Multiple regulation over growth direction, band structure, and dimension of monolayer WS2 by a quartz substrate

A substrate plays a crucial role in controlled growth and property modulation of two-dimensional (2D) transition-metal dichalcogenides (TMDCs). In this work, we report multiple regulation over growth direction, band structure, and dimension of an epitaxial monolayer (1L) WS2 by an m-plane quartz substrate. The as-grown WS2 is oriented on a 2-fold symmetric m-quartz based on an anisotropic lattice match, which is distinct from that on c-sapphire. Owing to the large thermal expansion coefficient, the m-quartz generates a large compressive thermal strain in the as-grown WS2. By manipulating this thermal strain, the band structure of 1L-WS2 can be in situ regulated and a direct-indirect band gap transition occurs when the thermal strain exceeds 0.5%. Moreover, the unique atom distribution of the m-plane quartz established an anisotropic diffusion barrier for adlayer monomers which restricted the growth of WS2 uniaxially. By exploiting this, the dimension of WS2 can be tailored from a 2D triangle to a one-dimensional ribbon with controlled growth time. This work not only deepens the understanding of the relationship between a substrate and a material but also provides an effective way to directly regulate the as-grown TMDCs with desirable structures and properties.