TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg T1 - Ressourcensicherung durch Recycling von Sekundärrohstoffen T2 - Systemwissen für die vernetzte Energie- und Mobilitätswende KW - Lithiumbatterie KW - Funktionelles Recycling KW - Nickel-Mangan-Cobalt-Oxid KW - NMC KW - Raman-Spektroskopie KW - Laugung Y1 - 2019 SN - 978-3-9816861-7-3 SP - 170 EP - 181 PB - Vereinigung für Betriebliche Bildungsforschung e.V. CY - Berlin ET - 1. Auflage ER - TY - GEN A1 - Rietig, Anja A1 - Acker, Jörg T1 - Kinetic studies on acidic wet chemical etching of silicon in binary and ternary mixtures of HF, HNO3 and H2SiF6 T2 - Physical Chemistry Chemical Physics Y1 - 2023 U6 - https://doi.org/10.1039/d3cp03188h SN - 1463-9084 SN - 1463-9076 VL - 25 IS - 38 SP - 26245 EP - 26257 ER - TY - CHAP A1 - Hünger, Klaus-Jürgen A1 - Acker, Jörg A1 - Danneberg, Matti A1 - Herold, Steven T1 - Quantification of stress states in quartzite surfaces by using RAMAN spectroscopy T2 - 27th Annual Conference of the German Crystallographic Society / Zeitschrift für Kristallographie. Supplement Y1 - 2019 SN - 978-3-11-065403-5 SN - 0930-486X VL - 39 SP - S. 122 PB - De Gruyter CY - Berlin ER - TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg T1 - Ressourcensicherung durch Recycling von Sekundärrohstoffen T2 - Systemwissen für die vernetzte Energie- und Mobilitätswende KW - Recycling KW - Lithium-Ionen-Batterien KW - Elektroschrott KW - Edelmetalle Y1 - 2022 UR - https://www.ibbf.berlin/assets/images/Dokumente/220627_IBBF_Kompendium_2022_WEB_final%20(1).pdf SN - 978-3-9816861-8-0 SP - 141 EP - 152 PB - Vereinigung für Betriebliche Bildungsforschung e.V. CY - Berlin ET - 2. Auflage ER - TY - GEN A1 - Rietig, Anja A1 - Grafe, Hans-Joachim A1 - Acker, Jörg T1 - Understanding the Reasons for Erroneous Determinations of Boron in Silicon following Wet Chemical Digestion in HF/HNO3 T2 - Proceedings of the Silicon for the Chemical & Solar Industry XVI KW - boron KW - silicon KW - species KW - trace element Y1 - 2022 UR - https://ssrn.com/abstract=4123058 SN - 978-82-692919-0-2 U6 - https://doi.org/10.2139/ssrn.4123058 ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - About determining reliable etching rates and the role of temperature in kinetic experiments on acidic wet chemical etching of silicon T2 - Physical Chemistry Chemical Physics Y1 - 2023 UR - https://pubs.rsc.org/en/content/articlelanding/2023/cp/d2cp05837e U6 - https://doi.org/10.1039/D2CP05837E SN - 1463-9084 VL - 25 IS - 16 SP - 11387 EP - 11397 ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - Comprehensive stoichiometric studies on the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures T2 - Physical chemistry, chemical physics KW - silicon KW - etching KW - stoichiometry KW - hydrogen KW - nitrogen oxides KW - mechanism Y1 - 2022 UR - https://pubs.rsc.org/en/content/articlelanding/2022/cp/d1cp05418j U6 - https://doi.org/10.1039/d1cp05418j SN - 1463-9076 VL - 24 IS - 5 SP - 3094 EP - 3108 ER - TY - CHAP A1 - Herold, Steven A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - The influence of lattice deformations on the etch rates of potassium hydroxide on silicon T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - One of the most common methods to analyse silicon materials is Raman-spectroscopy.[1] More recently there is a focus in the analysis of lattice deformations during sample preparations.[2] These deformations not only increase the chance of crack formation but also increases the chemical reactivity of the silicon towards etch processes or oxidation processes.[3] In this contribution, we will present our latest results on the influence of lattice deformations induced by scratches and saw damage on the etch rate of potassium hydroxide. The lattice deformation will be measured using Raman-microscopy and correlated with the height difference measured with confocal microscopy. It will be shown that the etch rate strongly depends on the lattice deformation and that the etch rate will increase by up to the factor 10 in areas with tensile deformation. KW - silicon KW - etching KW - Raman spectroscopy KW - lattice strain KW - saw damage KW - confocal microscopy Y1 - 2018 SP - S. 198 PB - Universität des Saarlandes CY - Saarbrücken ER - TY - GEN A1 - Acker, Jörg A1 - Sieber, Tim A1 - Langner, Thomas A1 - Herold, Steven ED - Andresen, Birger ED - Nygaard, Lars ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard ED - Page, Ingrid Gamst T1 - The impact of lattice strain on the reactivity of silicon T2 - Silicon for the Chemical and Solar Industry XIV N2 - The present study is focused on the question of how lattice strain mechanically introduced into silicon alters the chemical reactivity of the silicon atoms that are affected by the strain field on a microscopic length scale. The magnitude and local distribution of lattice strain are extracted from confocal Raman microscopy measurements. The reactivity of Si is expressed by the etch rate of Si after treatment with HF–HNO3–H2SiF6 mixtures. Then, the local etch rate is calculated from the local etch depth as determined by confocal microscopy. It has been found that tensile strain leads to the highest enhancement of the etch rate, followed by a compressive strain increase in the etch rate. KW - silicon KW - etching KW - Raman spectroscopy KW - lattice strain KW - stress KW - mechanical activation KW - mechanochemistry KW - confocal microscopy Y1 - 2018 SP - 11 EP - 20 PB - The Norwegian University of Science and Technology CY - Trondheim ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg ED - Andresen, Birger ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard ED - Page, Ingrid T1 - Advanced insights into the stoichiometry and kinetics of the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures T2 - Silicon for the Chemical and Solar Industry XV N2 - The stoichiometry and kinetics of wet chemical etching of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures was investigated. The side reactions and main reaction pathways were identified by quantifying all reaction products. The relationship between the concentration of undissociated HNO3 and the consumption of HNO3, as well as the formation of H2 as a function of the mixing ratios were found by varying the etching mixture composition systematically. Based on the etching rates determined, kinetic models for the reaction- and diffusion-controlled reaction mechanism are presented as well as the interrelation between the etchant composition and the transition between reaction- and diffusion-controlled etching. KW - silicon KW - etching KW - Raman KW - etch rate KW - mass spectrometry KW - hydrogen KW - nitrous gases Y1 - 2020 SN - 978-82-997357-9-7 SP - 145 EP - 159 PB - The Norwegian University of Science and Technology CY - Trondheim ER - TY - GEN A1 - Herold, Steven A1 - Acker, Jörg T1 - Measurement of the temperature dependence of lattice deformations in silicon using Raman microscopy T2 - Journal of Applied Physics N2 - The effect of heating and cooling in the range of 25–900 °C on the lattice deformations of diamond wire-sawn polycrystalline and scratched monocrystalline silicon surfaces was studied in detail using Raman microscopy. Mechanically treated silicon surfaces contain tensile or compressive strained silicon with varying deformation strength and areas with high-pressure silicon phases and amorphous silicon. It is shown that compressive deformed silicon relaxes after heating the sample to 600 °C, while tensile deformed silicon only relaxes after multiple heating and cooling cycles. Raman measurements during the heating and after the cooling phases reveal the individual thermal expansion and relaxation behavior of the deformed silicon states. Compressive deformed silicon relaxes during the heating phase, while tensile deformed silicon relaxes during the cooling phase. It is, therefore, possible to separately relax certain deformation states using thermal annealing without changing the topography of the surface. KW - Raman spectroscopy KW - mechanical stress KW - silicon KW - crystallization KW - relaxation KW - thermal treatment KW - solar cell Y1 - 2019 UR - https://aip.scitation.org/doi/10.1063/1.5090476 U6 - https://doi.org/10.1063/1.5090476 SN - 1089-7550 VL - 126 ER - TY - CHAP A1 - Herold, Steven A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - Measurement of the temperature dependence of lattice deformations in silicon using Raman microscopy T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - One of the most common methods to analyse silicon materials is Raman-spectroscopy.[1] More recently there is a focus in the analysis of lattice deformations during sample preparations.[2] These deformations not only increase the chance of crack formation but also increases the chemical reactivity of the silicon towards etch processes or oxidation processes.[3] In this contribution, we will present our latest Raman evaluation technique for silicon lattice deformation and a way to control them using rapid thermal annealing. The transitions and relaxation of different lattice deformation states after the rapid heating to up to 900°C will be analysed in detail, while also the recrystallisation of amorphous silicon will be discussed from the aspects of lattice deformations. It will be shown that during the tempering the lattice deformation on scratched, indented or diamond wire sawn samples homogenises to a mainly weak tensile deformed state and that these homogenisation processes happen only up to certain critical temperatures. KW - silicon KW - lattice strain KW - Raman microscopy KW - phase transition Y1 - 2018 SP - S. 197 PB - Universität des Saarlandes CY - Saarbrücken ER - TY - GEN A1 - Grafe, Hans-Joachim A1 - Löser, Wolfgang A1 - Schmitz, Steffen A1 - Sakaliyska, Miroslava A1 - Wurmehl, Sabine A1 - Eisert, Stefan A1 - Reichenbach, Birk A1 - Acker, Jörg A1 - Rietig, Anja A1 - Ducke, Jana T1 - NMR investigation of boron impurities in refined metallurgical grade silicon T2 - Physica status solidi. A, Applications and Materials Science N2 - The nuclear magnetic resonance (NMR) method was applied for tracking boron impurities in the refining process of metallurgical grade (MG) silicon. From the NMR signal of the 11B isotope at an operating temperature 4.2 K, the boron concentration can be estimated down to the order of 110 wppm B. After melting and resolidification of MG-Si alloyed with Ca and Ti, a major fraction of B impurities remains in the Si solid solution as inferred from the characteristic NMR frequency. The alloying element Ti does not form substantial fractions of TiB2. Acid leaching of crushed powders of MG-Si alloyed with Ca and Ti can diminish the initial impurity content of B suggesting its accumulation in the grain boundary phases. KW - boron KW - impurity KW - intermetallic compounds KW - nuclear magnetic resonance KW - silicon KW - transition-metal diboride KW - Si-Al melt KW - removal KW - solidification Y1 - 2015 UR - http://onlinelibrary.wiley.com/doi/10.1002/pssa.201431908/full U6 - https://doi.org/10.1002/pssa.201431908 SN - 1862-6319 VL - 212 IS - 9 SP - 2031 EP - 2036 ER - TY - GEN