Periodic Spiral Ripples on VS2 Flakes: A Tip-Enhanced Raman Investigation

Using atmospheric-pressure chemical vapor deposition, we have synthesized vanadium disulfide (VS2) flakes with a metallic 1T phase that display nanoscale spiral surface ripples. To understand the origin of these chiral patterns in these transition metal dichalcogenides, tip-enhanced Raman spectroscopy and Kelvin probe force microscopies were jointly used to investigate their crystal structure, possible oxidation, and electronic properties, respectively. We found that the surface corrugation consists of small crystalline domains with distinct orientations. The change in local orientation is observed concomitantly with a spectral shift of the lattice modes of VS2 and results in the formation of grain boundaries between the domains with distinct orientation. Additionally, the periodic surface structure is modulating the work function of VS2 by 14 meV.