@misc{MeinelKoschwitzHeinemannetal., author = {Meinel, Birgit and Koschwitz, Tim and Heinemann, Robert and Acker, J{\"o}rg}, title = {The texturization process during horizontal acidic etching of multi-crystalline silicon wafers}, series = {Materials Science in Semiconductor Processing}, volume = {26}, journal = {Materials Science in Semiconductor Processing}, issn = {1369-8001}, doi = {10.1016/j.mssp.2014.08.047}, pages = {695 -- 703}, abstract = {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.}, language = {en} } @misc{BueckerHoffmannAcker, author = {B{\"u}cker, Stefan and Hoffmann, Volker and Acker, J{\"o}rg}, title = {Determination of Fluorine by Molecular Absorption Spectrometry of AlF Using a High-Resolution Continuum Source Spectrometer and a C2H2/N2O Flame}, series = {Current Analytical Chemistry}, volume = {10}, journal = {Current Analytical Chemistry}, number = {3}, issn = {1573-4110}, pages = {426 -- 434}, abstract = {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.}, language = {en} } @inproceedings{AckerDuckeRietigetal., author = {Acker, J{\"o}rg and Ducke, Jana and Rietig, Anja and M{\"u}ller, Tim and Eisert, Stefan and Reichenbach, Birk and L{\"o}ser, Wolfgang}, title = {Segregation, grain boundary milling, and chemical leaching for the refinement of metallurgical-grade silicon for photovoltaic application}, series = {Silicon for the Chemical and Solar Industry XII, Trondheim, 2014}, booktitle = {Silicon for the Chemical and Solar Industry XII, Trondheim, 2014}, editor = {Oye, Harald A. and Brekken, Harald and Rong, Harry and Tangstad, Merete and Tveit, Halvard}, publisher = {Department of Materials Science and Engineering, Norwegian University of Science and Technology}, address = {Trondheim}, isbn = {978-82-997357-8-0}, pages = {177 -- 188}, abstract = {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.}, language = {en} } @inproceedings{RietigAcker, author = {Rietig, Anja and Acker, J{\"o}rg}, title = {A new and fast method for determination of boron, phosphorus and other trace elements in metallurgical grade silicon}, series = {Silicon for the Chemical and Solar Industry XIII, Kristiansand, 2016}, booktitle = {Silicon for the Chemical and Solar Industry XIII, Kristiansand, 2016}, editor = {Nygaard, Lars and Pachaly, Bernd and Page, Ingrid Gamst and Rong, Harry and Tangstad, Merete and Tveit, Halvard}, publisher = {Department of Materials Science and Engineering, Norwegian University of Science and Technology}, address = {Trondheim}, pages = {95 -- 106}, abstract = {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.}, language = {en} } @misc{AckerLangnerMeineletal., author = {Acker, J{\"o}rg and Langner, Thomas and Meinel, Birgit and Sieber, Tim}, title = {Saw Damage as an Etch Mask for the Acidic Texturization of Multicrystalline Silicon Wafers}, series = {Materials Science in Semiconductor Processing}, volume = {74}, journal = {Materials Science in Semiconductor Processing}, issn = {1369-8001}, doi = {10.1016/j.mssp.2017.09.039}, pages = {238 -- 248}, abstract = {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.}, language = {en} } @misc{SieberDuckeRietigetal., author = {Sieber, Tim and Ducke, Jana and Rietig, Anja and Langner, Thomas and Acker, J{\"o}rg}, title = {Recovery of Li(Ni0.33Mn0.33Co0.33)O2 from Lithium-Ion Battery Cathodes: Aspects of Degradation}, series = {Nanomaterials}, volume = {9}, journal = {Nanomaterials}, number = {2}, issn = {2079-4991}, doi = {10.3390/nano9020246}, pages = {246 -- 259}, abstract = {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.}, language = {en} } @misc{HeroldAcker, author = {Herold, Steven and Acker, J{\"o}rg}, title = {Measurement of the temperature dependence of lattice deformations in silicon using Raman microscopy}, series = {Journal of Applied Physics}, volume = {126}, journal = {Journal of Applied Physics}, issn = {1089-7550}, doi = {10.1063/1.5090476}, pages = {7}, abstract = {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.