Stable anionic sites on hydrogenated (111) surfaces of cubic boron nitride resulting from hydrogen atom removal under chemical vapor deposition conditions

Abstract

In plasma or hot-filament assisted chemical vapor deposition of cubic boron nitride (cBN), the formation of a surface radical site by hydrogen atom removal from a hydrogenated (111) surface was expected to be followed by the formation of an anionic vacant site (AVS) by capturing an electron, since this yields a closed shell structure of the site atom. This possibility was investigated by ab initio as well as by semiempirical molecular orbital calculations using large cluster models. The stabilization energy of the AVS on cBN(111) with a boron top layer, namely (111) B, was 1.8–2.3 eV; this value is comparable with that of diamond. On the other hand, that of cBN(111) on a nitrogen surface, namely (111) N, amounted to 5.3–5.9 eV. The nucleophilic nature of the AVS with a lone pair of electrons suggests electrophilic reagents for related reactions. This helped us to propose SN2 growth reactions for diamond growth both on diamond and cBN(111) surfaces. The difference in chemical reactivity between (111) N and (111) B could be interpreted in terms of the “hard” and “soft” acid base concept that has been renewed by the frontier orbital theory.