Chemical Vapor Deposition Grown Wafer-Scale 2D Tantalum Diselenide with Robust Charge-Density-Wave Order.

2D metallic transition metal dichalcogenides (MTMDCs) are benchmark systems for uncovering the dimensionality effect on fascinating quantum physics, such as charge-density-wave (CDW) order, unconventional superconductivity, and magnetism, etc. However, the scalable and thickness-tunable syntheses of such envisioned MTMDCs are still challenging. Meanwhile, the origin of CDW order at the 2D limit is controversial. Herein, the direct synthesis of wafer-scale uniform monolayer 2H-TaSe2 films and thickness-tunable flakes on Au foils by chemical vapor deposition is accomplished. Based on the thickness-tunable 2H-TaSe2, the robust periodic lattice distortions that relate to CDW orders by low-temperature transmission electron microscopy are directly visualized. Particularly, a phase diagram of the transition temperature from normal metallic to CDW phases with thickness by variable-temperature Raman characterizations is established. Intriguingly, dramatically enhanced transition temperature from bulk value ≈90 to ≈125 K is observed from monolayer 2H-TaSe2, which can be explained by the enhanced electron-phonon coupling mechanism. More importantly, an ultrahigh specific capacitance is also obtained for the as-grown TaSe2 on carbon cloth as supercapacitor electrodes. The results hereby open up novel avenues toward the large-scale preparation of high-quality MTMDCs, and shed light on their applications in exploring some fundamental issues.