Methanol adsorption on Si(1 0 0)2×1 investigated by high-resolution photoemission

The adsorption of methanol on Si(1 0 0)2×1 has been investigated at room temperature by high-resolution synchrotron radiation photoemission in the exposure range: 0.01–0.15 L. A combined evidence for a dissociative mechanism has been obtained from the analysis of the photoemission spectral features, which shows the absence of the ionization peak mainly based on the σO−H bond in the valence band and the identification of a Si–O related component in the Si 2p core spectrum after adsorption. The line-shape analysis of the Si 2p core level shows the rising of two surface-related components upon adsorption. Their energy location allows for the assignment to Si–H and Si–OCH3 bonds, as resulting from the interaction of the molecular fragments (H atom and methoxy group) with the surface. The growth of the Si–H and Si–OCH3 related spectral components upon adsorption has been followed by a careful curve-fitting of the Si 2p line. The intensity increase of the new adsorption-induced components almost completely parallels the progressive intensity decrease of the surface dimer components, as found by the relative quantitative analysis of the Si 2p peak components. The analysis of the C 1s photoemission core-line suggests that no C–O bond rupture occurs at low exposure. A further fragmentation of the CH3O– group occurs at higher exposure (>20 L), as we previously found for methanol adsorption on Si(1 1 1)7×7.