Characteristics of plate-like and color-zoning cubic boron nitride crystals

The polarities of a kind of plate-like and color-zoning cubic boron nitride (cBN) crystal were extensively investigated by microscopy, chemical etching, XPS, Raman scattering, and current-voltage measurements. The {1 1 1}B faces and {1¯1¯1¯}N faces of the cBN samples can be easily distinguished by optical microscope as there are a lot of defects incorporate in {1¯1¯1¯}N sectors serving as the color centers, while the {1 1 1}B sectors have less defects and are nearly colorless. Both XPS and Raman spectra also revealed the uneven distributions of N vacancies and substitutional impurities in cBN crystals. The determination of {1 1 1}B faces and {1¯1¯1¯}N faces can also be verified by the results of the chemical etching because the {1¯1¯1¯}N faces have much faster etch rates than the {1 1 1}B faces. According to XPS, the {1 1 1}B faces have more C and O contaminations than the {1¯1¯1¯}N faces, however the {1¯1¯1¯}N faces have larger atomic ratio of B:N after surface cleaning by Ar+ sputtering. In the Raman spectra of the {1¯1¯1¯}N sectors of cBN, several small broad infrared-active phonon bands emerge nearby TO and LO modes because of the disorder-activated Raman scattering. As for the {1 1 1}B sectors, this phenomenon disappears. In addition, the {1 1 1}B faces have much smaller leakage current than the {1¯1¯1¯}N faces, which indicates that the {1 1 1}B sectors have higher crystalline quality.