Cl2 dissociation on Si(100)-(2x1):: A statistical study by scanning tunneling microscopy

A statistical analysis of the dissociative chemisorption of Cl-2 on the Si(100)-(2 x 1) surface at 300 K has been carried out in;he CI coverage range up to 0.17 ML using scanning tunneling microscopy. The adsorption of two Cl atoms on Si dimer sites in adjacent silicon dimer rows was found to be kinetically favored (probability P is 0.52). Cl-2 dissociation also occurs with Cl atoms bonded to neighboring Si dimers in the same dimer rows (P = 0.33). Cl-2 dissociation on a single Si dimer is least likely (P = 0.15). The least probable Cl pair configuration on a single Si dimer at room temperature is most favored thermodynamically, indicating that kinetic factors control the site selection process at 300 K. The observed selectivity of the CI pair configurations produced at 300 K, is consistent with Cl-2 dissociative chemisorption occurring through a mobile precursor-mediated channel. At increasing Cl-2 exposure, the density of the fully Cl-terminated dimers increases, and at saturation the surface consists of only these chlorine configurations. Tunneling spectroscopy has been employed to characterize the Cl-saturated Si(100) surface, and it has been found that filled-state images mainly probe the bonding sigma(d) states of the Si-Si dimers. Empty-state images probe the antibonding sigma(Si-Cl)* states in the overlayer. [S0163-1829(98)09735-5].