Chemical shifts of SiH stretching frequencies at Si(100) surfaces pre-exposed to oxygen in the submonolayer range

Abstract

The Si-H stretching vibrations have been measured with high resolution electron energy loss spectroscopy (EELS) and Si(100) 2 × 1 surfaces pre-exposed at room temperature to submonolayer coverages of oxygen. The absorption of atomic hydrogen at room temperatures and subsequent isochronal annealing makes evident different stages of oxidation. The Si-H stretching frequencies vary between 261 and 283 meV, depending on the number of the adjacently bound oxygen atoms. The upward shift in frequency, empirically described in terms of Pauling's electronegativity sum for the next-nearest neighbors of the hydrogen atoms, is in agreement with infrared band frequencies for oxygenated polysilane samples and for air exposed hydrogenated a-films. Empirical relations indicate that the Si-H bonding distance decreases from 1.50 to 1.46 Å as the number of oxygen next-nearest neighbors increases from zero to three. Simultaneously, the s character of the Si-H bond is increased from 0.42 to 0.61.