity in the development of tumor radioresistance for the development of new biomarkers to predict radiation treatment outcome.
Material and Methods
The employed methodological approaches include gene expression analysis, comparative genomic hybridization array, proteomic analysis, metabolic profiling, in vitro radiobiological clonogenic survival assays, assessment of the histone methylation marks and CSC marker expression, analysis of DNA damage repair and oxidative stress response. This study is based on the different models including tumor cell lines and their radioresistant derivatives, prostate cancer xenografts, ex vivo treated tissues and analysis of the publicly available TCGA prostate cancer datasets.
Results
Our study revealed that irradiation causes long-term upregulation in the expression of stem cell markers and induces tumor cell reprogramming. Furthermore, radioresistant and tumorigenic cell populations undergo a phenotypic switch during the course of radiotherapy. This phenotypic plasticity is associated with genetic, epigenetic and metabolic changes induced by irradiation. Expression of CSC markers and proteins involved in glutamine metabolism can be used to predict clinical outcome of prostate cancer patients.
Conclusion
Our studies suggest that radioresistant properties of prostate cancer cells are dynamic in nature and that combination of irradiation with therapeutic agents which prevent tumor cell reprogramming and metabolic switch may restore the cytotoxic effects of irradiation in radioresistant CSC populations.
References:
Cojoc M et al. Cancer Res. 2015; 75(7):1482-94;
Peitzsch C et al. Cancer Res. 2016; 76(9):2637-51;
Kurth I et al. Oncotarget 2015; 6(33):34494-509;
Krause M et al. Advanced Drug Delivery Reviews, 2016, pii: S0169-409X(16)30052-7.

Keywords: Metabolism; radioresistance; prostate cancer

  • Contribution to proceedings
    ESTRO36, 05.-09.05.2017, Vienna, Austria
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 123(2017), S201
    DOI: 10.1016/S0167-8140(17)30815-0

Permalink: https://www.hzdr.de/publications/Publ-26986
Publ.-Id: 26986


Measurement of foam flow using Ultrasound Doppler Velocimetry + Froth dynamics by Neutron Imaging

Heitkam, S.; Nauber, R.; Büttner, L.; Czarske, J.; Eckert, K.

The flowing behavior of liquid foam and froth is only scarcely investigated. One reason for that is, that no adequate measurement technique exists. Also, industrial flotation applications could be improved by monitoring the froth flow in the process.

In this work, the Ultrasound Doppler Velocimetry has been used to measure the velocity distribution inside liquid foam. To that end, an array of ultrasound transducers sends pulses into the foam and receiving the echoes. Sound pulses are reflected at moving particles and air-liquid interfaces. The echoes reveal the longitudinal velocity distribution on the beam axis. Multiplexing of the array allows for 2D-1C measurement.

Comparing with optical measurement it is demonstrated, that the velocity uncertainty at 2.5 Hz frame rate is below 15 percent and the spatial resolution better than 10 mm. These parameters allow for on-line monitoring of industrial processes as well as scientific investigation of three-dimensional froth and foam flows.

Keywords: Foam; Froth; Flotation; Ultrasound Dopller Velocimetry; Neutron Imaging

  • Lecture (Conference)
    Flotation17, 12.-16.11.2017, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-26982
Publ.-Id: 26982


Profile of European proton and carbon ion therapy centers assessed by the EORTC facility questionnaire.

Weber, D. C.; Abrunhosa-Branquinho, A.; Bolsi, A.; Kacperek, A.; Dendale, R.; Geismar, D.; Bachtiary, B.; Hall, A.; Heufelder, J.; Herfarth, K.; Debus, J.; Amichetti, M.; Krause, M.; Orecchia, R.; Vondracek, V.; Thariat, J.; Kajdrowicz, T.; Nilsson, K.; Grau, C.

BACKGROUND:

We performed a survey using the modified EORTC Facility questionnaire (pFQ) to evaluate the human, technical and organizational resources of particle centers in Europe.
MATERIAL AND METHODS:

The modified pFQ consisted of 235 questions distributed in 11 sections accessible on line on an EORTC server. Fifteen centers from 8 countries completed the pFQ between May 2015 and December 2015.
RESULTS:

The average number of patients treated per year and per particle center was 221 (range, 40-557). The majority (66.7%) of centers had pencil beam or raster scanning capability. Four (27%) centers were dedicated to eye treatment only. An increase in the patients-health professional FTE ratio was observed for eye tumor only centers when compared to other centers. All centers treated routinely chordomas/chondrosarcomas, brain tumors and sarcomas but rarely breast cancer. The majority of centers treated pediatric cases with particles. Only a minority of the queried institutions treated non-static targets.
CONCLUSIONS:

As the number of particle centers coming online will increase, the experience with this treatment modality will rise in Europe. Children can currently be treated in these facilities in a majority of cases. The majority of these centers provide state of the art particle beam therapy.

Permalink: https://www.hzdr.de/publications/Publ-26981
Publ.-Id: 26981


Radiation Resistance in KRAS-Mutated Lung Cancer Is Enabled by Stem-like Properties Mediated by an Osteopontin-EGFR Pathway.

Wang, M.; Han, J.; Marcar, L.; Black, J.; Liu, Q.; Li, X.; Nagulapalli, K.; Sequist, L. V.; Mak, R. H.; Benes, C. H.; Hong, T. S.; Gurtner, K.; Krause, M.; Baumann, M.; Kang, J. X.; Whetstine, J. R.; Willers, H.

Lung cancers with activating KRAS mutations are characterized by treatment resistance and poor prognosis. In particular, the basis for their resistance to radiation therapy is poorly understood. Here, we describe a radiation resistance phenotype conferred by a stem-like subpopulation characterized by mitosis-like condensed chromatin (MLCC), high CD133 expression, invasive potential, and tumor-initiating properties. Mechanistic investigations defined a pathway involving osteopontin and the EGFR in promoting this phenotype. Osteopontin/EGFR-dependent MLCC protected cells against radiation-induced DNA double-strand breaks and repressed putative negative regulators of stem-like properties, such as CRMP1 and BIM. The MLCC-positive phenotype defined a subset of KRAS-mutated lung cancers that were enriched for co-occurring genomic alterations in TP53 and CDKN2A. Our results illuminate the basis for the radiation resistance of KRAS-mutated lung cancers, with possible implications for prognostic and therapeutic strategies. Cancer Res; 77(8); 2018-28. ©2017 AACR.

Permalink: https://www.hzdr.de/publications/Publ-26980
Publ.-Id: 26980


Heat shock protein 70 and tumor-infiltrating NK cells as prognostic indicators for patients with squamous cell carcinoma of the head and neck after radiochemotherapy: A multicentre retrospective study of the German Cancer Consortium

Stangl, S.; Tontcheva, N.; Sievert, W.; Shevtsov, M.; Niu, M.; Schmid, T.; Pigorsch, S.; Combs, S.; Haller, B.; Balermpas, P.; Rödel, F.; Rödel, C.; Fokas, E.; Krause, M.; Linge, A.; Lohaus, F.; Baumann, M.; Tinhofer, I.; Budach, V.; Stuschke, M.; Grosu, A.; Abdollahi, A.; Debus, J.; Belka, C.; Maihöfer, C.; Mönnich, D.; Zips, D.; Multhoff, G.

Tumor cells frequently overexpress heat shock protein 70 (Hsp70) and present it on their cell surface, where it can be recognized by pre-activated NK cells. In our retrospective study the expression of Hsp70 was determined in relation to tumor-infiltrating CD56+ NK cells in formalin-fixed paraffin embedded (FFPE) tumor specimens of patients with SCCHN (N = 145) as potential indicators for survival and disease recurrence. All patients received radical surgery and postoperative cisplatin-based radiochemotherapy (RCT). In general, Hsp70 expression was stronger, but with variable intensities, in tumor compared to normal tissues. Patients with high Hsp70 expressing tumors (scores 3-4) showed significantly decreased overall survival (OS; p = 0.008), local progression-free survival (LPFS; p = 0.034) and distant metastases-free survival (DMFS; p = 0.044), compared to those with low Hsp70 expression (scores 0-2), which remained significant after adjustment for relevant prognostic variables. The adverse prognostic value of a high Hsp70 expression for OS was also observed in patient cohorts with p16- (p = 0.001), p53- (p = 0.0003) and HPV16 DNA-negative (p = 0.001) tumors. The absence or low numbers of tumor-infiltrating CD56+ NK cells also correlated with significantly decreased OS (p = 0.0001), LPFS (p = 0.0009) and DMFS (p = 0.0001). A high Hsp70 expression and low numbers of tumor-infiltrating NK cells have the highest negative predictive value (p = 0.00004). In summary, a strong Hsp70 expression and low numbers of tumor-infiltrating NK cells correlate with unfavorable outcome following surgery and RCT in patients with SCCHN, and thus serve as negative prognostic markers.

Keywords: Hsp70; IHC; NK cells; SCCHN; prognostic biomarker; retrospective trial

  • Open Access Logo International Journal of Cancer 142(2018)9, 1911-1925
    Online First (2017) DOI: 10.1002/ijc.31213

Permalink: https://www.hzdr.de/publications/Publ-26978
Publ.-Id: 26978


Tumor heterogeneity determined with a γH2AX foci assay: A study in human head and neck squamous cell carcinoma (hHNSCC) models

Rassamegevanon, T.; Löck, S.; Range, U.; Krause, M.; Baumann, M.; von Neubeck, C.

PURPOSE:

This study aimed to analyze the intra-tumoral heterogeneity of γH2AX foci in tumor specimens following ex vivo radiation to evaluate the potential of γH2AX foci as predictors for radiosensitivity.
MATERIAL AND METHODS:

γH2AX foci were quantified in tumor specimens of 3hHNSCC tumor models with known differences in radiosensitivity after reoxygenation in culture medium (10h, 24h), single dose exposure (0Gy, 4Gy), and fixation 24h post-irradiation. Multiple, equally treated samples of the same tumor were analyzed for foci, normalized and fitted in a linear mixed-effects model.
RESULTS:

The ex vivo reoxygenation time had no significant effect on γH2AX foci counts. A significant intra model heterogeneity could be shown for FaDu (p=0.033) but not for SKX (p=0.167) and UT-SCC-5 (p=0.082) tumors, respectively. All tumor models showed a significant intra-tumoral heterogeneity between specimens of the same tumor (p<0.01) or among microscopic fields of a particular tumor specimen (p<0.0001).
CONCLUSION:

Similar results for ex vivo γH2AX foci between 10h and 24h reoxygenation time support the applicability of the assay in a clinical setting. The high intra-tumoral heterogeneity underlines the necessity of multiple analyzable samples per patient and therewith the need for an automated foci analysis.

Copyright © 2017 Elsevier B.V. All rights reserved.

Keywords: Biomarker; Radiosensitivity; Tumor heterogeneity; γH2AX foci

Permalink: https://www.hzdr.de/publications/Publ-26977
Publ.-Id: 26977


Development of a genetic sensor that eliminates p53 deficient cells

Mircetic, J.; Dietrich, A.; Paszkowski-Rogacz, M.; Krause, M.; Buchholz, F.

The TP53 gene fulfills a central role in protecting cells from genetic insult. Given this crucial role it might be surprising that p53 itself is not essential for cell survival. Indeed, TP53 is the single most mutated gene across different cancer types. Thus, both a theoretical and a question of significant practical applicability arise: can cells be programmed to make TP53 an essential gene? Here we present a genetic p53 sensor, in which the loss of p53 is coupled to the rise of HSV-TK expression. We show that the sensor can distinguish both p53 knockout and cells expressing a common TP53 cancer mutation from otherwise isogenic TP53 wild-type cells. Importantly, the system is sensitive enough to specifically target TP53 loss-of-function cells with the HSV-TK pro-drug Ganciclovir both in vitro and in vivo. Our work opens new ways to programming cell intrinsic transformation protection systems that rely on endogenous components.

Permalink: https://www.hzdr.de/publications/Publ-26974
Publ.-Id: 26974


Comparison of detection methods for HPV status as a prognostic marker for loco-regional control after radiochemotherapy in patients with HNSCC.

Linge, A.; Schötz, U.; Löck, S.; Lohaus, F.; von Neubeck, C.; Gudziol, V.; Nowak, A.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Bunea, H.; Grosu, A.; Abdollahi, A.; Debus, J.; Ganswindt, U.; Lauber, K.; Pigorsch, S.; Combs, S.; Mönnich, D.; Zips, D.; Baretton, G.; Buchholz, F.; Krause, M.; Belka, C.; Baumann, M.

OBJECTIVE:

To compare six HPV detection methods in pre-treatment FFPE tumour samples from patients with locally advanced head and neck squamous cell carcinoma (HNSCC) who received postoperative (N = 175) or primary (N = 90) radiochemotherapy.
MATERIALS AND METHODS:

HPV analyses included detection of (i) HPV16 E6/E7 RNA, (ii) HPV16 DNA (PCR-based arrays, A-PCR), (iii) HPV DNA (GP5+/GP6+ qPCR, (GP-PCR)), (iv) p16 (immunohistochemistry, p16 IHC), (v) combining p16 IHC and the A-PCR result and (vi) combining p16 IHC and the GP-PCR result. Differences between HPV positive and negative subgroups were evaluated for the primary endpoint loco-regional control (LRC) using Cox regression.
RESULTS:

Correlation between the HPV detection methods was high (chi-squared test, p < 0.001). While p16 IHC analysis resulted in several false positive classifications, A-PCR, GP-PCR and the combination of p16 IHC and A-PCR or GP-PCR led to results comparable to RNA analysis. In both cohorts, Cox regression analyses revealed significantly prolonged LRC for patients with HPV positive tumours irrespective of the detection method.
CONCLUSIONS:

The most stringent classification was obtained by detection of HPV16 RNA, or combining p16 IHC with A-PCR or GP-PCR. This approach revealed the lowest rate of recurrence in patients with tumours classified as HPV positive and therefore appears most suited for patient stratification in HPV-based clinical studies.

Keywords: DKTK-ROG; HNSCC; HPV; Loco-regional control; Radiochemotherapy; p16

Permalink: https://www.hzdr.de/publications/Publ-26970
Publ.-Id: 26970


Thionine-graphene oxide covalent hybrid and its interaction with light.

Krzyszkowska, E.; Walkowiak-Kulikowska, J.; Stienen, S.; Wojcik, A.

Graphene oxide sheets (GO) were covalently functionalized with thionine molecules. The obtained hybrid material, Th-GO, was characterized by means of scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Subsequently, the interaction of light with the free dye molecules and with dye molecules bound to the graphene oxide sheets was probed via UV-Vis spectroscopy, fluorescence spectroscopy and femtosecond pump-probe spectroscopy. The experimental results proved that thionine was successfully grafted onto the GO sheets, however, only one of the two amino groups of thionine was always involved in the amide bond formation. The Th-GO hybrid suspended in N,N-dimethylformamide (DMF) exhibited suppressed fluorescence as compared to the free dye in the same solvent, pointing to an efficient interaction between the photoexcited dye and the graphene sheets. Yet, no electron transfer products were detected by transient absorption measurements, even though there was a shortening of the singlet excited state lifetime of thionine (from the 567 ps for the free dye to the 313 ps for the dye in Th-GO). These results can be rationalized in terms of a fast back electron transfer process or possibly an energy transfer process.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26965
Publ.-Id: 26965


Synchrotron X-ray Imaging and Numerical Modelling of Dendritic Sidebranch Evolution during Coarsening

Neumann-Heyme, H.; Shevchenko, N.; Eckert, K.; Grenzer, J.; Beckermann, C.; Eckert, S.

We study the local dynamics of dendritic side arms during coarsening by combining in-situ radiography observations with numerical and analytical models. A flat sample of a Ga-In alloy is partially solidified and then held isothermally in a vertical temperature gradient. The evolving dendritic microstructure is visualized by synchrotron X-ray imaging at the BM20 beamline (ESRF, France). The resulting 2D images provide a high resolution in space and time at low noise levels, enabling accurate dynamical measurements. Throughout the initial growth stage there is evidence of solutal natural convection, which however vanishes towards the subsequent coarsening processes. During the coarsening stage, the time evolution of essential geometrical features of side branches was captured by automated image processing. This data is used to quantify the dynamics of three basic evolution scenarios for side branches: retraction, pinch-off and coalescence. We exploit the universal dynamics of sidearm necks during pinch-off to determine the product of liquid diffusivity and capillarity length, 𝐷𝑑0, as a parameter that is crucial in the calibration of quantitative reference models. By employing an idealized phase-field model for the evolution of a single side branch, we are able to predict the behaviour of selected side branches from the experiment in a consistent way.

Keywords: Dendritic Solidification; Coarsening Dynamics; Material Properties

  • Contribution to proceedings
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK, 978-1-908549-29-7, 214-217
  • Lecture (Conference)
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK

Permalink: https://www.hzdr.de/publications/Publ-26964
Publ.-Id: 26964


Neoadjuvant radiochemotherapy decreases the total amount of tumor infiltrating lymphocytes, but increases the number of CD8+/Granzyme B plus (GrzB) cytotoxic T-cells in rectal cancer

Jarosch, A.; Sommer, U.; Bogner, A.; Reißfelder, C.; Weitz, J.; Krause, M.; Folprecht, G.; Baretton, G. B.; Aust, D. E.

