Thermal treatment effect on the magnetoelectric properties of (Ni0.5Zn0.5)Fe2O4/Pt/Pb(Zr0.3Ti0.7)O3 heterostructured thin films

Magnetoelectric (ME) property modulation in heterostructured (Ni_0.5Zn_0.5)Fe₂O₄/Pt/Pb(Zr_0.3Ti_0.7)O₃ (NZFO/Pt/PZT) thin films on platinized Si substrate by thermal annealing condition variation was studied. In an attempt to prevent interfacial reaction between NZFO and PZT layers during high temperature annealing, thin Pt layer was deposited which can serve as inter-diffusion barrier as well as electrode. The ferroelectric, magnetic, and ME properties of the heterostructured film were noticeably modulated due to microstructural evolution and clamping relaxation developed during thermal annealing process. Room temperature ME voltage coefficient of the heterostructured thin films was enhanced with increasing annealing temperature and reached to 29 mV/cm·Oe when annealed at 650 °C.     

Electrophoretic deposition of nanocrystalline TiO2 films on Ti substrates for use in flexible dye-sensitized solar cells

Nanocrystalline TiO₂ films were prepared on flexible Ti-metal sheets by electrophoretic deposition followed by chemical treatment with tetra-n-butyl titanate (TBT) and sintering at 450 °C. X-ray diffraction (XRD) analysis indicates that TBT treatment led to the formation of additional anatase TiO₂, which plays an important role in improving the interconnection between TiO₂ particles, as well as the adherence of the film to the substrate, and in modifying the surface properties of the nanocrystalline particles. The effect of TBT treatment on the electron transport in the nanocrystalline films was studied by intensity-modulated photocurrent spectroscopy (IMPS). An increase in the conversion efficiency was obtained for the dye-sensitized solar cells with TBT-treated nanocrystalline TiO₂ films. The cell performance was further optimized by designing nanocrystalline TiO₂ films with a double-layer structure composed of a light-scattering layer and a transparent layer. The light-scattering effect of the double-layer nanocrystalline films was evaluated by diffuse reflectance spectra. Employing the double-layer nanocrystalline films as the photoelectrodes resulted in a significant improvement in the incident photo-to-current conversion efficiency of the corresponding cells due to enhanced solar absorption by light scattering. A high conversion efficiency of 6.33% was measured under illumination with 100 mW cm⁻² (AM 1.5) simulated sunlight.     

Tunability of optical constants of Se-Ge-Ag thin films based on change in resistivity with temperature for solar cells

Thin films of semiconductor Se₈₀Ge_20-xAg_x (x = 0, 3, 6, 9, 12 and 15 at.%) were deposited by the thermal evaporation technology. Through optical and electrical characterization, the influence of the Ag ratio on the photoelectric parameters of Se–Ge thin film was studied. The X-ray diffraction pattern showed the amorphous nature of the deposited films as well as the polycrystalline state when the films were annealed at the maximum crystallization temperature (415 K), which was determined by the first derivative of the resistivity curve with respect to temperature. The crystallization kinetics of the film was extracted from the electrical analysis by measuring the change in resistivity with temperature. The electrical results of the thin film showed three regions; namely, amorphous, extended (crystalline) and hopping. In the extended and hopping states, the activation energy and pre-exponential factors were calculated. The optical constants, extinction coefficient and refractive index were calculated using the transmittance and reflectance of the grown Se₈₀Ge_20-xAg_x films. The energy gaps of the films were estimated in the strong absorption regions. The changes in the bandgap energy of the film by thermal annealing can help to produce materials with acceptable band gaps for use as absorber layers in solar cell applications. Also, the results provide microscopic insights and studies on the structure, electr-othermal and optical properties of Ag metal-doped GeSe as a back contact of solar cells.     

