Pressure-Induced Phase Transition in Multilayered Vanadium Diselenide Nanosheets

Layered transition-metal dichalcogenides have recently attracted considerable attention due to their unique mechanical and opto-electronic properties. Here, we report the investigation of structural, vibrational, and electronic properties of vanadium diselenide (VSe2) nanosheets up to a pressure of 33 GPa by diamond anvil cell-based pressure-induced studies. The experimental results indicate a structural transition from the metallic trigonal (P (3) over bar m1) to a metallic monoclinic (C2/m) phase at similar to 7 GPa, consistent with our ab initio calculations. A decrease in the metallic nature of the trigonal phase is evident from the reduction in the width of the Fermi level band crossing in the high-pressure monoclinic phase. Transmission electron microscopy analyses reveal that VSe2 nanosheets recover the original ambient structure upon decompression. Raman spectroscopy studies at high pressures identify an A(1g) soft phonon (similar to 236 cm(-1)) and an E-g phonon (208 cm(-1)) that show normal hardening and consequently phase instability at similar to 7 GPa. Using our experimental Raman mode Gruneisen parameters gamma(i), the thermal expansion coefficient alpha(v) of the Vse(2) nanosheets at ambient temperature is obtained as -0.96 x 10(-6) K-1. This pressure-tuned behavior of these layered nanomaterials can be beneficial in the calibration and development of novel nanodevices using Vse(2) nanosheets under an extreme stress environment.