An oxygen-rich, tetrahedral surface phase on high-temperature rutile VO$_2$(110)$_\text{T}$ single crystals

TL;DR

This study provides an atomic-scale analysis of the VO₂(110) surface, revealing an oxygen-rich reconstructed phase with a tetrahedral surface structure, supported by experimental and theoretical methods, relevant for its applications.

Contribution

It introduces a new structural model for the VO₂(110) surface reconstruction, supported by experimental data and DFT calculations, highlighting its stability over previous models.

Findings

Reconstruction forms an oxygen-rich (2×2) superstructure.

The surface features rings of corner-shared tetrahedra.

The reconstructed surface is more stable than previous models.

Abstract

Vanadium dioxide undergoes a metal-insulator transition (MIT) from an insulating (monoclinic) to a metallic (tetragonal) phase close to room temperature, which makes it a promising functional material for many applications, e.g. as chemical sensors. Not much is known about its surface and interface properties, although these are critical in many of its applications. This work presents an atomic-scale investigation of the tetragonal rutile VO$_2$(110)$_\text{T}$ single-crystal surface and reports results obtained with scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS), supported by density-functional theory-based (DFT) calculations. The surface reconstructs into an oxygen-rich (2$\times$2) superstructure that coexists with small patches of the underlying, unreconstructed (110)-(1$\times$1) surface. The best structural model for the (2$\times$2) surface termination, conceptually derived from a vanadium pentoxide (001) monolayer, consists of rings of corner-shared tetrahedra. Over a wide range of oxygen chemical potentials this reconstruction is more stable than the unreconstructed (110) surface as well as models proposed in the literature.