Film growth and relationship between microstructure and mechanical properties of a-C:H:F films deposited by PECVD

Results of a systematic investigation on the effects of some deposition parameters (partial pressure of CF₄ and self-bias voltage) on the microstructure, mechanical and tribological properties of a-C:H:F films are presented. The films were deposited by r.f.-PECVD using CH₄–CF₄ mixtures. The film composition was measured by ion beam analysis and, combining these results with the film thickness, the film density was determined. The structural arrangement was probed by Raman spectroscopy and the chemical bonding was investigated by infrared absorption and X-ray photoelectron spectroscopies. The hardness was measured by microindentation and the internal stress was determined by measuring the changing of the substrate curvature after the film deposition. The friction coefficient was measured by lateral force microscopy. The results indicate that the properties of a-C:H:F films are controlled by the ionic bombarding during the film growth. For a fixed self-bias, the increase of the CF₄ partial pressure leads to a transition from diamond-like to a polymer-like structure, to a higher fluorine incorporation and to a decrease of both hardness and internal stress. The friction coefficient decreases too. The fluorine incorporation also increases with the increase of the self-bias and was associated to higher plasma decomposition. Fluorine-poor polymer-like films were deposited at low self-bias (−50 V). In both situations, fluorine incorporation occurs at the expenses of the hydrogen content and the reduction of the energy of the bombarding species results in less dense and soft films with a polymer-like structure.     

Spectral Selective Solar Light Enhanced Photocatalysis: TiO<Subscript>2</Subscript>/TiAlN Bilayer Films

We demonstrate that spectral selective photocatalytic multilayer films can be tailored such that they can harness the full solar spectrum for enhanced photocatalytic gas-phase oxidation of acetaldehyde. Thin films of anatase TiO₂ were deposited on a thin solar absorber TiAlN film to fabricate bilayer TiO₂/TiAlN films by dc magnetron sputtering on aluminium substrates. The structural and optical properties of the films were characterized by X-ray diffraction and Raman spectroscopy. The reaction rate and quantum yield for acetaldehyde removal was measured and an almost tenfold enhancement of the quantum yield was observed for the TiO₂/TiAlN films compared with the single TiO₂ film, on par with enhancements achieved with new heterojunction photocatalysts. The results were interpreted by a temperature-induced change of the reaction kinetics. Absorption of simulated solar light illumination resulted in a temperature increase of the TIAlN film that was estimated to be at most 126 K. We show that a concomitant temperature increase of the top layer TiO₂ by 100 K shifts the water gas-surface equilibrium from multilayer to submonolayer coverage. We propose that this is the main reason for the observed enhancement of the photocatalytic activity, whereby gas phase molecules may come in direct contact with free surface sites instead of having to diffuse through a thin water film. The implications of the results for judicious control of temperature and relative humidity for efficient gas-phase photocatalysis and exploitation of selective solar absorbing films are discussed.     

Effects of the sulfurization temperature on sol gel-processed Cu2ZnSnS4 thin films

As a promising and alternative solar absorber material, the copper–zinc–tin–sulfide compound (Cu₂ZnSnS₄) has been drawing attention in recent years for the production of cheap thin-film solar cells owing to the high natural abundance and non-toxicity of all the constituents, a tunable direct-band-gap energy and a large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu₂ZnSnS₄ deposition. In this study, we have produced Cu₂ZnSnS₄ thin films via the sol–gel technique and subsequent sulfurization. The effects of the sulfurization temperature on the structural, morphological, compositional and optical properties of the films were investigated. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. The crystallinity of the films increased with an increasing sulfurization temperature. From the surface images and the results of the composition analysis, it was found that the films are uniform, composed of homogenously distributed grains and have compositions with Cu deficit. The values of the optical absorption coefficients for the films were found to be 10⁴ cm^?1 based on absorbance spectroscopy. The optical band-gap values were estimated to be between 1.32 and 2.27 eV depending on the sulfurization temperature.     

