Interaction of water vapor with bare and hydrogenated diamond film surfaces

Abstract

In this work we study changes in the chemical state of hydrogenated and bare diamond film surfaces after their exposure to water (a mixture of D 2O and H 2O) vapor. For this purpose X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) measurements were performed. From XPS showing the O (1s) binding energy peak, water molecules adsorb on both types of surfaces. The result of their interaction is different, however, for hydrogenated diamond as compared to the bare surface. Mild annealing (to 300 °C) of the water exposed hydrogenated diamond surface, results in complete disappearance of the O (1s) peak which indicates desorption of water. The same treatment of the water exposed bare diamond surface, induces only minor changes in the oxygen concentration. This effect suggests that water molecules mostly physisorb on the hydrogenated surface, whereas considerable part of them undergo dissociation when collide with the bare surface with which they form chemical bonds. This assumption is fully confirmed by HREELS measurements. On the bare diamond surface the vibrational losses detected by HREELS can be attributed to CO, C–O–D (C–O–H), and C–D (C–H) surface bonds. Their intensity only moderately decreases after annealing of the sample to 300 °C. Water vapor exposure of the hydrogenated surface results in appearance in the HREELS spectrum only features related to O–D vibrations and bending modes of water molecules. These spectral structures disappear following annealing to 300 °C.