Fabrication and characterization of ITO thin films on heat-resistant transparent flexible clay films

Transparent conductive indium tin oxide (ITO) thin films were deposited on transparent flexible clay films with heat resistant and high gas barrier properties by rf magnetron sputtering. The electrical, structural, and optical properties of these films were examined as a function of deposition temperature. A lowest resistivity of 4.2 × 10^− 4 Ωcm and an average transmittance more than 90% in the visible region were obtained for the ITO thin films fabricated at deposition temperatures more than 300 °C. It was found that ITO thin films with low resistivity and high transparency can be achieved on transparent flexible clay film using conventional rf magnetron sputtering at high temperature, those characteristics are comparable to those of ITO thin films deposited on a glass substrate.     

Annealing driven performance and optical effects in nanocrystalline SnO2 thin films induced by pulsed delivery

Tin dioxide thin films were prepared successfully by pulsed laser deposition techniques on glass substrates. The thin films were then annealed for 30 min from 50 °C to 550 °C at 50 °C intervals. The influence of the annealing temperature on the microstructure and optical properties of SnO₂ thin films was investigated using X-ray diffraction, optical transmittance and reflectance measurements. Various optical parameters, such as optical band gas energy, refractive index and optical conductivity were calculated from the optical transmittance and reflectance data recorded in the wavelength range 300-2500 nm. We found that the SnO₂ thin film annealed at temperatures up to 400 °C is a good window material for solar cell application. Our experimental results indicated that SnO₂ thin films with the high optical quality could be synthesized by pulsed laser deposition techniques.     

Low temperature sputter deposition of SnOx:Sb films for transparent conducting oxide applications

SnO_x:Sb films have been prepared by reactive dc magnetron sputtering from a metallic target, with the aim of evaluating the potential of SnO_x:Sb as an attractive low-cost alternative to In₂O₃:Sn (ITO) for TCO applications. The deposition was performed without any additional heating of the substrates. The films were subsequently analysed regarding their optical, electrical and structural properties. Our results show that there is only a narrow process window for the sputter deposition of transparent and conducting tin oxide films at low temperature. A sharp minimum in resistivity of 4.9 mΩ cm is observed at an oxygen content of approximately 17% in the sputtering gas. Under these deposition conditions, the SnO₂:Sb films turn out to be both highly transparent and crystalline. At lower oxygen content (10-15%) the SnO_x:Sb films are substoichiometric, as revealed by Rutherford backscattering, and show a low transmission and high resistivity due to numerous defects and the presence of the SnO phase. At higher oxygen content (> 17%) excess oxygen is incorporated into the films, which is attributed to an increase of oxygen ion bombardment. This leads to a degradation of the electrical properties and a decrease of the density of the films, whilst the optical transmittance slightly improves.     

Effects of thermal treatment on the characteristics of boron and tantalum-doped ZnO thin films deposited by the electrospraying method at atmospheric pressure

Metal-doped (B and Ta) ZnO thin films were deposited by the electrospraying method onto a heated glass substrate. The structural, electrical and optical properties of the films were investigated as a function of dopant concentration in the solution and also as a function of annealing temperature. The results show that all the prepared metal-doped ZnO films were polycrystalline in nature with a (0 0 2) preferred orientation. As the amounts of dopant were increased in the starting solution, the crystallinity and transmittance decreased. On the other hand, heat treatment of the films enhanced the transmittance, Hall mobility, carrier concentration and crystallinity. It was also observed that 2 at.% is the optimal doping amount in order to achieve the minimum resistivity and maximum optical transmittance. As-deposited films have high resistivity and low optical transmittance. The annealing of the as-deposited thin films in air resulted in the reduction of resistivity. Depending on the characteristics of dopant, mainly ionic radius, the effects of dopant were studied on the properties of ZnO thin films. Boron and tantalum have been considered as dopants, tantalum being the superior of the two, since it showed the lower resistivity and higher carrier concentration as well as higher mobility. The minimum value of resistivity was 1.95 × 10^− 4 Ω cm (15 Ω/□) with an optical transmittance more than 93% in the visible region and minimum resistivity of 2.16 × 10^− 4 Ω cm (18 Ω/□) with an optical transmittance greater than 96% for 2 at. % tantalum- and boron-doped ZnO films respectively. The present values of resistivities were closer to the indium tin oxide (ITO) resistivity and also closest to the lowest resistivity values among the ZnO films that were previously reported. The prepared films exhibit the good crystalline structure, homogenous surface, high optical transmittance and low resistivity that are preferable for optical devices.     