Although neoadjuvant radiochemotherapy (nRCTx) is an established oncological treatment in patients with advanced rectal cancer, little is known about its effects on the tumor microenvironment. Quantity and composition of tumor infiltrating lymphocytes (TILs) are known to influence patients’ prognosis but nRCTx-induced modifications are still unclear. We determined the composition of the immune cell infiltrate in rectal cancer after nRCTx and its influence on tumor regression, local recurrence rate and survival. We investigated density and composition of tumor infiltrating CD3C and CD8C T-cells and the quantity and ratio of CD8C/GrzBC T-cells to CD8C T-cells in 130 rectal cancers after nRCTx compared to a cohort of 30 primarily resected rectal cancers. Furthermore, we analyzed 22 pretherapeutic rectal cancer biopsies, later
treated with nRCTx and surgery to evaluate nRCTx-inducedmodifications of the tumor microenvironment.
The total numbers of CD3C and CD8C T-cells in tumor stroma (p < 0.001) and tumor Epithelium (p < 0.001 CD3; 0.002 CD8) were significantly lower in rectal cancers after nRCTx compared to primarily resected cases, while the ratio of CD8C/GrzBC T-cells to CD8C T-cells was significantly increased in the nRCTx cohort (p < 0.001). In multivariate analyses, CD8C/GrzBC T-cells in the tumor stroma were significantly associated with high regression grade and a lower likelihood of local recurrence (p D 0.029).
nRCTx modifies the tumor microenvironment of rectal cancer leading to a total decrease of TILs, but a relative increase in CD8C/GrzBC T-cells in the tumor stroma. CD8C/GrzBC T-cells may contribute to local tumor control and the better outcome.

Keywords: rectal cancer; histological tumor regression; granzyme B (GrzB); neoadjuvant radiochemotherapy; Tumor microenvironment

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26963
Publ.-Id: 26963


Laboratory experiments on dynamo action and magnetorotational instability

Stefani, F.

Magnetic fields of planets, stars and galaxies are produced by the homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once generated, magnetic fields can foster cosmic structure formation by destabilizing, via the magnetorotational instability (MRI), Keplerian flows that would be otherwise hydrodynamically stable.
For a long time, both effects had been the subject of purely theoretical and numerical research. This changed in 1999 when the threshold of magnetic-field self-excitation was crossed in the two liquid sodium experiments in Riga and Karlsruhe [1]. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest, such as field reversals and excursions. Liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, and Socorro have contributed further important findings. MRI-related research was partly successful with the observation of the helical MRI [2] and the azimuthal MRI [3] at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). First evidence of the current-driven Tayler instability (TI) in a liquid metal was obtained here, too [4].
The lecture gives a cursory account of the recent laboratory experiments on dynamo action and magnetically triggered flow instabilities. It concludes with an overview about future experiments, with special focus on the precession-driven liquid sodium experiment and the large-scale MRI experiment that are under construction in the framework of the DRESDYN project at HZDR [5].

[1] Gailitis, A. et al., Rev. Mod. Phys. 74 (2002), 973-990
[2] Stefani, F. et al., Phys. Rev. Lett. 97 (2006), 184502
[3] Seilmayer, M. et al., Phys. Rev. Lett. 113 (2014), 024505
[4] Seilmayer, M. et al., Phys. Rev. Lett. 108 (2012), 244501
[5] Stefani, F. et al., IOP Conf. Ser.: Mater. Sci. Eng. 228 (2017), 012002

  • Invited lecture (Conferences)
    Séminaires de l'IRAP, 18.01.2018, Toulouse, France

Permalink: https://www.hzdr.de/publications/Publ-26962
Publ.-Id: 26962


Tidally synchronized Tayler-Spruit and Babcock-Leighton type dynamos

Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.

The usual explanation of the Hale cycle of the solar magnetic field builds on intrinsic features of the solar dynamo, comprising the turbulent resistivity and the intensities of the alpha effect, the Omega effect and the meridional circulation. However, the dissimilarity of the sequence of solar cycles with a random walk in phase, and their remarkable synchronization with the 11.07 years period of the alignment of the tidally dominant planets Venus, Earth and Jupiter has not remained unobserved.
Asking for a viable physical mechanism that could link the very weak planetary forces with solar dynamo action, we focus on the helicity oscillations that were recently found in simulations of the current-driven, kink-type Tayler instability that is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantly excited by m=2 perturbations that reflect tidal oscillations. Specifically, we speculate that the 11.07 years tidal oscillation may lead to a 1:1 resonant excitation of the oscillation of the associated alpha effect. In the framework of simple dynamo model of the Tayler-Spruit type, we recover the 22.14-year cycle of the solar dynamo. Interestingly, slight parameter changes of this model lead to transitions between oscillatory and pulsatory behaviour with maintained phase coherence, which might serve as an analogue of the behaviour during grand minima.
We have also tested similar dynamo models of the Babcock-Leighton type, for which we have pursued two ideas on how such a synchronization could work. The first one bears on the concept of a sensitive flux storage capacity of the tachocline, which might be easily influenced by minor perturbations as provoked by tidal forces, the second one on periodic changes of the Omega effect. In either case, and in contrast to this easy and robust synchronizability of Tayler-Spruit type dynamos, the model proved rather rather stubborn to synchronization.

  • Lecture (others)
    GDRI Dynamo Meeting, 27.-29.11.2017, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-26961
Publ.-Id: 26961


Dynamos, instabilities, inverse problems: Paul Roberts' legacy for experimental MHD

Stefani, F.

Retracing Paul Roberts' footsteps, I survey the recent experimental activities related to dynamo action, magnetically triggered flow instabilities, Alfvén waves, and magnetic flow tomography. I'm certain he will be most pleased by those developments that have superseded some of the pessimistic prognoses made in his seminal 1967 book: "Since processes of self-excitation are out of the question..." (p. 172), is just a case in point.

  • Invited lecture (Conferences)
    Fifty years after Roberts’ MHD: Dynamos and planetary flows today (PHR2017), 16.-17.11.2017, London, UK

Permalink: https://www.hzdr.de/publications/Publ-26960
Publ.-Id: 26960


Of Mikes and butterflies

Stefani, F.

More often than not, after having worked for some time on a problem related to dynamos or magnetic instabilities, I said to myself: "I should have read Michael Proctor before!" Actually, not many scientists have influenced magnetohydrodynamics so profoundly as he did. In a personally biased selection, I discuss some experimental and theoretical MHD topics which were strongly influenced by Michael Proctor's ideas. Those include: 1) The distinction between convective and absolute instabilities, which turned out to be essential for the experimental demonstration of the dynamo effect in Riga and the helical magnetorotational instability (MRI) in Dresden, 2) the Malkus-Proctor effect, as nicely illustrated by the saturation mechanism of the Riga dynamo, 3) double-diffusive magnetic instabilities, such as buoyancy instabilities, but also helical and azimuthal MRI and Super-AMRI, 3) spectral degeneracies of dynamo operators in diabolic or exceptional points, and their (putative) role for reversals of the geodynamo, 4) highly nonlinear dynamo mechanisms, such as MRI dynamos and Tayler-Spruit dynamos.

  • Lecture (others)
    MREP 2017, 11.-12.09.2017, Cambridge, UK

Permalink: https://www.hzdr.de/publications/Publ-26959
Publ.-Id: 26959


Laboratory experiments and numerical simulations on magnetic instabilities.

Stefani, F.; Gellert, M.; Kasprzyk, C.; Paredes, A.; Rüdiger, G.; Seilmayer, M.

Magnetic fields of planets, stars, and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both hydromagnetic dynamo action and magnetically triggered flow instabilities had been the subject of purely theoretical research. Meanwhile, however, the dynamo effect has been observed in large-scale liquid sodium experiments in Riga, Karlsruhe, and Cadarache. In this chapter, we summarize the results of some smaller liquid metal experiments devoted to various magnetic instabilities, such as the helical and the azimuthal magnetorotational instability, the Tayler instability, and the different instabilities that appear in a magnetized spherical Couette flow. We conclude with an outlook on a large scale Tayler-Couette experiment using liquid sodium, and on the prospects to observe magnetically triggered instabilities of flows with positive shear.

Keywords: Dynamo; Magnetorotational instability

  • Book chapter
    Lühr H., Wicht J., Gilder S., Holschneider M.: Magnetic fields in the solar system. Astrophysics and Space Science Library, vol. 448, Cham: Springer, 2018, 978-3-319-64291-8, 125-152
    DOI: 10.1007/978-3-319-64292-5_5

Permalink: https://www.hzdr.de/publications/Publ-26958
Publ.-Id: 26958


Evaporation-assisted magnetic separation of rare earth ions in aqueous solutions

Lei, Z.; Fritzsche, B.; Eckert, K.

This work aims to answer the question of why an enrichment of paramagnetic ions can be observed in a magnetic field gradient [1] despite the presence of a counteracting Brownian motion. For that purpose, we study a rare earth chloride (DyCl3) solution in which weak evaporation is adjusted by means of small differences in the vapor pressure in a specially developed cell, see Fig. 1.
The temporal evolution of the refractive index field of this solution, as a result of heat and mass transfer, is measured by means of a Mach-Zehnder interferometer. We develop a numerical algorithm which splits the refractive index field into two parts, one space-dependent and conservative and the other time-dependent and transient. By using this algorithm in conjunction with a numerical simulation of the temperature and concentration field, we are able to show that 90% of the refractive index in the evaporation-driven boundary layer is caused by an increase in the concentration of Dy(III) ions. A simplified analysis of the gravitational and magnetic forces, entering the Rayleigh number, leads to a diagram of the system's instability. Accordingly, the enrichment layer of elevated Dy(III) concentration is placed in a spatial zone dominated by a field gradient force. This leads to the unconditional stability of this layer in the present field. The underlying mechanism is the levitation and reshaping of the evaporation-driven boundary layer by the magnetic field gradient [2].

[1] X. Yang, K. Tschulik, M. Uhlemann, S. Odenbach, K. Eckert, J. Phys. Chem. Lett. 3 (2012), 3559–3564.
[2] Z. Lei, B. Fritzsche, K. Eckert, submitted to J. Phys. Chem. C (2017).

Keywords: magnetic separation; rare earth; interferometry

  • Lecture (Conference)
    International Conference on Magneto-Science 2017 (ICMS 2017), 23.-27.10.2017, Reims, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26957
Publ.-Id: 26957


Laser ion acceleration using the Draco Petawatt facility at HZDR

Zeil, K.; Obst, L.; Rehwald, M.; Brack, F.; Metzkes, J.; Kraft, S.; Schlenvoigt, H.-P.; Ziegler, T.; Jahn, A.; Kroll, F.; Kluge, T.; Schramm, U.

Demanding applications like radiation therapy of cancer are pushing the frontier of laser driven proton accelerators with controlled and well-defined proton beam properties. This talk will give an overview of recent achievements at the high-contrast high power laser source DRACO at the HZDR in Dresden (Germany). The laser system was recently upgraded by an additional Petawatt (PW) amplifier stage and new front end components finally providing high contrast pulses of >500 TW on target at 1 Hz pulse repetition rate. In first experiments the delivery of these pulses on target was demonstrated and the feasibility of worldwide first controlled volumetric irradiation of a specifically developed tumor model, grown on the ears of nude mice with laser-accelerated protons was investigated. In order to efficiently capture and shape the divergent TNSA proton beam, a setup of two pulsed high-field solenoid magnets will be presented to reliably generate homogeneous dose distributions in lateral direction and in depth.
The performance of laser based proton and ion acceleration and the scaling of the laser energy to achieve increased ion energies strongly depend on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse. Re-collimating single plasma mirror devices have been implemented into the Draco laser beam lines and the talk will summarize on measurements of the resulting contrast enhancement comparing different techniques. With the achieved contrast enhancement, laser proton acceleration and proton energy scaling were investigated within the TNSA regime using ultra-thin foil targets and implications for the radiobiological experiments will be discussed.

  • Lecture (Conference)
    Laser and Plasma Acceleration Workshop, 28.08.2017, Jeju Island, South Korea

Permalink: https://www.hzdr.de/publications/Publ-26956
Publ.-Id: 26956


Laser ion acceleration using the Draco Petawatt facility at HZDR - experiments and radio-biological application

Zeil, K.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Brack, F.; Kroll, F.; Metzkes, J.; Prencipe, I.; Huebl, A.; Kluge, T.; Bussmann, M.; Kraft, S.; Ziegler, T.; Bernert, C.; Jahn, A.; Gaus, L.; Schramm, U.

Demanding applications like radiation therapy of cancer are pushing the frontier of laser driven proton accelerators with controlled and well-defined proton beam properties. This talk will give an overview of recent achievements at the high-contrast high power laser source DRACO at HZDR. The laser system was recently upgraded by an additional Petawatt (PW) amplifier stage and new front end components finally providing high contrast pulses of >500 TW on target at 1 Hz pulse repetition rate. In first experiments with the new PW beam line of Draco the feasibility of worldwide first controlled volumetric irradiation of a specifically developed tumor model, grown on the ears of nude mice with laser-accelerated protons was investigated. In order to efficiently capture and shape the divergent TNSA proton beam, a setup of two pulsed high-field solenoid magnets was used. In the talk the reliable generation of homogeneous dose distributions lateral and in depth will be discussed.

The performance of laser based ion acceleration and the scaling of the laser energy to achieve increased ion energies strongly depend on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse. With such contrast enhancement techniques laser proton acceleration using ultra-thin foil targets as well as a renewable debris-free hydrogen jet (in collaboration with SLAC and European XFEL) target was investigated with a laser pulse energy of 3 J and duration of 30 fs and show robust TNSA proton pulses with energies of up to 25 MeV. An important implication of this is the demonstration of a credible path toward high repetition rate laser-based ion acceleration applications.

  • Invited lecture (Conferences)
    International Conference on High Energy Density Sciences, 21.4.2017, Tokio-Yokohama, Japan

Permalink: https://www.hzdr.de/publications/Publ-26955
Publ.-Id: 26955


Evolution of the Interfacial Area in Dendritic Solidification

Neumann-Heyme, H.; Eckert, K.; Beckermann, C.

The specific area of the solid-liquid interface is an important integral measure for the morphological evolution during solidification. It represents not only the inverse of a characteristic length scale of the microstructure, but it is also a key ingredient in volume-averaged models of alloy solidification. Analytical descriptions exist for either pure coarsening or pure growth processes. However, all alloy solidification processes involve concurrent growth and coarsening. In the present study, the kinetics of the solid-liquid interface of a dendrite are studied using a 3D phase-field model. The simulation results are combined with data from recent synchrotron tomography experiments to study the influence of the cooling rate and alloy composition on the evolution of the interfacial area. A general relation for the specific interfacial area of dendrites is presented that is valid over the entire range of cooling rates, including isothermal coarsening.

Keywords: Dendritic Solidification; Interfacial Area; Phase-Field Simulation

  • Contribution to proceedings
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK
    Evolution of the Interfacial Area in Dendritic Solidification, 978-1-908549-29-7, 193-196
  • Lecture (Conference)
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK

Permalink: https://www.hzdr.de/publications/Publ-26954
Publ.-Id: 26954


Research at the Dresden High Magnetic Field Laboratory

Wosnitza, J.

  • Invited lecture (Conferences)
    Seminar at the Department of Chemistry, Graduate School of Science, Osaka University, 22.09.2017, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-26953
Publ.-Id: 26953


Therapie des kleinzelligen Lungenkarzinoms im Stadium „limited disease“. RCT normo- oder hyperfraktioniert?

Frosch, S.; Troost, E. G. C.

Die simultane Radiochemotherapie (RCT) ist beim kleinzelligen Lungenkarzinom der Therapiestandard im Stadium „limited disease“. Aktuell besteht allerdings noch eine Kontroverse über den Bestrahlungsablauf und die optimale Bestrahlungsdosis. Bisherige Daten zeigten die Überlegenheit einer akzeleriert-hyperfraktionierten Bestrahlung mit täglich zwei Fraktionen im Vergleich zur konventionell fraktionierten Bestrahlung mit täglich einer Fraktion, jedoch auf Kosten von mehr Toxizität [1]. Allerdings war in dieser Studie die Gesamtdosis in beiden Gruppen gleich; Kritiker postulieren, dass eine höhere Gesamtdosis – einmal pro Tag appliziert – im konventionellen Therapiearm die Ergebnisse hätte verbessern können.

  • InFo Onkologie 21(2018)1, 27-28

Permalink: https://www.hzdr.de/publications/Publ-26952
Publ.-Id: 26952


The FFLO state in layered organic superconductors

Wosnitza, J.

  • Invited lecture (Conferences)
    International Conference on Electron Correlation in Superconductors and Nanostructures, 17.-20.08.2017, Odessa, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-26951
Publ.-Id: 26951


FFLO states in layered organic superconductors

Wosnitza, J.

  • Invited lecture (Conferences)
    QCNP 2017 Quantum Criticality & Novel Phases, 26.02.-01.03.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26950
Publ.-Id: 26950


Stereotactic radiosurgery for brainstem metastases : In experienced hands a good treatment option with excellent risk-benefit ratio

Khademalhosseini, Z.; Khademolhosseini, M.; Kummer, B.; Krause, M.

