@misc{GrafeLoeserSchmitzetal., author = {Grafe, Hans-Joachim and L{\"o}ser, Wolfgang and Schmitz, Steffen and Sakaliyska, Miroslava and Wurmehl, Sabine and Eisert, Stefan and Reichenbach, Birk and Acker, J{\"o}rg and Rietig, Anja and Ducke, Jana}, title = {NMR investigation of boron impurities in refined metallurgical grade silicon}, series = {Physica status solidi. A, Applications and Materials Science}, volume = {212}, journal = {Physica status solidi. A, Applications and Materials Science}, number = {9}, issn = {1862-6319}, doi = {10.1002/pssa.201431908}, pages = {2031 -- 2036}, abstract = {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.}, language = {en} } @misc{RietigGrafeAcker, author = {Rietig, Anja and Grafe, Hans-Joachim and Acker, J{\"o}rg}, title = {New insights into boron species in acidic digestion solutions of boron-doped silicon}, series = {Journal of Analytical Atomic Spectrometry}, volume = {36}, journal = {Journal of Analytical Atomic Spectrometry}, number = {11}, issn = {1364-5544}, pages = {2492 -- 2500}, abstract = {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.}, language = {en} } @misc{RietigGrafeAcker, author = {Rietig, Anja and Grafe, Hans-Joachim and Acker, J{\"o}rg}, title = {Understanding the Reasons for Erroneous Determinations of Boron in Silicon following Wet Chemical Digestion in HF/HNO3}, series = {Proceedings of the Silicon for the Chemical \& Solar Industry XVI}, journal = {Proceedings of the Silicon for the Chemical \& Solar Industry XVI}, isbn = {978-82-692919-0-2}, doi = {10.2139/ssrn.4123058}, pages = {14}, language = {de} }