Hydrogen-induced surface structuring of a cubic boron nitride (100) face studied by low-energy electron diffraction and electron spectroscopic techniques

Abstract

The surface structure and secondary-electron-emission fine structure of single-crystal cubic boron nitride (100), exposed to hydrogen-plasma or argon-ion sputtering, was studied in situ with low-energy electron diffraction, secondary-electron-emission spectroscopy, electron-energy-loss spectroscopy, and Auger electron spectroscopy. Low-energy argon irradiation is capable of disrupting local ordering on the cubic boron nitride surface and to transform the near-surface region into ${\mathrm{sp}}^{2}$-type bonding. The effect of hydrogen-plasma treatment is to etch the ${\mathrm{sp}}^{2}$ amorphous layer away and regenerate ${\mathrm{sp}}^{3}$ crystallinity on the surface. However, prolonged hydrogen-etching results in the faceting of the (100) face and changes surface symmetry from (100) 2\ifmmode\times\else\texttimes\fi{}1 into (111) 1\ifmmode\times\else\texttimes\fi{}1. The secondary-electron-emission spectra of cubic boron nitride were measured in the 0--50-eV electron kinetic-energy range in order to identify fine structures related to conduction-band states. These fine structures are found to be highly sensitive to long-range order, and their occurrence is characteristic of crystal perfection. The effect of cumulative argon sputtering is to degrade the secondary-electron-emission fine structures and suppress the secondary-electron yield. The excitation of the cubic boron nitride bulk plasmon at 36.8-eV electron loss energy is identified as the primary true secondary-electron production channel. Suppression of the bulk plasmon due to near-surface disorder results in the degradation of secondary-electron production from the surface. In contrast, hydrogen-plasma treatment of the amorphorized surface regenerates the bulk plasmon, the secondary-electron-emission fine structures as well as the total secondary-electron yield. The results provide strong evidence that the secondary-electron emission from surfaces is a sensitive function of near-surface order.