Fig. 5: Facilitated rutile TiO₂ epitaxy by Δμ_O across the TiO₂/VO₂ interface.

a Ti L-edge XAS spectra of TiO₂ grown on VO₂ templates under different \(pO_2\) (H24mT, H6mT). The Ti L_2,3-edge XAS signals from the H6mT were more intense and sharper than from H24mT. b XPS spectra of the Ti 2p core level of H24mT, H6mT. negligible Ti³⁺ contribution from the H6mT was observed compared to H24mT in TiO₂/VO₂ heterostructures, which reveals the suppression of V_O formation even at the surface of TiO₂ as a result of increased oxygen transport across TiO₂/VO₂ interface under low \(pO_2\). Both XAS and XPS results reveal increased perfection of rutile TiO₂ films after growth at low \(pO_2\). c First-principles density functional theory (DFT) calculations to determine values of the lower and upper limit of the chemical potential of μ_O for TiO₂ and VO₂ formation. TiO₂ is the only stable compound at − 9.624 eV ≤ μ_O ≤ − 8.767 eV. Comparison of the formation energies of V_O in rutile VO₂ and TiO₂ as a function of Fermi level in the band gap of TiO₂. d Increased thermodynamic driving force Δμ_O, assisted by high ionic kinetics k, across the interface increased the perfection of registry in the lattice of TiO₂ films by increasing “effective” \(pO_2\) and lowering the activation barrier for epitaxy with concurrent emergence of a metallic VO_2-δ sacrificial templates.