Thickness-dependent metal-to-insulator transition in epitaxial VO₂ films

Abstract

The metal-to-insulator transition (MIT) of VO 2 films with a thickness of 3-100 nm on TiO 2 (001) substrates has been investigated. When varying the film thickness from 10 to 100 nm, the MIT temperature was first kept at 290 K in the range of 10-14 nm, and then increased with thickness increasing due to the strain relaxation. The origin of the suppressed transition in VO 2 films thinner than 6 nm was also investigated. When prolonging the in situ annealing time, the sharpness, amplitude and width of the transition for 4 nm thick films were all increased, suggesting improved crystallinity rather than Ti diffusion from the substrates. In addition, the MIT was suppressed when the VO 2 films were covered by a TiO 2 layer, indicating that the interface effect via the confinement of the dimerization of the V atoms should be the main reason.

Reducing orbital occupancy in VO2 suppresses Mott physics while Peierls distortions persist

“…In fact, interdiffusion of Ti ions from commonly used rutile TiO 2 substrates has been known to occur during growth of VO 2 films, but has thus far only been considered as a detriment to the MIT and the intrinsic properties have not been thoroughly studied. [12][13][14][15][16][17] Starting with VO 2 /TiO 2 films with near atomically sharp interfaces, in this Rapid Communication we controllably introduce Ti interdiffusion to study its effect on the orbital occupancy of VO 2 . We determine Tiincorporated VO 2 films to display no evidence of an electronic MIT, exhibiting the low resistivity characteristic of metallic VO 2 at all temperatures.…”

Thickness dependence of electronic structures in VO2 ultrathin films: Suppression of the cooperative Mott-Peierls transition

“…The vacuum-transferring of the grown samples prevented the overoxidation of the surface layer (see Fig. S3 in Supplemental Material [49]) that had been an obstacle in previous studies on the thickness-dependence of VO2 [36][37][38][39][40][41][42]. The XAS spectra were also measured in situ with linearly polarized light via measurement of the sample drain current.…”

“…Moreover, the increment of electron-electron correlation (Mott instability) due to the dimensional crossover effects concomitant with a decrease in film thickness [33][34][35] may also suppress the cooperative Mott-Peierls transition in VO2. Although this straightforward approach has been attempted by some groups so far [36][37][38][39][40][41][42][43][44], there is little consensus about the intrinsic behavior of ultrathin VO2 films in reducing the film thickness because these samples suffer from significant interdiffusion of the constituent cations at the interface [36][37][38][39][40][41][42][43] as well as inhomogeneous strain from the substrate [36][37][38] and surface overoxidation [36][37][38][39][40][41][42]. Therefore, systematic control of the dimensionality while keeping the fundamental chemical and crystallographic structural parameters fixed is crucial to obtaining information on how the electronic structures and characteristic dimerization of VO2 change as a function of film thickness.…”

Enhanced Thermochromic Properties of Vanadium Dioxide (VO2)/Glass Heterostructure by Inserting a Zr-Based Thin Film Metallic Glasses (Cu50Zr50) Buffer Layer

“…This could be due to the larger crystal size in the non-buffered VO 2 thin films [32]. The samples with smaller or larger ∆H values can be applied in different fields and the ∆H value is closely connected with the quality of crystallization and crystallite dimension in the VO 2 thin films [33][34][35]. From Table 1, it can be seen that the ∆H values of the buffered VO 2 thin films are much smaller than the non-buffered one.…”