}, language = {en} } @misc{RietigLangnerAcker, author = {Rietig, Anja and Langner, Thomas and Acker, J{\"o}rg}, title = {A revised model of silicon oxidation during the dissolution of silicon in HF/HNO₃ mixtures}, series = {Physical chemistry, chemical physics}, volume = {21}, journal = {Physical chemistry, chemical physics}, issn = {1463-9076}, doi = {10.1039/c9cp04429a}, pages = {22002 -- 22013}, abstract = {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.}, language = {en} } @misc{DuckeAcker, author = {Ducke, Jana and Acker, J{\"o}rg}, title = {R{\"u}ckgewinnung von Platin, Palladium und Rhodium aus Autoabgaskatalysatoren: Bestimmung der Edelmetallgehalte im Eisensammler mittels ICP-OES}, series = {Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts}, journal = {Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts}, editor = {Vogt, Carla}, edition = {1. Auflage}, publisher = {TU Bergakademie Freiberg}, address = {Freiberg}, pages = {S3/2}, abstract = {Fahrzeugkatalysatoren enthalten wertvolle Edelmetalle wie Platin (Pt), Palladium (Pd) und Rhodium (Rh), wodurch ausgediente und funktionsunf{\"a}hige Katalysatoren zu einem begehrten Recyclinggut in einem hart umk{\"a}mpften Marktsegment werden. Das h{\"a}ufigsten Aufbereitungsverfahren f{\"u}r Altkatalysatoren ist ein Schmelzprozess, in dem vorzerkleinerte Katalysatorfraktionen unter definierter Zugabe von Hilfsstoffen mit Kupfer als Kollektormetall aufgeschmolzen werden. Die Edelmetalle reichern sich im fl{\"u}ssigen Kupfer an, w{\"a}hrend 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 preisg{\"u}nstiger als Kupfer, es kann unter optimalen Schmelzbedingungen bis zu 9\% an Edelmetallen aufnehmen, w{\"a}hrend 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 h{\"a}tte. Eine Methode zur pr{\"a}zisen Quantifizierung der Edelmetallgehalte im Eisensammler existierte bisher nicht. Im Rahmen eines Forschungsprojektes wurde deshalb ein Bestimmungsverfahren zur zuverl{\"a}ssigen 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 bez{\"u}glich des Einsatzes an Probenmaterial (f{\"u}r den Aufschluss) und Aufschlusschemikalien zeigt. Die analytischen Herausforderungen lagen in der Probenhomogenisierung zur repr{\"a}sentativen Probenahme, in der Entwicklung eines Mikrowellen-Aufschlussverfahrens und in der Entwicklung einer Methode zur Pr{\"a}zisionsanalytik 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 zuverl{\"a}ssiges, pr{\"a}zises und kosteneffizientes Quantifizierungsverfahren f{\"u}r diese Edelmetalle in dieser besonderen Matrix zu entwickeln.}, language = {de} } @misc{SieberRietigDuckeetal., author = {Sieber, Tim and Rietig, Anja and Ducke, Jana and Acker, J{\"o}rg}, title = {Direkte Feststoffanalyse von Hauptkomponenten in Kathodenmaterialien von Lithiumbatterien mittels HRCS-GF-AAS}, series = {Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts}, volume = {2019}, journal = {Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts}, editor = {Vogt, Carla}, edition = {1. Auflage}, publisher = {TU Bergakademie Freiberg}, address = {Freiberg}, pages = {S1/4}, abstract = {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 S{\"a}uren 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. Zus{\"a}tzlich wird das Probenmaterial einer Feststoffverd{\"u}nnung mit matrixverwandten Komponenten unterzogen. Die Verd{\"u}nnung senkt zum einen die Konzentration und die Gefahr der Verschleppung der Analyten und beg{\"u}nstigt zum anderen die Freigabe des Analyten aus der Probenmatrix. Durch Aufnahme von Extinktions-Zeit-Verl{\"a}ufen im Temperaturbereich von 200 - 2600 °C konnten die Freisetzungstemperaturen f{\"u}r jeden Analyten bestimmt werden. Nach anschließenden Optimierungen der Pyrolyse- und Atomisierungstemperaturen wurde mithilfe der Einzeloxide f{\"u}r jeden Analyten die Linearit{\"a}t des Messsignals gepr{\"u}ft und der Arbeitsbereich festgelegt. Durch Vermessung von variierenden Oxidmischungen und Mischoxiden, sowie Zusatz m{\"o}glicher weiterer Interferenten, wie dem Bindermaterial PVDF wurden Spezifit{\"a}t, Selektivit{\"a}t und Robustheit der Methode {\"u}berpr{\"u}ft. 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 pr{\"a}zise Analyse der Hauptkomponenten Li, Ni, Mn und Co erlaubt.}, language = {de} }