Conductive and transparent Bi-doped ZnO thin films prepared by rf magnetron sputtering

Bi-doped ZnO thin films were grown on glass substrates by ratio frequency (rf) magnetron sputtering technique and followed by annealing at 400 °C for 4 h in vacuum (~ 10^− 1 Pa). The effect of argon pressure on the structural, optical, and electrical properties of the Bi-doped films were investigated. The XRD patterns show that the thin films were highly textured along the c-axis and perpendicular to the surface of the substrate. Some excellent properties, such as high transmittance (about 85%) in visible region, low resistivity value of 1.89 × 10^− 3 W cm and high carrier density of 3.45 × 10²⁰ cm^− 3 were obtained for the film deposited at the argon pressure of 2.0 Pa. The optical band gap of the films was found to increase from 3.08 to 3.29 eV as deposition pressure increased from 1 to 3 Pa. The effects of post-annealing treatments had been considered. In spite of its low conductivity comparing with other TCOs, Bi-doping didn't appreciably affect the optical transparency in the visible range of ZnO thin films.     

Filtered vacuum arc deposition of undoped and doped ZnO thin films: Electrical, optical, and structural properties

Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50-400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO₂, In₂O₃:Sn (ITO), ZnO:Al (AZO), ZnO:Ga, ZnO:Sb, ZnO:Mg and several types of zinc-stannate oxides (ZnSnO₃, Zn₂SnO₄), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post-deposition treatment has also been applied to improve the properties of TCO films.The deposition rate of FVAD ZnO and ZnO:M thin films, where M is a doping or alloying metal, is in the range of 0.2-15 nm/s. The films are generally nonstoichiometric, polycrystalline n-type semiconductors. In most cases, ZnO films have a wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as-deposited n-type thin ZnO film is in the range 0.2-6 × 10^− 5 Ω m, carrier electron density is 10²³-2 × 10²⁶ m^− 3, and electron mobility is in the range 10-40 cm²/V s, depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ∼ 3.3 eV and its extinction coefficient (k) in the visible and near-IR range is smaller than 0.02, the optical transmission of 500 nm thick ZnO film is ∼ 0.90.     

Synthesis and characterization of spray deposited PdO-NiO-SDC composite anode material for potential application in IT-SOFC

The synthesis of mixed conducting PdO-NiO-SDC composite films has been reported for the first time by a simple and cost effective spray pyrolysis technique. The films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. The structure, morphology and electrical properties of the films were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM) and impedance spectroscopy (IS). The substrate and annealing temperatures were optimized for obtaining nano-crystalline, porous, adherent and composite films with PdO, NiO and SDC phases. Films showed good microstructure with sufficient porosity and good connectivity of the deposited material. Crystallite size of the deposited material was found to be in the range of 7-9 nm. The deposited film showed high oxygen ion conductivity, 3.94 × 10⁻¹ S cm⁻¹ at 350 °C. Due to their nano-crystalline, porous and composite nature the spray deposited PdO-NiO-SDC films may have high three phase boundary area and hence can be considered as an anode for intermediate temperature solid oxide fuel cells.     

