SOLIDIONIC

Electrochemical control of optical and conducting properties of vanadium dioxide thin films: hydrogen and lithium intercalation.

1. Introduction.

VO₂ undergoes a first-order metal-insulator phase transition (MIT) with a few orders of magnitude change of conductivity and associated structural transition at a tempera-ture of about 68°C in the bulk. The transition is accompanied by a fast (~10-13s) change in the dielectric function, which has sparkled numerous potential applications ofVO₂in ultrafast modulators, switchable polarizers, beam-steering, and thermo-chromic devices operable from submillimeter up to near-IR range.

Fig. 1 Chemical hydrogen insertion in thin films

2. Chemical and electrochemical hydrogen insertion in thin films VO₂ (Fig. 1).

It was shown that hydrogen insertion can shift the temperature of MIT up to 20°C or more for films up to 100 nm. It was used two techniques : heating in aqueous solu-tions of alcohols and electrolysis of aqueous solutions of NaCl. The hydrogen content has been determined by electrical conductivity and/or by light reflection.

Fig. 2 Electrochemical Li insertion

3.Electrochemical Li insertion (Fig 2)

It was shown that at the electrolysis of

‘LiJ – DMFA’ solution Li can be inserted into the film. It has brought about the shift of hyste-resis loop to lower tem-peratures and changing its form. This effect is more stable than after hydrogen insertion.

4. Electrochemical insertion in special thin films based on VO₂. and isotopic exchange of them with nonaqueous solutions of LiJ.

Li insertion into special multilayers films of VO_n (1,56LiJ – DMFA’ solution. Then it was immersed into solution ‘7LiJ – DMFA’. SIMS study has revealed that the moving of isotopic front was remarkably slower than chemical one at the insertion.

5. Isotopic exchange Li⁺(DMFA) Li⁰(Hg)

The kinetics of isotopic exchange and thermodynamical isotopic effect of Li isotopes interphase redistribution and their affect on the potential of lithium heterojunction were studied to understand the mechanism of lithium electrochemical processes

Yu.M.Baikov, V.A. Klimov Ioffe Physical Technical Institute of RAS, Saint-Petersburg 194021 Russian Federation