Effect of silver (Ag) ions irradiation on the structural,optical and photovoltaic properties of Mn doped TiO2 thin films based dye sensitized solar cells

Dye sensitized solar cell (DSSC) is an emerging energy harvesting tool which converts direct sunlight into electrical energy. These cells have much better properties in contrast with silicon based solar cells because of their flexible nature, light weight, low cost, environment friendly nature, and involvement of a simple manufacturing process. Since, a photoanode is the backbone of DSSC, we synthesized a pure and 1% manganese (Mn) doped titanium dioxide (TiO₂) films by sol-gel method which are irradiated with silver (Ag) ions at two different concentrations (2 × 10¹⁴ and 4 × 10¹⁴) ions-cm^?2. X-ray diffraction revealed that Mn doping followed by Ag irradiation transformed TiO₂ from pure anatase to rutile phase. Ultraviolet–visible spectroscopy exposed the reduction in band gap of TiO₂ film during this doping and irradiation process. Therefore, absorption is enhanced with red shift in UV-range. When these films are used as a photoanode in DSSC, 1% Mn doped TiO₂ film exposed with Ag at the concentration of (2 × 10¹⁴) ions-cm^?2 exhibited maximum efficiency of 2.40%.     

Effects of composition and stacking sequence on dielectric properties of the multilayered (Pb,Sr)TiO3 thin films for tunable device application

Multilayered (Pb_1−xSr_x)TiO₃ (PST(x)) thin films consisted of uniform, PST(x) and heterostructure, PST(x)–PST80 were synthesized by coating the solutions with different Sr contents (50 ≤ x, Sr(mol%) ≤80), respectively. Their structural and dielectric properties were investigated in terms of composition and stacking sequence of each film. Among uniform PST(x) thin films, the PST60 films showed the highest dielectric constant and tunability, while so lower figure of merit which is an important parameter for microwave tunable device application was obtained due to relatively higher dielectric loss. In an effort to bring down the dielectric loss, the PST(x) thin films were alternately coated with PST80 thin layer. Dielectric properties of the heterostructured PST(x)–PST80 films were found to be dependent on the intrinsic dielectric values of each film composition and corresponding phase transition temperature shift effect. Furthermore, surface roughness became smoother by inserting PST80 thin layer, resulting in decrease in dielectric loss. In case of the PST60–PST80 heterostructured film, despite of slight decrease in tunability, the figure of merit on account of lowered dielectric loss was effectively improved (>40%), compared to that of the uniform PST60 film.     

A composite poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) and Pt film as a counter electrode catalyst in dye-sensitized solar cells

A composite poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) and platinum (PProDOT-Et₂/Pt) film was prepared for using as a counter electrode (CE) catalyst in a dye-sensitized solar cell (DSSC). Four composite films were prepared by electropolymerization of ProDOT-Et₂ on indium tin oxide (ITO) conducting glass, followed by Pt sputtering for 10, 30, 120, and 720 s. The Pt content in the composite film was verified by energy dispersive X-ray spectroscopy (EDX). The composite films possessed three-dimensional (3D) porous structures, as determined by scanning electron microscopy (SEM). The DSSC with the composite film that was subject to 10 s of Pt deposition (PProDOT-Et₂/Pt-10 s) exhibited the highest solar to electricity conversion efficiency (η) of 6.68%, while the cells with the bare polymer film (PProDOT-Et₂) and Pt that was sputtered for 720 s (s-Pt-720 s) demonstrated efficiencies of 4.76% and 6.43%, respectively. The cell photovoltaic parameters were substantiated through dark current, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analyses. Incident photon-to-current conversion efficiency (IPCE) curves were used to explain the cell photocurrent behaviors.     

Photoelectrocatalytic degradation of bisphenol A in aqueous solution using a Au–TiO2/ITO film

A series of Au–TiO₂/ITO films with nanocrystaline structure was prepared by a procedure of photo-deposition and subsequent dip-coating. The Au–TiO₂/ITO films were characterized by X-ray diffraction, scanning electronic microscopy, electron diffraction, X-ray photoelectron spectroscopy, and UV–VIS diffuse reflectance spectroscopy to examine the surface structure, chemical composition, the chemical state of metal, and the light absorption properties. The photocatalytic activity of the Au–TiO₂/ITO films was evaluated in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of bisphenol A (BPA) in aqueous solution. Compared with a TiO₂/ITO film, the degree of BPA degradation using the Au–TiO₂/ITO films was significantly higher in both the PC and PEC processes. The enhancement is attributed to the action of Au deposits on the TiO₂ surface, which play a key role by attracting conduction band photoelectrons. In the PEC process, the anodic bias externally applied on the illuminated Au–TiO₂/ITO film can further drive away the accumulated photoelectrons from the metal deposits and promote a process of interfacial charge transfer.     

