Adsorption of water on Si(100)-(2×1): A study with density functional theory

Abstract

Adsorption of water on the Si(100)-(2×1) surface has been investigated using density functional theory and cluster models of the surface. The reaction pathway and geometries of the product, the transition state and a molecular precursor state are described. There is no energy barrier to dissociative chemisorption. Adsorbed H and OH fragments are most stable when bonded to the same surface dimer with the hydroxyl oriented away from the surface dimer bond. The orbital and electrostatic interactions that determine the adsorbate and transition state geometries are analyzed. Surface distortion (dimer buckling) is a recurring theme in this analysis. Interactions of adsorbed molecular fragments with each other and with dangling bonds have significant effects, modifying the adsorbate geometry and leading to adsorbate islanding. Calculated vibrational frequencies of adsorbed H2O on Si(100)-(2×1) are discussed. The theoretical results are consistent with most available experimental results, and provide a microscopic description of the interactions that account for the observations.