Fundamental steps towards interface amorphization during silicon oxidation: Density functional theory calculations

Abstract

Density functional theory calculations reveal a two-step scenario for silicon oxidation nucleation. We detail a quasibarrierless semihexagonal oxide nucleus, involving an unexpected adjacent dimer oxygen bridging bond. It is formed upon ${\text{O}}_{2}$ chemisorption at 0.5 monolayer on $\text{Si}(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$. This structure arises from the difficulty to systematically insert oxygen atoms into first neighbor Si--Si bonds. While silanone structures, characterized by a $\text{Si}=\text{O}$ strand, effectively accommodate oxygen at lower coverages, the stabilization of this hexagonal-like pattern on a cubic substrate at low temperatures and at higher coverages demonstrates the ability of oxygen atoms to deeply modify the arrangement of silicon atoms on the surface and to impose a specific structure. It is believed to offer a key natural pathway toward the formation of an abrupt crystalline semiconductor/amorphous oxide transition.