TiO2 films prepared by micro-plasma oxidation method for dye-sensitized solar cell

Nanocrystalline TiO₂ films are widely investigated as the electrodes of dye-sensitized solar cell(s) with different preparation methods. In this paper, thin titanium dioxide films have been prepared on titanium plates by the micro-plasma oxidation method in the sulfuric acid solution. The thin TiO₂ films were sensitized with a cis-RuL₂(SCN)₂·2H₂O (L = cis-2,2′-bipyridine-4,4′-dicarboxylic acid) ruthenium complex and implemented into a dye-sensitized solar cell configuration. The influence of reaction current density (10, 15, 20, 25 and 30 A dm⁻²) on the structural and the surface morphology of the films was investigated by X-ray diffraction, scanning electron microscopy, atom force microscopy and X-ray photoelectricity spectroscopy. Impedance analysis for dye-sensitized solar cells was carried out by electrochemical impedance spectroscopy. The results show that the rise of current density leads to the increase in the amount of rutile and the thickness of the TiO₂ film, which makes the TiO₂ films have different photovoltages and photocurrents. The relatively higher photoelectricity properties were obtained in the TiO₂ films prepared at a current density of 20 A dm⁻². The open-circuit voltage and the short-circuit current are 605 mV and 165 μA cm⁻², respectively.     

Optical and photoelectrochemical properties of a TiO2 thin film doped with a ruthenium–tungsten bimetallic complex

Optical and photoelectrochemical (PEC) properties of a TiO₂ thin film electrode doped with a new variation of ruthenium–(4,4′dimethyl-2,2′-bipyridine)–isothiocyanato–tungsten[bis-(phenyl-1,2-ethilenodithiolenic)] bimetallic complex (BM) were investigated. Physical adsorption process was used to immobilise the BM on the TiO₂ thin film. Crystalline structure and surface morphology of the thin films were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) techniques. N3 commercial dye was also used as a dopant to the TiO₂ films for comparison. Light absorption spectra and bandgap energy of the thin films were determined using UV–vis spectroscopy. Light absorption of the TiO₂ thin film doped with BM was better than the TiO₂ doped with the N3 commercial dye. Band edges of the TiO₂ thin film and the BM were determined via cyclic voltammetry (CV) measurements. Top-edge of the BM valence band (VB) was more positive than the bottom edge of the conduction band (CB) of the TiO₂ film (vs. NHE). PEC analysis indicated that photocurrent of TiO₂ doped with the BM electrode was higher than TiO₂ doped with the N3 in the beginning of illumination process, but the performance was defeated after a while. Based on the optical properties and the PEC analyses, BM has potential to be used as dye sensitisers for a PEC cell.     

Synthesis and characterization of sol gel derived nontoxic CZTS thin films without sulfurization

Recently, great attention has been paid to the development of earth rich and nonhazardous Copper Zinc Tin Sulfide (CZTS–Cu₂ZnSnS₄) thin films for application in photovoltaic devices owing to its high absorption coefficient over the visible and infrared region. However, sulfurization process is an indispensable step in growing stoichiometric thin film using conventional physical vapor deposition. Hence, it is imperative to devise a liquid based technique without intentional sulfurization for the optimum quality growth of CZTS thin films. In the current work, layer-by-layer sol-gel deposition technique was utilized to grow high quality CZTS thin films without sulfurization and their structural and optical characteristics were investigated using XRD studies and UV-visible spectroscopy respectively. The morphology and chemical composition of the prepared CZTS films are estimated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis respectively. Highly absorbing and crystalline CZTS films have been successfully grown in the present work which could be further utilized as an absorber layer in photovoltaic applications.     