Epitaxial growth of tin ferrite thin films using pulsed laser deposition technique

Epitaxial thin films of tin ferrite (SnFe₂O₄) were deposited on (0 0 2) oriented strontium titanate (SrTiO₃) substrate using pulsed laser deposition method. The quality and epitaxial nature of the films were investigated by X-ray diffraction technique. The phi scan of the film and the substrate shows four folds symmetry indicating cube-on-cube epitaxial growth of the film on the substrate. The optical bandgap of the film was estimated to be 2.6 eV using optical transmittance data. Magnetic measurements indicate that the coercive field and remnant magnetization of the film decrease with increase in temperature. The presence of hysteresis loop in M vs. H plot at room temperature indicates the ferromagnetic nature of the film.     

Constitution, microstructure, and battery performance of magnetron sputtered Li-Co-O thin film cathodes for lithium-ion batteries as a function of the working gas pressure

Li-Co-O thin film cathodes have been deposited onto Si and stainless steel substrates by RF magnetron sputtering from a ceramic LiCoO₂ target at various working gas pressures from 0.15 to 25 Pa. Composition, crystal structure and thin film morphology were examined and properties such as intrinsic stress, conductivity and film density were determined. As-deposited films at 0.15 Pa as well as in the range between 5 Pa and 10 Pa working gas pressure showed a nanocrystalline metastable rocksalt structure with disordered cation arrangement and were nearly stoichiometric. To induce a cation ordering the films were annealed in a furnace at temperatures between 100 and 600 °C for 3 h in argon/oxygen atmosphere (Ar:O₂ = 4.5:5) of 10 Pa. This cation ordering process was observed by XRD and Raman spectroscopy. For the films deposited at 10 Pa gas pressure an annealing temperature of 600 °C leads to the formation of the high temperature phase HT-LiCoO₂ with a layered structure. The Raman spectrum of the films deposited at 0.15 Pa and annealed at 400 °C indicates the formation of the low temperature phase LT-LiCoO₂ with a cubic spinel-related structure, which is assumed to be stabilized due to high compressive stress in the film. The electrochemical characterisation of annealed thin film cathodes revealed that the discharge capacity strongly depends on the crystal structure. Thin Li-Co-O films with a perfect layered HT-LiCoO₂ structure showed the highest discharge capacities.     

Influence of oxygen gas content on the structural and optical properties of ZnO thin films deposited by RF magnetron sputtering at room temperature

Zinc oxide (ZnO) thin films were deposited on sapphire (0001) substrates at room temperature by radiofrequency (RF) magnetron sputtering at oxygen gas contents of 0%,25%,50% and 75%,respectively.The influence of oxygen gas content on the structural and optical properties of ZnO thin films was studied by a surface profile measuring system,X-ray diffraction analysis,atomic force microscopy,and UV spectrophotometry.It is found that the size of ZnO crystalline grains increases first and then decreases with the increase of oxygen gas content,and the maximum grain size locates at the 25% oxygen gas content.The crystalline quality and average optical transmittance (>90%) in the visible-light region of the ZnO film prepared at an oxygen gas content of 25% are better than those of ZnO films at the other contents.The obtained results can be attributed to the resputtering by energetic oxygen anions in the growing process.     

Doping and annealing effects on ZnO:Cd thin films by sol-gel method

In this article, ZnO:Cd films were successfully deposited on glass substrates by a sol-gel technique. The influence of doping concentration and annealing temperature effects was carefully investigated. All films exhibited c-axis preferential orientation and optical transparency with visible transmittance >80%. The minimum room temperature resistivity of 0.0341 Ω cm was obtained with 10 at.% Cd doping under 600 °C annealing temperature. The optical band gap of ZnO:Cd film was reduced as Cd doping concentration increased, while the band gap increased with the increase of annealing temperature.     

The effect of substrate bias voltage on PbTe films deposited by magnetron sputtering

The PbTe films were deposited onto ITO glass substrate by radio frequency magnetron sputtering. Effect of external direct current electrical field applied between substrate and target on the quality of films was investigated. Stylus surface profile, X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the films. The film thickness was measured by a conventional stylus surface profile. The crystal structure and lattice parameters of films were determined by using XRD. The surface morphology of the films was measured by AFM. The absorption coefficients and optical band gaps of films were found from FTIR. The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated. All the obtained films were highly textured with a strong (2 0 0) orientation. With increasing bias voltage to −30 V, the property of crystal structure, surface morphology and absorption coefficients and resistivity were improved. However, further increase of substrate bias leads to transformation of the property.     