A1 - Herold, Steven A1 - Acker, Jörg T1 - Strain enhanced chemical oxidation of silicon wafer T2 - Materials Science in Semiconductor Processing N2 - The effect of strain through mechanical processing on the formation of silicon dioxide, one of the most important chemical reactions for the fabrication of semiconductors, biosensors or photovoltaics, has not yet been studied in detail. In this study, we use the surface modification of silicon by alkylsilanes and Raman microscopy techniques to visualise where different oxidants react preferentially on mechanically processed surfaces. We found that HNO3, H2O2 as well as H2SiF6 only oxidise tensile strained silicon areas and do not oxidise unstrained silicon even after long reaction times. Furthermore, a comparison between H2O2 and HNO3 in the presence of HF was also carried out and it was shown that H2O2/HF only etches away tensile strained areas, whereas HNO3/HF initially attacks the tensile strained areas but also forms NOx species. These NOx species then lead to a strain unselective, geometry-based etching mechanism. These results lead to new possibilities in strain lithography,high-precision etching, as well as in the structuring of biosensors and localisation of surface modifications. KW - silicon KW - lattice strain KW - oxidation KW - Raman KW - confocal microscopy Y1 - 2021 U6 - https://doi.org/10.1016/j.mssp.2021.106105 SN - 1369-8001 VL - 135 ER - TY - GEN A1 - Meinel, Birgit A1 - Koschwitz, Tim A1 - Heinemann, Robert A1 - Acker, Jörg T1 - The texturization process during horizontal acidic etching of multi-crystalline silicon wafers T2 - Materials Science in Semiconductor Processing N2 - Horizontal wet-chemical etching of silicon wafers in an HF/HNO3/H2SiF6 mixture is the most widely-used technique to texturize multi-crystalline silicon wafers for solar cell production. For the first time, the etch rates were determined separately for the upper and lower side during the horizontal texturization and the their different morphologies. The dependency of the surface morphology from the etch rate and etch depth is proven. Furthermore, the influence of the temperature and stirring rates on the morphological development for the upper and lower side of the wafer were examined. From temperature-dependent measurements, activation energies in the range from 17 kJ/mol to 40 kJ/mol on the upper side and from 23 kJ/mol to 40 kJ/mol on the lower side dependent from the etching time were determined. The observed results reveal a connection between the etch depth, the agitation of the etch solution, the morphology and the reflectivity of the separate wafer sides. KW - Acidic etching KW - Surface properties KW - Confocal microscopy KW - Reflectivity KW - Activation energy KW - silicon KW - HF/HNO3 mixture KW - solar cell Y1 - 2014 UR - http://www.sciencedirect.com/science/article/pii/S136980011400482X U6 - https://doi.org/10.1016/j.mssp.2014.08.047 SN - 1369-8001 VL - 26 SP - 695 EP - 703 ER - TY - GEN A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - A revised model of silicon oxidation during the dissolution of silicon in HF/HNO₃ mixtures T2 - Physical chemistry, chemical physics N2 - The stoichiometry of wet chemical etching of silicon in concentrated HF/HNO₃ mixtures was investigated. The formation of nitrogen species enriched in the etching mixture and their reactivity during the etching process was studied. The main focus of the investigations was the comprehensive quantification of the gaseous reaction products using mass spectrometry. Whereas previously it could only be speculated that nitrogen was a product, its formation was detected for the first time. The formation of hydrogen, N₂, N₂O and NH₄⁺ showed a dependence on the etching bath volume used, which indicates the formation of nitrogen compounds by side reactions. Simultaneously, the ratio of the nitrogen oxides, NO and NO₂, formed decreases with increasing etching bath volume, while nitric acid consumption increases, so that the formation of NO₂ could also be identified as a side reaction. Based on the stoichiometries obtained, a new reaction scheme for the reduction of nitric acid during etching in HF/HNO₃ mixtures and an electron balance for the oxidation of silicon is presented. KW - silicon KW - etching KW - mechanism KW - nitrogen oxide KW - hydrogen KW - mass spectrometry KW - Raman spectroscopy KW - kinetics Y1 - 2019 UR - https://pubs.rsc.org/en/content/articlelanding/2019/CP/C9CP04429A#!divAbstract U6 - https://doi.org/10.1039/c9cp04429a SN - 1463-9076 VL - 21 SP - 22002 EP - 22013 ER - TY - GEN A1 - Brachmann, Erik A1 - Seifert, Marietta A1 - Neumann, Niels A1 - Alshwawreh, Nidal A1 - Uhlemann, Margitta A1 - Menzel, Siegfried A1 - Acker, Jörg A1 - Herold, Steven A1 - Hoffmann, Volker A1 - Gemming, Thomas T1 - Electroless-Deposited Platinum Antennas for Wireless Surface Acoustic Wave Sensors T2 - Materials N2 - In an effort to develop a cost-efficient technology for wireless high-temperature surface acoustic wave sensors, this study presents an evaluation of a combined method that integrates physical vapor deposition with electroless deposition for the fabrication of platinum-based planar antennas. The proposed manufacturing process becomes attractive for narrow, thick, and sparse metallizations for antennas in the MHz to GHz frequency range. In detail, narrow platinum-based lines of a width down to 40 μm were electroless-deposited on γ-Al2O3 substrates using different seed layers. At first, the electrolyte chemistry was optimized to obtain the highest deposition rate. Films with various thickness were prepared and the electrical resistivity, microstructure, and chemical composition in the as-prepared state and after annealing at temperatures up to 1100 ∘C were evaluated. Using these material parameters, the antenna was simulated with an electromagnetic full-wave simulation tool and then fabricated. The electrical parameters, including the S-parameters of the antenna, were measured. The agreement between the simulated and the realized antenna is then discussed. KW - wireless SAW sensor KW - high-temperature KW - antenna KW - electroless deposition KW - platinum film Y1 - 2019 UR - https://www.mdpi.com/1996-1944/12/7/1002 U6 - https://doi.org/10.3390/ma12071002 SN - 1996-1944 VL - 12 IS - 7 SP - 1002 EP - 1014 ER - TY - GEN A1 - Bücker, Stefan A1 - Hoffmann, Volker A1 - Acker, Jörg T1 - Determination of Fluorine by Molecular Absorption Spectrometry of AlF Using a High-Resolution Continuum Source Spectrometer and a C2H2/N2O Flame T2 - Current Analytical Chemistry N2 - The molecular absorption of the diatomic AlF molecule in the C2H2/N2O flame was studied using a highresolution continuum source flame atomic absorption spectrometer. AlF has a structured absorption spectrum in the range of 227.30 nm and 227.80 nm. From this band system, the remarkably narrow absorption band at 227.66 nm proved to be the optimum for analytical purposes. The signal intensity was studied as a function of the C2H2 : N2O ratio, the aspiration flow, and the aluminum concentration added to the analytical solution to generate the AlF molecules in the flame. The AlF molecule formation is significantly affected by the bonding state of the fluorine source used. Compared to ionic bound fluorine, organic bound fluorine leads to a markedly less sensitive molecular absorbance of AlF. Furthermore, several ions, such as Na+, K+ and NH4+, and acids, such as HCl, CH3COOH, and HNO3, affect the AlF signal intensity severely. It has to be concluded that the determination of fluorine by AlF F MAS only leads to reliable analytical results in simple matrices. KW - AlF KW - fluorine determination KW - high resolution continuum source absorption spectrometry KW - molecular absorption spectrometry KW - non-spectral interference KW - diatomic molecule Y1 - 2014 SN - 1573-4110 SN - 1875-6727 VL - 10 IS - 3 SP - 426 EP - 434 ER - TY - CHAP A1 - Acker, Jörg A1 - Ducke, Jana A1 - Rietig, Anja A1 - Müller, Tim A1 - Eisert, Stefan A1 - Reichenbach, Birk A1 - Löser, Wolfgang ED - Oye, Harald A. ED - Brekken, Harald ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard T1 - Segregation, grain boundary milling, and chemical leaching for the refinement of metallurgical-grade silicon for photovoltaic application T2 - Silicon for the Chemical and Solar Industry XII, Trondheim, 2014 N2 - The present work describes a completely new approach to the solidification refinement of metallurgical-grade silicon. The new process comprises the following steps: (i) The first step involves adding auxiliary metals to the molten silicon in order to segregate the metallic and non-metallic impurities in the secondary phase after cooling. (ii) The melt is rapidly cooled in the cellular solidification regime. This generates a Si microstructure with a defined cell size in which all cell boundaries are surrounded by the secondary phase. Furthermore, the secondary phase should form an interconnected three-dimensional network. (iii) The solids are crushed by shockwaves using electrohydraulic fragmentation techniques. The shockwaves lead to preferential crushing at the interface between the silicon and the secondary phase. (iv) The secondary phases are fast and effectively removed by microwave-assisted high-pressure leaching that was newly developed for this process. The potential of the new refinement procedure is demonstrated with auxiliary metals Ca, Al, and Ti. This new procedure yields a significant decrease in phosphorous and metal impurities. KW - silicon KW - leaching KW - hydrometallurgy KW - solar cell KW - segregation KW - etching Y1 - 2014 SN - 978-82-997357-8-0 SP - 177 EP - 188 PB - Department of Materials Science and Engineering, Norwegian University of Science and Technology CY - Trondheim ER - TY - GEN A1 - Hünger, Klaus-Jürgen A1 - Danneberg, Matti A1 - Herold, Steven A1 - Acker, Jörg T1 - Stress conditions in quartzite and their quantification by Raman spectroscopy T2 - Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete N2 - The silica solubility of aggregates is one of the most important components of the alkali-silica reaction. It is a surface-controlled process that always still requires more detailed studies to better understand the reaction mechanism. Since strained quartz releases more SiO2 into the pore solution, the properties of grains, crystals and their structure can should be directly quantified. In other work, various possibilities were tested for this purpose in order to obtain analyses of the surface and to correlate these with the mortar bar tests, for example. However, a quantifiable direct measurement of quartz crystal states with satisfactory results has not yet been performed. In this thesis polarization and reflected light microscopy in combination with Raman and confocal microscopy is used to obtain quantifiable data by direct measurement of the strained crystals. First measurements show new surprising signals besides the Raman main peak of the quartz. Such signals cannot be found on the whole sample, but only at places where strains are expected, e.g. at contact zones between different quartz crystals