Comparative Analysis of VO₂ Thin Films Prepared on Sapphire and SiO₂/Si Substrates by the Sol–Gel Process

Abstract

VO 2 thin films were successfully grown on sapphire and SiO 2 /Si substrates by the sol-gel process. The VO 2 phase was well formed during simplified low pressure annealing in oxygen. The films prepared on sapphire directly crystallized to the VO 2 phase without passing through intermediate phases with increasing the annealing temperature, resulting in highly [010]oriented films on Al 2 O 3 (10 " 1 10) substrate. In contrast, the polycrystal films grown on SiO 2 /Si reached the final VO 2 phase with passing through several phases. Mixed phases existed at the interface between the film and substrate. For the films on sapphire, the phases with low-valent vanadium appeared drastically at the interface region along the depth, whereas the phase of the polycrystal film slowly changed into a low valence state at the initial stage of the interface and then returned to a high value. And both films showed an abrupt change in resistivity at the different transition temperature. The property of the interface may affect the crystallization and the metal-insulator transition of the films.

Vanadium oxide thin films and fibers obtained by acetylacetonate sol–gel method

“…2), and the temperature dependence of resistance for this sample (Fig. 3) demonstrates the conductivity jump at the transition of up to more than two orders of magnitude which is in agreement with the results of some other authors for vanadium dioxide thin films on silicon substrates (see, e.g., [8] and references therein). Film thickness is d = 80 nm.…”

“…There are different routes for the vanadium oxide films sol-gel preparationthe hydrolysis of alkoxides, the technique based on melt quenching [4,[6][7][8][9], the acetylacetonate chemical method [10] in which the VO2 films are deposited onto Si substrates using VO(acac)2 as a precursor. VO (acac)2 offers certain advantages when compared with vanadium alkoxides because of its stability against precipitation and excessive hydrolysis.…”

Effect of the substrate on the insulator–metal transition of vanadium dioxide films

“…The oxygen transport to the interface goes via grain boundary diffusion. It cannot be excluded that the silicon diffuses into the VO 2 film as well via grain boundary diffusion and forms V x Si y O along the grain boundaries, 19 although such a minor grain boundary Si contamination of the VO 2 cannot be proven by our analytical XTEM for several reasons. Our AES investigations (see the following) did not show the presence of Si in the film either.…”

Aqueous citrato-oxovanadate(iv) precursor solutions for VO2: synthesis, spectroscopic investigation and thermal analysis

“…18 In these routes, VO 2 is commonly prepared starting from vanadium alkoxides. 5,19,20 However, such alkoxides are scarcely available, expensive and very reactive to ambient humidity. 18 Alternatively, aqueous synthesis routes are proposed by Livage et al and Dachuan et al who prepared VO 2 films starting from a V 2 O 5 gel or sol, respectively.…”