Ion beam modification of TiO2 films prepared by Cat-CVD for solar cell

The effects of nitrogen ion bombardment on TiO₂ films prepared by the Cat-CVD method have been studied to improve the optical and electrical properties of the material for use in Si thin film solar cells. The refractive index n and the dark conductivity of the TiO₂ film increased with irradiation time. The refractive index n of the TiO₂ film was changed from 2.1 to 2.4 and the electrical conductivity was improved from 3.4 × 10^− 2 to 1.2 × 10^− 1 S/cm by the irradiation. These results are due to the formation of Ti-N bonds and oxygen vacancies in the film.     

Influence of cobalt ion implantation on optical properties of titanium dioxide thin films

Nano-crystalline TiO₂ thin films were synthesized by using sol-gel and spin-coating techniques on glass substrates for photo-catalytic applications. Prior to deposition, a TiO₂ colloidal suspension was synthesized by microwave-induced thermal hydrolysis of the titanium tetrachloride aqueous solution. In this study, the deposited TiO₂ coating with a grain size of 13 ± 2 nm was uniform without aggregation. Co ion implantation into the as-calcined TiO₂ thin films was conducted with fluences of 1 × 10¹⁵-1 × 10¹⁶ doses/cm² at 40 keV. In addition to the emission of TiO₂, the photoluminescence study showed the presence of another Co-related optical center at 405 nm in the Co-implanted TiO₂ thin films. Due to the strong capability of forming impurity compounds between the energetic cobalt ions and TiO₂, the photoluminescence emission and UV-Vis absorption efficiencies were improved.     

Optical properties of TiO2 thin films after Ag ion implantation

Metal plasma ion implantation has being successfully developed for improving the electronic and optical properties of semiconductor materials. Prior to deposition, a TiO₂ colloidal suspension was synthesized by microwave-induced thermal hydrolysis of the titanium tetrachloride aqueous solution. The TiO₂ thin film was optimized to obtain a high-purity crystalline anatase phase by calcinations at 550 °C. The TiO₂ coating was uniform without aggregation, which provided good photo conversion efficiency. Ag ion implantation into the as-calcined TiO₂ thin films was conducted with 1 × 10¹⁵ ~ 1 × 10¹⁶ ions/cm² at 40 keV. The peak position and intensity of the photoluminescence and UV-Vis absorption spectra are quite sensitive to Ag doping. The optical characterization showed a shift in optical absorption wavelength towards infrared ray side, which was correlated with the structure variation of the Ag⁺ implanted TiO₂. Due to the strong capability of forming compounds between the energetic silver ions and TiO₂, the photoluminescence emission and UV-Vis absorption efficiencies were improved.     

Influence of gamma irradiation on the refractive index of Fe-doped barium titanate thin films

Polycrystalline Fe-doped barium titanate (Fe-doped BaTiO₃) thin films were grown by thermal decomposition of the precursors deposited from a sol-gel system onto quartz substrates. The changes in the transmittance spectra induced by gamma irradiation on the Fe-doped BaTiO₃ thin films were quantified. The values for the optical energy band gap were in the range of 3.42-3.95 eV depending on the annealing time. The refractive index of the film, as measured in the 350-750 nm wavelength range was in the 2.17-1.88 range for the as prepared film, and this increased to 2.34-1.95 after gamma irradiation at 15 kGy. The extinction coefficient of the film was in the order of 10⁻² and increased after gamma irradiation. We obtained tuneable complex refractive index of the films by exposure to various gamma rays doses.     

Spray deposition and property analysis of anatase phase titania (TiO2) nanostructures

Anatase phase titanium dioxide thin films have been deposited at various substrate temperatures by chemical spray pyrolysis of an aerosol of titanyl acetylacetonate. Deposited TiO₂ films were nanocrystalline and preferentially oriented along [101] direction, uniform and adherent to the glass substrate. Best films processed at 450 °C were characterized to analyze its phase composition, texture, roughness, optical and electrical properties. X-ray photoelectron spectroscopy revealed that the surface of the film has only the Ti⁴⁺ cations to form perfect TiO₂ stoichiometry with less amount of hydration. Atomic force microscopy image demonstrated the existence of homogeneous and rough surface, suitable for electrocatalytic applications. The film has an optical transmittance more than 90% and the refractive index of 2.07 was recorded at the wavelength 633 nm. Due to nano-sized grains, obtained optical band gap (3.65 eV) of the TiO₂ thin film was larger than that of the bulk TiO₂ (3.2 eV). Calculated porosity of the films 0.44, revealed the porous nature of the films. Hall measurements indicated that these materials are p-type and yield a carrier density of the order 8.8 × 10²⁰ cm⁻³ and a carrier mobility of 0.48 × 10⁻⁶ cm²/Vs. The dc electrical conductivity was therefore very low (8.91 × 10⁻⁶ S/cm) because of lower value of mean free path of the charge carriers (4.36 × 10⁻¹¹ cm). It gives an impression that the process of spray pyrolysis provides an easy way to tailor make thin films possessing superior properties.     

