Sensitivity of Raman spectra excited at 325 nm to surface treatments of undoped polycrystalline diamond films

Abstract

AbstractAbout 20 μm thick films were deposited in the same run by MPCVD at 900 °C on Si substrates and then hydrogenated in situ during 30 min with a hydrogen plasma at the same temperature. Their surfaces were kept as prepared or more or less strongly oxidized by annealing at 600 °C under ambient atmosphere or by sulphochromic acid or aqua regia treatments. Raman spectra were excited at 325 and 632.8 nm. Spectra of the as‐prepared sample exhibit structures around 2835 and 2895 cm–1 from monohydride carbon–hydrogen ascribed to the atomically flat (111) and (100) areas, respectively, on the facets of the sample surface crystallites. The decrease of these structures in the normalized spectra after the various oxidation treatments confirms these assignments. The decrease is smaller for the aqua regia treatment than for the two other treatments which give similar effects. Other Raman signals from sp2 C around 1589 cm–1 and CHx bonds around 2930, 2952, 3025 and 3050 cm–1 originate from species at the surface and within the films. Their variation with the oxidizing treatments indicates a significant contribution from the surface species. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)