INFRARED REFLECTION ABSORPTION-SPECTROSCOPY STUDY OF THE CHEMISORPTION OF SMALL MOLECULES (H-2, O-2 AND H2O) ON SILICON

For infrared reflection-absorption spectroscopy (IRRAS) in the single external reflection mode, a well-known limitation is the diminished sensitivity for adsorbates on semiconducting vs metallic substrates substrates. We describe a technique in which an optically thin semiconductor film is deposited in ultra high vacuum on a metal and spectra recorded at grazing incidence in p-polarization. Using this approach, spectra have been obtained down to 650 cm(-1) for H, O, OH and (CH3)2CHO-(isopropoxy) adsorbed at coverages of up to one monolayer on Si films (about 40 to 120 angstrom thick) on Ni(001). Isotope experiments have also been done using 18O2 and D2. The technique illustrated by these results is expected to be useful in studies of amorphous semiconductor surface chemistry and of the growth of such materials by chemical vapor deposition.