Poster abstract

A number of reasonably small (250 um x 250 um x 100 um) single crystals of HPHT cubic boron nitride have been studied by micro Raman spectroscopy and low temperature photoluminescence microscopy using 325 nm and 488 nm laser excitation. The crystals were grown with the aid of various catalysts so as to produce samples that varied from B-rich to N-rich stoichiometries. Raman spectra were investigated as a function of stoichiometry and specimen temperature up to 1300ºC. Fine structure associated with the TO and LO Raman peaks was noted and its possible relationship to extended defects in the material is under investigation. Two new optical systems have been discovered and the results are currently being analysed. Particularly fine examples of the 387 nm centre have been encountered and the phonon coupling is associated with unusually low energy phonons. A tentative explanation of this coupling will be presented in terms of a resonant mode caused by tungsten, used as a catalyst, incorporated into the BN lattice. TEM, EELS and CBED investigations confirm that the samples are uncontaminated by hexagonal BN.