or cracks and sometimes inside of quartz grains too. Thus, a method may have been found to quantify the strained state of different quartz crystals in natural quartzite rocks. KW - ASR; quartzite; Raman microscopy; surface analysis Y1 - 2021 SN - 978-972-49-2315-4 SP - 185 EP - 192 PB - LNEC ER - TY - GEN A1 - Markowski, Jens A1 - Arellano-Garcia, Harvey A1 - Meissner, André A1 - Acker, Jörg T1 - Comparative studies on the quality of recovered secondary graphites from the recycling of lithium-ion traction batteries T2 - Sustainable Minerals N2 - Automotive technology is increasingly determined by drives based on electric motors in combination with batteries. The lithium-ion traction battery is a storage medium that combines high electrical efficiency with compact dimensions and relatively low weight. For the recycling of the cathode coatings (esp. Ni, Mn, Co) and peripheral battery components a variety of recycling options already exist. The graphite coating of the anodes has hardly been the focus of research activities to date. State of the art is currently the melting of the complete Copper-anode foils including graphite coating, whereby the graphite contributes only as a carbon carrier to the recycling of the copper. Separation and reuse of the very high-quality graphite on an industrial scale has not yet taken place. At the BTU, a methodology has been developed, with which recovered anode graphites from traction batteries can be comprehensively characterised chemically and mechanically-physically. On this basis, targeted preparation for secondary applications is possible. The secondary graphites achieve a quality that allows them to be reused as second-use anode material and for other applications. KW - Graphitrecycling KW - Li-Ionen-Traction Batteries Y1 - 2023 UR - https://www.ceecthefuture.org/resource-center/comparative-studies-on-the-quality-of-recovered-secondary-graphites-from-the-recycling-of-lithium-ion-traction-batteries PB - Mining Engineering CY - Falmouth (UK) ER - TY - GEN A1 - Meinel, Birgit A1 - Koschwitz, Tim A1 - Blocks, Christian A1 - Acker, Jörg T1 - Comparison of diamond wire cut and silicon carbide slurry processed silicon wafer surfaces after acidic texturisation T2 - Materials Science in Semiconductor Processing N2 - Our work focuses on the acidic etching of silicon wafers, cut via diamond wire (DW) or silicon carbide slurry process (SP). The DW and SP as-cut wafer surface structures have a significant impact on the evolution of the two resultant and different etched morphologies. The time-dependent development of the surface morphology for mono- and multi-crystalline wafers is compared and analyzed via etch rates, reflectivity measurements and confocal microscopy. The as-cut structure of the differently sawn wafers defines a template where the etch attack preferentially occurs and predetermines the texturisation of the etched surface. Based on the experimental results it is possible to lower the reflectivity of the SP-sawn wafers by varying the acidic mixture. On the contrary, the DW-sawn wafers obtain only a small enlargement of the folded surface area during acidic texturisation and no influence of different acidic etch solutions on the reflectivity values was found. To create homogeneously texturized DW-sawn wafers of low reflectivity, an adaptation of the sawing process as well as the development of new etchants and new etch conditions is necessary. KW - Surface morphology KW - Confocal microscopy KW - Acidic etching KW - Texturisation KW - Diamond wire sawing KW - Slurry sawing KW - silicon KW - solar cell KW - chemical analysis Y1 - 2014 UR - http://www.sciencedirect.com/science/article/pii/S1369800114001875 U6 - https://doi.org/10.1016/j.mssp.2014.03.046 SN - 1369-8001 VL - 26 SP - 93 EP - 100 ER - TY - CHAP A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - Dissolution of silicon in HF/HNO3 mixtures: A revised model T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - The dissolution of Si in HF/HNO3 consists of a set of complex reactions and thus a large number of reaction products. The most comprehensive picture of this reaction, the role of the involved reaction products and the reactivity of the HF/HNO3 mixtures depending on their composition is drawn by Steinert et al..[1]-[3] Based on the first systematic investigations on hydrogen formation by Hoffmann et al.[4], Acker et al. succeeded a first mass and electron balance for the reaction of silicon in HF/HNO3.[5] However, there is still a lack in interpretation of the mass end electron balances arising from several nitrous oxides. So far, the identified nitrogen oxides NO, NO2 and N2O were considered in sum[5] and neither separated nor individually studied or quantified. The aim of this work is to complete the mass and electron balance by the contribution of the individual nitrous oxides and to identify their individual formation pathways. Kinetic measurements of the NO and NO2 formation during the dissolution of Si, NO2 turns out as a result from the oxidation of the primary product NO by the HNO3 in the etching mixtures. Subsequently, NO and NO2 react to N2O3 dissolved in the acid mixture. The kinetics of both reactions were individually studied by bubbling NO in HF/HNO3 mixtures of different composition. The already identified intermediary species N4O62+ turns out to be formed by disproportionation of dissolved NO2 via N2O4 without dissolution of silicon. A detailed kinetic studied showed, that only dissolved N2O3 and not the intermediate N4O62+ contribute to the dissolution rate of silicon in HF/HNO3 acid mixtures. Finally, kinetic measurements revealed that the formed H2 reduces gaseous NO yielding to the final gaseous reaction products N2, N2O as well as to ammonium ions which all are formed with identical reaction rate. This reaction is assumed to proceed via NH2OH as intermediate. As result of the identification and quantification of intermediary and final reaction products a new reaction scheme needs to be established leading to a new approach to the mass and electron balance for the oxidation of silicon during the dissolution in HF/HNO3 mixtures. KW - silicon KW - etching KW - Raman spectroscopy KW - mass spectrometry KW - gas analysis KW - reaction mechanism Y1 - 2018 SP - S. 199 PB - Universität des Saarlandes CY - Saarbrücken ER - TY - GEN A1 - Herold, Steven A1 - Acker, Jörg ED - Zschech, Ehrenfried T1 - Analysis of the strain dependent acidic etch rate on diamond wire sawn silicon wafer T2 - 7th Dresden Nanoanalysis Symposium : “Nano-scale characterization for cutting-edge materials research and sustainable materials development”, Abstract booklet N2 - Processing of silicon in microelectronics, photovoltaics and micromechanics includes thermal and mechanical processing that can lead to a change in the silicon lattice, such as phase transitions or lattice deformations which have a crucial impact on the mechanical properties and the chemical resistance of silicon. In this work the correlation between lattice deformations and the etching of silicon using a HF/HNO3 solution is investigated. Here we use Raman microscopy to quantify and qualify strain on mechanically treated silicon, as well as confocal microscopy to measure the topography and to calculate the local etch rate. Additionally, a thermal treatment is used to selectively relax strained silicon for better understanding the effect of a selective kind of strain on the etching mechanism. Our results show that only in tensile strained areas, with a deformation strength of at least 2 cm-1, small cracks are formed within the first 10 seconds of etching. After all strained silicon is etched away the etch process mainly depends on the resulting surface texture. The enhanced oxidation rate of tensile strained silicon by nitric acid is also shown exemplary by the surface modification using nitric acid and trichloro(octyl)silane. Y1 - 2019 UR - https://www.nanoanalytik.fraunhofer.de/content/dam/nanoanalytik/de/documents/7th_Dresden_Nanoanalysis_Symposium_abstracts.pdf SP - 46 PB - Fraunhofer IKTS Dresden CY - Dresden ER - TY - GEN A1 - Langner, Thomas A1 - Sieber, Tim A1 - Acker, Jörg T1 - Studies on the deposition of copper in lithium-ion batteries during the deep discharge process T2 - Scientific Reports N2 - End-of-life lithium-ion batteries represent an important secondary raw material source for nickel, cobalt, manganese and lithium compounds in order to obtain starting materials for the production of new cathode material. Each process step in recycling must be performed in such a way contamination products on the cathode material are avoided or reduced. This paper is dedicated to the first step of each recycling process, the deep discharge of lithium-ion batteries, as a prerequisite for the safe opening and disassembling. If pouch cells with different states of charge are connected in series and deep-discharged together, copper deposition occurs preferably in the cell with the lower charge capacity. The current forced through the cell with a low charge capacity leads, after lithium depletion in the anode and the collapse of the solid-electrolyte-interphase (SEI) to a polarity reversal in which the copper collector of the anode is dissolved and copper is deposited on the cathode surface. Based on measurements of the temperature, voltage drop and copper concentration in the electrolyte at the cell with the originally lower charge capacity, the point of dissolution and incipient deposition of copper could be identified and a model of the processes during deep discharge could be developed. KW - lithium ion battery KW - discharge KW - continuum source AAS KW - REM-EXD KW - recycling Y1 - 2021 UR - https://www.nature.com/articles/s41598-021-85575-x U6 - https://doi.org/10.1038/s41598-021-85575-x SN - 2045-2322 IS - 11 ER - TY - GEN A1 - Spindler, Mario A1 - Herold, Steven A1 - Acker, Jörg A1 - Brachmann, Erik A1 - Oswald, Steffen A1 - Menzel, Siegfried A1 - Rane, Gerd T1 - Chemical etching of Tungsten thin films for high-temperature surface acoustic wave-based sensor devices T2 - Thin Solid Films N2 - Surface acoustic wave devices are widely used as wireless sensors in different application fields. Recent developments aimed to utilize those devices as temperature sensors even in the high temperature range (T > N 300 degrees C) and in harsh environmental conditions. Therefore, conventional materials, which are used for the substrate and for the interdigital transducer finger electrodes such as multilayers or alloys based on Al or Cu have to be exchanged by materials, which fulfill some important criteria regarding temperature related effects. Electron beam evaporation as a standard fabrication method is not well applicable for depositing high temperature stable electrode materials because of their very high melting points. Magnetron sputtering is an alternative deposition process but is also not applicable for lift-off structuring without any further improvement of the structuring process. Due to a relatively high Ar gas pressure of about 10(-1) Pa, the sidewalls of the photoresist line structures are also covered by the