Seeded growth of high-quality transition metal dichalcogenide single crystals via chemical vapor transport

Abstract

Transition metal dichalcogenides (TMDs) are van der Waals layered materials with sizable and tunable bandgaps, offering promising platforms for two-dimensional electronics and optoelectronics. To this end, the bottleneck is how to acquire high-quality single crystals in a facile and efficient manner. As one of the most widely employed methods of single-crystal growth, conventional chemical vapor transport (CVT) generally encountered problems including the excess nucleation that leads to small crystal clusters and a slow growth rate. To address these issues, a seed crystal is introduced to suppress the nucleation and an inner tube is adopted as both a separator and a flow restrictor, favoring the growth of large-sized and high-quality TMD single crystals successfully. Three examples are presented: the effective growth of millimeter-sized MoSe₂ and MoTe₂ single crystals, and the greatly shortened growth period for a PtSe₂ single crystal, all of which are synthesized in high quality according to detailed characterization. The mechanism of seeded CVT is discussed. Furthermore, a phototransistor based on exfoliated multi-layered MoSe₂ displays an excellent photoresponse under ambient conditions, and considerably rapid rise and fall times of 110 and 125 μs are obtained, which might be contributed by the good crystallinity of the as-grown crystal. This work paves the way for developing a facile and versatile method to synthesize high-quality TMD single crystals in the laboratory.