Identification of higher order silanes during monosilane pyrolysis using gas chromatography-mass spectrometry

There is a deficit of ways to detect higher order silane isomers during silane pyrolysis. Thus, a novel instrument utilizing gas chromatography-mass spectrometry (GC-MS) for detection of higher order silanes has been developed. The instrument enables us to separate higher order silane species using gas chromatography before they are introduced to the mass spectrometer, thereby obtaining spectra of separate isomers, rather than overlaid spectra. In this contribution we describe the details of the GC-MS system. We compare our GC-separated mass spectra of mono-, di- and trisilane to mass spectra of these species available in the literature. Further, we present mass spectra of the tetrasilane isomers n-tetrasilane (n-Si4H10), silyltrisilane (i-Si4H10) and cyclotetrasilane (cyclo-Si4H8) and of the pentasilane isomers n-pentasilane (n-Si5H12), silyltetrasilane (i-Si5H12) disilyltrisilane (neo-Si5H12) and cyclopentasilane (cyclo-Si5H10). Six of these mass spectra are previously unpublished. Based on the fragmentation pattern in the tetra- and pentasilane mass spectra, we are able to acquire mass spectra of silanes with up to eight silicon atoms. Finally, we apply the novel detection technique to a silane pyrolysis reactor to track the outlet concentration of higher order silanes as function of reactor temperature. We believe that the detection technique that we present here may open the door for validation of monosilane pyrolysis models, and thus constitute a roadmap for future research in this field.