Structures and electrochromic properties of Ta 0.1W 0.9O x thin films deposited by pulsed laser ablation

Abstract

Thin films of Ta 0.1W 0.9O x were deposited on indium tin oxide (ITO) coated glass substrates by reactive pulsed laser ablation in O 2 ambient gas at substrate temperatures of 20, 200, 400, and 600 °C. X-ray diffraction (XRD) results showed that Ta 0.1W 0.9O x films crystallized mainly to a tetragonal phase at a substrate temperature of 600 °C, while films deposited at lower substrate temperatures were amorphous. Lattice constants of polycrystalline Ta 0.1W 0.9O x film deposited in 5.32 Pa O 2 are almost the same as those of stoichiometry Ta 0.1W 0.9O 2.95 material, which indicates a truly congruent ablation has been achieved by the laser ablation technique. Films deposited in lower O 2 pressures have poor crystallinity and may contain a lot of defects (oxygen vacancies). For all the temperatures investigated, Ta 0.1W 0.9O x films appear almost colorless when deposited in 5.32 Pa O 2, while films have colors of light blue, blue and black when deposited in 2.66, 1.33 and 0.13 Pa O 2, respectively. Optical transmittance for as-deposited Ta 0.1W 0.9O x films and the films subjected to H + intercalation/deintercalation in 0.1 M H 3PO 4 electrolyte was also measured. H + ion insertion under an applied electrical potential causes the colors of the Ta 0.1W 0.9O x films change from almost colorless (5.32 Pa film) or light blue (2.66 Pa film) to deep blue, while the color contrast between as-deposited and H + intercalated films is not so significant for the 1.33 and 0.13 Pa films. The H + ion insertion and extraction processes are fully reversible for the amorphous films, while the optical transmittance of polycrystalline films after the H + ion extraction process is still low and does not recover to that of as-deposited state.