Crystallization of layered metal-dichalcogenides films on amorphous substrates

Anisotropic materials with layered structure, like MoS2 and WSe2, play an important role in a number of technologies. Some of these applications (lubrication, photovoltaics) require polycrystalline films oriented with their c axis perpendicular to the substrate surface (type-II texture), which is the thermodynamically favorable texture. However, films with the substrate ∥c (type-I texture) are usually obtained. We report that an ultrathin (<10 nm) metal-chalcogenide interlayer eutectics, like Ni3Se2, SnSe<thin>2, or InSe disentangle the growth mode of the film from the underlying amorphous substrate, and hence, WSe2 films with a perfect type-II texture and crystallites at least a few mm2 large are obtained at temperatures as low as 700 °C (van der Waals rheotaxy–vdWR). The mechanism for this growth mode is proposed.