Hydrogen chemisorption and thermal desorption on the diamond C(111) surface

Abstract

Temperature programmed desorption (TPD) and low energy electron diffraction (LEED) were utilized to study the interaction of atomic hydrogen with single crystal diamond C(111) surface. From isotherm and isostere analysis of TPD spectra acquired at various sample heating rates ranging from 0.6 K/s to 30 K/s, the kinetic parameters were extracted. It is found that molecular hydrogen desorption from the C(111) surface exhibits the first-order kinetics. This result is confirmed by no apparent shift in peak temperatures of TPD spectra for hydrogen coverage above 0.2 ML. At lower coverage regime, the isothermal desorption experiment also indicates the first-order desorption kinetics. A nearly coverage-independent activation energy of (3.7±0.1) eV and a prefactor of (9.5±4.0)×1013 s−1 are obtained except at relatively low coverages (below ∼0.2 ML). In addition, the half-order LEED spots intensity decreases linearly with increase of the hydrogen coverage and drops to zero at ∼0.5 ML. These results are interpreted with a model that during adsorption hydrogen atoms segregate to form metastable, highly hydrogenated domains from where hydrogen atoms recombine and desorb concertedly as the substrate surface is heated up. The comparison of this work with the hydrogen adsorption and desorption on silicon surfaces is also discussed.