Thermal-programmed desorption (TPD) of deuterium from Di(111) surface: Presence of two adsorption states

Deuterium desorption from diamond (111) surface was investigated by thermal-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and low energy electron diffraction (LEED). Annealing of diamond (111) deuterated surface results in (2 x 2)/(2 x 1) reconstruction. Activated deuterium adsorption on Di(111) surface, pre-treated in MW hydrogen plasma, was performed in situ for doses in the 0.14-30 L range (1 L = 10(-6) Torr x s). Within this dose-range the (2 x 2)/(2 x 1) reconstruction did not revert into the (1 x 1) structure. The deuterium coverage for the highest adsorption dose (30 L) was estimated as similar to 0.5 ML. It was found that deuterium desorbs out of two distinct adsorption sites, beta(1) and beta(2) from the reconstructed (111) diamond surface. No thermal-induced redistribution of deuterium between the beta(1) and beta(2) adsorption sites was observed. Based on the TPD peak shapes and their dependence on coverage, a first order kinetics was assumed for the desorption process, The beta(1) and beta(2) adsorption states were attributed to monohydride (C-D) formation on Di(111) planes and diamond edges, respectively. The desorption kinetic parameters were calculated with the following results: beta(1) (high temperature TPD peak): K = 5 x 10(12) s(-1), E-act = 80 kcal mol(-1) and beta(2) (low temperature TPD peak): K = 5 x 10(12) s(-1); E-act = 67 kcal mol(-1). (C) 1997 Elsevier Science S.A.