Quasiparticle self-consistent (QS) GW calculations are performed for bulk and monolayer V2O5. The orbital character of the bands and the bulk monolayer difference at the LDA level are discussed first. We find that the QSGW self-energy overestimates the gap by an unusually large amount. The main reason for this is identified to be the lattice polarization effect: the large LO-TO splittings in this polar material enhance the screening and reduce the screened Coulomb interaction affecting the gap. The effect is estimated to reduce the screened Coulomb interaction and hence the self-energy by a factor 0.38 (for bulk) and brings the calculated optical response functions in fairly good agreement with experiment. For monolayer V2O5, we find that the QSGW gap varies as 1/L with L the size of the spacing between the monolayers in a supercell. This results from the long-range nature of the self-energy Σ = iGW and the similar 1/L behavior of the dielectric screening.

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VO with a layered van der Waals (vdW) structure has been widely studied because of the material's potential in applications such as battery electrodes. In this work, microelectronic devices were fabricated to study the electrical and optical properties of mechanically exfoliated multilayered VO flakes. Raman spectroscopy was used to determine the crystal structure axes of the nanoflakes and revealed that the intensities of the Raman modes depend strongly on the relative orientation between the crystal axes and the polarization directions of incident/scattered light. Angular dependence of four-probe resistance measured in the van der Pauw (vdP) configuration revealed an in-plane anisotropic resistance ratio of ∼100 between the a and b crystal axes, the largest in-plane transport anisotropy effect experimentally reported for two-dimensional (2D) materials to date. This very large resistance anisotropic ratio is explained by the nonuniform current flow in the vdP measurement and an intrinsic mobility anisotropy ratio of 10 between the a and b crystal axes. Room-temperature electron Hall mobility up to 7 cm/(V s) along the high-mobility direction was obtained. This work demonstrates VO as a layered 2D vdW oxide material with strongly anisotropic optical and electronic properties for novel applications.