Permalink: https://www.hzdr.de/publications/Publ-26949
Publ.-Id: 26949


SDF-1/CXCR4 expression in head and neck cancer and outcome after postoperative radiochemotherapy

De-Colle, C.; Mönnich, D.; Welz, S.; Boeke, S.; Sipos, B.; Fend, F.; Mauz, P.-S.; Tinhofer, I.; Budach, V.; Jawad, J. A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Bayer, C.; Belka, C.; Pigorsch, S.; Combs, S. E.; Lohaus, F.; Linge, A.; Krause, M.; Baumann, M.; Zips, D.; Menegakis, A.

Introduction

Outcome after postoperative radiochemotherapy (RT-CT) for patients with advanced head and neck squamous cell carcinomas (HNSCC) remains unsatisfactory, especially among those with HPV negative tumours. Therefore, new biomarkers are needed to further define subgroups for individualised therapeutic approaches. Preclinical and first clinical observations showed that the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12) play an important role in tumour cell proliferation, survival, cancer progression, metastasis and treatment resistance. However, the data on the prognostic value of SDF-1/CXCR4 expression for HNSCC are conflicting. The aim of our hypothesis-generating study was to retrospectively explore the prognostic potential of SDF-1/CXCR4 in a well-defined cohort of HNSCC patients collected within the multicenter biomarker study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG).
Material and methods

Patients with stage III and IVA HNSCC of the oral cavity, oropharynx and hypopharynx were treated with resection and adjuvant radiotherapy (RT) with ≥60 Gy and concurrent cisplatin-based chemotherapy (CT). Tissue micro-arrays (TMAs) from a total of 221 patients were generated from surgical specimens, 201 evaluated for the SDF-1 and CXCR4 expression by immunofluorescence and correlated with clinico-pathological and outcome data.
Results

In univariate and multivariate analyses intracellular SDF-1 expression was associated with lower loco-regional control (LRC) in the entire patient group as well as in the HPV16 DNA negative subgroup. CXCR4 expression showed a trend for lower LRC in the univariate analysis which was not confirmed in the multivariate analysis. Neither for SDF-1 nor CXCR4 expression associations with distant metastasis free or overall survival were found.
Conclusions

Our exploratory data support the hypothesis that overexpression of intracellular SDF-1 is an independent negative prognostic biomarker for LRC after postoperative RT-CT in high-risk HNSCC. Prospective validation is warranted and further exploration of SDF-1/CXCR4 as a potential therapeutic target to overcome treatment resistance in HNSCC appears promising.

Permalink: https://www.hzdr.de/publications/Publ-26947
Publ.-Id: 26947


The PD-1/PD-L1 axis and human papilloma virus in patients with head and neck cancer after adjuvant chemoradiotherapy: A multicentre study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG).

Balermpas, P.; Rödel, F.; Krause, M.; Linge, A.; Lohaus, F.; Baumann, M.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Gkika, E.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Stangl, S.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Multhoff, G.; Combs, S. E.; Welz, S.; Zips, D.; Lim, S. Y.; Rödel, C.; Fokas, E.

We examined the prognostic role of PD-1+ and CD8+ tumor infiltrating lymphocytes (TILs), and PD-L1+ cells in patients with squamous cell carcinoma of the head and neck (SCCHN) treated with surgery and postoperative chemoradiotherapy (CRT). FFPE samples from 161 patients were immunohistochemically stained for PD-1, CD8 and PD-L1. The immune marker expression was correlated with clinicopathologic characteristics, and overall survival (OS), local progression-free survival (LPFS) and distant metastases free-survival (DMFS), also in the context of HPV16 DNA/p16 status. The median follow-up was 48 months (range: 4-100). The 2-year-OS was 84.1% for the entire cohort. High PD-1 and PD-L1 expression were more common in patients with positive HPV16 DNA (p < 0.001 and p = 0.008, respectively) and high infiltration by CD8+ TILs (p < 0.001 for both markers). High PD-L1 expression correlated with superior OS (p = 0.025), LPFS (p = 0.047) and DMFS (p = 0.048) in multivariable analysis, whereas no significance could be demonstrated for PD-1. Patients with CD8high /PD-L1high expression had favorable outcome (p < 0.001 for all endpoints) compared to other groups. We validated the superior OS data on CD8high /PD-L1high using the Cancer Genome Atlas TCGA dataset (n = 518; p = 0.032). High PD-L1 expression was a favorable prognostic marker in HPV16-negative but not HPV16-positive patients. In conclusion, HPV-positive tumors showed higher expression of immune markers. PD-L1 expression constitutes an independent prognostic marker in SCCHN patients post-adjuvant CRT. In conjunction with CD8 status, these data provide an important insight on the immune contexture of SCCHN and are directly relevant for future treatment stratification with PD-1/PD-L1 immune checkpoint inhibitors to complement CRT.

Keywords: CD8; HPV; PD-1/PD-L1; SCCHN; chemoradiotherapy; prognostic

Permalink: https://www.hzdr.de/publications/Publ-26945
Publ.-Id: 26945


Prompt gamma spectroscopy for range control with CeBr3.

Martins, P. M.; Bello, R. D.; Rinscheid, A.; Roemer, K.; Werner, T.; Enghardt, W.; Pausch, G.; Seco, J.

Prompt gamma spectroscopy for range control with CeBr3.

Permalink: https://www.hzdr.de/publications/Publ-26944
Publ.-Id: 26944


Magnetically induced cavitation for the dispersion of nanoparticles in liquid metals

Sarma, M.; Gerbeth, G.; Grants, I.; Kaldre, I.; Bojarevics, A.

Dispersion of particles to produce metal matrix nanocomposites (MMNC) can be achieved by means of ultrasonic vibration of the melt using ultrasound transducers. However direct transfer of this method to produce steel composites is not feasible because of the much higher working temperature. Therefore, an inductive technology for contactless treatment by acoustic cavitation was developed. This report describes the samples produced to assess the feasibility of the proposed method for nano-particle separation in steel. Stainless steel samples with inclusions of TiB2, TiO2, Y2O3, CeO2, Al2O3 and TiN have been created and analyzed. Additional experiments have been performed using light metals with an increased value of the steady magnetic field using a superconducting magnet with a field strength up to 5 T.

Keywords: MMC production; Steel composites; Cavitation treatment

  • Contribution to proceedings
    XVIII International UIE-Congress Electrotechnologies for Material Processing, 06.-09.06.2017, Hannover, Deutschland: Vulkan-Verlag GmbH, 978-3-8027-3095-5

Permalink: https://www.hzdr.de/publications/Publ-26938
Publ.-Id: 26938


Prospective data registration and clinical trials for particle therapy in Europe

Langendijk, J.; Orrechhia, R.; Haustermans, K.; Zips, D.; Balosso, J.; Lievens, Y.; Weber, D.; Grau, C.; Troost, E.

To enhance evidence-based introduction of particle therapy in Europe, one of the work packages within the European Proton Therapy network (EPTN) will focus on uniform data registration and defining methodological criteria for phase I, II and III clinical trials. The main objective of EPTN WP1 is to establish a uniform prospective data registration program for all patients treated with particle therapy in Europe. This will be supported by EORTC through existing and new additional QA-platforms and IT-infrastructures for data collection with different formats. In addition, EPTN WP1, to enhance high quality clinical trials, EPTN-WP1 will define the requirements for high quality clinical trials and set up an infrastructure for methodological support.

Keywords: Particle therapy; PROMs; registry

Permalink: https://www.hzdr.de/publications/Publ-26937
Publ.-Id: 26937


Azimuthal magnetorotational instability with super-rotation

Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.

It is demonstrated that the azimuthal magnetorotational instability (AMRI) also works with radially increasing rotation rates contrary to the standard magnetorotational instability for axial fields which requires negative shear. The stability against non-axisymmetric perturbations of a conducting Taylor–Couette flow with positive shear under the influence of a toroidal magnetic field is considered if the background field between the cylinders is current free. For small magnetic Prandtl number Pm->0 the curves of neutral stability converge in the (Hartmann number, Reynolds number) plane approximating the stability curve obtained in the inductionless limit Pm=0. The numerical solutions for Pm=0 indicate the existence of a lower limit of the shear rate. For large Pm the curves scale with the magnetic Reynolds number of the outer cylinder but the flow is always stable for magnetic Prandtl number unity as is typical for double-diffusive instabilities. We are particularly interested to know the minimum Hartmann number for neutral stability. For models with resting or almost resting inner cylinder and with perfectly conducting cylinder material the minimum Hartmann number occurs for a radius ratio of 0.9. The corresponding critical Reynolds numbers are smaller than 10000.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26936
Publ.-Id: 26936


Quasi-free (p,pN) scattering of light neutron-rich nuclei around N = 14

Diaz Fernandez, P.; Alvarez-Pol, H.; Crespo, R.; Cravo, E.; Atar, L.; Deltuva, A.; Aumann, T.; Avdeichikov, V.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boillos, J. M.; Boretzky, K.; Borge, M. J. G.; Caamano, M.; Cabanelas, P.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkall, J.; Chartier, M.; Chulkov, L. V.; Cortina-Gil, D.; Datta Pramanik, U.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fernandez-Dominguez, B.; Fraile, L. M.; Freer, M.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Golubev, P.; Göbel, K.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Holl, M.; Hufnagel, A.; Ignatov, A.; Johansson, H. T.; Jonson, B.; Jurciukonis, D.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knyazev, A.; Kröll, T.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lindberg, S.; Machado, J.; Marganiec, J.; Moro, A. M.; Movsesyan, A.; Nacher, E.; Najafi, A.; Nikolskii, E.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietras, B.; Pietri, S.; Plag, R.; Reifarth, R.; Ribeiro, G.; Rigollet, C.; Rossi, D.; Röder, M.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Syndikus, I.; Taylor, J. T.; Tengblad, O.; Thies, R.; Togano, Y.; Vandebrouck, M.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Wheldon, C.; Wilson, G.; Winfield, J. S.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.

In this work we investigate for the first time the quasi-free scattering reactions (p,pn) and (p,2p) simultaneously for the same projectile in inverse and complete kinematics for radioactive beams with the aim to study the evolution of single-particle properties from N = 14 to N = 15.

Keywords: quasi-free scattering reactions radioactive beams single-particle

Permalink: https://www.hzdr.de/publications/Publ-26935
Publ.-Id: 26935


Comparing the outcome of proton beam irradiation with experimental x-ray and clinical photons in a sophisticated 3-D assay setup

Sorour, N.; Hussein, R.; von Neubeck, C.; Lühr, A.; Schölch, S.; Beyreuther, E.; Pawelke, J.; Kunz-Schughart, L. A.

Background and Aim:
Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer with a median survival of <6 months. The role of radiotherapy in PDAC treatment is consistently under debate. Recent studies imply the superiority of proton versus photon irradiation and propose a benefit for pancreatic cancer patients. We therefore aimed at a systematical comparison of the treatment outcome of PDAC cells when exposed to different beams (photons, protons). Our study included the technical setup, establishment, and application of a multicellular 3-D assay to assess the putatively „curative“ biological endpoint of spheroid control probabilities (SCP).

Materials and Methods:
Four PDAC cell line models were applied in 96-well liquid-overlay spheroid culture. A clinical LINAC (6 MV) at a dose rate of 3 Gy/min and an experimental X-ray tube (220 kV) at a dose rate of 1.3 Gy/min were used for photon irradiation. For proton exposure, spheroids were placed within a spread-out Bragg peak (SOBP) of a double scattered proton beam (150 MeV) and irradiated with a dose rate of 3, 6 and 10 Gy/min. After single-dose irradiation (0-30 Gy), radioresponse was evaluated by a 60-day post-treatment monitoring of spheroid integrity, recovery, and volume growth.

Results and Conclusions:
For proton irradiation, variations in the dose rate were proven to neither alter the SCP nor the spheroid volume growth behavior. SCP and SCD50 (spheroid control dose 50%) turned out to be reproducible read-outs for 3-D culture treatment outcome. Experimental and clinical photon beams led to similar response of PDAC 3-D models. However, all spheroids showed a higher sensitivity to protons reflected by a significant reduction in the SCD50 values and an RBE of 1.2-1.5. New combinatorial treatment strategies with protons are now under evaluation.

  • Lecture (Conference)
    DEGRO 2018, 21.06.2018, Leipzig, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 194(2018), S29-S30
    DOI: 10.1007/s00066-018-1301-7

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26934
Publ.-Id: 26934


Sensitization of pancreatic cancer cells to photons and protons via enzymotherapeutic metabolic targeting of arginine

Sorour, N.; Hussein, R.; von Neubeck, C.; Lühr, A.; Stasyk, O.; Kunz-Schughart, L. A.

Background and Aim:
The abnormal metabolism of pancreatic ductal adenocarcinoma (PDAC) cells offers some interesting points of attack. About 20-30% of PDACs are described to be auxotrophic for arginine because of a reduced or complete loss of anabolic protein expression and/or activity. New strategies for the treatment of this deadly disease should consider the combination of radiotherapy with novel metabolic targeting modalities. We found various arginine deprivation therapy (ADT) approaches to radiosensitize several non-auxotrophic cancer cell types. Hence, we hypothesized that enzymotherapeutic ADT should be particularly efficient in radiosensitizing auxotrophic PDACs to both photons and protons.

Materials and Methods:
Human and murine cell lines reflecting auxotrophic PDACs in patients were studied. ADT was achieved with 2 U/ml of recombinant human arginase in the presence and absence of citrulline. Single dose irradiation of 0-30 Gy was applied with a 200kV X-ray tube and a 150 MeV double-scattered proton beam. Treatment response was assessed by 2-D clonogenic survival and/or 3-D spheroid control probability (SCP) assays. Our specifically designed setup allowed the testing of innovative treatment regimens including proton therapy with/without ADT and Gemcitabine (Gem).

Results and Conclusions:
ADT led to a massive sensitization to X-ray in all PDAC models. Sensitization in 3-D culture was reflected by a significantly reduced SCP and spheroid control dose 50% (SCD50) with an RBE of 2.0. Cells showed a higher sensitivity in the 3-D assay to protons than photons but ADT still further improved the radioresponse. As an example, the RBE of protons plus ADT versus photons alone in one human PDAC spheroid typel was 3.9. In the same model, proton therapy outcome was hardly affected by Gem; however, the combination of ADT with Gem and proton therapy was particularly effective with an exceptional RBE compared to photons of 5.0. Extended mechanistic studies are ongoing; transfer in vivo is envisioned.

  • Lecture (Conference)
    DEGRO 2018, 21.06.2018, Leipzig, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 194(2018), S96
    DOI: 10.1007/s00066-018-1301-7

Permalink: https://www.hzdr.de/publications/Publ-26933
Publ.-Id: 26933


Single molecule level measurements: salen molecule

Kilibarda, F.; Sendler, T.; Mortensen, M.; Gothelf, K.; Erbe, A.

The research presents novel ideas and directions which are supposed to overcome the obstacles conditioned by larger and larger deviations from the Moor's law. One of the possible solutions of the problem lies in the field of Molecular Electronics. We attempt to reduce the size and power needed to operate the device by using single molecules as building blocks in our circuits. This not only offers new features but also self-organizing properties. In order to choose the correct building blocks for our future circuits, we first characterize them. One of the prominent techniques is the Mechanically Controllable Break Junction (MCBJ). With this method we can examine properties of electron transport through single molecules, and determine parameters such as molecular energy level and metal-molecule coupling strength. The technique is demonstrated on salen and salen derivatives. The research shows that we can successfully tune molecular energy levels by the use of chemical doping.

Keywords: Scaling; molecular electronics; single molecule; self-organizing; MCBJ; break junction; characterization; electron transport; energy level; salen; energy level tuning; chemical doping

  • Poster
    Trends in Nanoscience 2017, 27.-30.03.2017, Kloster Irsee, Bavaria, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26932
Publ.-Id: 26932


Molecular characterization in liquid and cryogenic environments

Kilibarda, F.; Strobel, A.; Lokamani, M.; Sendler, T.; Mortensen, M.; Gothelf, K.; Erbe, A.

Current industrial scaling processes are reaching limits. We see not only diminishing returns with further scaling attempts, but also physical limitations that come more and more into play. In our research we offer a novel approach, to use single molecules as electronic components.
This approach offers not only size improvements, but also a reduction in power consumption and costs. Our research focuses on classifying different molecules with the help of Mechanically Controlled Break Junction (MCBJ). Here we present two different kinds of measurements.
One is performed in liquid solution and under ambient conditions, and the other one in a cryogenic environment, under vacuum.
As a test bed for these measurements we use salen and 𝐶₆₀ molecules, respectively. In the case of salen molecules, we show, how chemical doping influences energy levels and affects electron transport through the molecule. The experimental results are supported by quantum chemical calculations. The 𝐶₆₀ measurements demonstrate that we can remove the influence of the solvent by in situ molecular evaporation into the nanoscopic junction. Additionally, operation under vacuum allows us to use more reactive metals for the nano-junction, and thus vary metal-molecule orbital overlap, where in traditional approach contacts are made out of noble metals like gold.

Keywords: Scaling; single molecule; molecular electronics; MCBJ; break junction; electron transport; energy level; quantum chemical calculation; cryogenic; solvent; chemical doping; salen; 𝐶₆₀

  • Poster
    DPG-Frühjahrstagung, 11.-16.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26931
Publ.-Id: 26931


Design rules for molecular electronics: Theoretical and experimental approach

Lokamani, L.; Kilibarda, F.; Wolf, J.; Zahn, P.; Huhn, T.; Gemming, S.; Erbe, A.

