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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 -