Suppression of Strain Relaxation in VO2/TiO2 Multilayered Films

Abstract

Strained VO2 films grown on (001) rutile TiO2 exhibit an abrupt insulator-to-metal transition (IMT) around room temperature. The transition temperature (Tc) increases when the critical thickness of ∼15 nm is exceeded. The strain relaxation is responsible for crack formation. Here, we show that inserting thin TiO2 layers suppresses the strain relaxation of VO2. We fabricated several VO2/TiO2/VO2 trilayer films on (001) TiO2 substrates. Each film had a VO2 film of 8 nm, but the TiO2 thickness was varied. Strained VO2/TiO2 multilayer films show IMT with clear hysteresis around room temperature when the TiO2 thickness exceeds 4 nm. In addition, we fabricated 8 nm thick VO2/9 nm thick TiO2 multilayered films. Tc is maintained around room temperature even though the total VO2 thickness is ∼50 nm. The present results provide a useful design concept of thin-film materials for thermochromic applications of strained VO2.