Scanning tunneling microscopy of the phase transition between H/Si(100)-(2x1) and H/Si(100)-(3x1)

The transition from H/Si(100)-(2x1) to H/Si(100)-(3x1) that occurs upon dosing atomic hydrogen at 400 K has been studied using scanning tunneling microscopy. It is characterized by a series of interactions between hydrogen and the strained silicon bonds via local adsorption and thermal decomposition of dihydride units. The transition starts from a paired H adsorption on a monohydride dimer on the 2x1 surface, followed by the formation of local 3x1 domains. The growth of 3x1 domains is found anisotropic along the dimer row direction due to characteristic antiphase boundaries. A lateral dihydride-row diffusion has been observed, indicating that the local 3x1 domains are correlated in their expansions, suggesting a plausible pathway for conversion of the spreading 3x1 domains into a well-defined phase. Etching species have always been found on the surface, which are related to defects on the initially clean surface and breaking of back bonds during atomic hydrogen dosing.