Diarylethenes, a class of photosensitive molecules which exhibit photochromism, can be switched between open- and closed-ring isomers. In break-junction experiments diarylethene derivatives in open and closed-ring forms can be distinguished by a low and high conductance state respectively with a difference in current levels of about one order of magnitude.

Here, we explore the underlying design rules for modulating electronic transport in derivatives of diarylethene. In particular, we analyze the effect on molecular orbitals due to various electron accepting and donating groups and in turn the modulation of the conductance properties of single molecules attached to gold electrodes.

We have demonstrated that the mechanically controllable break junction (MCBJ) technique can be used to classify and determine the properties of electronic transport through single organic molecules. We present an outlook on experimental methods for exploring the underlying design rules for diarylethene molecules and derivatives. As a result, we show how the addition of different side groups modifies electronic behavior of the molecules.

Keywords: Diarylethenes; photosensitive molecules; photochromism; molecular switch; break junction; MCBJ; conductance modulation; conductance; molecular design rules; single molecule; side group

  • Poster
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26930
Publ.-Id: 26930


Constructing nanoelectronic circuits by top-down and bottom-up strategies

Kilibarda, F.; Sendler, T.; Deb, D.; Khan, B. M.; Teschome, B.; Erbe, A.

The construction of nanoelectronic circuits requires the development of bottom-up strategies, which can be combined with top-down structuring. We show how reconfigurable silicon nanowires are produced using electron-beam lithography and reactive ion etching. Such structures can be used as large-scale electrodes to networks of self-assembled electronics on the nanoscale. As a first step towards the development of nanoscale circuits by self-organization, we demonstrate the construction of nanoscale metallic wires based on metallized DNA origamis. Active building blocks with smallest dimensions on the molecular scale are developed in single molecule contacts. The properties of those junctions need to be characterized. We have demonstrated that the mechanically controllable break junction (MCBJ) technique can be successfully used to determine the properties of electronic transport through single organic molecules and that the participating molecular energy levels and the metal-molecule coupling can be characterized using this technique. Further developments are based on the use of more complex molecules, which can, for example, be used as single molecule switches. We present the first demonstration of a single molecule junction, in which the molecule is switched in situ from the non-conducting off-state to the conducting on-state.

Keywords: silicon nanowire; e-beam lithography; lithography; self-assembled electronics; DNA origami; single molecule; MCBJ; electron transport; molecular switch

  • Poster
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26929
Publ.-Id: 26929


Investigation of fluids in macrocrystalline and microcrystalline quartz in agate using Thermogravimetry-Mass-Spectrometry

Richter-Feig, J.; Möckel, R.; Götze, J.; Heide, G.

Gaseous and liquid fluids in agates (banded chalcedony – SiO2) of different localities were investigated systematically by thermogravimetry-mass-spectrometry in a temperature range between 25°C and 1450°C for the first time. Chalcedony and macrocrystalline quartz from twelve agate samples have been investigated: Germany (Schlottwitz, St. Egidien, Chemnitz and Zwickau), Brazil (Rio Grande do Sul), Scotland (Ayrshire) and the USA (Montana). They originate from mafic and felsic volcanic rocks as well as hydrothermal and sedimentary environments.
The results were evaluated concerning compounds of hydrogen with fluorine, chlorine, nitrogen, carbon and sulfur. Additionally, oxygen compounds were recognized with hydrogen, fluorine, nitrogen, sulfur and carbon. The nature of the compounds was identified based on their mass-charge-ratio and the intensity ratios of the associated fragments. Due to interferences of different compounds with the same mass-charge-ratio, only H2O, HF, NO, S, SO, CO3 as well as several hydrocarbon compounds (for example CO32- or CO) could be properly identified. The main degassing temperatures were detected around 500 °C and 1000 °C. Generally, a difference between quartz and chalcedony concerning the composition of their fluids could not be found. The results indicate a silica source for the agate formation from aqueous solutions, but also the possible role of fluorine compounds. Additionally, CO2 and other fluids were involved in the alteration of volcanic rocks and the mobilization and transport of SiO2.

Keywords: agate; quartz; fluids; thermogravimetry-mass-spectrometry; chalcedony

Permalink: https://www.hzdr.de/publications/Publ-26928
Publ.-Id: 26928


Modified Calix[4]crowns as Molecular Receptors for Barium

Steinberg, J.; Bauer, D.; Reissig, F.; Köckerling, M.; Pietzsch, H.-J.; Mamat, C.

A series of modified calix[4]crown-6 derivatives was synthesized to chelate the heavy group 2 metal barium, which serves as non-radioactive surrogate for radium-223/-224; radionuclides with promising properties for radiopharmaceutical use. These calixcrowns were functionalized either with cyclic amide moieties or proton-ionizable groups and the corresponding barium complexes were synthesized. Stability constants of these complexes were measured using NMR and UV/Vis titration techniques to determine logK values between 4.1 and 6.4. Further extraction studies were performed to characterize the binding affinity of calixcrowns to radioactive barium-133. Additionally, the ligands containing cyclic amides were investigated regarding their barriers for rotation using temperature dependent NMR measurements.

Keywords: Calix-crown; radiolabeling; barium-133; radium; extraction

Permalink: https://www.hzdr.de/publications/Publ-26927
Publ.-Id: 26927


Experimental study of accretion processes in X-ray binary stars using an external magnetic field

Kroll, F.; Pelka, A.; Albertazzi, B.; Brack, F.; Brambrink, E.; Cowan, T.; Drake, P.; Falize, E.; Filipov, E.; Kuramitsu, Y.; Kuranz, C.; Lamb, D.; Levesque, J.; Li, C.; Manuel, M.; Michel, T.; Morita, T.; Ozaki, N.; Pikuz, S.; Rigon, G.; Rödel, M.; Sakawa, Y.; Schramm, U.; Shimogawara, H.; van Box Som, L.; Koenig, M.

Here we report on recent results from an experiments carried out at LULI2000 using the nanosecond beam to generate a high-density plasma flow by laser-driven rear-side shock breakout. The sample was positioned inside a pulsed coil generating a magnet field of ~15T in order to study the influence of the magnetic field on the plasma flow. In addition, an obstacle was placed behind the sample to investigate the formation of a return shock. As diagnostics we used laser-driven X-ray point projection radioscopy driven by the pico2000 beam and optical Schlieren Imaging, shadowgraphy, and Streaked Optical Pyrometry from two sides.

Accretion processes are among the most important phenomena in high-energy astrophysics since they are widely believed to provide the power supply in various astrophysical objects and they are the main source of radiation in several binary systems [1]. Understanding the complex physical processes that allow releasing gravitational energy in form of radiation is fundamental to interpret the high-energy astronomical observations [2]. Among the different X-ray binary systems are cataclysmic variable stars, close binary systems containing a white dwarf that accretes matter from a late type Roche-lobe filling secondary star [3]. They provide unique insight on accretion processes in extreme astrophysical regimes since sources of luminosity other than the accretion region itself are relatively weak.

In some cataclysmic variable stars, the magnetic field is strong enough (B>10MG) to prevent the formation of an accretion disk and to channel the accreting plasmas onto the compact object magnetic poles, leading to the formation of an accretion column and impacts the white dwarf atmosphere. By fulfilling similarity properties and scaling laws these processes can be scaled to laboratory length and time scales und thus can be studied using high energy laser-matter interactions. [4] Up to now experiments used a tube in order to collimate the plasma flow generated [5]. This induced spurious effects such as wall shocks and tube explosion that are necessary to avoid. Here we instead applied a pulsed high-field magnetic coil in order to study the coupling of radiative processes in a supersonic plasma flow with magnetic effects. Both the dynamics of high-density and low-density regions of the flow were investigated by utilizing a combination of X-ray radiography and optical Schlieren imaging.

  • Invited lecture (Conferences)
    International Symposium on Topical Problems of Nonlinear Wave Physics (NWP-2017) - LaB Workshop, 22.-28.07.2017, Moscow - St.-Petersburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-26926
Publ.-Id: 26926


Formation of orthorhombic (Zr,Ta)O₂ in thin Zr-Ta-O films

Lehninger, D.; Rafaja, D.; Wünsche, J.; Schneider, F.; von Borany, J.; Heitmann, J.

The formation of orthorhombic (Zr,Ta)O2 was found in annealed thin Zr-Ta-O films with various tantalum concentrations deposited by co-sputtering a ZrO2 target and a mixed ZrO2/Ta2O5 target. In the as-deposited state, all films were amorphous. After annealing, tetragonal (Zr,Ta)O2 for [Ta]/([Ta]+[Zr]) < 0.19 and orthorhombic (Zr,Ta)O2 for [Ta]/([Ta]+[Zr]) > 0.19 were formed. Thin films with excess of tantalum ([Ta]/([Ta]+[Zr])> 0.5) decomposed into two orthorhombic phases upon crystallization: (Zr,Ta)O2 and tantalum-rich (Ta,Zr)2O5. The Rietveld analysis of Xray diffraction patterns revealed that the crystal structure of (Zr,Ta)O2 can be described with the non-centrosymmetric space group Pbc21. The broad range of tantalum concentrations, in which orthorhombic (Zr,Ta)O2 is formed as a single crystalline phase, is promising for the use of this
compound in ferroelectric field effect transistors.

Keywords: Zr-Ta-O thin films; Orthorhombic (Zr; Ta)O2; ferroelectric field effect transistors

  • Open Access Logo Applied Physics Letters 110(2017), 262903
    Online First (2017) DOI: 10.1063/1.4990529

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26925
Publ.-Id: 26925


Evolutionary Algorithm for Automated IBA Spectra Fitting

Heller, R.

In order to extract chemical compositions and layer thicknesses of layered samples from IBA spectra (RBS, ERD, etc.) experimentalists usually have to take the following approach: Simulation of a theoretical spectrum for an initial target configuration and comparison to the measured data followed by the successive adjustment of the target model iteratively until simulation result and experimental spectrum fit together. For multi-layer samples this procedure can get rather time consuming, especially when a series of similar samples with varying layer thickness and/or stoichiometry has to be analyzed.
Although modern IBA spectrum simulation software like SimNRA[1] or WINDF[2] have become quite powerful and handy tools, the analysis of IBA spectra consumes still a significant fraction of an IBA scientist’s working time. SimNRA offers therefore the opportunity to partially fit layer thicknesses and/or elemental ratios for a given layer within a certain region of a spectrum. WINDF goes a step further and has an automated spectrum fitting included which is based on a simulated annealing algorithm. However, it takes the user quite some time to set up the boundary conditions and fit parameters until the actual fit procedure can be initiated. Furthermore, the outcome of the fit procedure in some cases requires multiple re-adjustments of the boundary conditions / fit parameters.
In the present contribution, we present a new approach for automated IBA spectra fitting by implementing an evolutionary algorithm. We will show that this powerful algorithm is very well suited and robust for complete and fast IBA spectrum fitting with minimum input of boundary conditions. Furthermore, the benefits of this algorithm over other ones and the particular differences to simulated annealing are pointed out.
Based on this algorithm a software package has been developed, written in the programming language Java that is platform independent and comprises a clean and easy-to-use graphical user interface. We will introduce this software in a basic overview.

Keywords: IBA Fit routine evolutionary algorithm

  • Poster
    Ion Beam Analysis, 08.-13.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-26924
Publ.-Id: 26924


Preparation of small animal irradiation experiemnts with laser-accelerated protons

Kroll, F.; Beyreuther, E.; Brack, F.-E.; Gaus, L.; Karsch, L.; Kraft, S.; Metzkes, J.; Pawelke, J.; Schlenvoigt, H.-P.; Schürer, M.; Zeil, K.; Schramm, U.

Laser-driven ion acceleration has been considered a potential alternative for conventional accelerators that may provide for a more compact and cost-efficient particle therapy solution in the future. The beam properties of laser-accelerated beams strongly differ from quasi-continuous beams from synchrotrons or cyclotrons. Laser-driven ion bunches are typically picoseconds short, yet carry up to 10^13 particles with a broad energy spectrum and high divergence.

A current driving question is whether the highly intense pulsed ion beams obtain an equivalent biological effectiveness compared to quasi-continuous beams in the case that a living organism is irradiated. Therefore, a controlled small animal irradiation (LN229 glioblastoma cells on nude mouse ear) will be performed at the Dresden laser acceleration source Draco using an intense proton beam.

The talk gives a general overview on laser-acceleration efforts in the context of translational medical research at HZDR and focuses on the experimental preparation and characterization of a proton beamline based on two pulsed high-field (20 T) solenoid magnets. The magnets match the pulsed nature of the particle source and provide for efficient beam capture, transport and field formation. Two challenging experimental tasks will be critically discussed: First, 25 MeV proton beam production at mean dose rates of the order of Gy/min with a high degree of reproducibility. And second, the generation of homogeneous lateral and depth dose distributions by means of the beam transport system.

  • Lecture (Conference)
    BMTMedPhys 2017 - Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland
    DOI: 10.1515/bmt-2017-5044

Permalink: https://www.hzdr.de/publications/Publ-26923
Publ.-Id: 26923


Tunneling Magnetoresistance in MnRuGa based Magnetic Tunnel Junctions

Titova, A.; Fowley, C.; Borisov, K.; Betto, D.; Lau, Y. C.; Thiyagarajah, N.; Atcheson, G.; Coey, M.; Stamenov, P.; Rode, K.; Lindner, J.; Faßbender, J.; Deac, A.

Some intermetallic Heusler compounds display high spin polarization and low magnetic moment. Thin-film samples can possess huge uniaxial anisotropy fields, exceeding tens of teslas. This, combined with their tuneable properties, make these materials very attractive for THz based spin-transfer-torque oscillators. Recently new material from this family was discovered - MnRuGa (MRG) - the first experimentally achieved fully-compensated half-metallic ferrimagnet. Here we show that MRG can be integrated in perpendicular anisotropy magnetic tunnel junctions stacks. Tunneling magnetoresistance (TMR) ratios up to 40% are observed. We also demonstrate that the TMR exists even when the net magnetization of MRG is strictly zero, implying that, at compensation, MRG exhibits a sizable spin polarization. The role of different diffusion barrier layers between MRG and the tunneling barrier as well as annealing temperature was investigated.

This work is supported by the Helmholtz Young Investigator Initiative Grant No. VH-N6-1048.

Keywords: Ferrimagnetism; Half-metals; Magnetic Tunnel Junctions; Heusler Alloy

  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26922
Publ.-Id: 26922


Tunneling magnetoresistance with zero-moment half-metallic Mn2RuXGa

Titova, A.; Fowley, C.; Borisov, K.; Betto, D.; Lau, Y.-C.; Thiyagarajah, N.; Atcheson, G.; Coey, J. M. D.; Stamenov, P. S.; Rode, K.; Lindner, J.; Faßbender, J.; Deac, A. M.

Intermetallic Heusler compounds can possess high spin polarization, low magnetic moment, low Gilbert damping constant α, and huge uniaxial anisotropy fields, of the order of tens of tesla. Such a wide range of properties, most of them tunable, make these materials very attractive for spin-transfer-torque oscillators in the (sub-) THz range. A particularly suitable candidate is the near-cubic Heusler alloy of Mn, Ru, and Ga (MRG) [1]. Here, we show that tunneling magnetoresistance (TMR) of about ten percent can be achieved in MRG-based magnetic tunnel junctions (MTJs), and that the TMR can be improved by integrating different insertion layers acting as diffusion barriers between the half-metallic electrode and the tunnel barrier.

MRG-based stacks were deposited using a “Shamrock” fully automated sputter deposition tool by co-sputtering from a Mn2Ga and a Ru target. Changing the Ru concentration allows tuning the compensation temperature Tcomp between 2 and 450 K. The thin-film stacks were subsequently patterned into 20 × 20 μm2 junctions using standard UV lithography, prior to annealing in temperatures ranging from 250 °C to 350 °C. Selected samples were investigated by transmission electron microscopy (TEM).

The magnetic properties of the MTJs were analyzed by magnetotransport measurements as a function of applied bias voltage at room temperature. We found that 0.6 nm of Al acts as good diffusion barrier in Mn2RuXGa / MgO / CoFeB MTJs. Low-temperature measurements on the same device show TMR in excess of 40% close to zero bias [2]. In addition, we demonstrate non-zero TMR while cooling through the compensation temperature (where the magnetic moment is zero), indicating that magnetotransport in MRG is governed by one Mn sublattice only. This hypothesis is further supported by the fact that samples with Tcomp above room temperature exhibit inverted TMR as compared to samples that compensated below. The precise value of Tcomp is the result of a delicate balance between the moments carried by Mn ions on the 4c and 4a sites. Upon thermal annealing, this balance is slightly shifted due to partial annihilation of Mn anti-sites, and Tcomp may pass from above room temperature to below, giving rise to an inverted TMR response. The next step is to fabricate sub-µm devices based on MRG for detecting spin-transfer induced dynamics, which should occur at frequencies of several hundred GHz, given the ultra-high anisotropy of these.

This work is supported by the Helmholtz Young Investigator Initiative Grant No. VH-N6-1048.

Keywords: Ferrimagnetism; Half-metals; Magnetic Tunnel Junctions; Heusler Alloy

  • Lecture (Conference)
    Moscow International Symposium on Magnetism, 01.-05.07.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-26921
Publ.-Id: 26921


Computer simulation of the ternary problem – technical aspects and possibilities

Zedek, L.; Lippold, H.; Sembera, J.

