Thermal desorption of hydrogen from the diamond C(100) surface

Abstract

Temperature-programmed desorption (TPD) is used to measure the kinetics of hydrogen desorption from the C(100) surface. Two major desorption channels, attributed to hydrogen desorption from (2×1) domains ( α sites) and disordered domain boundaries sites ( β sites) were observed. The change in the morphology of the C(100) surface upon hydrogen adsorption/desorption leads to a variation in the intensity ratio between the two hydrogen desorption peaks. The degradation results in smaller (2×1) domains, as evidenced by deteriorated LEED patterns in which the characteristic (2×1) half-order spots disappear. The (2×1) LEED pattern can be restored on the degraded C(100) surface by repeated hydrogenation–annealing cycles in the temperature range 300–1100 K. Fitting the experimental TPD data with simulated curves from the two-site model shows that desorption from the α site obeys first-order kinetics with a prefactor of 1.4±0.9×10 13 s −1 and an activation energy of 80.3±1.3 kcal mol −1, whereas the process giving rise to the β peak follows second-order kinetics with a prefactor of 2.3±0.9×10 13 s −1 (expressed in first-order units) and an activation energy of 75.1±0.5 kcal mol −1. Possible mechanisms for first-order recombinative hydrogen desorption from the C(100)-(2×1) surface are also discussed.