Overview about the optical properties and mechanical stress of different dielectric thin films produced by reactive-low-voltage-ion-plating

Thin films of Ta₂O₅, Nb₂O₅, and HfO₂ were deposited by reactive-low-voltage-ion-plating (RLVIP) on unheated glass and silicon substrates. The film thickness was about 200 nm. Optical properties as well as mechanical film stress of these layers were investigated in dependence of various deposition parameters, i.e. arc current and oxygen partial pressure. For an arc current in the range between 40 and 50 A and an oxygen partial pressure of at least 11 · 10^− 4 mbar good results were obtained. The refractive index and film thickness were calculated from spectrophotometric transmission data using the Swanepoel theory. For example at 550 nm wavelength the refractive index for thin RLVIP-Nb₂O₅-films was found to be n₅₅₀ = 2.40. The optical absorption was obtained by photo-thermal deflection spectrometry. For the investigated materials absorption coefficients in the range of k = 5 · 10^− 4 at 515 nm wavelength were measured. The mechanical film stress was determined by measuring the difference in bending of silicon substrates before and after the deposition process. For dense films, i.e. no water vapour sorption on atmosphere, the mechanical film stress was always compressive with values of some hundred MPa. In case of films deposited with higher arc currents (I_arc > 60A) and lower oxygen pressure (< 15 · 10^− 4 mbar) the influence of a post deposition heat treatment at 350 °C for 4 h on air was also investigated. For these films the properties could clearly be improved by such treatment. However, by using lower arc currents and higher oxygen partial pressure during the ion plating process, immediately dense and environmental stable films with good optical as well as mechanical properties could be achieved without post deposition heat treatment. All the results obtained will be presented in graphs and diagrams.     

Third-order optical nonlinear absorption in Bi1.95La1.05TiNbO9 thin films

Single phase Bi_1.95La_1.05TiNbO₉ (LBTN-1.05) thin films with a layered aurivillius structure have been fabricated on fused silica substrates by pulsed laser deposition at 700 °C. The X-ray diffraction pattern revealed that the films are single-phase aurivillius. The band gap, linear refractive index and linear absorption coefficient were obtained by optical transmittance measurements. The film exhibits a high transmittance (> 70%) in visible-infrared region and the dispersion relation of the refractive index vs. wavelength follows the single electronic oscillator model. The nonlinear optical absorption property of the film was determined by the single beam Z-scan method using 800 nm with a duration of 100 fs. A large positive nonlinear absorption coefficient β = 5.95 × 10^− 8 m/W was determined experimentally. The results showed that the LBTN-1.05 is a promising material for applications in absorbing-type optical devices.     

Influence of metal plasma ion implantation on photo-sensitivity of anatase TiO2 thin films

Nano-scale TiO₂ thin films were synthesized by using sol-gel and spin-coating techniques on glass substrates for photo-catalytic applications. The Ti(IV) butoxide-based TiO₂ thin films were optimized for transforming into the high-purity crystalline anatase phase when calcined at 500 °C. To further enhance the photo-catalysis sensitivity of TiO₂ thin films for use in visible light environments, a metal plasma ion implantation process was implemented to modify the band gap electron configuration of Ti. Various transition metal atoms such as Ni, Cu, V, and Fe were ionized and accelerated at 20 keV to impinge on the surface of TiO₂ substrates at a dosage of 5 × 10¹⁵ ions/cm². ESCA analysis confirmed the binding energy shift of Ti by 0.8-1.2 eV, which accounted for the increased effective positive charge of Ti, resulting in more effective electron trapping capability and, thus, the electron-hole pair separation. In addition, the absorption spectroscopy demonstrated that optical absorption in the visible light regime occurred in specimens implanted with transition metal ions, likely due to the formation of extra impurity energy levels within the original TiO₂ band gap energy structure. Among all tested implant materials, the band gap energy of TiO₂ was effectively reduced by Cu and Fe ion implantation by 0.9-1.0 eV, which was sufficient enough to excite valence electrons over the band gap in visible light environments. The feasibility of the metal-doped TiO₂ thin films for effective applications under visible light irradiation was further confirmed by using super-hydrophilicity contact-angle measurement.     

