UV Photoconductivity of Nanocrystalline TiO₂Films Annealed in Oxygen

Abstract

The effects of annealing in reactive gases (H 2 , N 2 , O 2 ) upon the optoelectric properties of nanophased titanium dioxide (TiO 2 ) prepared by chemical vapour deposition (CVD) were investigated. The nanocrystalline structure containing nanosize grains and pores was analyzed by grazing-incidence small-angle scattering of synchrotron radiation (GISAX). The annealing (up to 1073 K) in H 2 and N 2 generally proved detrimental to photoconductivity due to the overall increase of the electrical conductivity of the samples. In this work, the result of UV (248-404 nm) photoconductivity measurements on TiO 2 films annealed in O 2 at 773 K and 1073 K are presented. A rather long illumination time (typically 2 h) enabled us to clearly distinguish two types of nonequilibrium photoconductivity variations with time. A fast exponential photoconductivity increase occurred during the initial stage of irradiation, while a slow power-type increase was observed in the later stage. A nonlinear combination of both functions was used in a numerical fitting procedure, which allowed precise determination of the asymptotic value of exponential photoconductivity increase. A relative quantum efficiency for both as-prepared and annealed samples exhibits a nonmonotonic variation with photon energy. Such wavelength-dependence variation might be due to the electronic density function structure at the valence-band edge, or near-valence-band levels in the gap. Generally, the samples annealed at higher temperatures exhibit a higher quantum efficiency and shorter time constants of the excitation processes, in the examined UV range.

Tailoring morphology, structure and photoluminescence properties of anodic TiO2nanotubes

“…GISAXS is an experimental technique that combines both grazing incidence and scattering at low angles. This technique has been developed and applied to morphological characterization of aggregates deposited or gathered on a flat substrate and the nanostructure of thin films and nanoporous materials (Car et al, 2002).…”

Highly conductive titanium oxide films by RF magnetron sputtering

“…6, negative ε 1 in the figure means a feature of metallic characteristics as same as in the conductivity characteristics for temperature dependence. From ε 2 , we can estimate a optical conductivity as 2 0 ε ε ω σ = op (6) σ op is about 50~100 S cm -1 in the middle infrared region. From Drude's model, theoretical complex dielectrics used in this paper are driven as follows [13]; (8) and assuming ω p given by fitting procedure in Fig.…”

“…Usually these films are optically transparent in visible region and highly resistive [1,2]． Irradiating UV light generates photo-current as like a semiconductor material [3][4][5][6]. .…”

Grazing-incidence small-angle X-ray scattering and reflectivity on nanostructured oxide films

“…In our previous papers a number of experimental methods for resolving nanostructure of these materials were presented [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Among them grazing-incidence small-angle X-ray scattering (GISAXS) was the best technique for complete morphological characterisation of nanostructured materials.…”