Deuterium adsorption-desorption from diamond (100) single crystal surfaces studied by TPD

Due to the crucial role of hydrogen in diamond CVD process the adsorption-desorption of hydrogen on different diamond surface planes has been studied thoroughly in recent years. Contradictory results and explanations have been reported in the literature regarding the mechanisms and dynamics of the above system. Deuterium adsorption-desorption from a Di(100) surface was investigated by TPD and LEED. It was found that hydrogen plasma treatment results in a well-defined reconstructed Di(100)- (2 x 1):H surface for which a high quality LEED pattern was observed at primary electron beam energy as low as 28 eV. Annealing of the diamond (100) hydrogenated surface at 1200 degrees C results in hydrogen desorption. The hydrogen-free Di(100)-(2 x 1) surface displays charging effects under low energy electron bombardment. Activated low-coverage deuterium adsorption on the Di(100) surface was performed in situ. The results show that deuterium desorbs from a single adsorption site, alpha(1), on the (100) diamond surface. Desorption from these sites obeys first order kinetics. Simulation of the TPD spectra yields K = 10(13) s(-1) and E-act = 88 kcal/mol for the deuterium desorption from well-defined surface. Repeated deuterium adsorption-thermal desorption cycles cause surface degradation which results in additional peaks in the TPD spectrum. A possible mechanism to the first order desorption kinetics is suggested. (C) 1998 Published by Elsevier Science S.A.