Influence of indium doping on the properties of spray deposited CdS0.2Se0.8 thin films

Polycrystalline indium doped CdS_0.2Se_0.8 thin films with varying concentrations of indium have been prepared by spray pyrolysis at 300 °C. The as deposited films have been characterized by XRD, AFM, EDAX, optical and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of indium doping concentration. AFM studies reveal that the RMS surface roughness of film decreases from 34.68 to 17.76 with increase in indium doping concentration up to 0.15 mol% in CdS_0.2Se_0.8 thin films and further it increases for higher indium doping concentrations. Traces of indium in CdS_0.2Se_0.8 thin films have been observed from EDAX studies. The optical band gap energy of CdS_0.2Se_0.8 thin film is found to decrease from 1.91 eV to 1.67 eV with indium doping up to 0.15 mol% and increase after 0.15 mol%. The electrical resistivity measurement shows that the films are semiconducting with minimum resistivity of 3.71 × 10⁴ Ω cm observed at 0.15 mol% indium doping. Thermoelectric power measurements show that films exhibit n-type conductivity.     

Reduction roasting–magnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90 wt% and TiO_2 content of 17.40 wt%. The results show that after reduction roasting–magnetic separation with sodium sulfate dosage of 2 wt% at roasting temperature of 1150 °C for roasting time of 120 min, metallic iron concentrate with total iron grade of 90.20 wt%, iron recovery rate of 97.56 % and TiO_2 content of 4.85 wt% is obtained and high-titanium slag with TiO_2 content of 57.31 wt% and TiO_2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy(SEM) and X-ray diffraction(XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO_2 content is obtained.     

Calcination Conditions on the Properties of Porous TiO2 Film

Porous TiO₂ films were deposited on SiO₂ precoated glass-slides by sol-gel method using PEG1000 as template. The strongest XRD diffraction peak at 2θ = 25.3° is attributed to [101] plane of anatase TiO₂ in the film. The increases of calcination temperature and time lead to stronger diffraction peak intensity. High transmittance and blue shift of light absorption edge are the properties of the film prepared at high calcination temperature. The average pore size of the films increases with the increasing calcination temperature as the result of TiO₂ crystalline particles growing up and aggregation, accompanied with higher specific surface area. Photocatalytic activity of porous TiO₂ films increases with the increasing calcination temperature. The light absorption edge of the films slightly moves to longer wavelength region along with the increasing calcination time. The mesoporous film calcinated at 500 °C for 2 h has the highest transmittance, the maximum surface area, and the maximum total pore volume. Consequently, the optimum degradation activity is achieved on the porous TiO₂ film calcinated at 500 °C for 2 h.     

Corrosion behavior of Zr–Nb–Cr cladding alloys

Zr-Nb-Cr alloys were used to evaluate the effects of alloying elements Nb and Cr on corrosion behavior of zirconium alloys. The microstructures of both Zr substrates and oxide films formed on zirconium alloys were characterized. Corrosion tests reveal that the corro- sion resistance of ZrxNb0.1Cr （x = 0.2, 0.5, 0.8, 1.1; wt%） alloys is first improved and then decreased with the increase of the Nb content. The best corrosion resistance can be obtained when the Nb concentration in the Zr matrix is nearly at the equilibrium solution, which is closely responsible for the formation of columnar oxide grains with protective characteristics. The Cr addition degrades the corrosion resistance of the Zrl.lNb alloy, which is ascribed to Zr（Cr,Fe,Nb）2 precipitates with a much larger size than β-Nb.     

