Preparation of Ta-Doped TiO2 Using Ta2O5 as the Doping Source

A novel method for preparing Ta-doped Ti02 via using Ta2 05 as the doping source is proposed. The preparation process combines the hydrothernlal fluorination of Ta2O5 and the subsequent formation of Ta-doped TiO2 sol. The results show that the doped sample annealed at 393 K generates an unstable intermediate NH4 TiOF3, which converts into anatase TiO2 with the increase of temperature. After annealing at ≥673K, the Ta-doped TiO2 nanocrystals with the grain size 〈20nm are obtained. Both the XRD and TG-DSC results confirm that Ta doping prevents the anatase-rutile crystal transition of TiO2. The band gap values of the doped samples, as obtained by UV-vis diffuse reflectance spectra, are smaller than that of pure anatase TiO2. The first-principle pseudopotential method calculations indicate that Ta5＋ lies in the TiO2 lattice at the interstitial position.

Effects of Substrate Temperature on Properties of Transparent Conductive Ta-Doped TiO_2 Films Deposited by Radio-Frequency Magnetron Sputtering

Ta-doped titanium dioxide films are deposited on fused quartz substrates using the rf magnetron sputtering technique at different substrate temperatures. After post-annealing at 550℃ in a vacuum, all the films are crystallized into the polycrystalline anatase TiO2 structure. The effects of substrate temperature from room temperature up to 350℃ on the structure, morphology, and photoelectric properties of Ta-doped titanium dioxide films are analyzed. The average transmittance in the visible region（400-800 nm） of all films is more than 73%.The resistivity decreases firstly and then increases moderately with the increasing substrate temperature. The polycrystalline film deposited at 150℃ exhibits a lowest resistivity of 7.7 × 10^-4Ω·cm with the highest carrier density of 1.1×10^21 cm^-3 and the Hall mobility of 7.4 cm^2·V^-1s^-1.

Influences of Pr and Ta doping concentration on the characteristic features of FTO thin film deposited by spray pyrolysis

The Pr and Ta separately doped FTO（10 at.% F incorporated Sn O2） films are fabricated via spray pyrolysis. The microstructural, topographic, optical, and electrical features of fluorine-doped TO（FTO） films are investigated as functions of Pr and Ta dopant concentrations. The x-ray diffraction（XRD） measurements reveal that all deposited films show polycrystalline tin oxide crystal property. FTO film has（200） preferential orientation, but this orientation changes to（211） direction with Pr and Ta doping ratio increasing. Atomic force microscopy（AFM） and scanning electron microscopy（SEM） analyses show that all films have uniform and homogenous nanoparticle distributions. Furthermore, morphologies of the films depend on the ratio between Pr and Ta dopants. From ultraviolet-visible（UV-Vis） spectrophotometer measurements, it is shown that the transmittance value of FTO film decreases with Pr and Ta doping elements increasing. The band gap value of FTO film increases only at 1 at.% Ta doping level, it drops off with Pr and Ta doping ratio increasing at other doped FTO films. The electrical measurements indicate that the sheet resistance value of FTO film initially decreases with Pr and Ta doping ratio decreasing and then it increases with Pr and Ta doping ratio increasing. The highest value of figure of merit is obtained for 1 at.% Ta- and Pr-doped FTO film. These results suggest that Pr- and Ta-doped FTO films may be appealing candidates for TCO applications.

Improvement of the light output and contact resistance of InGaN-based light-emitting diodes based on tantalum-doped indium tin oxide as p-type electrodes

This paper reports that highly transparent and low resistance tantalum-doped indium tin oxide （Ta-doped ITO） films contacted to p-type GaN have been prepared by the electron-beam evaporation technique. The Ta-doped ITO contacts become Ohmic with a specific contact resistance of $／sim 5.65／times 10^{ - 5}$$／Omega ／cdot$cm$^{2}$ and show the transmittance of $／sim $98% at a wavelength of 440nm when annealed at 500／du. Blue light emitting diodes （LEDs） fabricated with Ta-doped ITO p-type Ohmic contact layers give a forward-bias voltage of 3.21V at an injection current of 20mA. It further shows that the output power of LEDs with Ta-doped ITO contacts is enhanced 62% at 20mA in comparison with that of LEDs with conventional Ni/Au contacts

Transparent conductive SnO_(2)thin films via resonant Ta doping

Transparent conductive oxide(TCO)thin films are highly desired as electrodes for modern flat-panel displays and solar cells.Alternative indium-free TCO materials are highly needed,because of the scarcity and the high price of indium.Based on the mechanism of resonant doping,Ta has been identified as an effective dopant for SnO_(2)to achieve highly conductive and transparent TCO.In this work,we fabricated a series of Ta-doped SnO_(2)thin films(Sn_(1-x)Ta_(x)O_(2),x=0.001,0.01,0.02,0.03)with high conductivity and high optical transparency via a low-cost sol-gel spin coating method.The Sn_(0.98)Ta_(0.02)O_(2)film achieves the highest electrical conductivity of 855 S cm-1with a carrier concentration of2.3×10^(20)cm^(-3)and high mobility of 23 cm^(2)V^(-1)s^(-1).The films exhibit a very high optical transparency of 89.5%in the visible light region.High-resolution X-ray photoemission spectroscopy and optical spectroscopy were combined to gain insights into the electronic structure of the Sn_(1-x)Ta_(x)O_(2)films.The optical bandgaps of the films are increased from 3.96 eV for the undoped SnO_(2)to 4.24 eV for the Sn_(0.98)Ta_(0.02)O_(2)film due to the occupation of the bottom of conduction band by free electrons,i.e.,the Burstein-Moss effect.Interestingly,a bandgap shrinkage is also directly observed due to the bandgap renormalization arising from many-body interactions.The double guarantee of transparency and conductivity in Sn_(1-x)Ta_(x)O_(2)films and the low-cost growth method provide a new platform for optoelectronic and solar cell applications.

Highly efficient single-crystalline NaNb_(1-X)Ta_(X)O_(3)(X=0.125)wires:The synergistic effect of tantalum-doping and morphology on photocatalytic hydrogen evolution

For the first time in this work,we manage to synthesize single-crystalline NaNb_(0.875)Ta_(0.125)O_(3) wires by combining the advantages of one-dimensional(1 D)nanostructure and heteroatom doping strategy.Careful Ta doping was performed to figure out the correlation between morphological and structural evolution as well as the photocatalytic performance towards H2 generation.It was found that,the as-prepared NaNb_(0.875)Ta_(0.125)O_(3) wires presented a highest and stable photocatalytic performance,which was appropriately 41 and 2 folds higher than that of bare Na TaO_(3) and Na NbO3.The optical activity was mainly ascribed to the synergistic effect between appropriate Ta doping and perfect 1 D wire-like morphology,which resulted in fewer defects,improved charge transfer efficiency and higher reduction capability of electrons.On the other hand,a possible photocatalytic mechanism of photocatalytic H_(2) production was proposed in detail.This work creates a new perspective into designing multi-component materials and understanding the mechanism of H_(2) evolution,which offers new opportunities for solar-energy conversion.