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.     

Transparent p-type CuxS thin films

The effect of different mild post-annealing treatments in air, at 270 °C, for 4-6 min, on the optical, electrical, structural and chemical properties of copper sulphide (Cu_xS) thin films deposited at room temperature are investigated. Cu_xS films, 70 nm thick, are deposited on glass substrates by vacuum thermal evaporation from a Cu₂S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive crystalline CuS (covellite) films show high carrier concentration (∼10²² cm⁻³), low electrical resistivity (∼10⁻⁴ Ω cm) and inconclusive p-type conduction. After the mild post-annealing, these films display increasing values of resistivity (∼10⁻³ to ∼10⁻² Ω cm) with annealing time and exhibit conclusive p-type conduction. An increase of copper content in Cu_xS phases towards the semiconductive Cu₂S (chalcocite) compound with annealing time is reported, due to re-evaporation of sulphur from the films. However, the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice. In the most resistive films a Cu₂O phase is also observed, diminishing the amount of available copper to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%). The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper deficient in regards to the stoichiometric Cu₂S and exhibit stable p-type conductivity.     

Effect of annealing temperature on optical band-gap of amorphous indium zinc oxide film

The effect of annealing temperature on the electrical and optical properties of indium zinc oxide (IZO) (In₂O₃:ZnO = 90:10 wt.%) thin films has been investigated. The IZO thin films were deposited on glass substrates by radio frequency magnetron sputtering and then subjected to annealing in a mixed ambient of air and oxygen at 100, 200 and 300 °C. All the IZO films were found to have amorphous structure. With the increase of the annealing temperature, the carrier concentration decreased and the resistivity increased. The average transmittance of IZO thin films decreased slightly with annealing temperature. Interestingly, a systematic reduction of the optical band-gap from 3.79 eV to 3.67 eV was observed with annealing temperature. The change in optical band-gap was observed to be caused predominantly by Burstein-Moss band-gap widening effect suggesting unusual absence of band narrowing effect. The effects on optical and electrical properties of IZO films have been discussed in detail.     

LiCoO2 cathode thin film fabricated by RF sputtering for lithium ion microbatteries

Thin films of lithium cobalt oxide were deposited on Pt or Pt/Ti/quartz glass substrates by radio frequency (RF) magnetron sputtering at the substrate temperatures from room temperature to 500 °C. As the substrate temperature increased, the film structure changed from amorphous structure to crystallinity with a strong (003) texture as characterized by X-ray diffraction. The surface morphology and cross-section were observed using scanning electron microscopy. It was found that the films tended to crack at a high substrate temperature. Charge-discharge tests of these films were conducted and compared. The different electrochemical characteristics of these films were attributed to the modified crystallography, morphology, and thermal stress. The LiCoO₂ film deposited at 400 °C showed a well-defined 4.0 V voltage plateau on charge and a 3.9 V plateau on discharge, and delivered 54.5 μAh/cm² μm at the first discharge capacity, with good cycling performance, giving evidence that such films could be used as the thin film cathodes for lithium microbatteries.     

Effects of growth temperature on structure and electrical properties of dielectric (Ba,Sr)TiO3 capacitors with transparent conducting oxide electrodes

200 nm-thick BST thin films were grown on Zr-doped In₂O₃/SrTiO₃ (1 0 0) substrates at 550-750 °C. X-ray diffraction results show that the as-deposited BST films were polycrystalline with random crystallographic orientations. X-ray diffraction patterns reveal that the BST film grown at 650 °C had the best crystalline quality of all the deposition temperatures. Atomic force microscopy and secondary ion mass spectrometry showed that the surface and interface structures of the BST films became rough as the growth temperature increased. The BST film grown at 650 °C showed the best electrical properties, with a dielectric constant of 420 at 1 MHz, dielectric tunability of 32.1%, dielectric loss of 0.015 at 300 kV/cm, and a mean optical transmittance in visible wavelength of 71.3%.     