Physicochemical Properties of Spray-Deposited CoFe2O4 Thin Films

Cobalt ferrite thin films are deposited onto quartz glass substrates by chemical spray pyrolysis technique at different substrate temperatures using ferric nitrate and cobalt nitrate as precursors. Thermogravimetric analysis (TGA) study indicates the formation of CoFe₂O₄ by decomposition of cobalt and ferric nitrates after 800 °C. X-ray diffraction studies reveal that annealed films are polycrystalline in nature and exhibit spinel cubic crystal structure. Crystallite size varies from 39 to 44 nm with the substrate temperatures. Direct optical band gap energy of CoFe₂O₄ thin films is found to be 2.57 eV. The AFM images show that roughness and grain size of the CoFe₂O₄ thin film are about 9 and 138 nm, respectively. The measured DC resistivity of the deposited thin films indicates that as temperature increases the resistivity decreases indicating the semiconductor nature of the films. Decrease in dielectric constant (ε′) and loss tangent (tanδ) has been observed with frequency and attains the constant value at higher frequencies. The AC conductivity of cobalt ferrite thin films increases with increase in frequency. Thus, the prepared films show normal dielectric performance of the spinel ferrite thin film. Room-temperature complex impedance spectra show the incomplete semicircles as films exhibit high resistance values at lower frequencies.     

The effects of substrate temperature on refractive index dispersion and optical constants of CdZn(S0.8Se0.2)2 alloy thin films

The effect of substrate temperature on optical properties of CdZn(S_0.8Se_0.2)₂ thin films deposited onto glass substrates by the spray pyrolysis method has been investigated. The average optical transmittance of the films was over 74% in the visible range. The optical absorption studies reveal that the transition is direct with band gap energy values between 2.86 and 2.92 eV. The optical constants such as refractive index and dielectric constant of the films were determined. According to variation of the substrate temperature, the important changes in absorption edge, refractive index and the dielectric constant were observed. The refractive index dispersion curves of the films obey the single oscillator model and oscillator parameters changed with substrate temperature. The most significant result of the present study is to indicate that substrate temperature of the film can be used to modify in the optical band gaps and optical constants of CdZn(S_0.8Se_0.2)₂ thin films.     

Elaboration and characterization of nanocrystalline TiO2 thin films prepared by sol–gel dip-coating

Nanocrystalline TiO₂ thin films were deposited on a ITO coated glass substrate by sol–gel dip coating technique, the layers undergo a heat treatment at temperatures varying from 300 to 450 °C. The structural, morphological and optical characterizations of the as deposited and annealed films were carried out using X-ray diffraction (XRD), Raman spectroscopy, Atomic Force Microscopy (AFM), visible, (Fourier-Transform) infrared and ultraviolet spectroscopy, Fluorescence and spectroscopic ellipsometry. The results indicate that an anatase phase structure TiO₂ thin film with nanocrystallite size of about 15 nm can be obtained at the heat treatment temperature of 350 °C or above, that is to say, at the heat treatment temperature below 300 °C, the thin films grow in amorphous phase; while the heat treatment temperature is increased up to 400 °C or above, the thin film develops a crystalline phase corresponding to the titanium oxide anatase phase. We have accurately determined the layer thickness, refractive index and extinction coefficient of the TiO₂ thin films by the ellipsometric analysis. The optical gap decreases from 3.9 to 3.5 eV when the annealing temperature increases. Photocatalytic activity of the TiO₂ films was studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that films annealed above 350 °C had good photocatalytic activity which is explained as due to the structural and morphological properties of the films.     

Study of bactericidal efficiency of magnetron sputtered TiO2 films deposited at varying oxygen partial pressure

TiO₂ thin films have been deposited at different Ar:O₂ gas ratios (20:80,70:30,50:50,and 40:60 in sccm) by rf reactive magnetron sputtering at a constant power of 200 W. The formation of TiO₂ was confirmed by X-ray photoelectron spectroscopy (XPS). The oxygen percentage in the films was found to increase with an increase in oxygen partial pressure during deposition. The oxygen content in the film was estimated from XPS measurement. Band gap of the films was calculated from the UV-Visible transmittance spectra. Increase in oxygen content in the films showed substantial increase in optical band gap from 2.8 eV to 3.78 eV. The Ar:O₂ gas ratio was found to affect the particle size of the films determined by a transmission electron microscope (TEM). The particle size was found to be varying between 10 and 25 nm. The bactericidal efficiency of the deposited films was investigated using Escherichia coli (E. coli) cells under 1 h UV irradiation. The growth of E. coli cells was estimated through the Optical Density measurement by UV-Visible absorbance spectra. The qualitative analysis of the bactericidal efficiency of the deposited films after UV irradiation was observed through SEM. A correlation between the optical band gap, particle size and bactericidal efficiency of the TiO₂ films at different argon:oxygen gas ratio has been studied.     

