Dependence of short and intermediate-range order on preparation in experimental and modeled pure a-Si

Abstract

Variability in the short-intermediate range order of pure amorphous Si synthesized by different experimental and computational techniques is probed by measuring mass density, atomic coordination, bond-angle deviation, and dihedral angle deviation. It is found that there is significant variability in order parameters at these length scales in this archetypal covalently bonded, monoatomic system. This diversity strongly reflects preparation method and thermal history in both experimental and simulated systems. Where experiment and simulation do not quantitatively agree, this is partly due to inherent differences in analysis and time scales. Relaxed forms of amorphous Si quantitatively match continuous random networks generated by a hybrid method of bond-switching Monte Carlo and molecular dynamics simulation. Qualitative trends were identified in other experimental and computed forms of a-Si. Ion-implanted a-Si?s are less ordered than the relaxed forms. Preparation methods which narrowly avoid crystallization such as experimental pressure-induced amorphization or simulated melt-quenching result in the most disordered structures. As no unique form of amorphous Si exists, there can be no single model for the material.