metallization, which subsequently prevents a successful lift-off process. In this study, we investigate the chemical etching of thin tungsten films as an intermediate step between magnetron sputtering deposition of thin tungsten finger electrodes and the lift-off process to remove sidewall covering for a successful patterning process of interdigital transducers. KW - SAW devices KW - Tungsten electrodes KW - Magnetron sputtering KW - Wet-chemical etching KW - Lift-off structuring Y1 - 2016 UR - http://www.sciencedirect.com/science/article/pii/S004060901630116X U6 - https://doi.org/10.1016/j.tsf.2016.04.035 VL - 612 SP - 322 EP - 326 ER - TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg ED - Nygaard, Lars ED - Pachaly, Bernd ED - Page, Ingrid Gamst ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard T1 - A new and fast method for determination of boron, phosphorus and other trace elements in metallurgical grade silicon T2 - Silicon for the Chemical and Solar Industry XIII, Kristiansand, 2016 N2 - A new method for accurate and precise determination of non-metallic and metallic impurities in silicon was developed and statistically validated. The first step is the fast dissolution of silicon in a microwave-assisted high pressure system to minimize a loss of phosphorus. The essential innovation is the use of the concentrated digestion solution for ICP-OES measurements. This approach avoids the common removal of the silicon and acid matrix by volatilization, which can cause considerable losses of boron. Finally, for the ICP-OES measurements in such high-silicon matrices the optimum measuring conditions were determined and a careful selection of emission lines with respect to selectivity, spectral and non-spectral inferences and matrix effects was performed. The method of matrix matched calibration (MMC) is used for quantification of the impurities’ contents. For Al, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zr and P the validation was performed against certified reference materials (IPT134, IPT135, NIST57b). To validate the determination of boron 9 silicon samples of different boron contents from three interlaboratory comparisons were used. The new procedure allows the determination of impurities of 4N-silicon (12 elements) with high precision and accuracy. KW - silicon KW - ICP-OES KW - impurity KW - chemical analysis KW - boron KW - phosphorus Y1 - 2016 UR - https://www.ntnu.no/trykk/publikasjoner/Silicon%20for%20the%20chemical%20and%20solar%20industry%20XIII/ SP - 95 EP - 106 PB - Department of Materials Science and Engineering, Norwegian University of Science and Technology CY - Trondheim ER - TY - GEN A1 - Sieber, Tim A1 - Ducke, Jana A1 - Rietig, Anja A1 - Langner, Thomas A1 - Acker, Jörg T1 - Recovery of Li(Ni0.33Mn0.33Co0.33)O2 from Lithium-Ion Battery Cathodes: Aspects of Degradation T2 - Nanomaterials N2 - Nickel–manganese–cobalt oxides, with LiNi0.33Mn0.33Co0.33O2 (NMC) as the most prominent compound, are state-of-the-art cathode materials for lithium-ion batteries in electric vehicles. The growing market for electro mobility has led to a growing global demand for Li, Co, Ni, and Mn, making spent lithium-ion batteries a valuable secondary resource. Going forward, energy- and resource-inefficient pyrometallurgical and hydrometallurgical recycling strategies must be avoided. We presented an approach to recover NMC particles from spent lithium-ion battery cathodes while preserving their chemical and morphological properties, with a minimal use of chemicals. The key task was the separation of the cathode coating layer consisting of NMC, an organic binder, and carbon black, from the Al substrate foil. This can be performed in water under strong agitation to support the slow detachment process. However, the contact of the NMC cathode with water leads to a release of Li+ ions and a fast increase in the pH. Unwanted side reactions may occur as the Al substrate foil starts to dissolve and Al(OH)3 precipitates on the NMC. These side reactions are avoided using pH-adjusted solutions with sufficiently high buffer capacities to separate the coating layer from the Al substrate, without precipitations and without degradation of the NMC particles. KW - lithium KW - nickel–manganese–cobalt oxide KW - NMC KW - leaching KW - recycling KW - SEM-EDX KW - Raman spectroscopy KW - lithium ion battery Y1 - 2019 UR - https://www.mdpi.com/journal/nanomaterials/special_issues/charact_nano UR - https://www.mdpi.com/2079-4991/9/2/246 U6 - https://doi.org/10.3390/nano9020246 SN - 2079-4991 VL - 9 IS - 2 SP - 246 EP - 259 ER - TY - GEN A1 - Langner, Thomas A1 - Rietig, Anja A1 - Acker, Jörg T1 - Raman spectroscopic determination of the degree of dissociation of nitric acid in binary and ternary mixtures with HF and H2SiF6 T2 - Journal of Raman Spectroscopy N2 - The oxidizing effect of nitric acid in aqueous solutions depends on the concentration of undissociated nitric acid. This makes the concentration of undissociated nitric acid an essential parameter to monitor and control the quality of silicon etching in the industrial manufacturing of solar cells. In the present study, a method known already is extended in such a way that the degree of dissociation of nitric acid can be determined by Raman spectroscopy in HF/HNO3/H2SiF6 acid mixtures over a broad concentration range for the first time and without using an internal or external standard to compensate the typical time‐dependent drift of a Raman spectrometer. The method developed requires the calculation of a peak area ratio from the areas of the unimpeded Raman signals assigned to nitrate (νN − O) at 1,048 cm−1 and to undissociated HNO3 (νN − OH) at 957 cm−1. The correlation between the peak ratio and the degree of dissociation of nitric acid revealed can be described by a simple empirical equation. Using this equation, the degree of dissociation of nitric acid can be determined over a broad concentration range in binary and ternary mixtures of HNO3 with HF and H2SiF6. The impact of the acids HF and H2SiF6 and the total water content in the degree of dissociation of nitric acid is discussed. KW - Raman spectroscopy KW - nitric acid KW - dissociation KW - hexafluosilicic acid KW - hydrofluoric acid KW - silicon KW - etching Y1 - 2020 U6 - https://doi.org/10.1002/jrs.5769 VL - 51 IS - 2 SP - 366 EP - 372 ER - TY - GEN A1 - Markowski, Jens A1 - Acker, Jörg A1 - Ducke, Jana A1 - Schelter, Matthias T1 - Recovery and secondary use of Nickel-Manganese-Cobalt-Material from Cathodes of electric car traction batteries T2 - 59th Annual Conference of Metallurgists : emerging technologies in materials and metallurgical industries : COM 2020 N2 - Automotive technology is increasingly determined by electric vehicles driven by high-performance lithium ion batteries (LIB). Li-ion batteries equipped with layered oxide cathodes, which are constituted by oxides of nickel, manganese and cobalt, are proven as storage devices that combine high electrical power, high cycling stability and compact dimensions. These batteries contain large amount of valuable elements, such as the cathodes consisting of cobalt and nickel, the electrode carrier foils consisting of copper and aluminium. Therefore, spent LIB’s are valuable secondary resources. Thermal processing as the classical recycling-technology for LIB’s is energy-intensive and allow only a partial recovery of some value elements. Scientists of the Brandenburg University of Technology (Germany) developed in collaboration with industrial partners (SME) a process, in which the complex system LIB is partly automated dismounted into its basic components. The core of this process is the separation of anodes and cathodes from each other and an almost complete recovery of the cathode material from the foil. The recovered cathode material has an enormous potential for a re-use in new LIB’s. By a proper combination of separation and post-treatment the material has a quality that is close to virgin cathode material. Preliminary studies made on LIB’s containing a fraction of recycled cathode material up to 50% show an electrical performance comparable to LIB’s made from virgin material. KW - Lithium-Ionen-Battery KW - NMC-Re-use Y1 - 2020 SN - 978-1-926872-47-6 VL - 2020 PB - Canadian Institute of Mining, Metallurgy and Petroleum ER - TY - GEN A1 - Langner, Thomas A1 - Sieber, Tim A1 - Rietig, Anja A1 - Merk, Virginia A1 - Pfeiffer, Lutz A1 - Acker, Jörg T1 - A Phenomenological and Quantitative View on the Degradation of Positive Electrodes from Spent Lithium-ion Batteries in Humid Atmosphere T2 - Scientific Reports N2 - The present study deals with the phenomenological observation of the corrosion of the positive electrode foil of lithium-ion batteries containing LiNi0.6Co0.2Mn0.2O2 (NMC) as cathode material. Due to the presence of moisture, localized water accumulation is formed on the NMC surface. The water absorbed by the electrolyte reacts with the NMC under Li+/H+ exchange and the resulting pH increase leads to dissolution of the carrier foil and characteristic salt-like blooms on the NMC surface. With the increase in the relative area occupied by the holes in the aluminum foil per time, a sufficiently suitable parameter was found with which to quantitatively determine the extent of corrosion. The degree of degradation depends on time and ambient humidity. It was shown that functional recycling with the water jet method is no longer applicable for degraded foils, since the mechanical stability of the foils decreases as corrosion progresses. Lithium, aluminum, sulfur and oxygen were detected in the blooms using SEM–EDX and Laser-Induced-Breakdown-Spectroscopy (LIBS). The underlying NMC layer was found to contain mainly aluminum and significantly lower lithium content than the non-degraded material. SEM and Raman microscopy analyses also showed that the active material is also locally degraded and therefore no longer suitable for functional recycling. KW - Analytical chemistry KW - lithium KW - cathode KW - materials KW - LIBS KW - Raman KW - SEM-EDX KW - degradation Y1 - 2023 U6 - https://doi.org/10.1038/s41598-023-32688-0 SN - 2045-2322 VL - 13 ER - TY - GEN A1 - Rietig, Anja A1 - Grafe, Hans-Joachim A1 - Acker, Jörg T1 - New insights into boron species in acidic digestion solutions of boron-doped silicon T2 - Journal of Analytical Atomic Spectrometry N2 - The exact and precise determination of the boron concentration in silicon is still a challenge. A systematic investigation dealing with the digestions of 60 silicon samples with HF-HNO3 and subsequent boron determination by ICP-OES revealed that the concentration found could be up to 60% lower than the actual boron concentration depending on the composition of the sample solution. As the original boron–silicon compound that was identified was colloidally precipitated in the presence of an excess of hydrofluoric acid and then partially retained by filtration or by the sample introduction system, systematic lower boron concentrations were determined. In acidic, HF-free digestion solutions, this compound existed in a soluble form parallel to the borate in B(OH)4−. In an excess of hydrofluoric acid, the compound was converted into the colloidal form and, in parallel, B(OH)4− was converted to tetrafluoroborate, BF4−. For the composition of the colloidal compound, a molar ratio of boron to silicon of 1 : 4 could be determined. 