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 result ing surfaces have been studied by changes in their Fuchs-Kliewer phono n spectrum. Both treatments produce near-surface reduction, as measure d by Auger electron spectroscopy. The phonon spectra are obtained by h igh-resolution electron energy loss spectroscopy (HREELS) using 2.8 eV electrons, with the electron loss data collected in the specular dire ction. Sputtered surfaces show great decreases in specularly diffracte d 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.