FUCHS-KLIEWER PHONON STRUCTURE AND SURFACE INTEGRITY OF NIO(100)

Defects have been deliberately introduced into NiO(100) single-crystal surfaces by Ar+ bombardment and by slow H-2 reduction, and the resulting surfaces have been studied by changes in their Fuchs-Kliewer phonon spectrum. Both treatments produce near-surface reduction, as measured by Auger electron spectroscopy. The phonon spectra are obtained by high-resolution electron energy loss spectroscopy (HREELS) using 2.8 eV electrons, with the electron loss data collected in the specular direction. Sputtered surfaces show great decreases in specularly diffracted intensity, but result in little change in the fundamental properties of the phonons. H-2-reduced surfaces show a more gradual decrease in total spectral intensity but yield an equally rapid decrease in phonon spectral intensity relative to that of the elastically scattered peak. At large reduction values, the phonon mode shifts to lower frequency. The changes in the phonon spectra are discussed in terms of current understanding of the nature of the defects created in Ar+ bombardment and in the H-2 reduction process.