Interaction between groundwater contaminants (e.g. radioactive elements), soil and humic matter plays a crucial role in transport prognoses. This type of interaction, denoted as the ternary problem, may speed up propagation of a contaminant in comparison with the case in the absence of humic compounds. It is very difficult (almost impossible) to find a simple description of the ternary problem in the form of chemical equations. This difficulty is caused by the complex nature of humic substances. Rather than with particular chemical equations, the ternary problem is commonly described by schematic expressions which consider groups of species. The usual approach for the problem formulation is grouping of species resulting in a system of differential and algebraic equations (DAE). This article introduces a different approach allowing a semi-automatic formulation of a system of ordinary differential equations (ODE) for the same problem. The proposed method enables to avoid an operator-splitting already during the model formulation process. The approach for the model formulation and its solution has been implemented using two different open-source software packages. The results have been compared with reference results of a traditional solution approach using DAE systems. The implementation in Python verified the possibility of automation of the formulation and solution. A sensitivity analysis has been performed to evaluate the behaviour of the system with respect to parameter variation.

Keywords: Chemical reaction simulation; Semi-analytical model; Semi-automatic formulation

Permalink: https://www.hzdr.de/publications/Publ-26920
Publ.-Id: 26920


Tunneling magnetoresistance in MnRuGa based Magnetic Tunnel Junctions

Titova, A.; Fowley, C.; Borisov, K.; Betto, D.; Lau, Y. C.; Thiyagarajah, N.; Atcheson, G.; Coey, M.; Stamenov, P.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A. M.

Nowadays great attention has been paid to the research of intermetallic Heusler compounds. These materials have widely tunable properties. They display high spin polarisation [1], low magnetic moment [2] and low Gilbert damping α [3]. Furthermore, these thin-film samples can possess huge uniaxial anisotropy fields, exceeding tens of Teslas [4]. Such a wide range of almost completely tunable properties make these materials very attractive for THz based spin-transfer-torque oscillators [6]. Here we have successfully integrated a compensated half-metallic ferrimagnet as a fixed layer in magnetic tunnel junctions (MTJ). Theoretically, this class of materials was predicted in 1995 by van Leuken and de Groot [7], but experimentally the zero-moment half-metal was realized only in 2014 [8] for a near-cubic Heusler alloy of Mn, Ru, and Ga (MRG). We showed that Tunneling Magnetoresistance (TMR) ratio reaches 40% in our stacks. We also demonstrate that the TMR exists even when the net magnetization of MRG is strictly zero, implying that, at compensation, MRG exhibits a sizable spin polarization [9]. We investigated the role of different diffusion barrier layers between MRG and the tunneling barrier as well as annealing temperature.

Keywords: Ferrimagnetism; Half-metals; Magnetic Tunnel Junctions; Heusler Alloy

  • Poster
    IEEE Magnetics Society Summer School, 18.-23.06.2017, Santander, Spain

Permalink: https://www.hzdr.de/publications/Publ-26919
Publ.-Id: 26919


Structural disorder induced magnetization in FeAl and FeRh: The perspectives for laterally patterned magnetic metamaterials

Semisalova, A. S.; Bali, R.; Wintz, S.; Barton, C.; Thomson, T.; Hlawacek, G.; Fowley, C.; Ehrler, J.; Bottger, R.; Potzger, K.; Lindner, J.; Fassbender, J.

The possibilities of fabrication of magnetic nanostructures using ion irradiation will be exampled with the recent achievements in FeAl and FeRh. Magnetization of both alloys at room temperature is highly sensitive to the structural state (ordered or disordered). This opens a way for lateral patterning of nanoscale ferromagnets embedded in paramagnetic (FeAl) or antiferromagnetic (FeRh) ordered matrix and studying the effect of planar geometry of magnetic interfaces.

  • Invited lecture (Conferences)
    META'17, The 8th International Conference on Metamaterials, Photonic Crystals and Plasmonics, 25.-28.07.2017, Incheon - Seoul, Korea

Permalink: https://www.hzdr.de/publications/Publ-26918
Publ.-Id: 26918


Multifrequency ferromagnetic resonance study of the antiferromagnetic-ferromagnetic phase transition in FeRh

Semisalova, A.; Ehrler, J.; Barton, C.; Thomson, T.; Lenz, K.; Fassbender, J.; Potzger, K.; Lindner, J.

The first order phase transition of an equiatomic FeRh thin film from the antiferromagnetic (AFM) to the ferromagnetic (FM) state was studied using broadband ferromagnetic resonance (FMR). The films were deposited on MgO(001) substrates by means of magnetron sputtering of an alloy target. The position and linewidth of the FMR signal have been investigated in the frequency range up to 50 GHz. Conclusions on the temperature dependence of the magnetic damping are presented. The linewidth was found to be strongly affected by the exchange coupling due to reversible nucleation of AFM and FM domains in FeRh within the temperature range of the phase transformation.

  • Poster
    DPG Spring Meeting 2017, 19.-25.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26917
Publ.-Id: 26917


Vortex dynamics in disks with tailored magnetisations

Ramasubramanian, L.; Fowley, C.; Kákay, A.; Yildirim, O.; Matthes, P.; Böttger, R.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S. E.; Deac, A. M.

The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been proposed for designing spin-torque-driven nano-oscillators [1]. Commercial applications require tuning of the output frequency by external parameters, such as applied fields or spin-polarized currents. However, the tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design [2, 3].

Using micromagnetic simulations, [4] we show that if regions with different saturation magnetisation can be induced in a magnetic disk, multiple precession frequencies can be generated. Experimentally we employ ion implantation as a promising method to fabricate such devices [5].

Disks with different radii- 0.5 µm to 4 µm, thicknesses- 25 nm and 30 nm and lateral electrical contacts were prepared using electron beam lithography followed by electron beam evaporation to study the formation of magnetic vortices with respect to size and thickness.

Magnetotransport measurements (Fig. 1(a)) show the presence of anisotropic magnetoresistance (AMR. The resonance frequencies measured using a lock-in technique on 25 nm thick permalloy disks are shown in Fig. 1(b). The disks were subsequently subjected to partial ion irradiation and the induced modification of the resonance frequency will be presented.

The Nanofabrication Facilities Rossendorf at the IBC is gratefully acknowledged.
Funding : Helmholtz Young Investigator Initiative Grant No. VH-N6-1048.

Keywords: frequency tunability; chromium implantation in permalloy; electrically detected dynamics

  • Poster
    MMM 2017 - 62nd Annual Conference on Magnetism and Magnetic Materials, 06.-10.11.2017, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-26916
Publ.-Id: 26916


Vortex dynamics in disks with tailored magnetisations

Ramasubramanian, L.; Fowley, C.; Kákay, A.; Yildirim, O.; Matthes, P.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S. E.; Deac, A. M.

The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been proposed for designing spin-torque-driven nano-oscillators [1]. Commercial applications require tuning of the output frequency by external parameters, such as applied fields or spin-polarized currents. However, the tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design [2, 3]. Micromagnetic simulations [4] have shown that if regions with different saturation magnetisation can be induced in a magnetic disk, multiple precession frequencies can be generated. Ion implantation is a promising method to fabricate such devices [5].

Disks with different radii- 0.5 µm to 4 µm and thicknesses- 25 nm and 30 nm were prepared using electron beam lithography followed by electron beam evaporation to study the formation of magnetic vortices with respect to size and thickness. The single disks were contacted by gold leads to study the interaction of spin polarized current on the magnetic vortex. The presence of vortex is verified by magneto optic Kerr effect (MOKE) and X-ray magnetic circular dichroism (XMCD).

Magnetotransport measurements on electrically contacted disks (Figure 1 (a)) show the presence of anisotropic magnetoresistance (AMR) in different disks with varying thickness (Figure 1 (b)). The resonance frequencies measured using a lock-in technique on 3 µm and 4 µm radii disks with 25 nm permalloy are 40.9 MHz and 29.5 MHz respectively. Modification of the resonance frequency by ion irradiation will be presented.

Keywords: frequency tunability; magnetic vortex

  • Poster
    The Moscow International Symposium on Magnetism (MISM), 01.-05.07.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-26915
Publ.-Id: 26915


Application of an immersed boundary method with analytical interface approximation to a bubble chain in liquid metal

Krull, B.; Schwarz, S.; Fröhlich, J.; Strumpf, E.; Shevchenko, N.; Roshchupkina, O.; Eckert, S.

Bubble-laden liquid metal flows are an important topic in metallurgy, where bubbles are used for stirring, to remove inclusions, to control chemical reactions, etc. The bubbles encountered in this flows are generally too large to remain spherical, but deform. Deformation can enhance separation of the wake behind the bubble noticeably increasing drag [1]. Furthermore, deformable bubbles lead to an increase of turbulent kinetic energy while having almost no impact on the mean flow, which is a significant difference to flows with spherical bubbles. Furthermore, the near-wall behavior of spherical and non-spherical bubbles differs [2,3]. The deformation of a stationary rising single bubble is well-understood [4]. However, for unsteady flows containing larger numbers of interacting bubbles the deformation and its impact on the flow is not known and therefore investigated in this work.

Keywords: bubbly flow; immersed boundary method; bubble deformation; bubble chain; liquid metal

  • Lecture (Conference)
    The 3rd International Conference on Numerical Methods in Multiphase Flows ICNMMF-III, 26.-29.06.2017, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-26914
Publ.-Id: 26914


Investigations of fluid flow effects on dendritic solidification: Consequences on fragmentation, macrosegregation and the influence of electromagnetic stirring

Shevchenko, N.; Neumann-Heyme, H.; Pickmann, C.; Schaberger-Zimmermann, E.; Zimmermann, G.; Eckert, K.; Eckert, S.

Solidification experiments and numerical simulations have been performed to improve the understanding of the complex interrelation between melt flow and the formation of dendritic structures during solidification of Al-Cu and Ga-In alloys. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Within this project special interest was focused on fragmentation and segregation phenomena. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. X-ray radioscopy was applied as a powerful tool for the visualization of dendritic growth and coarsening.

Keywords: Fluid flow; dendritic solidification; fragmentation; macrosegregation; electromagnetic stirring

Permalink: https://www.hzdr.de/publications/Publ-26913
Publ.-Id: 26913


Practice patterns of image guided particle therapy in Europe: a 2016 survey of the European Particle Therapy Network (EPTN)

Bolsi, A.; Peroni, M.; Amelio, D.; Dasu, A.; Stock, M.; Toma-Dasu, I.; Witt Nyström, P.; Hoffmann, A. L.

Background and Purpose: Image guidance is critical in achieving accurate and precise radiation delivery in particle therapy, even more than in photon therapy. However, equipment, quality assurance procedures and clinical workflows for image-guided particle therapy (IGPT) may vary substantially between centres due to a lack of standardization. A survey was conducted to evaluate the current practice of IGPT in European particle therapy centres.

Material and Methods: In 2016, a questionnaire was distributed among 19 particle therapy centres in 12 European countries. The questionnaire consisted of 30 open and 37 closed questions related to image guidance in the general clinical workflow, for moving targets, current research activities and future perspectives of IGPT.

Results: All centres completed the questionnaire. The IGPT methods used by the 10 treating centres varied substantially. The 9 non-treating centres were in the process to introduce IGPT. Most centres have developed their own IGPT strategies, being tightly connected to their specific technical implementation and dose delivery methods.

Conclusions: Insight into the current clinical practice of IGPT in European particle therapy centres was obtained. A variety in IGPT practices and procedures was confirmed, which underlines the need for harmonisation of practice parameters and consensus guidelines.

Keywords: Particle therapy; image guidance; survey

Permalink: https://www.hzdr.de/publications/Publ-26912
Publ.-Id: 26912


Realizing the insulator-to-metal transition in Se-hyperdoped Si via non-equilibrium material processing

Liu, F.; Prucnal, S.; Berencén, Y.; Zhang, Z.; Yuan, Y.; Liu, Y.; Heller, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

We report on the insulator-to-metal transition in Se-hyperdoped Si layers driven by manipulating the Se concentration via non-equilibrium material processing, i.e. ion implantation followed by millisecond-flash lamp annealing. Electrical transport measurements reveal an increase of the carrier concentration and conductivity with the increasing Se concentration. For the semi-insulating sample with Se concentrations below the Mott limit, quantitative analysis of the temperature dependence of the conductivity indicates a variable-range hopping mechanism with an exponent of s  =  1/2 rather than 1/4, which implies a Coulomb gap at the Fermi level. The observed insulator-to-metal transition is attributed to the formation of an intermediate band in the Se-hyperdoped Si layers.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26911
Publ.-Id: 26911


PT-symmetry and related geometrical structures

Günther, U.

In non-relativistic quantum mechanics, the dynamics of closed quantum systems is described by Hamiltonians which are self-adjoint in appropriately chosen Hilbert spaces. For PT-symmetric quantum systems, the Hamiltonians are in general no longer self-adjoint in standard Hilbert spaces, but rather they are self-adjoint in Krein spaces, Hilbert spaces endowed with indefinite metric structures. Moreover, the spectra of PT-symmetric Hamiltonians are symmetric with regard to the real axis in the spectral plane. Apart from Hamiltonians with purely real spectra this includes also Hamiltonians whose spectra may contain sectors of pairwise complex-conjugate eigenvalues. Considering families of parameter-dependent Hamiltonians one can arrange for parameter-induced passages from sectors of purely real spectra to sectors of complex-conjugate spectral branches. Corresponding passages can be regarded as PT-phase transitions from sectors of exact PT-symmetry to sectors of spontaneously broken PT-symmetry. Approaching a PT-phase transition point, the eigenvectors of the Hamiltonian tend toward their isotropic limit --- an, in general, infinite-dimensional (Krein-space) generalization of the light-cone limit in Minkowski space. At a phase transition, the Hamiltonian is no longer diagonalizable, but similar to an arrangement of nontrivial Jordan-blocks. The interplay of these structures is briefly reviewed with special emphasis on the related Lie-algebraic and Lie-group aspects. With the help of Cartan-decompositions associated hyperbolic structures and Lie-triple-systems are discussed for finite-dimensional setups as well as for their infinite-dimensional generalizations (Hilbert-Schmidt (HS) Lie groups, HS Lie algebras, HS Grassmannians). The interconnection of Krein-space structures and PT-phase transitions is demonstrated on two exactly solvable models: PT-symmetric Bose-Hubbard models and PT-symmetric plaquette arrangements.

Keywords: PT symmetry; PT phase transitions; Krein spaces; Jordan blocks; Lie algebras; Lie triple systems; Hilbert-Schmidt Lie groups; HS Lie algebras; HS Grassmannians; PT-symmetric Bose-Hubbard models; plaquette arrangements

  • Invited lecture (Conferences)
    Symmetry 2017 - The First International Conference on Symmetry, 16.-18.10.2017, Barcelona, Spain
  • Open Access Logo Abstract in refereed journal
    Proceedings / MDPI AG 2(2018), 25
    DOI: 10.3390/proceedings2010025

Permalink: https://www.hzdr.de/publications/Publ-26910
Publ.-Id: 26910


PT quantum mechanics: finite-dimensional and infinite-dimensional matrix models and their Lie group structures

Günther, U.

Structural features of PT-symmetric quantum mechanical matrix models are discussed: hidden group theoretical aspects, Lie triple systems following from Cartan decompositions of the corresponding Lie algebras, projectivization embeddings to resolve singularities at PT phase transitions. Starting from these structural findings for finite-dimensional PT-symmetric matrix setups, possible technically feasible extensions toward infinite-dimensional Hilbert-Schmidt Lie groups, Fredholm groups and PT-symmetry related Hilbert-Schmidt Grassmannians are sketched. Concrete physical setups where these features show up are briefly discussed.

Keywords: PT symmetry; phase transitions; Lie algebras; Lie triple systems; PT phase transitions; Hilbert-Schmidt Lie groups; Fredholm groups; Hilbert-Schmidt Grassmannians

  • Invited lecture (Conferences)
    15th Conference “Mathematics in Technical and Natural Sciences”, 17.-22.09.2017, Zakopane, Poland

Permalink: https://www.hzdr.de/publications/Publ-26909
Publ.-Id: 26909


ESUO activities: an update

Froideval, A.

The European Synchrotron and free-electron laser (FEL) User Organisation (ESUO) established in 2010, is now representing about 30.000 users of the European synchrotron and FEL radiation facilities. This user community is distributed over 30 European countries and is represented within the ESUO board by 1 up to 4 national delegate(s) per country, depending on the size of the user community in that country. In the present talk, the past, recent and future ESUO activities are presented.

Keywords: European synchrotron and FEL user organisation (ESUO); European projects; scientific collaborations; European synchrotron and FEL radiation facilities

  • Lecture (others)
    3rd Meeting of the European User Offices, 23.-24.10.2017, Lund, Sweden

Permalink: https://www.hzdr.de/publications/Publ-26908
Publ.-Id: 26908


Unusual Coulomb effects in graphene

Winnerl, S.