Preparation of anatase TiO2 thin films by vacuum arc plasma evaporation

Anatase titanium dioxide (TiO₂) thin films with high photocatalytic activity have been prepared with deposition rates as high as 16 nm/min by a newly developed vacuum arc plasma evaporation (VAPE) method using sintered TiO₂ pellets as the source material. Highly transparent TiO₂ thin films prepared at substrate temperatures from room temperature to 400 °C exhibited photocatalytic activity, regardless whether oxygen (O₂) gas was introduced during the VAPE deposition. The highest photocatalytic activity and photo-induced hydrophilicity were obtained in anatase TiO₂ thin films prepared at 300 °C, which correlated to the best crystallinity of the films, as evidenced from X-ray diffraction. In addition, a transparent and conductive anatase TiO₂ thin film with a resistivity of 2.6 × 10^− 1 Ω cm was prepared at a substrate temperature of 400 °C without the introduction of O₂ gas.     

Influence of calcination ambient and film thickness on the optical and structural properties of sol-gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol-gel derived TiO₂ thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO₂. Films calcined in argon or in low vacuum (∼2 × 10⁻¹ mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of ∼300-450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO₂ films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range ∼200-300 nm, band gap energy and crystallite size of TiO₂ films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO₂ films may be tailored during calcination period.     

Dye-sensitized solar cells with TiO2 nanocrystalline films prepared by conventional and rapid thermal annealing processes

Titanium oxide (TiO₂) thin films are prepared by the sol-gel method and annealed at 600 °C by conventional (CTA) and rapid thermal annealing (RTA) processes on fluorine-doped tin oxide -coated glass substrates for application as the work electrode for the dye-sensitized solar cells (DSSC). TiO₂ thin films are crystallized using a conventional furnace and the proposed RTA process at annealing rates of 5 °Cmin⁻¹ and 600 °Cmin⁻¹, respectively. The TiO₂ thin films are characterized by X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller analysis. Based on the results, the TiO₂ films crystallized by RTA show better crystallization, higher porosity and larger surface area than those of CTA. The short-circuit photocurrent and open-circuit voltage values increased from 5.2 mAcm⁻² and 0.6 V for the DSSC with the CTA-derived TiO₂ films to 8.3 mAcm⁻² and 0.68 V, respectively, for the DSSC containing RTA-derived TiO₂ films.     

Fabrication of highly conductive Ta-doped SnO2 polycrystalline films on glass using seed-layer technique by pulse laser deposition

We discuss the fabrication of highly conductive Ta-doped SnO₂ (Sn_1 − xTa_xO₂; TTO) thin films on glass by pulse laser deposition. On the basis of the comparison of X-ray diffraction patterns and resistivity (ρ) values between epitaxial films and polycrystalline films deposited on bare glass, we proposed the use of seed-layers for improving the conductivity of the TTO polycrystalline films. We investigated the use of rutile TiO₂ and NbO₂ as seed-layers; these are isostructural materials of SnO_2, which are expected to promote epitaxial-like growth of the TTO films. The films prepared on the 10-nm-thick seed-layers exhibited preferential growth of the TTO (110) plane. The TTO film with x = 0.05 on rutile TiO₂ exhibited ρ  = 3.5 × 10^− 4 Ω cm, which is similar to those of the epitaxial films grown on Al₂O₃ (0001).     

Structural,optical and electrical properties of In4Sn3O12 films prepared by pulsed laser deposition

Highly conducting (σ ∼ 2.6 × 10³ Ω⁻¹ cm⁻¹) In₄Sn₃O₁₂ films have been deposited using pulsed laser deposition (PLD) on glass and quartz substrates held at temperatures between 350 and 550 °C under chamber pressures of between 2.5 and 15 mTorr O₂. The crystallinity and the surface roughness of the films were found to increase with increasing substrate temperature. Electron concentrations of the order of 5 × 10²⁰ cm⁻³ and mobilities as high as 30 cm² V⁻¹ s⁻¹ were determined from Hall effect measurements performed on the films. Fitting of the transmission spectral profiles in the ultra-violet–visible spectrum has allowed the determination of the refractive index and extinction coefficient for the films. A red-shift in the frequency of plasmon resonance is observed with both increasing substrate temperature and oxygen pressure. Effective masses have been derived from the plasma frequencies and have been found to increase with carrier concentration indicating a non-parabolic conduction band in the material In₄Sn₃O₁₂. The optical band-gap has been determined as 3.8 eV from the analysis of the absorption edge in the UV. These results highlight the potential of these films as lower In-content functional transparent conducting materials.     

