10:30 AM - 10:45 AM
▲ [20a-C302-6] Stepwise Insulator-to-Metal Transition of VO2/TiO2 Multilayer Films
Keywords:Epitaxial film, Phase transition, Vanadium dioxide
It is known that VO2 epitaxial films grown on (001) TiO2 single crystal exhibit insulator-to-metal transition (MIT) near room temperature that is much lower than that of bulk VO2(68 °C). Therefore, VO2/(001) TiO2 has attracted attention as a candidate for optoelectronic devices that control electrical conductivity as well as infrared transmission. However, there are several issues to be solved; The critical thickness of VO2 on (001) TiO2 is extremely thin (~20 nm), and crack formation occurs upon MIT due to the lattice strain. To address these issues, we examined VO2/TiO2 multilayer films.
X-ray reflectivity and out-of-plane XRD patterns of the resultant MLs indicate that the VO2/TiO2 MLs were successfully fabricated as designed. Figure 1 shows the ρ−T of the resultant VO2/TiO2 MLs. The 8-nm-thick and 40-nm-thick single layer VO2 exhibit an abrupt and gradual one-step MIT respectively, consistant with previous report. On the other hand, VO2/TiO2 MLs shows a stepwise MIT behavior. Moreover, with increasing layer number, the Tc gradually increases accompanied by the disappearance of the stepwise behavior. The stepwise MIT usually suggests the existence of multiphases with different Tc. Figure 2 shows topographic AFM images of the single layer VO2 and VO2/TiO2 ML after heating/cooling cycles. Although some cracks were formed in the case of the 40-nm-thick single layer VO2 after cycling, the VO2/TiO2 ML did not show cracks. These results suggest that multilayer fabrication would be effective to increase the VO2 thickness and suppress crack formation.
X-ray reflectivity and out-of-plane XRD patterns of the resultant MLs indicate that the VO2/TiO2 MLs were successfully fabricated as designed. Figure 1 shows the ρ−T of the resultant VO2/TiO2 MLs. The 8-nm-thick and 40-nm-thick single layer VO2 exhibit an abrupt and gradual one-step MIT respectively, consistant with previous report. On the other hand, VO2/TiO2 MLs shows a stepwise MIT behavior. Moreover, with increasing layer number, the Tc gradually increases accompanied by the disappearance of the stepwise behavior. The stepwise MIT usually suggests the existence of multiphases with different Tc. Figure 2 shows topographic AFM images of the single layer VO2 and VO2/TiO2 ML after heating/cooling cycles. Although some cracks were formed in the case of the 40-nm-thick single layer VO2 after cycling, the VO2/TiO2 ML did not show cracks. These results suggest that multilayer fabrication would be effective to increase the VO2 thickness and suppress crack formation.