On the origin and the structure of the first sharp diffraction peak of amorphous silicon

TL;DR

This paper investigates the origin and structure of the first sharp diffraction peak in amorphous silicon, linking it to specific atomic correlations and second-neighbor distances through modeling and analysis.

Contribution

It provides a detailed analysis of the FSDP in amorphous silicon, identifying key atomic shells and deriving a relation between the FSDP position and second-neighbor distances.

Findings

FSDP position and intensity are mainly determined by radial correlations at ~15 Å.

Second and fourth radial shells are the primary contributors to the FSDP.

An approximate relation between FSDP position and second-neighbor distance is established.

Abstract

The structure of the first sharp diffraction peak (FSDP) of amorphous silicon (${\it a}$-Si) near 2 Angstrom$^{-1}$ is addressed with particular emphasis on the position, intensity, and width of the diffraction curve. By studying a number of continuous random network (CRN) models of ${\it a}$-Si, it is shown that the position and the intensity of the FSDP are primarily determined by radial atomic correlations in the amorphous network on the length scale of 15 Angstroms. A shell-by-shell analysis of the contribution from different radial shells reveals that the key contributions to the FSDP originate from the second and fourth radial shells in the network, which are accompanied by a background contribution from the first shell and small residual corrections from the distant radial shells. The results from numerical calculations are complemented by a phenomenological discussion of the relationship between the peaks in the structure factor in the wavevector space and the reduced pair-correlation function in the real space. An approximate functional relation between the position of the FSDP and the average second-neighbor distance of Si atoms in the amorphous network is derived, which is corroborated by numerical calculations.