Structures and electrochromic properties of Ta₀.₁W₀.₉Oₓ thin films deposited by pulsed laser ablation
By Zeng, X. & Osseo-Asare, K.
Published in Thin Solid Films
2004
Abstract
Thin films of Ta₀.₁W₀.₉Oₓ were deposited on indium tin oxide (ITO) coated glass substrates by reactive pulsed laser ablation in O₂ ambient gas at substrate temperatures of 20, 200, 400, and 600 °C. X-ray diffraction (XRD) results showed that Ta₀.₁W₀.₉Oₓ 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 Ta₀.₁W₀.₉Oₓ film deposited in 5.32 Pa O₂ are almost the same as those of stoichiometry Ta₀.₁W₀.₉O₂.₉₅ material, which indicates a truly congruent ablation has been achieved by the laser ablation technique. Films deposited in lower O₂ pressures have poor crystallinity and may contain a lot of defects (oxygen vacancies). For all the temperatures investigated, Ta₀.₁W₀.₉Oₓ films appear almost colorless when deposited in 5.32 Pa O₂, while films have colors of light blue, blue and black when deposited in 2.66, 1.33 and 0.13 Pa O₂, respectively. Optical transmittance for as-deposited Ta₀.₁W₀.₉Oₓ films and the films subjected to H+ intercalation/deintercalation in 0.1 M H₃PO₄ electrolyte was also measured. H+ ion insertion under an applied electrical potential causes the colors of the Ta0.1W0.9Ox 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.