Nitridation of silicon powder studied by XRD, Si MAS NMR and surface analysis techniques |
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Authors: | K J D MacKenzie C M Sheppard K Okada Y Kameshima |
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Affiliation: | a New Zealand Institute for Industrial Research and Development, PO Box 31-310 Lower Hutt, New Zealand b Department of Inorganic Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152, Japan |
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Abstract: | The nitridation of elemental silicon powder at 900–1475 °C was studied by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), XRD, thermal analysis and 29Si MAS NMR. An initial mass gain of about 12% at 1250–1300 °C corresponds to the formation of a product layer about 0·2 μm thick (assuming spherical particles). XPS and XAES show that in this temperature range, the surface atomic ratio of N/Si increases and the ratio O/Si decreases as the surface layer is converted to Si2N2O. XRD shows that above 1300 °C the Si is rapidly converted to a mixture of - and β-Si3N4, the latter predominating >1400 °C. In this temperature range there are only slight changes in the composition of the surface material, which at the higher temperatures regains a small amount of an oxidised surface layer. By contrast, in the interval 1400–1475 °C, the 29Si MAS NMR chemical shift of the elemental Si changes progressively from about −80 ppm to −70 ppm, in tandem with the growth of the Si3N4 resonance at about −48 ppm. Possible reasons for this previously unreported change in the Si chemical shift are discussed. © |
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Keywords: | nitridation X-ray methods Si3N4 silicon |
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