Suppression of Strain Relaxation in VO₂/TiO₂ Multilayered Films

Abstract

Strained VO 2 films grown on (001) rutile TiO 2 exhibit an abrupt insulator-to-metal transition (IMT) around room temperature. The transition temperature (T c ) increases when the critical thickness of ∼15 nm is exceeded. The strain relaxation is responsible for crack formation. Here, we show that inserting thin TiO 2 layers suppresses the strain relaxation of VO 2 . We fabricated several VO 2 /TiO 2 /VO 2 trilayer films on (001) TiO 2 substrates. Each film had a VO 2 film of 8 nm, but the TiO 2 thickness was varied. Strained VO 2 /TiO 2 multilayer films show IMT with clear hysteresis around room temperature when the TiO 2 thickness exceeds 4 nm. In addition, we fabricated 8 nm thick VO 2 /9 nm thick TiO 2 multilayered films. T c is maintained around room temperature even though the total VO 2 thickness is ∼50 nm. The present results provide a useful design concept of thin-film materials for thermochromic applications of strained VO 2 .