11B-ss-NMR analysis revealed a tetrahedral geometry compound with a central boron atom surrounded by four silicon atoms. It is assumed that a soluble form with four –Si(OH)3 groups was present in the hydrofluoric acid-free solutions, while an insoluble form with four –SiF3 groups was present in HF-containing solution. KW - silicon KW - ICP-OES KW - etching KW - hydrofluoric acid KW - nitric acid KW - 11B-NMR KW - high-precision chemical analysis KW - boron KW - digestion Y1 - 2021 UR - https://pubs.rsc.org/en/content/articlelanding/2021/ja/d1ja00190f SN - 1364-5544 VL - 36 IS - 11 SP - 2492 EP - 2500 ER - TY - GEN A1 - Sieber, Tim A1 - Rietig, Anja A1 - Ducke, Jana A1 - Acker, Jörg ED - Vogt, Carla T1 - Direkte Feststoffanalyse von Hauptkomponenten in Kathodenmaterialien von Lithiumbatterien mittels HRCS-GF-AAS T2 - Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts N2 - Zur Bestimmung der metallischen Hauptkomponenten in Lithium-Batterie-Kathodenmaterialien ist der nasschemische Aufschluss mit anschließender ICP-OES-Analyse oft das Mittel der Wahl. Da dieses Verfahren jedoch recht zeitaufwendig ist und den Einsatz starker Säuren erfordert, wurde eine Methode zur direkten Feststoffanalyse mittels HRCS-GF-AAS (high resolution continuum source graphit furnace atom absorption spectrometry) nach dem STPF-Konzept (stabilized temperature platform furnace) entwickelt. Die hohen Analytkonzentrationen erfordern dabei die Messung auf den vergleichsweise wenig intensiven Linien Li = 323,2657 nm, Ni = 294,3912 nm, Mn = 321,6945 nm und Co= 243,5823 nm. Zusätzlich wird das Probenmaterial einer Feststoffverdünnung mit matrixverwandten Komponenten unterzogen. Die Verdünnung senkt zum einen die Konzentration und die Gefahr der Verschleppung der Analyten und begünstigt zum anderen die Freigabe des Analyten aus der Probenmatrix. Durch Aufnahme von Extinktions-Zeit-Verläufen im Temperaturbereich von 200 - 2600 °C konnten die Freisetzungstemperaturen für jeden Analyten bestimmt werden. Nach anschließenden Optimierungen der Pyrolyse- und Atomisierungstemperaturen wurde mithilfe der Einzeloxide für jeden Analyten die Linearität des Messsignals geprüft und der Arbeitsbereich festgelegt. Durch Vermessung von variierenden Oxidmischungen und Mischoxiden, sowie Zusatz möglicher weiterer Interferenten, wie dem Bindermaterial PVDF wurden Spezifität, Selektivität und Robustheit der Methode überprüft. Abschließend erfolgte anhand realer Proben (Recyclinggut aus Lithium-Batterie-Kathoden) ein Vergleich zwischen den Ergebnissen der direkten Feststoffanalyse mittels HRCS-GF-AAS und dem bereits etablierten Verfahren der ICP-OES Analyse nach nasschemischem Aufschluss. Nach umfangreicher Methodenentwicklung kann ein Verfahren der direkten Feststoffanalyse von Recylinggut aus Kathodenmaterialien von Lithium-Ionen-Batterien mittels HRCS-GF-AAS bereitgestellt werden, das eine schnelle und präzise Analyse der Hauptkomponenten Li, Ni, Mn und Co erlaubt. KW - continuum source KW - AAS KW - Feststoffanalytik KW - Feststoffstandard KW - Graphitrohr KW - Interferenz KW - NMC KW - Recycling KW - Lithium KW - Batterie Y1 - 2019 UR - https://tu-freiberg.de/en/canas/canas-2019-engl/final-program VL - 2019 SP - S1/4 PB - TU Bergakademie Freiberg CY - Freiberg ET - 1. Auflage ER - TY - GEN A1 - Meinel, Birgit A1 - Langner, Thomas A1 - Preis, Pirmin A1 - Wefringhaus, Eckard A1 - Acker, Jörg T1 - A two-step acidic texturization procedure for the manufacture of lowreflective multi-crystalline silicon solar wafer T2 - Solar Energy N2 - Texturization of multi-crystalline silicon wafers for photovoltaic application comprises the removal of the saw damage and shaping the topography of the bulk surface to create a surface with a low reflectivity, the so-called texture. Etching of multi-crystalline silicon wafers is usually carried out with acid mixtures consisting of hydrofluoric acid (HF), nitric acid (HNO₃) and hexafluorosilicic acid (H₂SiF₆). The present study reveals that such acid mixtures diluted by water or modified by the addition of ammonia solution, NH₃ (added as ammonium hydroxide solution, NH₄OH) can create textures with a significantly increased surface area exceeding that obtained by standard etching mixtures by a factor of 2.5–3. This yields a significantly reduced reflectivity of the etched wafer surface. However, the addition of water or NH₃ causes a very low etching rate, which makes such mixtures inapplicable for industrial application. To overcome this disadvantage, a two-step etching regime was developed to produce surface-enlarged solar wafers within a timespan typical for industrial production lines. This procedure comprises a first step of slow etching with a NH₃-modified etching mixture to pre-shape the ascut wafer surface. The second etching step is performed with a typical HF/HNO₃/H₂SiF₆ etching mixture that finalizes the texturization. Electrical measurements made on solar cells produced from such etched wafer confirm the improved surface quality of the two-step etched wafer compared to the reference wafer. KW - acidic texturization KW - multi-crystalline silicon KW - reflectivity KW - solar cell parameter KW - topography KW - confocal microscopy Y1 - 2019 U6 - https://doi.org/10.1016/j.solener.2019.09.051 SN - 0038-092X VL - 193 SP - 395 EP - 402 ER - TY - GEN A1 - Rietig, Anja A1 - Acker, Jörg T1 - Development and validation of a new method for the precise and accurate determination of trace elements in silicon by ICP-OES in high silicon matrices T2 - Journal of Analytical Atomic Spectrometry N2 - A new method for the accurate and precise determination of impurities in silicon was developed and statistically validated. Particular attention was paid to the correct determination of the non-metals boron and phosphorus. Instead a time-consuming open vessel digestion under mild conditions, the dissolution of silicon took place in a microwave-assisted high-pressure system. The essential innovation of the presented method is the direct use of the concentrated digestion solution for ICP-OES measurements. This approach avoids the commonly used, time-consuming method that requires the removal of silicon and acid matrix by volatilisation, which is the most critical step in the determination of boron; however, the ICP-OES measurement in such high silicon matrices requires an entirely new optimisation of the measuring conditions, including the careful selection of emission lines with respect to selectivity and, spectral and non-spectral inferences. For quantification of the impurities contents, the methods of matrix matching (MMC) and multiple standard addition (MSA) were used. After optimisation of the spike concentrations for MSA, the qualities of both methods were compared through a statistical analysis. For the metallic impurities Al, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zr and P, the validation was performed against certified reference materials (IPT134, IPT135, NIST57b). To validate boron, 9 silicon samples with different contents of boron from three interlaboratory comparisons were used. The new procedure allows for the determination of the impurities of 4N-silicon (12 elements). KW - impurities KW - inductively coupled plasma emission spectroscopy KW - silicon KW - microwave-assisted digestion KW - high silicon matrix KW - multiple standard addition KW - boron KW - phosphorus Y1 - 2017 UR - http://pubs.rsc.org/en/content/articlelanding/2017/ja/c6ja00241b#!divAbstract U6 - https://doi.org/10.1039/C6JA00241B VL - 32 IS - 2 SP - 322 EP - 333 ER - TY - GEN A1 - Acker, Jörg A1 - Langner, Thomas A1 - Meinel, Birgit A1 - Sieber, Tim T1 - Saw Damage as an Etch Mask for the Acidic Texturization of Multicrystalline Silicon Wafers T2 - Materials Science in Semiconductor Processing N2 - The surface of multicrystalline silicon solar cells are etched by mixtures of HF, HNO3 and H2SiF6 in order to remove saw damage caused by wafer slicing, as well as to create a water surface topography that provides a low reflectance for incident light, otherwise known as the texture. Topographically analyzing wafer surfaces before and after etching has revealed that the saw damage controls the texturized wafer surface’s final topography.The first key factor is the dimension and magnitude of the plastic stress field introduced by indenting SiC grains into the wafer surface during the wafering process. The second key factor is that lattice-stressed silicon is etched at a higher rate than unstressed bulk silicon. At the wire entrance, side sharp and large SiC grains create the deepest indention pits, and therefore the deepest of the water surface stress fields. The lattice-disturbed silicon inside these pits is etched at a higher rate compared to the pit’s side walls, which are uniformly attacked across the wafer area. Consequentially, existing pits deepen, and these areas generate the wafer’s lowest reflectivity. At the wire exit side, a higher number of smaller and rounder SiC particles indent the surface and create more numerous and shallower indention pits compared to the wire entrance side. The resulting stress field is less deep, so less silicon is removed from inside of these pits during etching compared to the wire entrance side. This yields to a wafer surface region consisting of shallowly etched pits and higher reflectance. It is concluded that the saw damage acts like an etch mask in the texturization of multicrystalline silicon wafers. KW - silicon KW - texturization KW - acidic etching KW - multi-wire sawing KW - stress field KW - confocal microscopy KW - solar cell Y1 - 2018 UR - https://www.sciencedirect.com/science/article/pii/S1369800117313896 U6 - https://doi.org/10.1016/j.mssp.2017.09.039 SN - 1369-8001 VL - 74 SP - 238 EP - 248 ER - TY - GEN A1 - Ducke, Jana A1 - Acker, Jörg ED - Vogt, Carla T1 - Rückgewinnung von Platin, Palladium und Rhodium aus Autoabgaskatalysatoren: Bestimmung der Edelmetallgehalte im Eisensammler mittels ICP-OES T2 - Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts N2 - Fahrzeugkatalysatoren enthalten wertvolle Edelmetalle wie Platin (Pt), Palladium (Pd) und Rhodium (Rh), wodurch ausgediente und funktionsunfähige Katalysatoren zu einem begehrten Recyclinggut in einem hart umkämpften Marktsegment werden. Das häufigsten Aufbereitungsverfahren für Altkatalysatoren ist ein Schmelzprozess, in dem vorzerkleinerte Katalysatorfraktionen unter definierter Zugabe von Hilfsstoffen mit Kupfer als Kollektormetall aufgeschmolzen werden. Die Edelmetalle reichern sich im flüssigen Kupfer an, während alle anderen metallischen und nichtmetallischen Bestandteile eine oxidische Schlacke bilden. Ein Recyclingunternehmen im Bundesland Brandenburg hat diesen Prozess innovativ weiterentwickelt, indem es Eisen als Sammlermetall einsetzt. Eisen ist nicht nur preisgünstiger als Kupfer, es kann unter optimalen Schmelzbedingungen bis zu 9% an