Qucosa – Hemholtz-Zentrum Dresden-Rossendorf
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Novel Methods for Controlled Self-Catalyzed Growth of GaAs Nanowires and GaAs/AlxGa1-xAs Axial Nanowire Heterostructures on Si Substrates by Molecular Beam Epitaxy
Full text linkAnnual Report 2019 - Institute of Ion Beam Physics and Materials Research
Full text linkThe Institute of Ion Beam Physics and Materials Research conducts materials research for future applications in, e.g., information technology. To this end, we make use of the various possibilities offered by our Ion Beam Center (IBC) for synthesis, modification, and analysis of thin films and nanostructures, as well as of the free-electron laser FELBE at HZDR for THz spectroscopy. The analyzed materials range from semiconductors and oxides to metals and magnetic materials. They are investigated with the goal to optimize their electronic, magnetic, optical as well as structural functionality. This research is embedded in the Helmholtz Association’s programme “From Matter to Materials and Life”. Seven publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute.
After the scientific evaluation in the framework of the Helmholtz Programme-Oriented Funding (POF) in 2018 we had some time to concentrate on science again before end of the year a few of us again had to prepare for the strategic evaluation which took place in January 2020, which finally was also successful for the Institute
How to integrate geochemistry at affordable costs into reactive transport for large-scale systems: Abstract Book
Full text linkThis international workshop entitled “How to integrate geochemistry at affordable costs into reac-tive transport for large-scale systems” was organized by the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden Rossendorf in Feb-ruary 2020. A mechanistic understanding and building on that an appropriate modelling of geochemical processes is essential for reliably predicting contaminant transport in groundwater systems, but also in many other cases where migration of hazardous substances is expected and consequently has to be assessed and limited. In case of already present contaminations, such modelling may help to quantify the threads and to support the development and application of suitable remediation measures. Typical application areas are nuclear waste disposal, environmental remediation, mining and milling, carbon capture & storage, or geothermal energy production. Experts from these fields were brought together to discuss large-scale reactive transport modelling (RTM) because the scales covered by such pre-dictions may reach up to one million year and dozens of kilometers. Full-fledged incorporation of geochemical processes, e.g. sorption, precipitation, or redox reactions (to name just a few important basic processes) will thus create inacceptable long computing times. As an effective way to integrate geochemistry at affordable costs into RTM different geochemical concepts (e.g. multidimensional look-up tables, surrogate functions, machine learning, utilization of uncertainty and sensitivity analysis etc.) exist and were extensively discussed throughout the workshop. During the 3-day program of the workshop keynote and regular lectures from experts in the field, a poster session, and a radio lab tour had been offered. In total, 40 scientists from 28 re-search institutes and 8 countries participated
Annual Report 2019 - Institute of Resource Ecology
Full text linkThe Institute of Resource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden –Rossendorf (HZDR). Our research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Ra-diation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. The program NUSAFE, and therefore all work which is done at IRE, belong to the research field “Energy” of the HG
Advanced characterisation and optical simulation for the design of solar selective coatings based on carbon:transition metal carbide nanocomposites
No full textSolar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon: metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5 and 15% at 25 and 600ºC, respectively. The results of this study can be considered as predictive design tool for nanomaterial-based optical coatings in general
Solar selective coatings based on carbon:transition metal nanocomposites
No full textThe design of efficient and stable solar selective coatings for Concentrating Solar Power (CSP) central receivers requires a comprehensive knowledge about the incorporated materials. In this work solar selective coatings were grown by filtered cathodic vacuum arc (FCVA) deposition. The complete stacks consist of an infrared reflection layer, an absorber layer of C:ZrC nanocomposites and an antireflection layer. The Carbon-transition metal nanocomposites were studied as absorber materials because they show appropriate optical properties, i.e. high absorption in the solar region and low thermal emittance. Furthermore metal carbides are thermally and mechanically stabile in air at high temperatures. In order to optimize the absorber layer, the metal content was controlled by adjusting the pulse ratio between the two arc sources. The elemental composition of the absorber layers was determined by Ion Beam Analysis. X-Ray diffraction (XRD) measurements show the formation of metal carbides when the metal content is high enough. The optical properties of the deposited coatings were characterized by spectroscopic ellipsometry (SE). The reflectance spectra of the complete selective coating were simulated with the optical software CODE. Bruggeman effective medium approximation (EMA) was employed to average the dielectric functions of the two components which compose the nanocomposite in the absorber layer. Good agreement was found between simulated and measured reflectance spectra of the solar selective multilayer