The Effect of Heat Treatment of TiO2 Nanoparticles on Photovoltaic Performance of Fabricated DSSCs

The present work focuses on the synthesis of mixed phase TiO₂ nanoparticles with reduced band gaps without even being doped. The synthesis was carried out by chemical route followed by heat treatments at different temperatures to favor rutile incorporation in anatase network. The significance of different heat treatment temperatures on the phase composition of TiO₂ nanoparticles and its effect on optical band gap and the photovoltaic performance are analyzed. The thermal analysis, phases, morphology, and energy band gap of as-synthesized TiO₂ nanoparticles have been characterized by DTA/TG, x-ray diffraction, field-emission scanning electron microscope, transmission electron microscope, and UV-Vis-NIR, respectively. The results show the presence of rutile (~15 nm) and anatase phases (~17 nm) in “as-synthesized” TiO₂ nanoparticles. TiO₂ nanoparticles are heat treated for 2 h at 200, 400, and 600 °C in air. It is observed that heat treatment results in higher photoactivity in visible region of the solar radiation and the material demonstrated high photovoltaic performance in conjunction with N-719. The optical band gap values are found to be in the range of 2.59-2.88 eV. The dye-sensitized solar cells (DSSCs) fabricated by TiO₂ nanoparticles, heat treated at 600 ºC show the energy conversion efficiency (η) of 6.08% with high photo current density (J _sc) of 11.76 mA/cm². The work highlighted in this paper represents the realization of simple method of achieving low band gap semiconductors without being doped, for DSSCs applications.     

Thulium and Ytterbium-Doped Titanium Oxide Thin Films Deposited by Ultrasonic Spray Pyrolysis

Thin films of thulium and ytterbium-doped titanium oxide were grown by metal-organic spray pyrolysis deposition from titanium(IV)oxide bis(acetylacetonate), thulium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate) and ytterbium(III) tris(acetylacetonate). Deposition temperatures have been investigated from 300 to 600 °C. Films have been studied regarding their crystallinity and doping quality. Structural and composition characterisations of TiO₂:Tm,Yb were performed by electron microprobe, x-ray diffraction, and Fourier transform infrared spectroscopy. The deposition rate can reach 0.8 μm/h. The anatase phase of TiO₂ was obtained after synthesis at 400 °C or higher. Organic contamination at low deposition temperature is eliminated by annealing treatments.     

Sol–gel derived Ta-containing TiO_2 films on surface roughened NiTi alloy

The surface of NiTi alloy was roughened by NaOH–HCl treatment, and the Ta-containing TiO2 films were coated on the pretreated NiTi alloy by the sol–gel method. Thermal analyses indicate that the evaporation temperature of the organics decreases with the addition of tantalum ethoxide in the TiO2 sol, but the crystallization temperature of anatase increases. The NaOH–HCl pretreatment improves the film integrity, but cracks still form in the films at high Ta contents(C20 %, molar ratio) owing to the increasing film thickness. X-ray diffraction(XRD) confirms that the addition of Ta suppresses the crystallization of anatase. X-ray photoelectron spectroscopy(XPS) reveals that Ta exists as Ta2 O5 in the film. With the increase of Ta content, the hydrophilic conversion of the films under UV illumination is impeded, but their corrosion resistance in 0.9 % NaCl solution increases, tested by the potentiodynamic polarization. The coating samples have acceptable hemolysis ratios for biomaterials(\5). The introduction of Ta improves the anti-aggregating function of the TiO2 film in the platelet adhesion test.     