Low temperature processed highly conducting, transparent, and wide bandgap Gd doped CdO thin films for transparent electronics

Gadolinium (Gd) doped cadmium oxide (CdO) thin films are grown at low temperature (100 °C) using pulsed laser deposition technique. The effect of oxygen partial pressures on structural, optical, and electrical properties is studied. X-ray diffraction studies reveal that these films are polycrystalline in nature with preferred orientation along (1 1 1) direction. Atomic force microscopy studies show that these films are very smooth with maximum root mean square roughness of 0.77 nm. These films are highly transparent and transparency of the films increases with increase in oxygen partial pressure. We observe an increase in optical bandgap of CdO films by Gd doping. The maximum optical band gap of 3.4 eV is observed for films grown at 1 × 10⁻⁵ mbar. The electrical resistivity of the films first decreases and then increases with increase in oxygen partial pressure. The lowest electrical resistivity of 2.71 × 10⁻⁵ Ω cm and highest mobility of 258 cm²/Vs is observed. These low temperature processed highly conducting, transparent, and wide bandgap semiconducting films could be used for flexible optoelectronic applications.     

Effect of lanthanum doping on linear and nonlinear-optical properties of Bi3TiNbO9 thin films

Lanthanum doped Bi₃TiNbO₉ thin films (LBTN-x, La³⁺ contents x = 5%, 15%, 25% and 35 mol.%) with layered perovskite structure were fabricated on fused silica by pulsed laser deposition method. Their linear and nonlinear optical properties were studied by transmittance measurement and Z-Scan method. All films exhibit good transmittance (>55%) in visible region. For lanthanum doping content are x = 5%, 15% and 25 mol.%, the nonlinear absorption coefficient of LBTN-x thin films increases with the La³⁺ content, then it drops down at x = 35 mol.% when the content of La³⁺ in (Bi₂O₂)²⁺ layers is high enough to aggravate the orthorhombic distortion of the octahedra. We found that, 25 mol.% is the optimal La³⁺ content for LBTN-x thin films to have the largest nonlinear absorption coefficient making the LBTN-x film a promising candidate for absorbing-type optical device applications.     

AC powered reactive magnetron deposition of indium tin oxide (ITO) films from a metallic target

Transparent highly conductive indium tin oxide (ITO) films for low cost applications were deposited by a reactive dual magnetron sputter process using metallic targets. The magnetrons were equipped with rectangular (130 × 400 mm²) In:Sn targets (90 wt.% In/10 wt.% Sn). A sine wave power supply was used at a frequency of about 70 kHz. All experiments were done in the transition mode at a constant argon flow of 40 sccm and an oxygen flow varied between 35 and 70 sccm. The total pressure was kept constant at 0.4 Pa.The films were deposited onto silicon and float glass substrates which were either moved in an oscillatory manner (dynamic deposition) or fixed in front of the targets (static mode) during deposition. A dynamic deposition rate of about 100 nm × m/min was obtained at an average power of 2 kW/cathode. The film thickness was adjusted to 500 nm. At an optimised Ar/O₂ gas flow ratio of 0.6 we found an electrical resistivity as low as 1.2 × 10^− 3 Ω cm. The refractive index of these films was about 2.05 indicating a dense film structure, while the optical absorption of k = 10^− 2 qualifies these ITO films for many low cost applications. Moreover, the film structure and texture were investigated by XRD methods.Applying a static deposition we have achieved a lower electrical resistivity with a minimum value of 6 × 10^− 4 Ω cm. In this case, the resistivity and the transparency, respectively, were not constant over the substrate but depend on the lateral position in front of the target. To explain this inhomogeneity we have performed spatially resolved deposition rate and Langmuir probe measurements and related their results to film structure and properties. In order to improve the film properties at dynamic deposition the growth conditions have to be homogenised at all substrate positions.