Through in situ photoemission spectroscopy, we investigated the change in the electronic structures and V-V dimerization of dimensionality-controlled VO2 films coherently grown on TiO2(001) substrates. In the nanostructured films, the balance between the instabilities of a bandlike Peierls transition and a Mott transition is controlled as a function of thickness. The characteristic spectral change associated with temperature-driven metal-insulator transition in VO2 thick films holds down to 1.5 nm (roughly corresponding to five V atoms along the  direction), whereas VO2 films of less than 1.0 nm exhibit insulating nature without the V-V dimerization characteristic of VO2. These results suggest that the delicate balance between a Mott instability and a bandlike Peierls instability is modulated at a scale of a few nanometers by the dimensional crossover effects and confinement effects, which consequently induce the complicated electronic phase diagram of ultrathin VO2 films.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics