DEUTERIUM ADSORPTION-DESORPTION FROM DIAMOND(100) SINGLE-CRYSTAL SURFACES STUDIED BY TPD

Due to the crucial role of hydrogen in diamond CVD process the adsorpt ion-desorption of hydrogen on different diamond surface planes has bee n studied thoroughly in recent years. Contradictory results and explan ations have been reported in the literature regarding the mechanisms a nd 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(1 00)- (2 x 1):H surface for which a high quality LEED pattern was obser ved at primary electron beam energy as low as 28 eV. Annealing of the diamond (100) hydrogenated surface at 1200 degrees C results in hydrog en desorption. The hydrogen-free Di(100)-(2 x 1) surface displays char ging effects under low energy electron bombardment. Activated low-cove rage deuterium adsorption on the Di(100) surface was performed in situ . The results show that deuterium desorbs from a single adsorption sit e, 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 desorptio n cycles cause surface degradation which results in additional peaks i n the TPD spectrum. A possible mechanism to the first order desorption kinetics is suggested. (C) 1998 Published by Elsevier Science S.A.