In many semiconductors Coulomb scattering plays an essential role in the thermalization process of a non-equilibrium carrier distribution. Here we discuss three surprising and fascinating manifestations of Coulomb scattering in graphene.
The first observation concerns a double-bended saturation behavior of bleaching induced by near-infrared radiation. The complete bleaching at high fluences is related to Pauli blocking. At much lower fluences, however, the balance between scattering into or out of the optically probed regions in k-space via Coulomb interaction results in a qualitatively similar behavior [1].
The second phenomenon is the optically induced anisotropy in k-space for excitation with linearly polarized radiation and its relaxation to a Fermi-Dirac distribution. Polarization resolved pump-probe experiments at different photon energies provide strikingly direct insights into role of individual processes: Carrier-phonon scattering rapidly transforms the initial anisotropic non-equilibrium distribution into an isotropic one [2]. When carrier-phonon scattering is quenched by applying photon energies below the optical phonon energy, however, Coulomb interaction is the only strong source of scattering [3]. As Coulomb scattering in graphene is predominantly collinear, the anisotropy persists for fairly long times (a few ps).
The third set of experiments tackles the dynamics of graphene in a magnetic field perpendicular to the graphene layer. In this case, the band structure beaks up into a series of non-equidistant Landau levels (LLs). We study in detail the population and polarization dynamics of the levels with index -1, 0 and 1. Applying circularly polarized radiation allows one to selectively excite the energetically degenerate transitions LL-1  LL0 and LL0  LL1, respectively. Applying all four combinations of pumping and probing with left and right circularly polarized radiation reveals a surprising behavior: The possibility to deplete the zeroth Landau level while it is optically pumped at the same time [4]. This is caused by strong Auger scattering, the Coulomb process that thermalizes the carrier distribution in Landau quantized graphene. It also causes a fast dephasing of the microscopic polarization, as evidenced in four-wave-mixing experiments [5]. We discuss the possibility to apply Landau quantized graphene as a gain medium in a tunable laser and as a tunable nonlinear optical material.
We are grateful to a number of people, most importantly, from the experimental side, to M. Mittendorff, J. C. König-Otto, H. Schneider and M. Helm. Furthermore to E. Malic, A. Knorr and A. Belyanin for microscopic theory, and to C. Berger and W. A. de Heer for sample growth.
[1] T. Winzer, M. Mittendorff, S. Winnerl, H. Mittenzwey, R. Jago, M. Helm, E. Malic, and A. Knorr, Nature Commun. 8, 15042 (2017).
[2] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, Manfred Helm, and S. Winnerl, Nano Lett. 14, 1504 (2014).
[3] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).
[4] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Physics 11, 75 (2015).
[5] J. C. König-Otto, Yongrui Wang, Alexey Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H. Schneider, M. Helm, S. Winnerl, Nano Lett. 17, 2184 (2017).

Keywords: graphene; ultrafast dynamics; Coulomb scattering

  • Invited lecture (Conferences)
    Finite Systems in Nonequilibrium: From Quantum Quench to the Formation of Strong Correlations, 10.-30.09.2017, Natal, Brasil

Permalink: https://www.hzdr.de/publications/Publ-26907
Publ.-Id: 26907


Landau-quantized graphene as a nonlinear THz material

König-Otto, J. C.; Wang, Y.; Belyanin, A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.

Graphene, a gapless two-dimensional semiconductor, features constant optical absorption in a wide spectral range. In presence of a magnetic field, the linear band structure of graphene at low energies splits up into a series of non-equidistant Landau levels (LLs). Consequently, the optical absorption is redistributed into Landau-level resonances. Population inversion [1, 2] and strong optical nonlinearities [3] have been predicted for Landau-quantized graphene. Experimentally the population dynamics has been studied and direct evidence for strong Auger scattering in the time domain has been found [4]. In this presentation we show first experiments on the polarization dynamics and the scaling behavior of the four-wave mixing (FWM) signal.
The experiments were performed on almost intrinsic layers of epitaxial multilayer graphene grown on the C-terminated side of SiC. The sample was kept at 10 K in a split coil magnet with optical access. Using linearly polarized radiation at a frequency of 19 THz we investigated the LL-1 → LL0 and LL0 → LL1 transition, which were tuned into resonance by a magnetic field of 4.5 T. Employing radiation pulses with a duration of 4 ps from the free-electron laser FELBE, the degenerate FWM signals were recorded and compared to pump-probe signals. The FWM signal is essentially symmetric and reflects the pulse duration of radiation pulses. This indicates that the dephasing time of the microscopic polarization is faster than the pulse duration. The excited population, on the other hand, is present on much longer timescales. At low intensities, the FWM scales quadratically with the power of the incident beam, that delivers two photons for the FWM process. At incident fields above ~10 kV/cm saturation is observed. Furthermore, the magnetic field was tuned while keeping the photon energy fixed. This reveals a considerably smaller linewidth of the third-order susceptibility resonance as compared to the linewidth of the linear absorption measured by Fourier transform spectroscopy. This is consistent with the nonlinear scaling of the FWM signal. Our experimental results, in particular also the deduced value for the surface susceptibility of the order of 10-19 m3/V2, are in accord with theoretical predictions based on the density matrix formalism.
In summary, Landau-quantized graphene represents a strong nonlinear medium with a resonance tunable by the magnetic field. This may be interesting for nonlinear THz applications, such as frequency mixing and parametric generation.
We are grateful to C. Berger and W. A. de Heer from Georgia Tech and M. Orlita from LNCMI-CNRS in Grenoble for sample growth and linear magneto-spectroscopy measurements, respectively.

References
[1] F. Wendler and E. Malic, Sci. Rep. 5, 12646, 2015.
[2] Y. Wang, M. Tokman, and A. Belyanin Phys. Rev. Lett. 91, 033821 (2015).
[3] X. Yao and A. Belyanin, Phys. Rev. Lett. 108, 255503 (2012).
[4] M. Mittendorff, F. Wendler, E. Malic, E. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Phys. 11, 75 (2015).

Keywords: graphene; nonlinear optics; Landau quantization

  • Lecture (Conference)
    Optical Terahertz Science and Technology, 02.-07.04.2017, London, UK

Permalink: https://www.hzdr.de/publications/Publ-26906
Publ.-Id: 26906


Teilchenphysik in Bleistiftstaub: das Wundermaterial Graphen

Winnerl, S.

Kohlenstoff ist in Form von Graphit und Diamant den Menschen seit Jahrtausenden bekannt. Die erste Kohlenstoff Nanostruktur wurde in Form von Fullerenen („Fußballmoleküle“) in den 1980er Jahren entdeckt, es folgten Kohlenstoff-Nanoröhren in den 1990er Jahren. Im Jahr 2004 wurde schließlich Graphen, eine einzelne Schicht aus bienenwabenförmig angeordneten Kohlenstoffatomen, von Geim und Novoselov entdeckt und untersucht. Für diese Forschung wurden die beiden im Jahr 2010 mit dem Physik-Nobelpreis ausgezeichnet.
Graphen besitzt faszinierende grundlegende physikalische Eigenschaften. Insbesondere weisen Elektronen in Graphen eine Energie-Impuls Beziehung auf, wie man sie von Teilchen aus der Hochenergiephysik kennt. Wir werden diskutieren, wie sich dies auf weitere physikalische Eigenschaften auswirkt und einen kurzen Überblick geben, wie sich die mechanischen, optischen und elektrischen Eigenschaften von Graphen von anderen Materialien unterscheiden. Daraus lassen sich Schlüsse ziehen, für welche Anwendungen Graphen interessant ist.
Schließlich geben wir einen kurzen Einblick in unsere eigene Forschung an Graphen, die sich besonders mit der Dynamik von Graphen-Elektronen auf ultrakurzen Zeitskalen beschäftigt und dafür das Großgerät FELBE (Freie-Elektronen Laser am HZDR) verwendet.

  • Lecture (others)
    Seniorenakademie Dresden, 26.11.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26905
Publ.-Id: 26905


Magneto-structural correlations in Fe60Al40 thin films

Ehrler, J.; Potzger, K.; Grenzer, J.; Zhou, S.; Böttger, R.; Bali, R.

Magnetic materials become more significant for future data storage devices and spintronic applications. In certain alloy thin films like Fe60Al40, nano-sized ferromagnetic structures can be created by means of focused ion irradiation.[1,2,3] Fe60Al40 shows a disorder induced phase transition from the thermodynamically stable, chemically ordered B2 to the metastable A2 phase going along with an evolution of ferromagnetism and an increase of the lattice parameter (Figure 1). This can be explained with the higher local number of Fe-Fe nearest neighbors in the disordered state. The correlation between structural and magnetic properties in the phase transition regime, consisting of A2 and B2 phases, is uncertain as well as the influence of the ion type or the temperature treatment.
The effects of ion implantation on the structural and magnetic properties of 250 nm thick Fe60Al40 films, possessing A2 and B2 structure respectively, have been investigated by means of X-ray diffraction (XRD) and Vibrating sample magnetometry. From XRD measurements, the order parameter S and the peak shift due to the change of the lattice parameter have been derived and correlated with the magnetization. The irradiation of paramagnetic B2 Fe60Al40 with H+, He+ or Ne+ ions with different fluences at low temperatures led to an increase of the saturation magnetization (MS) which was expected to be directly related to the number of displacements per atom (dpa) by using the simulation program TRIM [4], independent on the ion species. However, unlike than expected, the induced magnetization differed but correlated directly with the measured lattice parameter. A significant change of lattice parameter and MS did not appear for proton irradiation at elevated temperatures (250 °C) where the ordered B2 phase was retained. Upon low temperature (LN2) hydrogen implantation of disordered A2 Fe60Al40 films, on the other hand, unlike for helium or neon irradiation, the lattice parameter and the saturation magnetization decreased indicating a little ordering. This might offer the possibility of H+ irradiation induced ordering of chemically disordered alloy thin films well below the ordering temperature.
Furthermore, the studies show that the structural and magnetic properties of 250 nm thick Fe60Al40 films are directly linked with each other (Figure 2) and do not depend on the type of treatment. The chemical disorder induced evolution of ferromagnetism comes along with an abrupt disappearance of the (100)-superlattice peak represented by the order parameter dropping to 0. Nevertheless, the role of defects remains uncertain since ion irradiation leads besides the structural disordering also to an increase of the defect concentration and a temperature treatment to structural ordering and an annealing of defects. However, as described beforehand, H+ implantation causes little ordering but also an increase of the open volume defect concentration, which was characterized by means of Positron annihilation spectroscopy. This offers the opportunity to differentiate between structural disorder and defect concentration.
Given the fact that the proton implanted films follow the shown general behavior a dependence on the structural order only can be assumed.

  • Lecture (Conference)
    Seminar der Professur Werkstofftechnik, 12.-13.01.2018, Meißen, Germany

Permalink: https://www.hzdr.de/publications/Publ-26904
Publ.-Id: 26904


Tuning the magnetic and structural properties of Fe60Al40 thin films by ion irradiation

Ehrler, J.; Bali, R.; Böttger, R.; Zhou, S.; Grenzer, J.; Potzger, K.

Magnetic materials become more significant for future data storage devices and spintronic applications. In certain alloy thin films like Fe60Al40, nano-sized ferromagnetic structures can be created by means of focused ion irradiation.[1,2,3] Fe60Al40 shows a disorder induced phase transition from the thermodynamically stable, chemically ordered B2 to the metastable A2 phase going along with an evolution of ferromagnetism and an increase of the lattice parameter (Figure 1). This can be explained with the higher local number of Fe-Fe nearest neighbors in the disordered state. The correlation between structural and magnetic properties in the phase transition regime, consisting of A2 and B2 phases, is uncertain as well as the influence of the ion type or the temperature treatment.
The effects of ion implantation on the structural and magnetic properties of 250 nm thick Fe60Al40 films, possessing A2 and B2 structure respectively, have been investigated by means of X-ray diffraction (XRD) and Vibrating sample magnetometry. From XRD measurements, the order parameter S and the peak shift due to the change of the lattice parameter have been derived and correlated with the magnetization. The irradiation of paramagnetic B2 Fe60Al40 with H+, He+ or Ne+ ions with different fluences at low temperatures led to an increase of the saturation magnetization (MS) which was expected to be directly related to the number of displacements per atom (dpa) by using the simulation program TRIM [4], independent on the ion species. However, unlike than expected, the induced magnetization differed but correlated directly with the measured lattice parameter. A significant change of lattice parameter and MS did not appear for proton irradiation at elevated temperatures (250 °C) where the ordered B2 phase was retained. Upon low temperature (LN2) hydrogen implantation of disordered A2 Fe60Al40 films, on the other hand, unlike for helium or neon irradiation, the lattice parameter and the saturation magnetization decreased indicating a little ordering. This might offer the possibility of H+ irradiation induced ordering of chemically disordered alloy thin films well below the ordering temperature.
Furthermore, the studies show that the structural and magnetic properties of 250 nm thick Fe60Al40 films are directly linked with each other (Figure 2) and do not depend on the type of treatment. The chemical disorder induced evolution of ferromagnetism comes along with an abrupt disappearance of the (100)-superlattice peak represented by the order parameter dropping to 0. Nevertheless, the role of defects remains uncertain since ion irradiation leads besides the structural disordering also to an increase of the defect concentration and a temperature treatment to structural ordering and an annealing of defects. However, as described beforehand, H+ implantation causes little ordering but also an increase of the open volume defect concentration, which was characterized by means of Positron annihilation spectroscopy. This offers the opportunity to differentiate between structural disorder and defect concentration.
Given the fact that the proton implanted films follow the shown general behavior a dependence on the structural order only can be assumed.

  • Poster
    HZDR PhD Seminar, 16.-18.10.2017, Seiffen, Germany

Permalink: https://www.hzdr.de/publications/Publ-26903
Publ.-Id: 26903


Tuning the magnetic and structural properties of Fe60Al40 thin films by ion irradiation

Ehrler, J.; Bali, R.; Böttger, R.; Zhou, S.; Grenzer, J.; Potzger, K.

Magnetic materials are significant for future data storage device and spintronic applications.
Recently it has been shown that nano-sized ferromagnetic structures can be generated within non-ferromagnetic B2-Fe60Al40 thin films via local ion-irradiation. Ion-irradiation leads to disordering, forming the ferromagnetic A2 phase. The mechanism of this disorder induced effect has been variously attributed to the increase in the number of Fe-Fe nearest neighbors due to disorder and the corresponding increase of the lattice parameter (a0) [1,2,3]. Considering a0 as an indicator for the disorder as the driving parameter for the ferromagnetic order, 250 nm thick B2-Fe60Al40 films irradiated with various ion species, i.e. H+, He+ and Ne+, have been investigated with respect to the correspondence between a0 and the saturation magnetization (MS).
The films have been prepared by magnetron sputtering and irradiated at the Ion Beam Center at the Helmholtz-Zentrum Dresden - Rossendorf. The irradiation-induced displacements per atom (dpa) were calculated with the help of the program TRIM [4]. The films have been irradiated at low
temperature (LN2) with an energy of 17 keV and a fluence of 4E17 ions/cm² for H+ ions and with 3.52E16 ions/cm² at 27 keV for He+. According to
TRIM, these implantation parameters induce the same dpa for the H+ and He+ irradiations. MS was measured by Vibrating sample magnetometry and the order parameter (S) as well as a0 were derived from X-ray diffraction.
The non-irradiated B2-ordered Fe60Al40 films (S=1) possess an MS of 5 kA/m and a0 of 2.89 Å. Despite similar ion-induced disorder, films irradiated with H+ and He+ showed an increased MS of 314 kA/m and 551 kA/m respectively. This suggests deviations from the TRIM calculations, in particular for the lighter H+ ion. Nevertheless, study of a vast number of films irradiated with H+, He+ as well as Ne+ at low and room temperature respectively shows a fundamental correlation between structural and magnetic properties of the Fe60Al40 films, independent of the implanted ion species or temperature treatment (see Figure 1).
The films exhibit a sharp transition at a0=2.91 Å, where MS rapidly increases, tracked exactly by a decrease of S, suggesting that MS depends on the increase of the Fe-Fe nearest neighbor interactions (as indicated by decreasing S) only being independent on a0. DFT calculations will help further understanding of this correlation.

  • Lecture (Conference)
    Moscow International Symposium on Magnetism 2017, 01.-06.07.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-26902
Publ.-Id: 26902


Tuning the magnetic and structural properties of Fe60Al40 thin films by ion irradiation

Ehrler, J.; Bali, R.; Böttger, R.; Zhou, S.; Grenzer, J.; Potzger, K.

