REACTIONS OF WATER AND METHANOL AT HYDROGEN-TERMINATED SILICON SURFACES STUDIED BY TRANSMISSION FTIR

A simple method for studying the reactivity of hydrogen-terminated sil icon surfaces via transmission FTIR spectroscopy is described. Abraded (100) single crystals of silicon, after etching in ammonium fluoride, show features in the IR spectrum that are assigned to Si-H stretching vibrations. Confirmation of the utility of this approach is demonstra ted in the reactions of the Si-H surfaces with water and methanol. Nat ive-oxide growth in the former case is evidenced by the appearance of two bands in the Si-O stretch region accompanied by a shift to higher frequency of the longitudinal polar Si-O vibrational mode with increas ed exposure, consistent with an island-growth model. Similarly, the re action with methanol generates two bands in the Si-O stretch region. H owever, the frequency and behaviour of these bands on further exposure to methanol are consistent with a chemisorbed methoxy species with li ttle oxidation taking place, contrary to previous reports.