Edelmetallen aufnehmen, während Kupfer eine maximale Aufnahme von nur 5% besitzt. Zur Bestimmung der Edelmetallgehalte wird in diese Branche die Kupfer-Dokimasi mit anschließender ICP-OES-Analyse angewandt, was im Falle des Eisensammlers ein Umschmelzen der Proben zur Folge hätte. Eine Methode zur präzisen Quantifizierung der Edelmetallgehalte im Eisensammler existierte bisher nicht. Im Rahmen eines Forschungsprojektes wurde deshalb ein Bestimmungsverfahren zur zuverlässigen Bestimmung von Pt, Pd und Rh in einem Bereich von 0,1% bis 5% neben einem Eisengehalt von mehr als 80% mittels ICP-OES nach einem MW-Aufschluss entwickelt, dessen Vorteil sich neben einer deutlichen Zeitersparnis auch bezüglich des Einsatzes an Probenmaterial (für den Aufschluss) und Aufschlusschemikalien zeigt. Die analytischen Herausforderungen lagen in der Probenhomogenisierung zur repräsentativen Probenahme, in der Entwicklung eines Mikrowellen-Aufschlussverfahrens und in der Entwicklung einer Methode zur Präzisionsanalytik mittels ICP-OES. Besonderes Augenmerk wurde auf die Identifizierung von spektralen und nichtspektralen Interferenzen gelegt, die durch variierende Gehalte von Nebenkomponenten der Altkatalysatoren und durch das linienreiche Emissionsspektrum der Hauptkomponente Eisen verursacht werden. Es gelang ein zuverlässiges, präzises und kosteneffizientes Quantifizierungsverfahren für diese Edelmetalle in dieser besonderen Matrix zu entwickeln. KW - ICP-OES KW - Präzisionsanalytik KW - Mikrowellenaufschluss KW - Matrixeffekte KW - Platin KW - Eisen KW - Interferenzen KW - Palladium KW - Rhodium Y1 - 2019 UR - https://tu-freiberg.de/canas SP - S3/2 PB - TU Bergakademie Freiberg CY - Freiberg ET - 1. Auflage ER - TY - GEN A1 - Herold, Steven A1 - Acker, Jörg T1 - Lattice strain enhanced acidic etching on as cut sawn silicon wafer T2 - Materials Science in Semiconductor Processing N2 - The mechanical processing of silicon wafers leads to a heterogeneous lateral strain distribution and various modifications of the silicon, both of which influence the resulting topography after acid etching. In this study we investigate the influence of local strains and the initial topography of slurry and diamond wire saw wafers on the acid etching mechanism. The strain distribution is quantified and qualified by Raman microscopy before and after thermal treatment, while the topography is characterized by confocal microscopy before and after etching. The thermal treatment was used to selectively relax strains and investigate the effect of the individual strains on the etching mechanism. We found that amorphous silicon and compressive strained silicon are mainly present on the top most surface of the saw damage and do not influence the chemical reactivity of acid etching. In contrast, highly reactive tensile strained silicon is found up to 2.7 μm deep in the saw damage and acts as an etching mask. Rapid etching of the tensile strained silicon by HF/HNO3/H2SiF6 leads to the formation of cracks with high local concentrations of intermediate species. These strains induced cracks are etched out together with the original saw damage induced cracks and trenches and form the final surface after etching. Furthermore, we can show how the tensile strain strength must have a relative Raman shift of at least −2 cm−1 to have an effect on the local etch rate. Our data demonstrate how mechanical treatment in combination with thermal treatment and acidic etching can be used to optimize the resulting topography for applications like photovoltaics. In addition, it provides a deeper insight into the acid etching mechanism for non-planar silicon wafers. KW - silicon KW - lattice strain KW - Raman microscopy KW - confocal microscopy KW - etching KW - reactivity Y1 - 2021 UR - https://www.sciencedirect.com/science/article/abs/pii/S1369800120315080 U6 - https://doi.org/10.1016/j.mssp.2020.105575 SN - 1873-4081 SN - 1369-8001 VL - 123 ER - TY - GEN A1 - Acker, Jörg A1 - Bücker, Stefan A1 - Hoffmann, Volker T1 - The Formation of AlF Molecules and Al Atoms in a C2H2/N2O Flame Studied by Absorption and Emission Spectrometry of Molecules and Atoms T2 - Current Analytical Chemistry N2 - The absorption of the diatomic molecule AlF in the C2H2/N2O flame at 227.66 nm reveals an interesting feature. The calibration curve of the AlF absorption plotted against a rising concentration of hydrofluoric acid in solutions of constant aluminum content consists of two subsequent linear sections of different slopes. The bend position is reproducibly found at a molar fluorine-to-aluminum ratio of 3, calculated from the composition of the studied solutions. To explain this behavior, the most prominent aluminum flame species Al, AlF, and AlO were recorded as a function of the burner gas composition and flame observation height, using a high-resolution continuum source flame absorption spectrometer. As a result, the two-sectioned calibration curve is explained by two different pathways of AlF molecule formation: At a molar fluorine-to-aluminum ratio of below 3, aluminum is transported into the flame by two parallel pathways. One is the common pathway in absence of fluorine via the reduction of oxidic and/or carbidic species by the flame gases. The second pathway comprises the formation of gaseous AlF3 and its decomposition into AlF molecules and, subsequently, Al atoms. The fractionation of AlF3 releases Al atoms much faster than through the reduction of the oxidic and/or carbidic species. At molar fluorine-to-aluminum ratios of above 3, all aluminum is introduced to the flame via gaseous AlF3. A further increase of the hydrofluoric acid concentration increases the fluorine atom concentration in the flame, so that the AlF formation is determined by the recombination of aluminum and fluorine atoms. KW - AlF KW - AlF3 KW - AlO KW - diatomic molecule KW - high-resolution continuum source absorption spectrometry KW - molecular absorption spectrometry KW - molecular emission spectrometry KW - air-acetylene flame Y1 - 2014 SN - 1875-6727 SN - 1573-4110 VL - 10 IS - 3 SP - 418 EP - 425 ER - TY - GEN A1 - Meißner, André A1 - Sieber, Tim A1 - Acker, Jörg ED - Andresen, Birger ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard ED - Page, Ingrid T1 - Lattice strain and phase transformations in silicon introduced by the precipitation of Cu3Si T2 - Silicon for the Chemical and Solar Industry XV N2 - The reaction of Si with CuCl was studied by a combination of Raman microscopy, confocal microscopy and SEM-EDX. Two reaction pathways were observed to proceed at the same time. The first one is a solid state reaction between Si and Cu or CuCl that leads to a massive nucleation of Cu3Si exactly at the interfacial contacts between CuCl and Si. This study shows how the presence of the Cu3Si phase can be clearly identified and distinguished from areas simply covered with copper by means of Raman microscopic measurements. The second reaction pathway identified proceeds via a short-range gas phase transport of CuCl at low temperatures. The immediate reaction of the transported CuCl to the Si surface causes the massive spread of Cu in the close neighborhood around the CuCl source particles, however, without a nucleation of Cu3Si. The nucleation of Cu3Si precipitates and the short-range transport of CuCl have a tremendous impact on the underlying Si matrix. Tensile- and compressive-strained Si are generated in the immediate vicinity of the precipitates and at their interface to the surrounding silicon. Indications of high-pressure modifications of Si were found. Those areas of the Si surface which are affected by the short-range transport of CuCl and covered with low concentrations of copper exhibit a significant tensile strain. As recently shown, tensile and compressive strain in Si have a significant impact on the reactivity of Si. It might be assumed that Cu3Si-induced lattice strain in Si affects the reactivity of Si in the Direct Reactions in a similar matter. KW - silicon KW - direct synthesis KW - copper silicide KW - cuprous chloride KW - Raman KW - lattice strain KW - reactivity Y1 - 2020 SN - 978-82-997357-9-7 SP - 47 EP - 56 PB - The Norwegian University of Science and Technology CY - Trondheim ER - TY - GEN A1 - Langner, Thomas A1 - Sieber, Tim A1 - Acker, Jörg T1 - Etching Shapes the Topography of Silicon Wafers: Lattice-Strain Enhanced Chemical Reactivity of Silicon for Efficient Solar Cells T2 - ACS Applied Nano Materials N2 - Multiwire sawing of silicon (Si) bricks is the state-of-the-art technology to produce multicrystalline Si solar wafers. The massive indentation of the abrasive Si carbide or diamond particles used leads to a heavily mechanically damaged layer on the wafer surface. Etching the surface layer using typical HF–HNO3–H2SiF6 acid mixtures reveals an unevenly distributed etch attack with etch rates several times higher than known for bulk Si etching. The present study follows the hypothesis that lattice strain, introduced by the sawing process, leads to an increase of the etch rate and determines the topography of the etched wafer, the so-called texture. Scratches were introduced into single crystalline Si surfaces in model experiments, and the magnitude and local distribution of lattice strain were extracted from confocal Raman microscopy measurements. The essential parameter used to describe the local reactivity of Si is the local etch rate, which was derived by confocal microscopy from the local height before and after etching. It was found that the reactivity of Si increases linearly with the magnitude of lattice strain. An increase in tensile strain raises the reactivity of Si significantly higher than an increase of compressive strain. The second decisive parameter is the reactivity of the etch mixture that correlates with the total concentration of the acid mixtures. Diluted acid mixtures with a low reactivity attack only the highest strained Si, whereas more concentrated and, therefore, more reactive acid mixtures can attack even slightly strained Si. Side effects, such as the behavior of amorphous or nanocrystalline Si and the generation of highly reactive intermediary species while etching, are discussed. The presence of unevenly distributed lattice strain of different magnitude and the resulting unevenly distributed reactivity of Si explain the features of a heterogeneous etch attack observed and the resulting topography of the etched wafer surface. KW - lattice strain KW - silicon KW - Raman microscopy KW - confocal microscopy KW - etching KW - reactivity KW - solar cell KW - mechanochemistry Y1 - 2018 U6 - https://doi.org/10.1021/acsanm.8b00906 VL - 1 IS - 8 SP - 4135 EP - 4144 ER - TY - CHAP A1 - Langner, Thomas A1 - Sieber, Tim A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - Lattice strain controls the etching of solar wafer surfaces T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - Multi-wire sawing using an abrasive SiC slurry or diamond wires constitutes the main slicing techniques for multi- and monocrystalline silicon crystals in photovoltaics. The massive mechanical load during the sawing process creates a wafer surface layer characterized by lattice defects, pits, fractures, rifts, cracks, amorphous Si and even some high-pressure Si modifications, otherwise known as saw damage.