Enhanced photocatalytic properties of N–P co-doped TiO<Subscript>2</Subscript> nanosheets with {001} facets

Nitrogen (N) and phosphorus (P) co-doped anatase TiO₂ nanosheets were realized by low-temperature self-doping N–TiO₂ followed by high-temperature P doping with foreign precursor. It is found that P doping process can maintain good TiO₂ nanosheets morphology with exposed {001} facets. Chemical state of dopants indicates that N and P atoms replace O on O sites in TiO₂ lattice. Compared with pure TiO₂ and N-doped TiO₂, N–P co-doped TiO₂ nanosheets exhibits stronger optical absorption and higher degradation rate of dye molecules in visible light regime. The enhanced photocatalytic properties are attributed to two factors. On one hand, N–P co-doping can effectively reduce band gap of TiO₂ from 3.20 to 2.48 eV, leading to an enhancement of the absorption in visible light regime. On the other hand, the presence of exposed {001} facets of TiO₂ nanosheets can induce the effective separation of photogenerated electrons and holes in reaction.     

Experimental and DFT Study of Structural and Optical Properties of Kesterite-Type Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Compound for Solar Cell Applications

In this work, Cu₂ZnSnS₄ (CZTS) thin films were prepared by thermal evaporation from Cu₂SnS₃ and ZnS initially mixed by a mechanical alloying process. Structural and optical properties of CZTS films have been studied. X-ray diffraction results showed that the semiconductor has the Kesterite structure, and the optical absorption coefficient and band gap energy of the thin films were about 10⁴ cm^?1 and 1.46 eV, respectively. The structural and optical properties of Kesterite CZTS, studied by using the full potential linearized augmented plane wave method within the density functional theory, showed good agreement with our experimental results. The surface morphological studies revealed the formation of a smooth, compact and uniform CZTS surface.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

Substrate temperature dependence of chemical state and magnetoresistance characteristics of Co–TiO2 nanocomposite films

Co−TiO₂ nanocomposite films were prepared via magnetron sputtering at various substrate temperatures. The films comprise Co particles dispersed in an amorphous TiO₂ matrix and exhibit coexisting ferromagnetic and superparamagnetic properties. When the substrate temperature increases from room temperature to 400 °C, Co particles gradually grow, and the degree of Co oxidation significantly decreases. Consequently, the saturation magnetization increases from 0.13 to 0.43 T at the same Co content by increasing the substrate temperature from room temperature to 400 °C. At a high substrate temperature, conductive pathways form among some of the clustered Co particles. Thus, resistivity rapidly declines from 1600 to 76 μΩ·m. The magnetoresistive characteristic of Co−TiO₂ films is achieved even at resistivity of as low as 76 μΩ·m. These results reveal that the obtained nanocomposite films have low Co oxidation, high magnetization and magnetoresistance at room temperature.     

Effect of TiO2 on thermal,structural and third-order nonlinear optical properties of Ca–La–B–O glass system

A series of calcium lanthanum metaborate glasses in the composition (wt%) of 23.88CaO–28.33La₂O₃–47.79B₂O₃ modified with TiO₂ up to 20 wt% are prepared by a melt quenching technique to study the influence of TiO₂ on their thermal, structural, linear and nonlinear optical properties. The differential thermal analysis (DTA) studies have demonstrated significant effects due to the presence of TiO₂ on the glass forming ability and crystallization situations. The glass with 15 wt% TiO₂ has achieved a eutectic composition and also exhibited a better glass forming ability among the glasses studied. The FT-IR spectra of these glasses show mainly vibration modes corresponding to stretching of BO₃ trigonal, BO₄ tetrahedral units and of B–O–B bending bonds. At higher concentrations of TiO₂, development of vibration band around 400 cm^?1 has indicated the formation of TiO₆ structural units in the glass network. The red shift of optical absorption edge (UV cutoff) shows a monotonous decrease in direct and indirect optical band gap energies (E_opt) with an increase of TiO₂ content in the glasses based on their absorption spectra. The optical transparency of these glasses is found to be varied from 64 to 87% within the wavelength range 450–1100 nm depending on the TiO₂ content. Besides these studies, linear refractive indices, the nonlinear optical properties of these glasses have also been evaluated.     

