Observation of Surface Hydroxylation on Cleaved MgO(001) Exposed by Water

Hydroxylation on cleaved MgO(001) surface by water exposure has been studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The used samples are MgO surfaces cleaved in air, exposed to water vapor and immersed in water. The immersed times are 0.01, 0.03, 0.1, 0.3, 1 and 3 h. Water molecules could not be found in the XPS spectra of all samples. Hydroxyl exists on the surface immediately after cleaved in air. The hydroxyl component in the XPS spectra becomes large with the immersed time up to 0.03 h. At the 0.1 h of the immersed time the component of Mg(OH)2 appears in the XPS spectrum and the component becomes larger with the immersed time. These results indicate that the hydroxylation makes progress by dissociative adsorption of water right after cleavage in air and the Mg(OH)2 component begin to grow from about 0.1 h of the immersed time.