Influence of Impurities on the Morphology and the Raman Spectra of Cubic Boron Nitride

It is still a challenging problem to understand the growth mechanisms of cubic boron nitride (c-BN) in the high pressure high temperature (HPHT) synthesis as well as to develop film deposition techniques (CVD- or PVD methods) of microcrystalline c-BN layers for protective or abrasive applications. It is possible to grow cm- seized diamond single crystals by HPHT- methods and to achieve microcrystalline diamond films by CVD- or PVD methods with good-mechanical properties, but regarding c-BN, even in the HPHT- process it is not possible to obtain well grown, large single crystals and up to now, film deposition methods lead only to the formation of nanocrystalline c-BN layers of weak quality. The structural analogy between carbon- and boron nitride sp2-and sp3- phases is only valid regarding their physical and mechanical properties, but there is a significant difference in their syntheses. In order to enhance and modify c-BN growth, the understanding of the growth mechanism is of significant importance. A detailed Raman spectroscopic characterization of HPHT- c-BN samples with distinct morphology and facettation indicates a correlation between crystal impurities and the resulting morphology. The results reveal a strong anisotropy of <100>- and <111>- growth directions of c-BN, which are affected by crystal impurities and their nature will be discussed. The presented study reveal significant information to modify c-BN growth and to realize the growth of microcrystalline films of cubic boron nitride.