Nanomechanical Properties of Amorphous and Polycrystalline SrTiO3 Transparent Thin Films Prepared by Ion Beam Sputtering

Transparent SrTiO₃ thin films were deposited on glass substrates by ion beam sputtering at various substrate temperatures. The structural characteristic of the deposited films shows the transition from amorphous phase to polycrystalline phase at 600 °C. The films exhibit a good transparency in the visible region (~80-85%) and a relatively smooth surface. The calculated band gaps for amorphous and polycrystalline films were ~4.20 and ~3.84 eV, respectively. The refractive index of the films increases with increasing the substrate temperature, and the extinction coefficient of the films in the visible region is in the order of 10^?3, indicating low optical loss. The nanomechanical properties of the films were investigated using nanoindentation technique. Young’s modulus and hardness for all films are found to be increased with the increase of substrate temperature.     

Preparation and oxygen-sensing properties of TiO2 porous thin films on alumina substrate

The titanium dioxide sols were synthesized with tetrabutyl titanate as precursor, diethanolamine（DEA） as complexing agent , polyethylene glycol （PEG） as organic template. The porous films were prepared by sol-gel method, The structures and morphology of the titanium dioxide porous films were characterized by FE-SEM. The formation mechanism of TiO2 porous films and the relation between the porous structure and oxygen-sensing properties of TiO2 films were studied. Ordered structure was formed by assembling between TiO2 colloid particles and the template molecules. PEG molecules acted on TiO2 colloid particles by hydrogen bond and bridge oxygen. The porous structure was formed after the organic template was decomposed when calcining the films. The diameter, amount and distribution of the pores in the films are related with the content of PEG. The pore diameter increases with increasing of content of PEG and the pore density reaches the maximum at certain content. Oxygen-sensitivity and response speed of porous TiO2 films are improved compared with films without pores. Both the sensitivity and response speed increase with the increasing of pore diameter and pore density. Oxygen-sensitivity reaches 3 order of magnitude at 800 ℃. Its response time from H2/N2 to O2/N2 atmosphere and vice versa is about 0.11 s and 0.12 s respectively. Although the sensitivity and response speed increase, the resistance-temperature properties of porous films are not notably improved with the increasing of the content of PEG.     

Effect of SiC Addition on Oxidation Behavior of ZrB<Subscript>2</Subscript> at 1273 K and 1473 K

The oxidation behavior of ZrB₂–SiC composites with different contents of SiC addition was investigated at 1273 and 1473 K in air for 12 h in this study. The SiC addition contents ranged from 0 to 30 wt%. The results showed that when ZrB₂–SiC composites were oxidized at 1273 K in air, a two-oxide layer-structure forms: a continuous glassy layer and a ZrO₂ layer contained unoxidized SiC. When SiC content is 5 and 10 wt%, the glassy layer is mainly composed by B₂O₃. When SiC content is 20 and 30 wt%, a borosilicate glass could be formed on the top layer, which could improve the oxidation resistance of ZrB₂. When ZrB₂–SiC composites were oxidized at 1473 K in air, the oxide layer was composed of ZrO₂ and SiO₂ and unreacted SiC. Additionally, when SiC addition content was higher than 10 wt%, a continuous borosilicate glass layer could be formed on the top of the oxide layer at 1473 K. With the increase of SiC content in ZrB₂, the oxide layer thickness decreased at both 1273 and 1473 K.