Molybdenum trioxide (MoO3) thin films prepared by cathodic electrodeposition on indium-tin-oxide coated glass substrates from aqueous peroxo-polymolybdate solutions have been studied as a function of sintering temperature (25-450 °C). Cyclic voltammetry, chronopotentiometry, chronoamperometry, and spectroelectrochemical measurements performed with MoO 3 thin films in 1 M LiClO4/propylene carbonate demonstrate that the electrochemical behavior (Li + insertion/extraction and coloration) is strongly dependent upon thermally induced changes in micro-/nanocrystallinity, which directly influence measured Li + diffusion properties as well as electroinsertion and electrochromic reversibilities. Structural analysis using X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy indicate that films heat treated at 100 °C or less exist as amorphous oxide-hydrates of molybdenum; whereas films heated to 250 °C exist as disordered, mixed-phase materials comprising monoclinic β-MoO 3 and orthorhombic R-MoO3. Crystallization to the more thermodynamically stable orthorhombic R-MoO3 occurs at 350 °C and above. The mixed-phase material exhibits inhomogeneous electrochemical activity, evidenced by the existence of complicated voltammetric and chronoamperometric responses. The effects of sintering temperature on ion insertion and electrocoloration properties are discussed.
Patterned thin films of titanium dioxide (TiO2), with micrometer-sized features, were prepared on transparent, conductive indium-tin oxide glass platforms via microtransfer molding and electrochemical deposition. The grating pattern produces optical diffraction, where the efficiency of diffraction (η) depends on the degree of contrast in refractive index between the patterned material and the surrounding medium. The refractive index of a representative micropatterned TiO2 film (anatase) was estimated, via solvent index matching experiments, to be 2.72sa value sufficiently large to achieve good contrast with air or water. A new method, based on the measurement of changes in diffraction efficiency, is described for the detection and evaluation of organic chemical adsorption on various titanium dioxide surfaces. The strategy is illustrated for the vapor-phase adsorption of chloroform on high-area amorphous, anatase, and rutile forms of titanium dioxide. The uptake of 2,4,5-trichlorophenol from aqueous solutions by amorphous TiO2 was also examined by the modulated optical-diffraction-grating technique.
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