Comparison of hydrogen desorption kinetics from Si(111)7 × 7 and Si(100)2 × 1

Abstract

Abstract The desorption kinetics of hydrogen from the β1 H2-TPD state on Si(111)7 × 7 and Si(100)2 × 1 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Isothermal LITD studies of H2 desorption from Si(111)7 × 7 revealed second-order kinetics with a desorption activation barrier of E d = 62±4 kcal mol pro-exponential factor of vd=91±10 cm2/s. In contrast, the desorption of hydrogen from Si(100)2 × 1 revealed first-orde kinetics with an activation barrier of E d = 58±2 kcal mol and a pre-exponential factor of vd=(5.5±0.5)×1015s−1. The desorption kinetics yielded similar upper limits for the Si-H bond energies, but different desorption mechanisms on Si(111)7 × 7 and Si(100)2 × 1. The TPD results were also in agreement with second-order H2 desorption kinetics on Si(111)7 × 7 and first-order kinetics on Si(100)2 × 1. The second-order kinetics on Si(111)7 × 7 were consistent with a recombinatory desorption mechanism involving randomly positioned hydrogen atoms. The first-order H2 desorption kinetics were attributed to the concerted desorption of H2 from two hydrogen atoms paired on the same silicon dimer on Si(100)2 × 1.