Spectroscopic analysis of selected silicon ceramics

Abstract

Silicon ceramics are popular in both commercial applications and material research. The purpose of this thesis is to present measurements and analysis of four different silicon ceramics: α, β and γ phases of silicon nitride and silicon oxynitride using soft x-ray spectroscopy, which analyses the electronic structure of materials by measuring the absorption and emission of x-ray radiation. Absorption and emission spectra of these materials are presented, many of which have not be previously documented. The results are compared to model spectra and together they provide information about the electronic structure of the material. Assignments of emission features to element, orbital, and site symmetry are performed for each material. Combinations of silicon and nitrogen emission spectra provide insight into the strained bonding structure of nitrogen. It is concluded that p-dπ interaction plays a role in the bonding arrangement of nitrogen and oxygen sites within these structures. The emission features of non-equivalent silicon sites within γ-Si₃N₄ are identified, which represents some of the first analysis of same element, non-equivalent sites in a material. Silicon absorption and emission spectra were plotted on the same energy scale to facilitate measurement of the band gap. Since previously measured band gaps are not well represented in literature, the measured band gaps were compared to values predicted using DFT calculations. The band gap values are in reasonable agreement to calculated values, but do not vary as widely as predicted.