SURFACE BONDING STATES OF NANO-CRYSTALLINE DIAMOND BALLS

Abstract

The rough surface of nano-crystalline diamond spheres induces surface electronic states which appear as a broadened pre-peak over approx. 15 eV at the C K-edge energy threshold for carbon in the parallel electron energy loss spectrum (PEELS). This appears to be at least partially due to 1s-π* transitions, although typically the latter occupy a range of only 4 eV for the sp2 edge of highly-oriented pyrollytic graphite (HOPG). No π* electrons appear in the conduction band inside the diamond particles, where all electrons are sp3 hybridized. PEELS data were also obtained from a chemical vapour deposited diamond film (CVDF) and gem-quality diamond for comparison with the spectra of nano-diamonds. The density of sp2 and sp3 states on the surface of diamond nano-crystals is calculated for simple structural models of the diamond balls, including some conjecture about surface structures. The results are used to interpret the sp2/sp3 ratios measured from the PEELS spectra recorded as scans across the particles. Surface roughness at the atomic scale was also examined using high-resolution transmission electron microscopy (HRTEM) and electron nano-diffraction patterns were used to confirm the crystal structures.