H2O adsorption kinetics on Si(111)7×7 and Si(111)7×7 modified by laser annealing

Abstract

The adsorption kinetics of H2O on Si(111)7×7 and Si(111)7×7 modified by laser annealing were studied using laser-induced thermal desorption and temperature-programmed desorption techniques at temperatures between 180 and 800 K. The laser-annealed Si(111)7×7 surface displayed an enhanced initial reactive sticking coefficient for H2O compared with the unmodified Si(111)7×7 surface. At 180 K, the initial reactive sticking coefficient was S0=6.9×10−1 on laser-annealed Si(111)7×7 compared with S0=1.9×10−2 on unmodified Si(111)7×7. This larger initial sticking coefficient is attributed to the creation of a more reactive surface structure formed by the laser annealing process. At higher oxygen coverages, the reactivity of the laser-annealed surface changed and displayed much slower H2O adsorption rates that were similar to the kinetics on Si(111)7×7. The decreasing initial reactive sticking coefficient versus increasing surface temperature suggested a precursor-mediated adsorption mechanism on both the Si(111)7×7 and laser-annealed Si(111)7×7 surfaces. After long H2O exposures, the oxygen coverage saturated at θO≊0.35 monolayers on Si(111)7×7 for temperatures between 300 and 700 K. At higher surface temperatures, the saturation coverage increased prior to SiO desorption at temperatures above 900 K. This increase was attributed to the creation of additional dangling bond adsorption sites following H2 desorption at temperatures above 700 K.