Magnetic materials become more significant for future data storage devices and spintronic applications. In certain alloy thin films like Fe60Al40, nano-sized ferromagnetic structures can be created by means of focused ion irradiation.[1,2,3] Fe60Al40 shows a disorder induced phase transition from the thermodynamically stable, chemically ordered B2 to the metastable A2 phase going along with an evolution of ferromagnetism and an increase of the lattice parameter (Figure 1). This can be explained with the higher local number of Fe-Fe nearest neighbors in the disordered state. The correlation between structural and magnetic properties in the phase transition regime, consisting of A2 and B2 phases, is uncertain as well as the influence of the ion type or the temperature treatment.
The effects of ion implantation on the structural and magnetic properties of 250 nm thick Fe60Al40 films, possessing A2 and B2 structure respectively, have been investigated by means of X-ray diffraction (XRD) and Vibrating sample magnetometry. From XRD measurements, the order parameter S and the peak shift due to the change of the lattice parameter have been derived and correlated with the magnetization. The irradiation of paramagnetic B2 Fe60Al40 with H+, He+ or Ne+ ions with different fluences at low temperatures led to an increase of the saturation magnetization (MS) which was expected to be directly related to the number of displacements per atom (dpa) by using the simulation program TRIM [4], independent on the ion species. However, unlike than expected, the induced magnetization differed but correlated directly with the measured lattice parameter. A significant change of lattice parameter and MS did not appear for proton irradiation at elevated temperatures (250 °C) where the ordered B2 phase was retained. Upon low temperature (LN2) hydrogen implantation of disordered A2 Fe60Al40 films, on the other hand, unlike for helium or neon irradiation, the lattice parameter and the saturation magnetization decreased indicating a little ordering. This might offer the possibility of H+ irradiation induced ordering of chemically disordered alloy thin films well below the ordering temperature.
Furthermore, the studies show that the structural and magnetic properties of 250 nm thick Fe60Al40 films are directly linked with each other (Figure 2) and do not depend on the type of treatment. The chemical disorder induced evolution of ferromagnetism comes along with an abrupt disappearance of the (100)-superlattice peak represented by the order parameter dropping to 0. Nevertheless, the role of defects remains uncertain since ion irradiation leads besides the structural disordering also to an increase of the defect concentration and a temperature treatment to structural ordering and an annealing of defects. However, as described beforehand, H+ implantation causes little ordering but also an increase of the open volume defect concentration, which was characterized by means of Positron annihilation spectroscopy. This offers the opportunity to differentiate between structural disorder and defect concentration.
Given the fact that the proton implanted films follow the shown general behavior a dependence on the structural order only can be assumed.

  • Poster
    IEEE International Magnetics Conference 2017, 24.-28.04.2017, Dublin, Ireland

Permalink: https://www.hzdr.de/publications/Publ-26901
Publ.-Id: 26901


Tuning of magnetic and structural properties of Fe60Al40 thin films by ion irradiation

Ehrler, J.; Bali, R.; Böttger, R.; Grenzer, J.; Potzger, K.

The effects of ion implantation on the structural and magnetic properties of Fe60Al40 films, possessing A2 and B2 structure respectively, have been investigated by means of X-ray diffraction and Vibrating sample magnetometry. The studies show that the magnetic properties of the 250 nm thick Fe60Al40 films, showing a phase transition from para- to ferromagnetic state, depend on the structural order only. The evolution of ferromagnetism comes along with an abrupt disappearance of the (100)-superlattice peak.
The irradiation of superparamagnetic B2 Fe60Al40 with H+, He+ or Ne+ ions with different fluences at low temperatures led to an increase of saturation magnetization (MS) going along with a lattice expansion induced by structural disorder. This effect didn’t appear for proton irradiation at elevated temperatures (250 ∘C) where the ordered B2 was retained. The low temperature hydrogen implantation of disordered A2 Fe60Al40 films on the other hand decreased, unlike helium or neon irradiation, the lattice parameter and MS indicating a little ordering.
This might offer the possibility of H+ irradiation induced ordering of A2 Fe60Al40 thin films well below the ordering temperature.

  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26900
Publ.-Id: 26900


Modeling Laser-Plasma Interaction under Extreme Conditions Towards In-Situ Pump-Probe Simulations

Garten, M.; Hübl, A.; Widera, R.; Burau, H.; Grund, A.; Metzkes, J.; Kluge, T.; Schramm, U.; Cowan, T.; Bussmann, M.

Laser-driven solid density plasmas can be used to generate highly energetic electrons and ions. Diagnosing properties within those plasmas at nm length scales and down to fs timescales is crucial in understanding the involved processes. This has recently become feasible through the advent of X-Ray Free Electron Lasers (XFELs). For instance, XFELs allow imaging the electron density distribution within plasmas via Small Angle X-Ray Scattering (SAXS). We present a scalable GPU-based software framework for simulating photon scattering processes of X-ray beams in matter using Monte-Carlo methods. These simulations enable us to produce synthetic SAXS signals from the interaction of a modeled X-ray pulse with an arbitrarily complex, 3D electron density distribution obtained e.g. from detailed particle-in-cell simulations. Additionally, we present radiation transport methods in our 3D3V fully-relativistic PIC code PIConGPU. These methods enhance modeling of self-imaging of solid-density plasmas and lay the foundation for in-situ simulations of pump-probe experiments. Our new framework allows for single and multiple scattering and is extendable to include complex physics processes like ionization, atomic excitation, and de-excitation along the photon path to further enhance its predictive capability.

Keywords: Laser-ion acceleration; simulation; HPC; PIConGPU; ParaTAXIS; particle-in-cell; X-Ray; XFEL; SAXS

  • Lecture (others)
    HZDR PhD Seminar, 16.-18.10.2017, Seiffen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26899
Publ.-Id: 26899


Modeling Multiple Coherent and Incoherent Photon Scattering in Solid-Density Plasmas with Particle-In-Cell Simulations

Garten, M.; Grund, A.; Hübl, A.; Burau, H.; Widera, R.; Pausch, R.; Debus, A.; Kluge, T.; Fortmann-Grote, C.; Schramm, U.; Cowan, T.; Bussmann, M.

Laser-driven solid density plasmas can be used to generate highly energetic electrons and ions. Diagnosing properties within those plasmas at nm length scales and down to fs timescales is crucial in understanding the involved processes. This has recently become feasible through the advent of X-Ray Free Electron Lasers (XFELs). For instance, XFELs allow imaging the electron density distribution within plasmas via Small Angle X-Ray Scattering (SAXS). We present a scalable GPU-based software framework for simulating photon scattering processes of X-ray beams in matter using Monte-Carlo methods. These simulations enable us to produce synthetic SAXS signals from the interaction of a modeled X-ray pulse with an arbitrarily complex, 3D electron density distribution obtained e.g. from detailed particle-in-cell simulations. Additionally, we present radiation transport methods in our 3D3V fully-relativistic PIC code PIConGPU. These methods enhance modeling of self-imaging of solid-density plasmas and lay the foundation for in-situ simulations of pump-probe experiments. Our new framework allows for single and multiple scattering and is extendable to include complex physics processes like ionization, atomic excitation and de-excitation along the photon path to further enhance its predictive capability.

Keywords: X-Ray; XFEL; SAXS; simulation; HPC; PIConGPU; ParaTAXIS; particle-in-cell

  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 25.-29.09.2017, La Biodola, Isola d'Elba, Italia

Permalink: https://www.hzdr.de/publications/Publ-26898
Publ.-Id: 26898


inSPECtor - integrated spectroscopy sensor system for laser-induced fluorescence and hyperspectral imaging

Seidel, P.; Lorenz, S.; Fuchs, M.; Gloaguen, R.

With the recently intensified development in key technologies such as renewable energy, electric mobility as well as high-tech computer and telecommunication systems, the robust detection and characterization of rare earth elements (REE) simultaneously gained in importance. It is essential not only for the safeguarding of a continuous supply with crucial REE by characterizing new and existing deposits, but also for the future recycling of today’s high-tech products and plants. Until now, hyperspectral absorption as well as emission spectroscopy have been proven to be capable of REE detection in different materials. While absorption spectroscopy has been successfully used for complex and natural samples, existing studies in laser-induced emission spectroscopy (or laser fluorescence) often focus mainly on synthetic crystals and single REE standards. Within this contribution, we focus on the qualitative and quantitative characterization of REE in natural minerals and complex rocks for their possible use as sensors in the mining industry. Based on the integration of emission and absorption spectroscopy techniques we propose a simple yet robust pathway for detection of REE in rock samples.

Keywords: Laser-induced fluorescence; mineral analysis; sensors in mining

  • Invited lecture (Conferences)
    Workshop on innovative technologies in exploration and mineral detection, 14.12.2017, Barcelona, Espana

Permalink: https://www.hzdr.de/publications/Publ-26897
Publ.-Id: 26897


Combination of Hyperspectral Absorption and Photoluminescence Spectroscopy for the Detection of Rare Earth Elements in Natural Minerals

Seidel, P.; Sharma, S.; Lorenz, S.; Fuchs, M.; Beyer, J.; Heitmann, J.; Gloaguen, R.

With the recently intensified development in key technologies such as renewable energy, electric mobility as well as high-tech computer and telecommunication systems, the robust detection and characterization of rare earth elements (REE) simultaneously gained in importance. It is essential not only for the safeguarding of a continuous supply with crucial REE by characterizing new and existing deposits, but also for the future recycling of today’s high-tech products and plants. Until now, hyperspectral absorption as well as emission spectroscopy have been proven to be capable of REE detection in different materials [1,2]. While absorption spectroscopy has been successfully used for complex and natural samples, existing studies in laser-induced emission spectroscopy (or laser fluorescence) often focus mainly on synthetic crystals and single REE standards. Within this contribution, we focus on the qualitative and quantitative characterization of REE in natural minerals and complex rocks for their possible use as sensors in the mining industry. Based on the integration of emission and absorption spectroscopy techniques we propose a simple yet robust pathway for detection of REE in rock samples.

[1] D. J. Turner, B. Rivard, L. Groat American Mineralogist, 99, 1335–1346 (2014)
[2] M. Gaft, G. Panczer, R. Reisfeld, E. Uspensky Phys. Chem. Minerals, 28, 347-363 (2001)

Keywords: Laser-induced fluorescence; mineral analysis; sensors in mining

  • Lecture (Conference)
    Photoluminescence in Rare Earths: Photonic Materials and Devices (PRE'17), 02.12.2017, Roma, Italien

Permalink: https://www.hzdr.de/publications/Publ-26896
Publ.-Id: 26896


p-type co-doping effect of (Ga,Mn)P: Magnetic and magneto-transport properties

Xu, C.; Yuan, Y.; Wang, M.; Hentschel, H.; Böttger, R.; Helm, M.; Zhou, S.

In this paper, we perform a comparison of magnetic and electrical properties between Mn-doped and (Mn, Zn) co-doped GaP dilute ferromagnetic semiconductors. Due to the shallow Zn impurity level (20–40 meV above the top of the III-V compounds valence band), the Zn co-doping leads to the increase of conductivity of (Ga,Mn)P, however both the Curie temperature and magnetization reduce, which is probably due to the suppression of active Mn substitution by Zn co-doping.

Keywords: Dilute ferromagnetic semiconductors; The Curie temperature; Magnetization; Co-doping; Magneto-transport

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26895
Publ.-Id: 26895


Improved background suppression for radiative capture reactions at LUNA with HPGe and BGO detectors

Boeltzig, A.; Best, A.; Imbriani, G.; Junker, M.; Aliotta, M.; Bemmerer, D.; Broggini, C.; Bruno, C. G.; Buompane, R.; Cavanna, A. C. F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Deboer, R. J.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Kochanek, I.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Piatti, D.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.; Wiescher, M.; Zavatarelli, S.

Direct measurements of small nuclear reaction cross sections require a low background in the signal region of interest to achieve the necessary sensitivity. We describe two complementary detector setups that have been used for studies of reactions with solid targets at the Laboratory for Underground Nuclear Astrophysics (LUNA): a high-purity germanium detector and a bismuth germanate (BGO) detector. We present the effect of a customised lead shielding on the measured background spectra in the two detector setups at LUNA. We developed a model to describe the contributions of environmental and intrinsic backgrounds in the BGO detector measurements. Furthermore we present an upgrade of the data acquisition system for our BGO detector, which allows us to exploit the features of the segmented detector and overcome some of the limitations encountered in previous experiments. We conclude with a discussion on the improved sensitivity of the presented setups, and the benefits for ongoing and possible future measurements.

Permalink: https://www.hzdr.de/publications/Publ-26894
Publ.-Id: 26894


Casting technology for ODS steels - dispersion of nanoparticles in liquid metals

Sarma, M.; Grants, I.; Kaldre, I.; Bojarevics, A.; Gerbeth, G.

Dispersion of particles to produce metal matrix nanocomposites (MMNC) can be achieved by means of ultrasonic vibration of the melt using ultrasound transducers. However, a direct transfer of this method to produce steel composites is not feasible because of the much higher working temperature. Therefore, an inductive technology for contactless treatment by acoustic cavitation was developed. This report describes the samples produced to assess the feasibility of the proposed method for nano-particle separation in steel. Stainless steel samples with inclusions of TiB2, TiO2, Y2O3, CeO2, Al2O3 and TiN have been created and analyzed. Additional experiments have been performed using light metals with an increased value of the steady magnetic field using a superconducting magnet with a field strength of up to 5 T.

Keywords: Photovoltaic silicon; ribbon-growth on substrate; numerical simulation

  • Open Access Logo IOP Conference Series: Materials Science and Engineering 228(2017), 012020

Permalink: https://www.hzdr.de/publications/Publ-26893
Publ.-Id: 26893


Helium and Neon ion based microscopy and nanofabrication

Hlawacek, G.

HIM nanofabrication overview

  • Lecture (Conference)
    SiC workshop, 08.12.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26892
Publ.-Id: 26892


Structuring magnetic and electronic materials using GFIS noble gas focused beams

Hlawacek, G.

New device concepts envisioned to solve some of the pressing problems in todays computing technology require new methodological approaches—both for manufacturing but also during initial research. In this presentation I want to highlight the potential and limitations of ion beams and in particular gas field ion sources based (GFIS) noble gas beams for this demanding development process.
In an first example I want to present results of low fluence ion beam structuring of alloys with interesting magnetic properties such as FeAl. This material undergoes a phase transition upon ion irradiation that converts the initially paramagnetic material into a ferromagnetic one. Using the highly localized irradiation possible in the helium ion microscope and low fluencies of only 1-5 Ne + per nm 2 we can locally change the properties and this create arbitrary shaped nano magnets. The fundamental properties of these electron spin controlling structures with critical dimensions as small as 20 nm can be studied by TEM holography or scanning transmission x-ray microscopy.
Other device concepts require the control of currents at the single electron level. In the second part of the talk I will present first results of the realization of a CMOS compatible single electron transistor (SET) that works at room temperature (RT). We employ a focused GFIS Ne beam to locally mix silicon into a thin silicon dioxide layer. During a subsequent thermal treatment a single silicon cluster with a diameter of only 2-3 nm forms in the oxide. The cluster is separated from the surrounding silicon by only 2 nm providing optimum tunnel distances for RT SET operation. This process is based on the small size of collision cascade in the HIM. A more CMOS compatible restriction of the mixed volume can be achieved by using broad beam irradiation and nano pillars. The first is a well established technique in semiconductor fabrication and latter can be mass fabricated using advanced lithography. In the so achieved restricted mixed volume a single cluster forms during the subsequent annealing.
Both examples highlight the flexibility of the GFIS technique and its potential for the rapid prototyping of new device concepts based on ion beam techniques.
This work has been partially funded by the European Unions Horizon 2020 Research and Innovation Program under grant agreement No. 688072 IONS4SET.

Keywords: HIM

  • Invited lecture (Conferences)
    MRS Fall Meeting, 28.11.2017, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-26891
Publ.-Id: 26891


Analytic approaches with focused ion beams

Hlawacek, G.; Klingner, N.; Heller, R.; Facsko, S.

Focused ion beams have become the number one tool for localized materials modification at the nanometer scale. While initially limited to Ga ions only the last decade has broadened the field by introducing commercial columns based on plasma sources, liquid metal alloy sources (LMAIS) and gas field ion sources (GFIS). The range of available ions now includes among others Li, Cs, many transition metals and notably several gases such H2, N2, He, Ne and Xe. While all of those have their benefits He has the highest potential to be used in high resolution analytical applications.

In this presentation I would like to present available solutions for FIB based nano-analytics that do not require an additional electron beam for the actual analysis, but where the ion is directly or indirectly responsible for the creation of the signal of interest. I will focus on the most wide spread methods which include Secondary Ion Mass Spectrometry (SIMS) [1], Backscatter Spectrometry (BS) [2], channeling [3], as well as Ionoluminescence [4].

Keywords: HIM

  • Invited lecture (Conferences)
    FIBiB, 06.11.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26890
Publ.-Id: 26890


Spatially controlled formation of nanostructures for magnetic and electronic applications

Hlawacek, G.

Gas field ion source (GFIS) based focused ion beam techniques historically also known as Helium Ion Microscopy (HIM) is recognized for its high resolution imaging and nanofabrication capabilities[1]. Over the last decade the tool has been utilized in many different ways. Applications include classical semiconductor materials, magnetic materials, 2D materials, nuclear materials but also biological materials.
In this presentation I want to highlight the potential and limitations of gas field ion sources based (GFIS) noble gas beams for new magnetic and electronic device concepts. In an first example I want to present results of low fluence ion beam structuring of alloys with interesting magnetic properties such as FeAl.
This material undergoes a phase transition upon ion irradiation that converts the initially paramagnetic material into a ferromagnetic one. Using the highly localized irradiation possible in the helium ion microscope and low fluencies of only 1-5 Ne per nm we can locally change the properties and this create arbitrary shaped nano magnets. The fundamental properties of these electron spin controlling structures with critical dimensions as small as 20 nm can be studied by TEM holography or scanning transmission x-ray microscopy.
Other device concepts require the control of currents at the single electron level. In the second part of the talk I will present first results of the realization of a CMOS compatible single electron transistor (SET) that works at room temperature (RT). We employ a focused GFIS Ne beam to locally mix silicon into a thin silicon dioxide layer. During a subsequent thermal treatment a single silicon cluster with a diameter of only 2-3nm forms in the oxide. The cluster is separated from the surrounding silicon by only 2nm providing optimum tunnel distances for RT SET operation. This process is based on the small size of collision cascade in the HIM. A more CMOS compatible restriction of the mixed volume can be achieved by using broad beam irradiation and nano pillars. The first is a well established technique in semiconductor fabrication and latter can be mass fabricated using advanced lithography. In the so achieved restricted mixed volume a single cluster forms during the subsequent annealing.
Both examples highlight the flexibility of the GFIS technique and its potential for the rapid prototyping of new device concepts based on ion beam techniques.
This work has been partially funded by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement No. 688072 “IONS4SET”.
[1] Gregor Hlawacek and Armin Gölzhäuser, editors. Helium Ion Microscopy. Springer International Publishing, Cham, 2016.

