FI-STM Investigation of Atomic Hydrogen Adsorption on the Si(100)2x1 Surface

摘要

A field ion-scanning tunneling microscopy study on hydrogen chemisorption on theSi(100)2x1 surface is presented. At low coverages, hydrogen atoms reside singly on top of the dimerized Si atoms, and are imaged brightly. The hydrogen chemisorption induces the buckling of dimers, indicating the strong bonding between Si and H atoms. With increasing coverage, both the 2x1 monohydride and 1x1 dihydride phases were formed. The former is imaged dark compared with the unreacted Si dimers, due to the reduction of the density of electronic states near the Fermi level. Surface etching was also observed. It was found that the corrosion of the surface is modest in the monohydride phase, while during the formation of the dihydride phase, the corrosion becomes significant. The behaviour of hydrogen desorption from the dihydride and monohydride phases was investigated as a function of annealing temperature. Our STM results support the mechanism that the desorbing H2 molecules are formed by combination of two hydrogen atoms forming the dihydride phase. Upon annealing at elevated temperatures, the Si overlayer stripes are formed by desorption of hydrogen from the etching products and the rearrangement of the Si atoms.