High Resolution Radial Distribution Function of Pure Amorphous Silicon

The structure factor $S\left(Q\right)$ of high purity amorphous Si membranes prepared by ion implantation was measured over an extended $Q$ range ( $0.03–55{Å}^{-1\mathrm{}}$). Calculation of the first neighbor shell coordination ( $C_1$) as a function of maximum $Q$ indicates that measurement of $S\left(Q\right)$ out to at least $40{Å}^{-1\mathrm{}}$ is required to reliably determine the radial distribution function (RDF). A $2\%$ change in $C_1$ and subtle changes in the rest of the RDF were observed upon annealing, consistent with point defect removal. After annealing at 600 °C, $C_1=3.88\mathrm{}$, which would explain why amorphous Si is less dense than crystalline Si.