Keywords: HIM

  • Invited lecture (Conferences)
    JASP, 07.09.2017, Fukuoka, Japan

Permalink: https://www.hzdr.de/publications/Publ-26889
Publ.-Id: 26889


Nanofabrication with the Helium Ion Microscope

Hlawacek, G.

Helium Ion Microscopy (HIM) [1,2] is best known for its high resolution imaging capabilities of both conductive as well as insulating samples. However, since the introduction of Ne as an imaging gas for the gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized.
While the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV Ne compared to 0.5 nm for 30 keV He) the user usually benefits from the much higher cross section for nuclear stopping. The latter results in a larger number of sputtered atoms and bonds broken directly by small impact parameter collisions.
Here, I first want to summarize results obtained over the last years using focused ion beam induced deposition (FIBID) using the HIM [3]. In addition I will show results on resist writing using the HIM.
Both approaches benefit from the negligible proximity effect in the HIM. This is related to the different energy distribution of the electrons created by the ion beam as well as the near absence of second or higher generation electrons. Consequently, line patterns with a half pitch of 4 nm have been reported [4]. For high aspect pillars this often results in narrow structures created using FIBID as compared to FEBID.
In the second part I will present results obtained using direct write milling low fluence ion beam irradiation and ion beam based mixing. In all three cases the electronic or magnetic properties of the target material will be altered at the nano-scale in a controlled way to achieve new functionality. The examples comprise • The fabrication of semiconducting graphene nano-ribbons by direct milling [5]

  • The fabrication of a lateral spin valve structure using low fluence ion irradiation [6]
  • The formation of individual 3 nm Si clusters for a room temperature single electron transistor
For all presented examples the critical length scale of the nanostructure is smaller or in the range of collision cascade. This size regime can not be accessed with traditional broad beam based ion irradiation and holds many promises but also challenges that need to be overcome to enable new device concepts and new functional materials on the nano-scale.

Keywords: HIM

  • Invited lecture (Conferences)
    CELINA, 15.09.2017, Porto, Portugal

Permalink: https://www.hzdr.de/publications/Publ-26888
Publ.-Id: 26888


Helium and Neon ion based microscopy and nanofabrication

Hlawacek, G.

Gas field ion source (GFIS) based focused ion beam techniques historically also known as Helium Ion Microscopy (HIM) is recognized for its high resolution imaging and nanofabrication capabilities [1]. Over the last decade the tool has been utilized in many different ways. Applications include classical semiconductor materials, magnetic materials, 2D materials, nuclear materials but also biological materials.
I will introduce the technique and discusse the different instrumentation add ons we utilize and develop in our lab. This includes ionoluminescence [2], in-situ electrical probing [3], and in-situ irradiation at elevated temperatures. Finally, I want to present how we achieve a world record lateral resolution for backscatter spectrometry using time-of-flight [4]. On the materials science part I will present examples from our own lab covering the various application fields, including patterning of magnetic [5] and 2D materials [3] but also structural characterization of epitaxial metal layers [6]. The capability to investigate insulating or biological samples without compromising the performance of the machine will be presented in the second part [7]. This unique feature of the helium ion microscope is possible thanks to the use of an electron flood gun for charge compensation.

Keywords: HIM

  • Invited lecture (Conferences)
    Physik Kolloquium, 03.07.2017, Leoben, Österreich

Permalink: https://www.hzdr.de/publications/Publ-26887
Publ.-Id: 26887


Spatially controlled ripple formation in the HIM using low voltages and high temperatures

Sottili, L.; Hlawacek, G.; Engler, M.; Facsko, S.

Ripple formation is a well known phenomenon that is observed
Conclusion
•Ripple formation has been facilitate by using a new home
Localized FIB based ripple formation
Temperature dependence Broad beam ripple formation with Ne
•Large area HIM patterning for many materials under low energy ion bombardment.
Often broad beam ion irradiation using energies of only a few keV is employed to create these self-organized patterns. We present for the first time ripple patterns that have been created in GaAs(001) using 5 keV Ne ions and elevated temperatures of up to 590 K in a Helium Ion Microscope (HIM). HIM is well known for its outstanding imaging and micro and nano fabrication capabilities.
However, most results so far have been achieved at room temperature and by using energies between 25 keV and 35 keV.
For this work we lowered the acceleration voltage to below 5 keV while maintaining an acceptable lateral resolution in the nm range .

Keywords: HIM; ripples

  • Poster
    Nanopatterning2017, 26.-30.06.2017, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-26886
Publ.-Id: 26886


Spatially controlled fabrication of individual silicon nano clusters using ion beam mixing and thermal treatment

Hlawacek, G.; Xu, X.; Prüfer, T.; Wolf, D.; Hübner, R.; Bischoff, L.; Möller, W.; Facsko, S.; von Borany, J.; Heinig, K. H.

The miniaturization of computing devices and the introduction of the internet of things creates an increasing demand for the development of low power devices.
Single electron transistors (SETs) are very low power dissipation devices and thus ideally suited for this demand. Combined with existing CMOS technology which is characterized by high speed and driving the existing draw backs of SETs are compensated. The development of such hybrid SET-CMOS devices is currently hindered by missing large scale manufacturing routes. For room temperature (RT) operation it is necessary to create a single nanocluster with a diameter below 5 nm exactly positioned between source and drain at a tunnel distance of only a few nanometers.
We show the first results on the way to a CMOS compatible fabrication process based on ion beam mixing and self-assembly to form a Si cluster with a size below 5 nm. Our process ensures that (a) the cluster size is small enough to allow RT operation, (b) the cluster is located at the correct tunnel distance between source and drain, (c) the clusters form at predetermined locations, and (d) the process is CMOS compatible. These goals are reached by a combination of localized ion beam mixing and a carefully tuned thermal treatment that leads to a self-assembly process that guarantees (a) and (b). In this initial demonstration of the single cluster formation process we utilize a Helium Ion Microscope to locally mix Si into a buried oxide layer. The highly focused Ne beam available in this instrument allows point like irradiation and hence reduces the mixing volume to (10nm) 3 . Subsequent annealing results in the formation of a single 2 nm Si cluster located less than 3 nm from the adjacent Si/SiO 2 interfaces.
Energy-filtered TEM (EFTEM) (Figure 1) has been utilized to reveal the presence of individual clusters. For a CMOS compatible fabrication process the restriction of the collision cascade and therefore the ion beam mixed volume will be realized by using broad beam irradiation of nanopillars with an embedded oxide layer and a diameter below 20 nm. The aim is to fabricate gate-all-around nanopillar RT-SETs together with state-of-the-art FETs. TRI3DYN and kMC simulations (Figure 2) are used to study these future works and compare them to the above discussed study based on focused ion beam irradiation.

This work is being funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).

Keywords: HIM

  • Lecture (Conference)
    EIPBN, 30.05.-02.06.2017, Orlando, USA
  • Lecture (Conference)
    eu-f-n, 04.07.2017, Graz, Österreich

Permalink: https://www.hzdr.de/publications/Publ-26885
Publ.-Id: 26885


Scanning Transmission Ion Microscopy

Hlawacek, G.; Krasheninnikov, A.; Klingner, N.; Möller, W.; Munnik, F.; Facsko, S.

Project presentation npSCOPE

Keywords: STIM; HIM

  • Lecture (others)
    npSCOPE kick off meeting, 16.-17.01.2017, Belvaux, Luxembourg

Permalink: https://www.hzdr.de/publications/Publ-26884
Publ.-Id: 26884


Strain doping driven metal-insulator transition in LaNiO3 films

Changan, W.; Parul, P.; Pei-Chun, W.; Ping-Chun, W.; Mao, W.; Chi, X.; Yujia, Z.; Roman, B.; Manfred, H.; Ying-Hao, C.; Shengqiang, Z.

Complex oxides are fascinating materials, in which the manipulation of charge, orbital and lattice degrees of freedom leads to numerous exciting phenomena. We report here the use of He ion irradiation to control the out-of-plane lattice constant of epitaxial LaNiO3 (LNO) thin films independently without a change of the in-plane lattice constant. All the LNO films with the fluence less than 1×1015 He/cm2 exhibit metallic behaviors along with a slight resistivity upturn at low temperature, whereas the film with 2.5×1015 He/cm2 shows metallicity at high temperature and insulator-like behavior at low temperature. Further, the fitting for the temperature dependent resistance indicates that electrical-conductivity carriers are mainly scattered by electron-boson interactions rather than electron-electron interactions. These results suggest that He ion irradiation can be an alternative route to tune the functionality of complex oxides.

  • Lecture (Conference)
    European Materials Research Society, 18.09.2017, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-26883
Publ.-Id: 26883


Coupling of magnetism and structural phase transition in V2O3/Co bilayers

Changan, W.; Chi, X.; Ye, Y.; Yu-Jia, Z.; Shengqiang, Z.

Exchange couplings across interfaces of hybrid magnetic heterostructures are being considered as unique opportunity for functional materials design. In this study, we show that both coercivity and magnetization of V2O3/Co bilayers are affected by the stress associated with structural phase transition across metal-insulator phase transition in V2O3. The change in coercivity is as large as 59% in a very narrow temperature range. The magnetic properties can be controlled by stress, which is significant for future multiferroic and spintronics applications.

  • Poster
    Deutsche Physikalische Gesellschaft, 19.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26882
Publ.-Id: 26882


Performance Enhancement of Reconfigurable Field Effect Transistors (RFETs)

Khan, M. B.; Deb, D.; Georgiev, Y. M.; Erbe, A.

Scaling down of CMOS faces strong challenges due to which advanced fabrication techniques, advanced materials, new device and logic concepts have gained importance. These concepts include undoped silicon nanowire based reconfigurable devices, which can be programmed as p- or n-channel FETs by controlling the electrostatic potential applied at gate electrodes. In this talk, fabrication and electrical characterization of undoped sub-20 nm silicon nanowires (SiNWs) will be reported. SiNWs are fabricated on intrinsic silicon-on-insulator (SOI) substrates in <110> and <100> crystal orientations using a top down approach. Hydrogen silsesquioxane (HSQ), a negative tone electron beam resist, is used for nano-patterning and as a hard mask for etching. Nanowire etching process is optimized using an inductively coupled plasma (ICP) source and C4F8/SF6/O2 mixed gas recipe at 18◦C. These NWs are subsequently silicidized to form Scottky junctions. Electrical characterization shows different charge carrier transport in <110> and <100> crystal orientations. Control over silicide formation to enhance the performance of these devices will be discussed.

  • Lecture (Conference)
    IHRS NanoNet Annual Workshop 2017, 16.-18.08.2017, Klingenberg-Colmnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-26881
Publ.-Id: 26881


Electrical characterization of sub-20 nm silicon nanowires fabricated using electron beam lithography and inductively coupled plasma etching

Khan, M. B.; Deb, D.; Georgiev, Y. M.; Erbe, A.

Scaling down of CMOS faces strong challenges due to which advanced fabrication techniques, advanced materials, new device and logic concepts have gained importance. These concepts include undoped silicon nanowire based reconfigurable devices, which can be programmed as p-FET or n-FET by controlling the electrostatic potential applied at gate electrodes. In this work, fabrication and electrical characterization of undoped sub-20 nm silicon nanowires (SiNWs) is reported. SiNWs are fabricated on intrinsic silicon-on-insulator (SOI) substrates in <110> and <100> crystal directions using a top down approach. Hydrogen silsesquioxane (HSQ), a negative tone electron beam resist, is used for nano-patterning and as a hard mask for etching. Nanowire etching process is optimized using an inductively coupled plasma (ICP) source and C4F8/SF6/O2 mixed gas recipe at 18 oC. These NWs are oxidized to form a SiO2 shell and subsequently silicidized. Final observations include different charge carrier transport in <110> and <100> crystal directions.

Keywords: Silicon nanowire; etching; lithography; schottky barrier devices

  • Poster
    Materials for Advanced Metallization, 26.-29.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-26880
Publ.-Id: 26880


A Cytomic Approach Towards Genomic Individuality of Neurons

Arendt, T.; Belter, B.; Brückner, M. K.; Ueberham, U.; Morawski, M.; Tarnok, A.

Here, we describe an approach for the DNA quantification of single cells in brain slices based on image cytometry (IC) that allows mapping the distribution of neurons with DNA content variation (DCV) in the context of preserved tissue architecture. The method had been optimized for DNA quantification of identified neurons but could easily be adapted to other tissues. It had been validated against chromogenic in situ hybridization (CISH) with chromosome-specific probes and laser microdissection followed by quantitative PCR (qPCR) of alu repeats. It can be combined with immunocytochemical detection of specific marker proteins which allow for further specification of cellular identity in the context of defined brain pathology. The method can be applied in a high-throughput mode where it allows analyzing 500,000 neurons per brain in a reasonable time. The combination of cytometry with molecular biological characterization of single microscopically identified neurons as outlined here might be a promising approach to study molecular individuality of neurons in the context of its physiological or pathophysiological environment. It reflects the concept of cytomics and will forward our understanding of the molecular architecture and functionality of neuronal systems.

Keywords: Ageing; Alzheimer’s disease; Aneuploidy; Cell death; Cellular individuality; Cytomics; DNA content variation; Genomic mosaic; Neurodegeneration; Polyploidy; Single-cell analysis

  • Book chapter
    Frade, Jose Maria, Gage, Fred H.: A Cytomic Approach Towards Genomic Individuality of Neurons, Paris: Springer, 2017, 978-1-4939-7279-1, 81-106
    DOI: 10.1007/978-1-4939-7280-7

Permalink: https://www.hzdr.de/publications/Publ-26879
Publ.-Id: 26879


Magneto-optical spectroscopy of diluted magnetic semiconductors GaMnAs prepared by ion implantation and further impulse laser annealing

Gan'Shina, E. A.; Golik, L. L.; Kun'Kova, Z. E.; Zykov, G. S.; Bykov, I. V.; Rukovishnikov, A. I.; Yuan, Y.; Böttger, R.; Zhou, S.

Ga1−xMnxAs layers prepared by ion implantation and subsequent pulsed laser annealing with the planned Mn concentrations of x = 0.01–0.08 have been studied using the magneto-optical transversal Kerr effect (TKE) and spectral ellipsometry. The spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) have been calculated for the layers. The obtained spectra of the diagonal PT components show that the layers under study maintain the zinc-blende crystal structure of the parent GaAs semiconductor. All studied samples reveal a strong TKE response at low temperatures with a dependence of an effective Curie temperature (at which TKE appears) on the Mn concentration. A number of extrema in the low-temperature TKE and MCD spectra are close to the energies of transitions in the Γ and L critical points of the parent semiconductor band structure that confirms the intrinsic ferromagnetism of the Ga1−xMnxAs layers. The MCD spectra shape and its change with Mn concentration increasing are discussed on a base of the valence-band model of ferromagnetism in DMS.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26878
Publ.-Id: 26878


Transition Metal Dichalcogenides under Ion Irradiation: From Defects to Atomic Structure Engineering

Ghorbani-Asl, M.; Kretschmer, S.; Krasheninnikov, A. V.

We study the effects of ion irradiation on suspended MoS₂ monolayer (ML) by using molecular dynamics (MD) combined with density-functional theory (DFT) calculations. We systematically study the production of defects in a free-standing MoS₂ ML under noble gas ions bombardment for a broad range of incident angles and ion energies and determine the probabilities of producing single Mo and S vacancies. By comparing MD trajectories and analytical models for binary collision, we identified both direct and indirect mechanisms for defect production. Our results demonstrate that a selective sputtering of S atoms from the upper or lower layer can be achieved by choosing ion energy and incidence angle. The probability of producing S vacancy from upper layer increases by tilting the ion beam from the normal direction. The results showed that the defects cross section for both S and Mo vacancy grows with ion mass while the values for S vacancy are much higher than Mo vacancy. We further show the possibility of producing stable mixed MoSX (X from group V or VII) compounds with different electronic properties using ion irradiation. These findings suggest a promising route for post-growth processing of these materials for engineering electronic devices.

Keywords: transition metal dichalcogenides; ion irradiation; defects; molecular dynamics; density-functional theory

  • Lecture (Conference)
    MRS Spring Meeting, 17.-21.04.2017, Phoenix, Arizona, United States

Permalink: https://www.hzdr.de/publications/Publ-26877
Publ.-Id: 26877


Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203] [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275] [276] [277] [278] [279] [280] [281] [282] [283] [284] [285] [286] [287] [288] [289] [290] [291] [292] [293] [294] [295] [296] [297] [298] [299]