V-doped Films Research Articles

Photocatalytic activity of V-doped TiO2 thin films for the degradation of methylene blue and rhodamine B dye solutions

Highly-transparent V-doped TiO2 thin films were prepared by sol-gel processing, spin coated on fused silica glass substrates, and annealed in air at 450 °C for 2 h. All of the films were comprised of anatase as the sole crystalline phase. The XPS data suggested that V formed an interstitial solid solution with anatase. The formation of an unsaturated solid solution at the lowest doping level of 0.05 mol% resulted in the formation of lattice defect sites, which enhanced anatase recrystallisation, grain growth, and crystallinity. In contrast, the formation of supersaturated/oversaturated solid solutions at the higher doping levels of 0.10–1.00 mol% resulted in lattice deformation, partial amorphisation, precipitation, and liquid formation. The coexistence of multiple valence states, viz., Ti4+/3+, V4+/3+, and possibly V5+ in the doped TiO2 films was attributed to intervalence charge transfer. Dye degradation tests revealed that the 0.05 mol% V-doped films showed the best photocatalyic performance and this was attributed to the combined effects of greater anatase crystallinity and reduced band gap. In contrast, increasing V-doping levels resulted in gradual decreases in the photocatalytic performance, which are attributed principally to the decrease in areal density of the surface-active sites owing to liquid-phase densification. The greater degradation of MB solution relative to that of RhB solution is attributed principally to the cationic nature of MB, which allows greater adsorption on the photocatalyst surface in comparison to the anionic RhB.

Structural, photoconductive, thermoelectric and activation energy measurements of V-doped transparent conductive SnO2 films fabricated by spray pyrolysis technique

This report investigated the structural, optical and electrical properties of V-doped SnO2 thin films deposited using spray pyrolysis technique. The SnO2:V films, with different V-content, were deposited on glass substrates at a substrate temperature of 550°C using an aqueous ethanol solution consisting of tin and vanadium chloride. X-ray diffraction studies showed that the SnO2:V films were polycrystalline only with tin oxide phases and the preferred orientations are along (1 1 0), (1 0 1), (2 1 1) and (3 0 1) planes. Using Scherrer formula, the grain sizes were estimated to be within the range of 25–36 nm. The variation in sheet resistance and optical direct band gap are functions of vanadium doping concentration. Field emission scanning electron microscopy (FESEM) revealed the surface morphology to be very smooth, yet grainy in nature. Optical transmittance spectra of the films showed high transparency of about ∼69–90% in the visible region, decreasing with increase in V-doping. The direct band gap for undoped SnO2 films was found to be 3.53 eV, while for higher V-doped films it shifted toward lower energies in the range of 3.27–3.53 eV and then increased again to 3.5 eV. The Hall effect and Seebeck studies revealed that the films exhibit n-type conductivity. The thermal activation energy, Seebeck coefficient and maximum of photosensitivity in the films were found to be in the range of 0.02–0.82 eV (in the low-temperature range), 0.15–0.18 mV K−1 (at T = 350 K) and 0.96–2.84, respectively.

Low Critical Concentration of Metal–Insulator Transition of Vanadium Doped Amorphous Boron

The metal–insulator transition (MIT) of V- and Zr-doped amorphous boron films (V x B 100- x , Zr x B 100- x ) was studied. The temperature dependences of the electrical conductivity, the X-ray diffraction patterns and the X-ray absorption fine structures were measured for the samples. The compositional boundary of the metal–insulator transition is found between x = 2.9 and 3.7 in V x B 100- x , and between x = 11 and 14 in Zr x B 100- x . It is considered that at the transition, the network of B 12 icosahedral clusters remains unchanged for V-doped films, while the network changes into an intermetallic compound-like structure for Zr-doped films. The low concentration of vanadium and no structural change for the transition of V-doped films are peculiar, while the critical concentration of Zr and the structural change of Zr-doped films are similar to those of transition-metal-doped amorphous silicon or germanium. The origin of the peculiarity of MIT for the V-doped films is discussed in relation to the metallic-covalent bonding conversion of the icosahedral clusters.

Effect of Nb 2O 5 seed layer on electrical properties of alkaline niobate based ferroelectric thin films

K 0.5Na 0.5NbO 3 and K 0.5Na 0.5Nb 0.995V 0.005O 3 ferroelectric thin films were prepared by a chemical solution deposition method. The Nb 2O 5 seed layer was introduced to investigate the electrical properties of the films. Crystalline structures and microstructures were analyzed by X-ray diffraction and scanning electron microscope at room temperature. The electrical properties were studied both for the films with and without Nb 2O 5 seed layer. It is found that the films' quality was modified by adding the seed layer, and the V-doping also plays an important role in improving the films quality. The ferroelectric and dielectric properties of the films were obviously enhanced by adding the seed layer, especially for the V-doped film. These results may be due to the better crystallization and microstructure of the films.

NO<sub>2</sub> Sensing Characteristics of Thin Film TiO<sub>2</sub>

The rutile-type TiO2 thin film doped with pentavalent additives such as Nb or Ta, prepared by a multi-target sputtering system, exhibited fairly good NO2 sensing characteristics over the range from 0 to 300ppm at 600°C. According to the Arrhenius plots between conductivity and reciprocal temperature, it seems that the doped Nb or Ta formed some impurity energy level in the forbidden band of TiO2, while V-doped film showed different conducting mechanism. In addition, high-temperature durability in oxydative and reductive exhaust gases was confirmed at 800°C.