Synthesis, characterization, and photoactivity of InTaO4 and In0.9Ni0.1TaO4 thin films prepared by electron evaporation

Abstract

InTaO 4 and In 0.9 Ni 0.1 TaO 4 thin films have been prepared by electron evaporation of successive layers of the single oxide components and posterior annealing at T Ͼ 800°C. The annealed thin films presented the monoclinic crystallographic structure typical of these mixed oxides. The electrical and optical behaviors of the films, assessed by C-V measurements, surface conductivity as a function of temperature, and UV-vis absorption spectroscopy, indicate that these oxides are wide band gap semiconductors with a variable dielectric constant depending on the annealing conditions. By reflection electron energy loss spectroscopy some electronic states have been found in the gap at an energy that is compatible with the activation energy deduced from the conductivity versus 1 / T plots for these oxides. The photoactivity of these materials has been assessed by looking to the evolution of the wetting contact angle as a function of the irradiation time. All the films became superhydrophilic when irradiated with UV light, while the In 0.9 Ni 0.1 TaO 4 thin films also presented a small partial decrease in wetting angle when irradiated with visible photons.

Substitutional Mechanism of Ni into the Wide-Band-Gap Semiconductor InTaO4 and Its Implications for Water Splitting Activity in the Wolframite Structure Type

“…It should be noted that the experimentally determined 2.6 eV band gap of InTaO 4 was substantially smaller than the 3.5–3.7 eV gaps later obtained from DFT calculations despite the fact that DFT methods are known to substantially underestimate the magnitude of semiconductor band gaps. ,, On the basis of trial DFT calculations, this discrepancy was suggested , to arise from oxygen vacancies within the material, an as-yet experimentally unverified hypothesis. It has also been suggested previously that the true gap of this compound is reflected in the strong absorption feature at 4.3 eV rather than in the much weaker lower energy features, a result supported by recent reflection electron energy loss spectroscopy (REELS) studies on InTaO 4 films prepared by physical vapor deposition . Given the extensive ongoing interest in this system, we initiated a comprehensive structural and electronic characterization of pristine and Ni-doped InTaO 4 with the goal of understanding and reconciling the unusual properties reported for this system.…”

“…It has also been suggested previously that the true gap of this compound is reflected in the strong absorption feature at 4.3 eV rather than in the much weaker lower energy features, 9 a result supported by recent reflection electron energy loss spectroscopy (REELS) studies on InTaO 4 films prepared by physical vapor deposition. 10 Given the extensive ongoing interest in this system, we initiated a comprehensive structural and electronic characterization of pristine and Ni-doped InTaO 4 with the goal of understanding and reconciling the unusual properties reported for this system. InTaO 4 crystallizes in the wolframite structure type (Figure 1) with the monoclinic space group P2/c (no.…”