AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP26
Preparation and Chemical Oxidation Kinetics of Microcrystalline Tungsten Bronze Thin Films

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: E.B. Kadossov, Oklahoma State University
Authors: E.B. Kadossov, Oklahoma State University
P. Rajasekar, Oklahoma State University
N.F. Materer, Oklahoma State University
Correspondent: Click to Email
Microcrystalline tungsten bronze (H@sub x@WO@sub 3@) thin films are prepared using wet chemical techniques or atomic hydrogen to reduce a tungsten oxide thin film. The oxide film is prepared by thermal oxidation of sputter deposited tungsten metal film on a quartz substrate. The crystallinity of these films is determined by X-ray diffraction. X-ray photoelectron and ultra-violet photoelectron spectroscopy show that these films are indistinguishable from conventionally prepared tungsten bronze powders. The quartz support allows the total amount of incorporated hydrogen in the film to be quantified by monitoring the absorbance at 900 nm. This technique is utilized to study the oxidation kinetics of these films by either oxygen gas or hydrogen peroxide aqueous solution. The resulting decay of the 900 nm absorbance intensity with time can be satisfactory fit to a kinetic model composed of two elementary steps. First, a proton must diffuse from the bulk to the surface. Next, a chemical reaction between the surface proton and the oxidant must occur. Conditions are such that the surface concentration of the oxidant adsorbed on the surface is effectively constant. In addition, this model implicitly assumes that the electron transfer step required for reduction of the oxidant is not rate limiting. From this kinetic model, both the proton diffusion coefficient and the surface activation energies can be estimated. The results are compared with previous nuclear magnetic resonances studies and electrochemical measurements.