Abstract
Extended-x-ray-absorption-fine-structure (EXAFS) studies above the nitrogen (∼400 eV) and oxygen (∼535 eV) absorption edges are reported for silicon nitride, silicon dioxide, and oxygen on a Si (111) surface. Measurements were carried out using soft-x-ray synchrotron radiation and employing the surface-sensitive secondary-electron-yield detection technique. EXAFS spectra of bulk and Si are analyzed to test the reliability of theoretical phase shifts and to derive experimental ones for the N-Si and O-Si systems. It is found that nearest-neighbor distances from low- atoms can be determined to an accuracy of ≲0.03 Å and second-nearest-neighbor separations to ≲0.05 Å using calculated phase shifts. The surface EXAFS spectrum of one of the initial oxidation stages (characterized by a Si chemical shift of 2.5 eV) reveals that the O-Si bond length is slightly (0.04 Å) larger than in Si. Analysis of the relative EXAFS amplitudes provides information on the oxygen-bonding geometry on the Si (111) surface. The importance and advantage of polarization-dependent surface EXAFS studies are discussed.
- Received 30 November 1978
DOI:https://doi.org/10.1103/PhysRevB.20.664
©1979 American Physical Society