Finite-size effects and short-range crystalline order in Si and SiO₂studied by X-ray absorption fine structure spectroscopy

The X-ray absorption near-edge structures from the Si 2p edge have been measured at high resolution, and compared to a theoretical calculation using a cluster multiple-scattering model. The absorption features near threshold are shown to be sensitive to the degree of short-range crystalline order, over a range of up to 40 AA. The real-space scattering cluster calculation establishes the connection between the short-range order, as reflected in cluster size or final-state electron damping, and the line-widths of sharp absorption features near the 2p edge. Results are shown for amorphous and crystalline Si, and silicon oxides in the form of quartz, obsidian, and thin films on single-crystal Si substrates.