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

Abstract

Abstract 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 × 2)/(2 × 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 × s). Within this dose-range the (2 × 2)/(2 × 1) reconstruction did not revert into the (1 × 1) structure. The deuterium coverage for the highest adsorption dose (30 L) was estimated as ∼0.5 ML. It was found that deuterium desorbs out of two distinct adsorption sites, β 1 and β 2 from the reconstructed (111) diamond surface. No thermal-induced redistribution of deuterium between the β 1 and β 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 β 1 and β 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: β 1 (high temperature TPD peak): K = 5 × 10 12 s −1 , E act = 80 kcal mol −1 and β 2 (low temperature TPD peak): K = 5 × 10 12 s −1 ; E act = 67 kcal mol −1 .