Comparison of H2 Desorption Kinetics from Si(111)7×7 and Si(100)2×l

Abstract

ABSTRACTThe desorption kinetics of hydrogen from the β1 H2 -TPD state on Si(111)7×7 and Si(100)2×l 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 energy of Ed = 62 ±4 kcal/mol and a preexponential factor of Vd = 92 ±10 cm2 /s. In contrast, H2 desorption from Si(100)2×l revealed first-order kinetics with an activation energy of Ed = 58 ±2 kcal/mol and a preexponential factor of Vd = 5.5 ±0.5 × 1015 s−1. The desorption kinetics yield similar upper limits for the Si-H bond energies but different desorption mechanisms on Si(lll)7×7 and Si(100)2×l.