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

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 O₂ chemisorption at 0.5 monolayer on Si(100)-(2×1). This structure arises from the difficulty to systematically insert oxygen atoms into first neighbor Si--Si bonds. While silanone structures, characterized by a Si=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.