Two-dimensional (2D) WS₂ offers great prospects for assembling next-generation optoelectronic and electronic devices due to its thickness-dependent optical and electronic properties. However, layer-number-controlled growth of WS₂ is still a challenge up to now. This work presents controlled growth of bilayer WS₂ triangular flakes by carbon-nanoparticle-assisted chemical vapor deposition (CVD) process. The growth mechanism is also proposed. In addition, the field effect transistors (FETs) based on monolayer and bilayer WS₂ are also fabricated and investigated. The bilayer FET displays a mobility of 34 cm²·V^-1·s^-1, much higher than that of the monolayer FET. The high figures of merit make bilayer WS₂ a promising candidate in high-performance electronics and optoelectronics.

In-plane symmetry is an important contributor to the physical properties of two-dimensional layered materials, as well as atomically thin heterojunctions. Here, we demonstrate anisotropic/isotropic van der Waals (vdW) heterostructures of ReS₂ and MoS₂ monolayers, where interlayer coupling interactions and charge separation were observed by in situ Raman-photoluminescence spectroscopy, electrical, and photoelectrical measurements. We believe that these results could be helpful for understanding the fundamental physics of atomically thin vdW heterostructures and creating novel electronic and optoelectronic devices.