Direct growth of NbSe2 and TiSe2 thin flakes via deposited film selenization

Abstract

We report the direct growth of thin flakes of NbSe2 and TiSe2 on c-plane sapphire substrate via the selenization of deposited Nb and Ti films, respectively. The effect of the cooling rate on the shapes of the NbSe2 thin flakes, for example, hexagons and triangles, was studied. In particular, rapid cooling after selenization of the deposited Nb film was found to be effective for growing triangular NbSe2 flakes. Raman spectroscopy of one sample prepared by rapid cooling revealed an unidentified vibration peak in addition to the prominent characteristic peaks of 2H-NbSe2. The Ti film could only be selenized by using sodium chloride as a transport agent, which resulted in the growth of TiSe2 thin flakes having a half-hexagonal shape without the incorporation of residual materials. Temperature-dependent resistances measurement, including the measurements of the temperature of maximum resistance and Rmax/R293K ratio, indicated a conventional charge-density wave transition in the TiSe2 thin flakes.