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vanadium selenide is a member of transition metal dichalcogenides (TMDs) with intriguing properties. It is currently the focus of research efforts to synthesize and disperse VSe2 nanoparticles, which have potential for use as a cancer therapy agent by inducing apoptosis in tumor cells.
However, the controllable fabrication of low dimensional TMDs with tuned defect structures on demand remains a challenge. In this article, we successfully synthesized single-layer VSe2 on Au(111) using molecular beam epitaxy (MBE), and elaborately investigated its structural transformation by a combination of STM and density functional theory (DFT).
We found that if VSe2 is deposited with a relative excess of V over Se, the surface becomes decorated with a hexagonal defect structure having no bulk analogue. Revealed by high resolution STM, the hexagonal pattern is actually constructed with regularly alternating bright and dark dots. The corresponding moire pattern is attributed to the lattice mismatch between as-grown VSe2 and the underlying Au(111) substrate.
Meanwhile, if excessive Se is deposited during the MBE growth, a defective architecture with streaked patterns emerges. This phase is reversible and can be converted into VSe2 with the moire periodicity by subsequent post annealing treatment and readdition of excess Se. This demonstrates that the structure of monolayer VSe2 can be controlled by subtle regulation of deposition ratios and thermal treatments. This work provides a valuable insight toward the controllable fabrication of TMDs with tailored defects and electronic structures on demand, which may promote their broad applications in catalysis and nanoelectronics.