Joint project: Umwandlungsmechanismen in Bentonitbarrieren - Subproject B: Einfluss von mikrobiellen Prozessen auf die Bentonitumwandlung
Full text linkConcerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters.Für die tiefengeologische Lagerung von Wärme-entwickelnden, hoch-radioaktiven Abfällen kommen Bentonite aufgrund ihrer hohen Quellfähigkeit und ihrer geringen hydraulischen Leitfähigkeit als geo-technische Barriere in Betracht, welche sich zwischen der technischen Barriere (Behälter mit Abfall) und der geologischen Barriere (Wirtsgestein) befindet. Im Rahmen des Verbundprojektes „UMB“ (Umwandlungsmechanismen in Bentonitbarrieren) der Kooperationspartner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Fachbereich Endlagersicherheitsforschung), der Universität Greifswald (Institut für Geographie und Geologie), der Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Arbeitsbereich Technische Mineralogie), der Technischen Universität München (TUM; Fachgebiet Theoretische Chemie, Quantenchemie) und dem Helmholtz-Zentrum Dresden Rossendorf (HZDR Institut für Ressourcenökologie) sollen abgesicherte, objektive Kriterien zur Auswahl geeigneter Bentonite für den Einsatz in Endlagern für wärmeentwickelnde Abfälle in Tonformationen entwickelt werden. Das HZDR analysierte hierfür die Entwicklung der mikrobiellen Diversität in den Bentoniten B36 und SD80 in Abhängigkeit von verschiedenen Parametern (Porenlösung, Temperatur, Anwesenheit von Substraten) um den möglichen Einfluss von Mikroorganismen auf die Umwandlungsprozesse im Bentonit zu erfassen. Die Bentonite wurden hierfür bei der GRS (Gesellschaft für Anlagen- und Reaktorsicherheit gGmbH) mit Opalinuston-Porenlösung bzw. verdünnter Gipshut-Lösung versetzt. Die Ansätze inkubierten in gasdichten Glasflaschen bei 25 °C, 60 °C und 90 °C für jeweils ein und zwei Jahre („Langzeit“). Des Weiteren wurden am HZDR B36 Mikrokosmen mit Opalinustonporenlösung angesetzt, welche für drei Monate bei 30 °C inkubierten („Kurzzeit“). Über die drei Monate verteilt wurden sechs Probenahmen durchgeführt, und die mikrobielle Diversität sowie ausgewählte geochemische Paramater bestimmt
Annual Report 2018 - Institute of Ion Beam Physics and Materials Research
Full text linkThe Institute of Ion Beam Physics and Materials Research conducts materials research for future applications in, e.g., information technology. To this end, we make use of the various possibilities offered by our Ion Beam Center (IBC) for synthesis, modification, and analysis of thin films and nanostructures, as well as of the free-electron laser FELBE at HZDR for THz spectroscopy. The analyzed materials range from semiconductors and oxides to metals and magnetic materials. They are investigated with the goal to optimize their electronic, magnetic, optical as well as structural functionality. This research is embedded in the Helmholtz Association’s programme “From Matter to Materials and Life”. Six publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute
Percolated Si:SiO2 Nanocomposites: Oven- vs. Millisecond Laser-induced Crystallization of SiOx Thin Films
Full text linkThree-dimensional nanocomposite networks consisting of percolated Si nanowires in a SiOx matrix, Si:SiO2, were studied. The structures were obtained by reactive ion beam sputter deposition of SiOx (x~0.6) thin films at 450 °C and subsequent crystallization using conventional oven as well as millisecond line focus laser annealing. Rutherford backscattering spectrometry, Raman spectroscopy, X-ray diffraction, cross-sectional and energy-filtered transmission electron microscopy were applied for sample characterization. While oven annealing resulted in a mean Si wire diameter of 10 nm and a crystallinity of 72 % within the Si volume, almost single-domain Si structures with 30 nm in diameter and almost free of amorphous Si were obtained by millisecond laser application. The structural differences are attributed to the different crystallization processes: Conventional oven tempering proceeds via solid state, millisecond laser application via liquid phase crystallization of Si. The 5 orders of magnitude larger diffusion constant in the liquid phase is responsible for the three times larger Si nanostructure diameter. In conclusion, laser annealing offers not only significantly shorter process times but moreover a superior structural order of nano-Si compared to conventional heating
Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-y(OxN1-x). Part 2: Experimental validation and durability tests at high temperature
No full textThe durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties.
Both SSC stacks were stable in single stage tests of 12 hours at 650°C. At 800°C, they underwent a structural transformation by full oxidation and they lost their solar selectivity. During cyclic durability tests, multilayer 1, comprised of TiN, Al0.64Ti0.36N and an Al1.37Ti0.54O top layer, fulfilled the performance criterion (PC) ≤ 5% for 300 symmetric, 3 hours long cycles at 600°C in air. Multilayer 2, which was constituted of four AlyTi1-y(OxN1-x) layers, met the performance criterion for 250 cycles (750 hours), but was more sensitive to these harsh conditions. With regard to the degradation mechanisms, the coarser microstructure of multilayer 1 is more resistant against oxidation than multilayer 2 with its graded oxygen content. These results confirm that the designed SSCs based on AlyTi1-y(OxN1-x) materials withstand breakdown at 600ºC in air. Therefore, they can be an exciting candidate material for concentrated solar power applications at high temperature