[1] This highly defect-rich surface causes the rapid recombination of electron-hole pairs, requiring that it be removed by etching in order to manufacture solar cells and to generate a surface morphology having a low reflectivity which directly affects the solar cell’s efficiency. However, etching of the saw damage features of a heterogeneous and laterally unevenly distributed etch attack and a significantly higher etch rate compared to the underlying bulk silicon.[2,3] The present study is focused on the question of how mechanically introduced lattice strain in single-crystalline silicon alters the chemical reactivity of the silicon atoms affected by the strain field on a microscopic length scale. The magnitude and local distribution of lattice strain were extracted from confocal Raman microscopy measurements according to Ref. 4. One of the parameters used to describe the reactivity of silicon is the local etch rate, which was derived from the local removal before and after etching by confocal microscopy. Wet-chemical etching was performed with HF-HNO3-H2SiF6 acid mixtures of different concentrations. It was found, that the reactivity of silicon increased linearly with the magnitude of lattice strain. In particular, an increase in tensile strain led to a higher increase in reactivity compared to the increase observed with growing compressive strain. The second decisive parameter is the reactivity of the etch mixture. Diluted acid mixtures with a low reactivity attack only the highest strained Si, whereas more concentrated and therefore more reactive acid mixtures are able to attack even slightly strained Si. Side effects, such as the behavior of amorphous or nanocrystalline Si and the generation of highly reactive intermediary species while etching, are discussed. KW - Raman spectroscopy KW - silicon KW - lattice strain KW - etching KW - confocal microscopy Y1 - 2018 SP - S. 201 PB - Universität des Saarlandes CY - Saarbrücken ER - TY - CHAP A1 - Meißner, André A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - Raman spectroscopic study on the formation of Cu3Si T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - The term “direct synthesis” is defined in the literature as the reactions between silicon and methyl chloride, hydrogen chloride and other reagents like chlorobenzene and ethyl chloride to yield various alkyl- or aryl substituted chlorosilanes.[1] These reactions have two features in common: (1) The reactivity of silicon - in terms of reaction start temperature, reaction rate and silane product distribution - is originated and controlled by the interaction with metals. (2) The reaction is fully under kinetic control since the formed silanes are the thermodynamically least stable products in the system Si-H-Cl-C.[2] Several authors consider Cu3Si as the catalytically active phase in the direct synthesis. It is assumed, that CuCl formed under the conditions of the direct synthesis reacts with Si according to Eq. 1 and 2 to yield Cu3Si.[1] (1) and (2) The present work describes a Raman microscopic study of the reaction of Si with Cu and CuCl with special emphasize given to the identification of the Cu3Si phase and the processes occurring in the surrounding bulk Si. There is one pathway in which a solid state reaction[3] between Si and CuCl leads to a massive nucleation of Cu3Si exactly at the position of the Si/CuCl solid-solid interface. The nucleation of Cu3Si creates such an enormous lattice strain so that several high-pressure modifications of Si can be identified at the reaction site and around. The second reaction pathway is controlled by a gas phase transport of CuCl at low temperatures. This transport pathway leads to a spread of Cu in nearest neighborhood close to the CuCl particles as well to a long range transport leading to a nucleation of microscopic Cu3Si precipitates away from the CuCl particles. Further studies on the reactivity of the Cu3Si containing reaction sites were performed and will be discussed in the presentation. KW - Raman spectroscopy KW - silicon KW - lattice strain KW - copper silicide KW - direct synthesis Y1 - 2018 PB - Universität des Saarlandes CY - Saarbrücken ER - TY - CHAP A1 - Sieber, Tim A1 - Ducke, Jana A1 - Acker, Jörg ED - Zschech, Ehrenfried T1 - Degradation of Li(Ni₀.₃₃MnCo₀.₃₃)O₂ in the recycling of lithium battery cathodes T2 - 6th Dresden Nanoanalysis Symposium - Abstract Booklet N2 - The compound Li(Ni₀.₃₃Mn₀.₃₃Co₀.₃₃)O₂(NMC) is the state-of-the-art lithium-ion battery cathode material. Due to the increasing demand NMC is of crucial economically importance for the worldwide emerging market of electromobility. Recycling of end-of-life lithium-ion batteries to recover NMC, in particular of batteries from automotive vehicles, is one future strategy to save costs and to become more independent from the supply of the essential elements Co and Mn. Several concepts for NMC recycling from lithium-ion batteries are based on wet-chemical process steps, in particular, to separate the NMC containing cathode layer from the underlying metal foil. However, NMC is very sensitive against the attack by water and reagents that are added to promote the separation process. The present study deals with the wet-chemical recycling of NMC using aqueous reagent solutions in a under varying process conditions. The recovered NMC samples are characterized in order to study the ongoing degradation at the surface of the NMC particles. In particular, two major degradation pathways are identified: (i) a preferential loss of lithium and nickel and (ii) the formation of passivation layers due to unwanted side reactions. DRIFT measurements are performed to study the NMC surface species after the recovery processes. SEM/EDX mappings are used to detect changes in the chemical composition in the surface region of the chemically treated NMC particles. Finally, a detailed study of the changes in the chemical state at the NMC particle surface is done by Raman microscopy by means of the deconvolution of the recorded spectra into their A1G component (representing the metal-oxide phonons) and into the Eg component (representing the oxide-metal-oxide phonons). As result of this study, the consequences of different wet-chemical process conditions on the quality of the recovered NMC material are discussed. KW - lithium battery KW - recycling KW - nickel manganese cobalt oxide KW - degradation KW - Raman microscopy KW - chemical analysis Y1 - 2018 UR - https://www.nanoanalytik.fraunhofer.de/content/dam/nanoanalytik/de/documents/6th_Dresden_Nanoanalysis_Symposium_abstracts.pdf SP - S. 52 PB - Fraunhofer IKTS Dresden CY - Dresden ER - TY - GEN A1 - Schönekerl, Stefan A1 - Acker, Jörg T1 - The Role of the Molecular Hydrogen Formation in the Process of Metal Ion Reduction on Multi-crystalline Silicon in a Hydrofluoric Acid Matrix T2 - Nanomaterials N2 - Metal deposition on silicon in hydrofluoric acid (HF) solutions is a well-established process for the surface patterning of silicon. The reactions behind this process, especially the formation or the absence of molecular hydrogen (H2) are controversially discussed in the literature. In this study, several batch experiments with Ag+, Cu2+, AuCl4– and PtCl62– in HF matrix and multi-crystalline silicon were performed. The stoichiometric amounts of the metal depositions, the silicon dissolution and the molecular hydrogen formation were determined analytically. Based on these data and theoretical considerations of the valence transfer, four reasons for the formation of H2 could be identified. Firstly, H2 is generated in a consecutive reaction after a monovalent hole transfer (h+) to a Si–Si bond. Secondly, H2 is produced as a result of a monovalent hole transfer to the Si–H bonds. Thirdly, H2 occurs if Si–Si back bonds of the hydrogen-terminated silicon are attacked by Cu2+ reduction resulting in the intermediate species HSiF3, which is further degraded to H2 and SiF62–. The fourth H2-forming reaction is the reduction of oxonium ions (H3O+) on the silver/, copper/ and gold/silicon contacts via monovalent hole transfer to silicon. In the case of (cumulative) even-numbered valence transfers to silicon, no H2 is produced. The formation of H2 also fails to appear if the equilibrium potential of the 2H3O+/H2 half-cell does not reach the energetic level of the valence bands of the bulk or hydrogen-terminated silicon. Non-hydrogen-forming reactions in silver, copper and gold deposition always occur with at least one H2-forming process. The PtCl62– reduction to Pt proceeds exclusively via even-numbered valence transfers to silicon. This also applies to the reaction of H3O+ at the platinum/silicon contact. Consequently, no H2 is formed during platinum deposition. KW - molecular hydrogen KW - metal deposition KW - silicon KW - etching KW - hydrofluoric acid KW - reaction kinetics KW - dissolution KW - chemical analysis Y1 - 2021 UR - https://www.mdpi.com/2079-4991/11/4/982 U6 - https://doi.org/10.3390/nano11040982 SN - 2079-4991 VL - 11 IS - 4 ER - TY - GEN A1 - Acker, Jörg A1 - Sieber, Tim A1 - Ducke, Jana A1 - Langner, Thomas A1 - Rietig, Anja T1 - Degradation effects on Li(Ni0.33Mn0.33Co0.33)O2 in the recovery of lithium battery cathodes T2 - Advanced Lithium Batteries for Automobile Applications - ABAA 12, Book of Abstracts N2 - The compound Li(Ni0.33Mn0.33Co0.33)O2 (NMC) is the state-of-the-art lithium-ion battery cathode material. Due to the increasing demand NMC is of crucial economically importance for the worldwide emerging market of electromobility. Recycling of end-of-life lithium-ion batteries to recover NMC, in particular of batteries from automotive vehicles, is one future strategy to save costs and to become more independent from the supply of the essential elements Co and Mn. Several concepts for NMC recycling from lithium-ion batteries are based on wet-chemical process steps, in particular, to separate the NMC containing cathode layer from the underlying metal foil. However, NMC is very sensitive against the attack by water and reagents that are added to promote the separation process. The present study deals with the wet-chemical recycling of NMC using aqueous reagent solutions in a under varying process conditions. The recovered NMC samples are characterized in order to study the ongoing degradation at the surface of the NMC particles. In particular, two major degradation pathways are identified: (i) a preferential loss of lithium and nickel and (ii) the formation of passivation layers due to unwanted side reactions. DRIFT measurements are performed to study the NMC surface species after the recovery processes. SEM/EDX mappings are used to detect changes in the chemical composition in the surface region of the chemically treated NMC particles. Finally, a detailed study of the changes in the chemical state at the NMC particle surface is done by Raman microscopy by means of the deconvolution of the recorded spectra into their A1G component (representing the