HYDROGEN-INDUCED SURFACE STRUCTURING OF A CUBIC BORON NITRIDE(100) FACE STUDIED BY LOW-ENERGY-ELECTRON DIFFRACTION AND ELECTRON SPECTROSCOPIC TECHNIQUES

The surface structure and secondary-electron-emission fine structure o f 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-energ y-loss spectroscopy, and Auger electron spectroscopy. Low-energy argon irradiation is capable of disrupting local ordering on the cubic boro n nitride surface and to transform the near-surface region into sp(2)- type bonding. The effect of hydrogen-plasma treatment is to etch the s p(2) amorphous layer away and regenerate sp(3) crystallinity on the su rface. However, prolonged hydrogen-etching results in the faceting of the (100) face and changes surface symmetry from (100) 2x1 into (111) 1x1. The secondary-electron-emission spectra of cubic boron nitride we re measured in the 0-50-eV electron kinetic-energy range in order to i dentify fine structures related to conduction-hand states. These fine structures are found to be highly sensitive to long-range order, and t heir occurrence is characteristic of crystal perfection. The effect of cumulative argon sputtering is to degrade the secondary-electron-emis sion fine structures and suppress the secondary-electron yield. The ex citation of the cubic boron nitride bulk plasmon at 36.8-eV electron l oss energy is identified as the primary true secondary-electron produc tion channel. Suppression of the bulk plasmon due to near-surface diso rder results in the degradation of secondary-electron production from the surface. In contrast, hydrogen-plasma treatment of the amorphorize d surface regenerates the bulk plasmon, the secondary-electron-emissio n fine structures as well as the total secondary-electron yield. The r esults provide strong evidence that the secondary-electron emission fr om surfaces is a sensitive function of near-surface order.