Epitaxial Growth of Rectangle Shape MoS2 with Highly Aligned Orientation on Twofold Symmetry a-Plane Sapphire.

Research on transition metal dichalcogenides (TMDs) has been accelerated by the development of large-scale synthesis based on chemical vapor deposition (CVD) growth. However, in most cases, CVD-grown TMDs are composed of randomly oriented grains, and thus contain many distorted grain boundaries (GBs), which seriously degrade their electrical and photoelectrical properties. Here, the epitaxial growth of highly aligned MoS2 grains is reported on a twofold symmetry a-plane sapphire substrate. The obtained MoS2 grains have an unusual rectangle shape with perfect orientation alignment along the [1-100] crystallographic direction of a-plane sapphire. It is found that the growth temperature plays a key role in its orientation alignment and morphology evolution, and high temperature is beneficial to the initial MoS2 seeds rotate to the favorable orientation configurations. In addition, the photoluminescence quenching of the well-aligned MoS2 grains indicates a strong MoS2 -substrate interaction which induces the anisotropic growth of MoS2 , and thus brings the formation of rectangle shape grains. Moreover, the well-aligned MoS2 grains splice together without GB formation, and thus that has negligible effect on its electrical transport properties. The progress achieved in this work could promote the controlled synthesis of large-area TMDs single crystal film and the scalable fabrication of high-performance electronic devices.