metal-oxide phonons) and into the Eg component (representing the oxide-metal-oxide phonons). As result of this study, the consequences of different wet-chemical process conditions on the quality of the recovered NMC material are discussed. KW - lithium ion battery KW - recycling KW - NMC KW - electromobility KW - degradation KW - Raman spectroscopy KW - cathode Y1 - 2019 SP - 28 PB - Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg CY - Ulm ET - 1. Auflage ER - TY - CHAP A1 - Acker, Jörg A1 - Langner, Thomas A1 - Koschwitz, Tim ED - Marciniec, Bogdan T1 - Lattice-strain induced chemical reactivity of silicon T2 - 8th European Silicon Days 2018, Conference Proceedings N2 - Silicon wafer for solar application are produced by multi-wire sawing from 12x12 cm2 silicon bricks. After slicing the wafer surface consists of a several micrometer surface layer of very heterogeneous constitution, the so called saw damage. The topmost layer of the saw damage consists of debris, amorphous silicon and high-pressure silicon phases followed by a very defect-rich and lattice-strained region of fractures, cracks, and rifts caused by the rupture of the silicon lattice during the slicing process [1,2]. Such a damaged surface exhibits very poor semiconductor properties; therefore the saw damage is removed by chemical etching using mixtures of HF, HNO3 and H2SiF6 in order to produce solar cells. Recent investigations showed that the etching of the saw damage is a very heterogeneous process [3-5]. The surface consists of spots at which the etching forms very rapidly deep grooves while other spots remain unetched over a considerably long time. Some of the rapidly formed grooves seem to remain their shape while others grow because of an attack of the side walls, however, without making these grooves significantly deeper. So far there is no explanation for this behavior. The present work is the first study about the locally resolved etching behavior of lattice-strained silicon. The surface of polished single-crystal wafers were scratched with a diamond tip under defined conditions. By means of confocal Raman microscopy the local state of the silicon lattice in and nearby the scratches were characterized in terms of compression and tensile stress with a lateral resolution of 2 μm. Then, the scratches were etched stepwise using HF-HNO3-H2SiF6 mixtures and measured by confocal microscopy to quantify the local removal of silicon and measured by confocal Raman microscopy to monitor the lattice state. For the first time this study reveals and quantifies the impact of tensile and compressive lattice stress on the etch rate of silicon with the major outcome, that stress leads to a significantly anisotropic etching behavior. From the time dependent development of the scratch profiles and the topography of the surrounding wafer areas a detailed picture about the formation of highly reactive species and etching behavior against unstrained silicon is deduced. KW - silicon KW - lattice strain KW - reactivity KW - etching KW - Raman microscopy KW - confocal microscopy Y1 - 2016 SP - S. 124 PB - Wielkopolska Centre for Advanced Technologies, Adam Mickiewicz University CY - Poznań, Poland ER - TY - GEN A1 - Acker, Jörg A1 - Bücker, Stefan A1 - Hoffmann, Volker T1 - Impact of the chemical form of different fluorine sources on the formation of AlF molecules in a C2H2/N2O flame T2 - Journal of Analytical Atomic Spectrometry N2 - The formation of diatomic AlF molecules was studied in a C2H2/N2O flame by means of a high-resolution continuum source flame absorption spectrometer using different fluorine containing compounds HF, H2SiF6, HBF4 and CF3COOH as fluorine sources. The fragmentation of these fluorine sources, as well the resulting impact on the AlF molecule formation, was derived from flame height distribution studies of the atomic and molecular species Al, AlO, Si, SiO, SiF, B and BF as a function of the fluorine concentration, the molar Al : F ratio and the burner gas composition. As a consequence, the used fluorine sources HF, H2SiF6, HBF4 and CF3COOH have been divided into two major groups. The first group of fluorine sources, covering HF, H2SiF6 and HBF4, decomposes during the drying of the aerosol under the formation of AlF3, which is the dominating species for the transport of aluminium into the flame. Its decomposition into AlF results in a high sensitivity of AlF molecular absorption at low flame observation heights. The second group of fluorine sources is exemplarily given by CF3COOH. In the upper parts of the flame the cleavage of the very stable C–F bond proceeds incompletely so that the sensitivity of the AlF molecular absorption is considerably lower than that for the other fluorine sources. In consequence, the AlF molecules are formed by the reaction between the fluorine atoms and the aluminium atoms, which are transported into the flame without the aid of fluorine, presumably via oxidic and/or carbidic species. The present investigations show that the sensitivity of the AlF molecular absorption and the pathway of AlF formation depend on the chemical form of the fluorine in the studied samples. KW - flame molecular absorption spectrometry KW - diatomic molecule KW - aluminum monofluoride KW - C2H2/N2O flame KW - hexafluorosilicic acid KW - tetrafluoro boric acid KW - trifluoro acetic acid KW - species fragmentation Y1 - 2016 UR - http://pubs.rsc.org/en/Content/ArticleLanding/2016/JA/C5JA00470E#!divAbstract U6 - https://doi.org/10.1039/C5JA00470E SN - 0267-9477 SN - 1364-5544 VL - 31 SP - 902 EP - 911 ER - TY - GEN A1 - Schönekerl, Stefan A1 - Acker, Jörg T1 - The Kinetics and Stoichiometry of Metal Cation Reduction on Multi-Crystalline Silicon in a Dilute Hydrofluoric Acid Matrix T2 - Nanomaterials N2 - In this study, the process of metal cation reduction on multi-crystalline silicon in a dilute hydrofluoric acid (HF) matrix is described using Ag(I), Cu(II), Au(III) and Pt(IV). The experimental basis utilized batch tests with various solutions of different metal cation and HF concentrations and multi-crystalline silicon wafers. The metal deposition kinetics and the stoichiometry of metal deposition and silicon dissolution were calculated by means of consecutive sampling and analysis of the solutions. Several reaction mechanisms and reaction steps of the process were discussed by overlaying the results with theoretical considerations. It was deduced that the metal deposition was fastest if the holes formed during metal ion reduction could be transferred to the valence bands of the bulk and surface silicon with hydrogen termination. By contrast, the kinetics were lowest when the redox levels of the metal ion/metal half-cells were weak and the equilibrium potential of the H3O+/H2 half-cells was high. Further minima were identified at the thresholds where H3O+ reduction was inhibited, the valence transfer via valence band mechanism was limited by a Schottky barrier and the dissolution of oxidized silicon was restricted by the activity of the HF species F−, HF2− and H2F3−. The findings of the stoichiometric conditions provided further indications of the involvement of H3O+ and H2O as oxidizing agents in addition to metal ions, and the hydrogen of the surface silicon termination as a reducing agent in addition to the silicon. The H3O+ reduction is the predominant process in dilute metal ion solutions unless it is disabled due to the metal-dependent equilibrium potential of the H3O+/H2 half-cell and the energetic level of the valence bands of the silicon. As silicon is not oxidized up to the oxidation state +IV by the reduction of the metal ions and H3O+, water is suspected of acting as a secondary oxidant. The stoichiometric ratios increased up to a maximum with higher molalities of the metal ions, in the manner of a sigmoidal function. If, owing to the redox level of the metal half-cells and the energetic level of the valence band at the metal–silicon contact, the surface silicon can be oxidized, the hydrogen of the termination is the further reducing agent. KW - silicon KW - etching KW - metal-assisted etching KW - kinetics KW - hydrofluoric acid KW - dissolution Y1 - 2020 UR - https://www.mdpi.com/2079-4991/10/12/2545 U6 - https://doi.org/10.3390/nano10122545 SN - 1747-681X VL - 10 IS - 12 ER - TY - CHAP A1 - Schönekerl, Stefan A1 - Acker, Jörg ED - Scheschkewitz, David ED - Kickelbick, Guido T1 - Behavior of electroless copper deposition onto multi-crystalline silicon in diluted hydrofluoric acid solutions T2 - 9th European Silicon Days, 9-12 September 2018, Saarbrücken, Germany, Book of abstracts N2 - The metal-assisted etching of Si is a method which has been studied for many years with regard to the creation of nanoscale surface structures, but much less research was done to elucidate the reaction processes. Most publications argue that either reduction of the metal cation could result in double charge transfer with concomitant hydrogen release or four-fold charge transfer without H2 formation [1]. Following, SiO2 is to be formed, which is subsequently converted into H2SiF6 by F-, HF2- or HF [2]. Due to the few reliable findings, own experiments were carried out. In this context, the deposition of Cu on multi-crystalline Si at various Cu2+ activities and different HF levels was investigated, and the H2 emission for these processes analysed. The results of the series of experiments indicate a different reaction behavior from the theory described above. Apparently, a slightly higher redox potential of the Cu2+/Cu+ half-cell compared to 2H+/H2 redox couple is sufficient to initiate the silicon dissolution process. The stoichiometric ratio between Cu deposition and Si dissolution process is strongly affected by the Cu2+ activity, but it is obviously not influenced by HF activity. At Cu2+ activities of < 2∙10-5 mol/kg less than one electron is nominally exchanged between metal cation and Si, and at activities of approx. 1∙10-2 mol/kg there is an almost four electron charge transfer. At activities > 1∙10-2 mol/kg the stoichiometric ratio and the Cu deposition and Si dissolution kinetics decrease, presumably due to the fact the compact Cu layer inhibits the transition of the dissolved Si into the etching solution. The shift in the stoichiometric ratio suggests the first Cu2+ based oxidative attack on Si enables the reaction of a further oxidizing agent. It is likely water will attack the silicon as second oxidant, since there is no dependence between the content of HF species in the etching solutions and the Si dissolution kinetics. This second reaction step seems to be associated with hydrogen evolution. The amount of hydrogen formation indicates that at a Cu2+ activity of < 2∙10-5 mol/kg calculative only one electron is transferred from Si to Cu2+ and H+, and at a Cu2+ activity of 1∙10-2 mol/kg four electrons in total. However, HF is necessary to convert the oxidized Si to the supposed formation of H3SiF, H2SiF2, HSiF3, and SiF4 and H2SiF6 respectively. KW - silicon KW - metal assisted etching KW - deposition KW - copper KW - dissolution Y1 - 2018 SP - S. 82 PB - Universität des Saarlandes CY - Saarbrücken ER -