Formation and properties of thin-film composites vanadium oxide/porous anodic aluminum oxide

Abstract

Nanostructured thin-film composites vanadium oxide/porous anodic aluminum oxide (VO/PAO) were investigated. Thin layers of vanadium oxide were formed by sol-gel deposition from the solution of vanadium isopropoxide in isopropanol with subsequent annealing in Ar atmosphere at 500°C. As a substrate, porous anodic aluminum oxide and Si/SiO2 with PAO and without it were used. The orienting effect of PAO on the formation of the vanadium oxide layer has been established. Using the techniques of X-ray diffraction and electron microscopy, the formation of the crystalline vanadium dioxide VO2 phase, the orientation of the grains, which correlates with the morphology of the PAO substrate, has been established. The influence of electrolyte and stresses during the filling of the pores of aluminum oxide on the formation of grains, nanoclusters, and agglomerates of vanadium oxide is analyzed. Electrical properties of the nanostructured vanadium oxide layer were investigated. The characteristic of electrical resistance indicate the reversible insulator-metal phase transition in vanadium dioxide. The capacitances-voltage characteristics of the Al/VO/PAO/Al sandwich structures had an asymmetric character with an increase in capacitance upon increasing the negative bias voltage on vanadium oxide. This effect is determined by the phase transition insulator-metal under the influence of electric field. In addition, injection of electrons from the Al electrode or their extraction from vanadium oxide as well as recharging of the VO/PAO interface states can exert the influence. The mechanism for vanadium dioxide formation on the orienting substrate made of porous anodic aluminum oxide is proposed.