Effects of deuterium adsorption-desorption on the state of diamond: Surface degradation and stabilization of sp(3) bonded carbon

Changes on the (100) diamond surface due to cyclic adsorption and desorption of deuterium were investigated by electron energy loss spectroscopy (EELS) and low energy electron diffraction (LEED) and the effects of surface degradation are discussed. After several deuterium adsorption-desorption thermal cycles it is determined that the diamond surface gradually degrades. This is reflected in the smearing of characteristic losses, the appearance of a loss peak at about 6 eV and a broad loss peak centered at 30 eV. The reconstructed surface, as observed by LEED, fades. It is suggested that this surface degradation results in an sp(2) bonded carbon layer. EELS measurements taken as a function of primary energy show that the degradation is localized on the uppermost surface layers. Deuterium adsorption on the degraded surface results in a decrease in intensity of the 6 eV loss peak which is associated with conversion of sp(2) bonded carbon to sp(3) hybridization. Thermal desorption of deuterium from the degraded surface results in the reappearance of the 6 eV loss peak, suggesting reversible formation of sp(2) bonded carbon on deuterium desorption. It is determined that exposure of a degraded diamond (100) surface to a microwave hydrogen plasma at 900 degrees C results in characteristic EELS features, and half-order LEED spots showing that this treatment leads to a (2 x 2)/(2 x 1) reconstructed surface.