Polarized Raman scattering in micrometer-sized crystals of triclinic vanadium dioxide

摘要

Triclinic vanadium dioxide VO_2 (T) films were produced using cathodic arc deposition. Under certain conditions, the film growth on sapphire substrates Al_2O_3 (001) is associated with the formation of triclinic monocrystals with lateral sizes of several tens of micrometers. Borders between different crystallites can be determined by Raman mapping analysis. X-ray diffraction measurements revealed that the micrometer-sized monocrystals had two different orientations-epitaxial (002) and non-epitaxial (201). The film was studied by polarized micro-Raman spectroscopy, which can be used to determine the orientation of any single crystallite. The Raman tensor elements of the VO_2 (T) phase were determined, and it was shown that though crystallographically triclinic VO_2 cell could be fitted by monoclinic one with a high degree of precision, such monoclinic approximation was not valid in terms of Raman spectroscopy. Contrary to the two types of phonons expected for the monoclinic crystal [having five nonzero (four independent) or four nonzero (two independent) Raman tensor elements], all phonons in VO_2 (T) have nine (six independent) generally nonzero tensor components.