Impact on nonlinear/linear optical and structural parameters in quaternary In15Ag10S15Se60 thin films upon annealing at different temperatures

In the present study, the effect of thermal annealing on structural, linear, and nonlinear optical properties of quaternary chalcogenide In₁₅Ag₁₀S₁₅Se₆₀ thin film has been reported. The bulk sample synthesized by the melt quenching technique was used for the thin film preparation by the thermal evaporation method. Post deposition, the thin films were annealed at different temperatures like 100 °C, 150 °C, 200 °C, and 250 °C for 2 hs. X-ray diffraction (XRD) and Raman spectroscopy were used for structural studies, which showed the increase in crystalline phases with the increase of annealing temperature. The morphological images taken by field emission scanning electron microscope (FESEM) showed the densification and enlargement of scattered grains for annealed films. Furthermore, the constituent elements and their percentage in the sample were confirmed by Energy dispersive X-ray analysis (EDX). The linear and nonlinear optical parameters were calculated from the transmittance data obtained from UV–Vis spectroscopy in the wavelength range of 600–1100 nm. There is a large reduction in third-order nonlinear susceptibility at the higher annealing temperature. Subsequently, the transmission increased, whereas the absorption decreased with the annealing temperature. The extinction coefficient decreased while there was an increase in optical bandgap for the annealed films due to the decrease in surface defects and disorder, which forms the localized states in the bandgap. The oscillator energy, dispersion energy, dielectric constant, optical conductivity were calculated and discussed in detail. The change in both linear and nonlinear parameters by thermal annealing could be useful for controlling the optical properties of In₁₅Ag₁₀S₁₅Se₆₀ thin film, which could be the preferable candidate for numerous photonic applications.     

Photovoltaic performance improvement of dye-sensitized solar cells based on tantalum-doped TiO2 thin films

Dye-sensitized solar cells based on a tantalum (Ta)-doped TiO₂ thin film prepared by the hydrothermal method show a photovoltaic efficiency of 8.18%, which is higher than that of the undoped TiO₂ thin film (7.40%). The Mott-Schottky plot indicates that the Ta-doped TiO₂ photoanode shifts the flat band potential positively and increases the electron density. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO₂. Furthermore, the increased electron density caused by the Ta-doped TiO₂ improves the fill factor of the solar cell. The increased electron density accelerates the transfer rate of electrons in the Ta-doped TiO₂ thin films by comparison to undoped films, which is confirmed by intensity-modulated photocurrent spectroscopy measurements.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.     

Reversible,repeatable and low phase transition behaviour of spin coated nanostructured vanadium oxide thin films with superior mechanical properties

Smooth, uniform and crystalline vanadium oxide thin films were deposited on quartz by spin coating technique with four different rpm i.e., 1000, 2000, 3000 and 4000 and subsequently post annealed at 350, 450 and 550?°C in vacuum. Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) techniques were utilized for microstructural characterizations and phase analysis, respectively, for vanadium oxide powder and deposited film. Nanorods were observed to be grown after vacuum annealing. X-ray photoelectron spectroscopy (XPS) technique was utilized to study the elemental oxidation state of deposited vanadium oxide films. Thermo-optical and electrical properties such as solar transmittance (τ_s), reflectance (ρ_s), absorptance (α_s), infrared (IR) emittance (ε_ir) and sheet resistance (R_s) of different thin films were evaluated. Based on the optical characteristics the optimized condition of the film processing was identified to be spin coated at 3000?rpm. Subsequently, the nanoindentation technique was utilized to measure hardness and Young's modulus of the optimized film. The measured nanomechanical properties were found to be superior to those reported for sputtered vanadium oxide films. Finally, temperature dependent phase transition characteristics of optimized vanadium oxide films were studied by differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition was found to occur in the range of 44–48?°C which was significantly lower than the phase transition temperature (i.e., 68?°C) of bulk VO₂.     