Transparent conducting Nb-doped anatase TiO2 (TNO) thin films sputtered from various oxide targets

Transparent conducting Nb-doped anatase TiO₂ (TNO) epitaxial films were sputtered from TiO₂-, Ti₂O₃-, and Ti-based targets at various oxygen partial pressures (Po₂). Using the TiO₂- and Ti₂O₃-based targets, highly conductive films showing a resistivity (ρ) of ~ 3 × 10^− 4 Ω cm could be formed without postdeposition treatment. In the case of the TNO films formed from the Ti-based target, reductive annealing had to be carried out at a temperature of 600 °C to achieve similar resistivity values. Thus, the use of oxide targets is preferable to obtain as-grown transparent conducting TNO films. In particular, the Ti₂O₃-based target is practically advantageous, because it offers a wide range of optimal Po₂ values at which ρ values of the order of 10^− 4 Ω cm are achievable.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

Large third-order optical nonlinearity of SrBi2Nb2O9 thin films fabricated by pulsed laser deposition

SrBi₂Nb₂O₉ (SBN) thin films with a single phase of layered perovskite structure have been fabricated on fused quartz substrates at room temperature by pulsed laser deposition. The XRD and AFM analysis indicated that the films had better crystallinity, less rough surface morphology, and larger grain size with increasing oxygen pressure. The nonlinear optical properties of the samples were determined using a single beam Z-scan technique at a laser wavelength of 532 nm with laser duration of 25 ps. The real and imaginary parts of the third-order nonlinear optical susceptibility χ⁽³⁾ of the films were measured to be 3.18 × 10^− 8 esu and 5.94 × 10^− 9 esu, respectively.     

The third-order optical nonlinearity of Bi3.25La0.75Ti3O12 ferroelectric thin film on quartz

Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin film was prepared on quartz substrates using chemical solution deposition. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refractive index coefficient γ and the nonlinear absorption coefficient β of the BLT thin film are − 1.915 × 10^− 12 cm² / W and − 6.764 × 10^− 8 m/W, respectively, the real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film are − 5.81 × 10^− 18 m² / V² and − 1.31 × 10^− 18 m² / V², respectively. Both the real and the imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ contribute to the nonlinearity of the film. These experimental results show that BLT thin film is a promising material for applications in nonlinear optical devices.     

Nonlinear optical properties of laser deposited CuO thin films

In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n₂ = − 3.96 × 10^− 17 m²/W, and nonlinear absorption coefficient, β = − 1.69 × 10^− 10 m/W, respectively.     

Visible light enhanced TiO2 thin film bilayer dye sensitized solar cells

Visible light enhanced nitrogen-sulfur (N-S) doped titanium dioxide (TiO₂) thin films were prepared by the sol-gel method using thiourea as a dopant. The physical and chemical properties of the TiO₂ thin films were greatly influenced by the amount of thiourea added to the sol-gel solution. The greatest shift to longer wavelengths for visible light absorption was observed with 0.6 g of thiourea in the precursor solution, while 0.4 g yielded the largest particle sizes. These single-cycle dip-deposited N-S doped TiO₂ thin films were used as visible light harvesters as well as blocking layers in dye sensitized solar cells. When deposited directly on conducting fluorine doped tin oxide electrodes, photo-conversion efficiencies were reduced. However, the opposite configuration, with N-S doped thin films on top of nanoporous TiO₂, yielded an increased open-circuit voltage of 0.84 V, a short-circuit current density of 9.86 mA cm⁻², and an overall conversion efficiency of 5.88% greater than that of a standard cell. The effectiveness of the blocking layer on the cell efficiencies was analyzed by electrochemical impedance spectroscopy.     

XAFS and CEMS study of dilute magneto-optical semiconductor, Fe doped TiO2 films

TiO₂ films doped with 6% Fe were prepared by pulsed laser deposition (PLD) under different oxygen pressures, and characterized by X-ray absorption fine spectra (XAFS) and conversion electron Mössbauer spectra (CEMS). The edge energy and spectrum profiles of Fe- and Ti K X-ray absorption showed only Fe³⁺ and Ti⁴⁺ states for rutile TiO₂ films prepared under 10^− 1 Torr, the metallic Fe and Ti⁴⁺ for rutile TiO₂ films prepared in 10^− 6 Torr, and the metallic Fe and the average valance of less than “4+” for Ti in Ti_nO_2n−x films prepared by the PLD under 10^− 8 Torr. The metallic Fe clusters are also found in the TEM images of Ti_nO_2n−x film. Magnetic property of Fe doped TiO₂ films prepared by PLD at high vacuum (10^− 6 and 10^− 8 Torr) is considered to originate mainly from the magnetic metal iron clusters.