Spray pyrolysis preparation of porous polycrystalline thin films of titanium dioxide containing Li and Nb
- PDF / 526,941 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 184 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Spray pyrolysis preparation of porous polycrystalline thin films of titanium dioxide containing Li and Nb Nickolay Golego, S. A. Studenikin,a) and Michael Cocivera Guelph-Waterloo Centre for Graduate Work in Chemistry, University of Guelph, Guelph, Ontario N1G 2W1, Canada (Received 23 February 1998; accepted 6 August 1998)
Titanium dioxide thin films prepared with and without lithium and niobium were as follows: uniform, crack-free, and stoichiometric, amorphous as-deposited at 300 ±C and below; polycrystalline anatase when deposited at 400 ±C or annealed at 500–800 ±C; and rutile when annealed at 900 ±C. Films prepared around 200 ±C were very porous, but the porosity decreased as the substrate temperature increased. Optical absorption spectra revealed an indirect bandgap of 3.0 eV for amorphous and anatase films, and a direct bandgap of the same value in rutile. Dark dc conductivity of undoped films was lower than 10210 (V ? cm)21 ; Hall effect measurements indicated that effective electron mobility was below 1 cm2y(V ? s). The presence of Nb and Li increased the conductivity by 2–3 orders of magnitude, similar to the effect of hydrogen annealing. Illumination increased the conductivity by several orders of magnitude, and the decay followed a multiexponential law extending into the 106 second range after irradiation was stopped. The electronic properties of the films were determined by oxygen-related surface states at grain boundaries. Samples containing Li exhibited considerable sensitivity to water vapor.
I. INTRODUCTION
Titanium dioxide has received a great deal of attention due to its high dielectric constant, thermal and chemical stability, nontoxicity, and ease of preparation. Thin films of titanium dioxide have been employed in gas and humidity sensors,1,2 dielectric layers,3 catalysts, nonlinear optics,4 and waveguides,5 electroluminescent,6 photochemical,7,8 and photovoltaic9 devices. Thin-film TiO2 , both undoped and containing various elements, was prepared by a variety of methods to give both single-crystalline and polycrystalline films. The present paper deals with preparation of polycrystalline thin-film TiO2 by spray pyrolysis from an aqueous solution of titanium peroxo-hydroxo complex (TPH).10 As well, a niobium peroxo-hydroxo complex (NPH) was synthesized and used as a Nb precursor, for the first time to our knowledge. Analogous complexes of other transition metals can be prepared and used conveniently for spray pyrolysis. Earlier we used TPH to prepare thin films of KTiOPO4 .10 More recently, a similar approach has been used to prepare TiO2 thin films11 ; however, little detail was presented concerning the properties of the precursor and the effect of deposition conditions on the morphology of the films. Using our experience with spraypyrolytic deposition of KTiOPO4 ,10 RbTiOPO4 ,12 and BaTiO3 ,13 we have prepared and characterized titanium a)
Permanent address: Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences, Nov
Data Loading...