Structural,optical and electrical properties of indium doped Cu2ZnSn(S,Se)4 thin films synthesized by the DC and RF reactive magnetron cosputtering

Element doping into the Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber is an effective method to optimize the performance of thin film solar cells. In this study, the Cu₂In_xZn_1-xSn(S,Se)₄ (CIZTSSe) precursor film was deposited by magnetron cosputtering technique using indium (In) and quaternary Cu₂ZnSnS₄ (CZTS) as targets. Meanwhile, the In content was controlled using the direct current (DC) power on In target (P_In). A single kesterite CIZTSSe alloy was formed by successfully doping a small number of In³⁺ into the main lattice of CZTSSe. The partial Zn²⁺ cations were substituted by In³⁺ ions, resulting in improving properties of CZTSSe films. Morphological analysis showed that large grain CIZTSSe films could be obtained by doping In. The well-distributed, smooth, and dense film was obtained when the P_In was 30 W. The band gap of CIZTSSe could be continuously adjusted from 1.27 to 1.05 eV as P_In increased from 0 to 40 W. In addition, the CIZTSSe alloy thin film at P_In = 30 W exhibited the best p-type conductivity with Hall mobility of 6.87 cm²V^?1s^?1, which is a potential material as the absorption layer of high-performance solar cells.     

Thermochromic properties of ZnO/VO2/ZnO films on soda lime silicate glass deposited by RF magnetron sputtering

A smart window based on VO₂ is a promising thermochromic (TC) glass that can regulate heat flow through windows by solar modulation near room temperature. TC glasses with high visible-light transmittance and large difference in infrared transmittance between high- and low-temperature VO₂ phases are required to save large amounts of energy in buildings. VO₂-based multilayer films with a buffer layer and/or an anti-reflective (AR) layer are used when the films are deposited by sputtering. In this study, VO₂-based multilayer films were prepared on soda lime glass using ZnO as both the buffer and the AR layers. The structure of the multilayer film was simulated using the optical constants measured from the deposited films. The effect of buffer and AR layers on the TC properties of VO₂-based multilayer films prepared by sputtering was investigated by simulation of the multilayer structure and deposition of the films with the simulated structure. The TC properties were measured and compared with the calculated properties. Improved TC properties (luminous transmittance (T_lum) of ～50%/46% (30 °C/80 °C) and solar modulation ability (ΔT_sol) of ～14%), compared to those without the buffer and AR layer, were obtained from the ZnO/VO₂/ZnO film deposited on glass. The calculated transmittances agree better with the measured ones when the optical constants measured directly from the deposited films are used and the roughnesses of the surface/interface of the multilayer films are considered in the calculation of the optical constants.     

Microwave photocatalysis III. Transition metal ion‐doped TiO2 thin films on mercury electrodeless discharge lamps: preparation,characterization and their effect on the photocatalytic degradation of mono‐chloroacetic acid and Rhodamine B

BACKGROUND: Mercury electrodeless discharge lamps (Hg‐EDLs) were used to generate UV radiation when exposed to a microwave field. EDLs were coated with doped TiO₂ in the form of thin films containing transition metal ions Mⁿ⁺ (M = Fe, Co, Ni, V, Cr, Mn, Zr, Ag). Photocatalytic degradation of mono‐chloroacetic acid (MCAA) to HCl, CO₂, and H₂O, and decomposition of Rhodamine B on the thin films were investigated in detail. RESULTS: Polycrystalline thin doped TiO₂ films were prepared by dip‐coating of EDL via a sol–gel method using titanium n‐butoxide, acetylacetone, and a transition metal acetylacetonate. The films were characterized by Raman spectroscopy, UV/Vis absorption spectroscopy, X‐ray photoelectron spectroscopy (XPS), electron microprobe analysis and by atomic force microscopy (AFM). The photocatalytic activity of doped TiO₂ films was monitored in the decomposition of Rhodamine B in water. Compared with the pure TiO₂ film, the UV/Vis spectra of V, Zr and Ag‐doped TiO₂ showed significant absorption in the visible region, and hence the photocatalytic degradation of MCAA had increased. The best apparent degradation rate constant (0.0125 min^?1), which was higher than that on the pure TiO₂ film by a factor of 1.7, was obtained with the Ag(3%)/TiO₂ photocatalyst. The effect of doping level of vanadium acetylacetonate on the photocatalytic efficiency of the V‐doped TiO₂ was determined. CONCLUSIONS: Transition metal ion‐doped TiO₂ thin films showed significant absorption in the visible region. The metal doped TiO₂ photocatalyst (with an appropriate amount of V, Zr and Ag) on the Hg‐EDLs increased the degradation efficiency of MCAA in a microwave field. Copyright © 2009 Society of Chemical Industry