Photoemission study of TiO2/VO2 interfaces

TL;DR

This study investigates the electronic properties of TiO2/VO2 interfaces using photoemission spectroscopy, revealing the influence of interface polarity and structural differences on metallic state formation.

Contribution

It provides new insights into how TiO2 capping layers affect VO2's electronic states and highlights the role of interface polarity and structural variations.

Findings

No metallic states observed below 300 K at TiO2/VO2 interfaces.

Polarity discontinuity influences electronic behavior at interfaces.

Stronger incoherent spectral features in rutile TiO2 capped samples.

Abstract

We have measured photoemission spectra of two kinds of TiO$_2$-capped VO$_2$ thin films, namely, that with rutile-type TiO$_2$ (r-TiO$_2$/VO$_2$) and that with amorphous TiO$_2$ (a-TiO$_2$/VO$_2$) capping layers. Below the Metal-insulator transition temperature of the VO$_2$ thin films, $\sim 300$ K, metallic states were not observed for the interfaces with TiO$_2$, in contrast with the interfaces between the band insulator SrTiO$_3$ and the Mott insulator LaTiO$_3$ in spite of the fact that both TiO$_2$ and SrTiO$_3$ are band insulators with $d^0$ electronic configurations and both VO$_2$ and LaTiO$_3$ are Mott insulators with $d^1$ electronic configurations. We discuss possible origins of this difference and suggest the importance of the polarity discontinuity of the interfaces. Stronger incoherent part was observed in r-TiO$_2$/VO$_2$ than in a-TiO$_2$/VO$_2$, suggesting Ti-V atomic diffusion due to the higher deposition temperature for r-TiO$_2$/VO$_2$.