The catalytic role of ultrathin Mn film in the oxidation of Si(111) 7×7 surface

The present work reports the results of the Auger electron spectroscopy study of the adsorption of molecular oxygen on Mn precovered silicon(111) surface. Mn is deposited in UHV at a rate of 0.15 ML/min at room temperature on a Si(111) 7×7 surface to obtain an epitaxial (1×1) surface phase for most coverages. Exposure of the Si surface precovered with overlayers of Mn to oxygen partial pressure shows the formation of silicon oxides. The formation of SiO2 in addition to SiO is clearly shown by the exposure of Si surface covered with less than a monolayer of Mn to oxygen. Adsorption of oxygen as well as oxidation of Si increases with increasing Mn thickness up to several monolayers. Thus, the presence of Mn leads to enhanced oxidation of Si surface manifesting its catalytic role. In all the present cases, Mn also gets oxidized along with Si and is observed as a chemically shifted peak and the appearance of a cross transition peak. An oxygen threshold coverage of 3 L is observed to be necessary to split the Mn(MVV) peak in case of very thick Mn layers. The role of Mn in providing active atomic O species for enhancement of Si oxidation is discussed in light of various mechanisms reported in the literature.