Influence of impurities on the morphology and Raman spectra of cubic boron nitride

Abstract

The understanding of the growth mechanism of cubic boron nitride (c-BN) is still a challenging problem in the high pressure high temperature (HPHT) synthesis as well as in the development of film deposition techniques (CVD- or PVD-methods). The analogy between carbon- and boron nitride phases (h-BN/graphite, c-BN/diamond, wurtzitic boron nitride (w-BN)/londsdaleit) is only valid regarding their structural aspects and mechanical properties, but there are significant differences in their syntheses. It is possible to grow centimeter-sized diamond single crystals by HPHT-methods and to achieve polycrystalline diamond films by CVD- or PVD-methods with good mechanical properties and an individual crystallite size in the size of micrometers. Regarding c-BN, even in the HPHT process it is difficult to obtain well grown, large single crystals, and PVD film deposition methods without selective etching led so far only to the formation of nanocrystalline c-BN layers. In order to enhance and modify c-BN growth, the understanding of the growth mechanism is of significant importance. HPHT crystallites of c-BN with distinct morphology were thoroughly examined with Raman spectroscopy, SEM and XRD, and a correlation between crystal impurities and crystal morphology could be established. The results clearly indicate a strong anisotropy of 〈1 0 0〉- and 〈1 1 1〉-growth directions, which is affected by crystal impurities, and indicate w-BN domains preferably on 〈1 1 1〉 facets of c-BN (polytypism). Such a behavior is less dominant in other more ionic isostructural binary compounds.