Preparation and properties of transparent conductive indium-tin-oxide/polyimide substrates via a sol-gel process

High temperature, flexible and colorless indium-tin-oxide (ITO) coated plastic substrates have been prepared from a series of thermally stable, high glass transition temperature (T_g) and colorless copolyimide films. The copolyimides were synthesized from 3,3′-diaminodiphenylsulfone, 9,9′-bis(4-aminophenyl) fluorene and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride monomers. Their T_gs were around 285-365 °C. The conductive ITO was synthesized by a sol-gel method, and then deposited onto the copolyimide films by a spin coating process. After thermal treatment at 300 °C under a nitrogen/hydrogen mixture gas for 24 h, the resistivity of the ITO film was 10⁻³ Ω cm, and its transmittance was 75% at the visible light region. Scanning electron microscopy and X-ray diffraction were used to observe the surface and morphology of the ITO films. UV-visible spectroscopy and the four-probe method were used to study their optical and electrical properties. The high performance ITO/plastic substrates can be used in the next generation flexible flat panel displays and solar cell.     

Stress measurements and calculations for vacuum- deposited MgF2 films

Previous in situ measurements of the intrinsic stress in thin crystalline dielectric films have been interpreted in terms of a stress mechanism due to forces at the grain boundaries. The same stress interpretations were given for metal films by Hoffman and coworkers several years ago.In the present work it is shown that the tensile stress is a decreasing function of impurity concentration in the MgF₂ films. A similar decrease occurs through water vapour adsorption. Assuming that the impurity is located mainly on the crystallite surface, as with adsorbed water molecules, this effect can also be interpreted using the grain boundary model which predicts a decreasing tensile stress with increasing crystal size. The results of stress measurements of MgF₂ films deposited onto heated substrates support this prediction.     

Preparation and properties of Cu-grafted transparent TiO2-nanosheet thin films

Transparent TiO₂ nanosheet thin films were prepared using layer-by-layer method with poly(diallyldimethylammonium chloride) as a counter polymer. The possibility of photocatalysis by the light in the long wavelength range was examined by grafting Cu on the film. Photocatalytic decomposition activity for gaseous 2-propanol under UV illumination without light for electron excitation of TiO₂ nanosheet was increased by Cu grafting, suggesting that the interfacial charge transfer mechanism is effective also for nanosheet films.     

Residual stress in obliquely deposited MgF2 thin films

MgF(2) films with a columnar microstructure are obliquely deposited on glass substrates by resistive heating evaporation. The columnar angles of the films increases with the deposition angle. Anisotropic stress does not develop in the films with tilted columns. The residual stresses in the films depend on the deposition and columnar angles in a columnar microstructure.     

Microstructure-related properties at 193 nm of MgF2 and GdF3 films deposited by a resistive-heating boat

MgF2 and GdF3 materials, used for a single-layer coating at 193 nm, are deposited by a resistive-heating boat at specific substrate temperatures. Optical characteristics (transmittance, refractive index, extinction coefficient, and optical loss) and microstructures (morphology and crystalline structure) are investigated and discussed. Furthermore, MgF2 is used as a low-index material, and GdF3 is used as a high-index material for multilayer coatings. Reflectance, stress, and the laser-induced damage threshold (LIDT) are studied. It is shown that MgF2 and GdF3 thin films, deposited on the substrate at a temperature of 300 degrees C, obtain good quality thin films with high transmittance and little optical loss at 193 nm. For multilayer coatings, the stress mainly comes from MgF2, and the absorption comes from GdF3. Among those coatings, the sixteen-layer design, sub/(1.4L 0.6H)8/air, shows the largest LIDT.     

Preparation and properties of reactively co-sputtered transparent conducting films

The method of reactive co-sputtering was used to determine the optimum dopant concentration for low resistivity In₂O₃/SnO₂ and SnO₂/Sb₂O₅ films. The optimum concentration of SnO₂ in In₂O₃ was approximately 10 mol. % and of Sb₂O₅ in SnO₂ about 7 mol. %. The resistivity increased sharply at lower dopant concentrations but changed only slightly at higher dopant concentrations. The lowest resistivity for reactively sputtered highly transparent In₂O₃/SnO₂ films was 1.5 × 10^-3 Ω cm and for SnO₂/Sb₂O₅ films 3 × 10^-3 Ω cm. Reactively sputtered In₂O₃/SnO₂ films show a strong (111) texture and have an extremely smooth surface.     

Cesium-incorporated indium-tin-oxide films for use as a cathode with low work function for a transparent organic light-emitting device

Transparent organic light-emitting devices (TOLEDs) were successfully fabricated utilizing a novel transparent conducting cathode with low work function. Cesium-incorporated indium-tin-oxide film was deposited on the organic layers with negligible damage by simultaneous operation of RF magnetron sputtering using an ITO target and vacuum evaporation of metallic cesium. Incorporation of cesium in the ITO film was confirmed by XPS analysis. The work function (4.3 eV) determined by photoelectron spectroscopy in air (PESA) was lower than that of 0.3-0.4-eV without cesium-incorporation and stable under the atmospheric environment. The electron injection efficiency of cesium-incorporated ITO cathode in the present transparent OLED fabricated was comparable to that of the previous double-layered structure comprising of ITO cathode and an organic buffer layer (BCP) doped by evaporation of cesium [T. Uchida, S. Kaneta, M. Ichihara, M. Ohtsuka, T. Otomo, D.R. Marx, Jpn. J. Appl. Phys., 44, No. 9 (2005) L282].     

Semiconducting transparent thin films: their properties and applications

The present state of the art of transparent, electrically conducting films, with special reference to In₂O₃, SnO₂ and Cd₂SnO₄, has been reviewed. Various production techniques currently in use, and typical parameters used in the processes have been discussed in detail. Electrical and optical properties of these films have been reported as a function of various parameters, e.g. substrate temperature, doping, oxygen pressure, etc. Finally, the applications of these films in research and industry have been discussed in detail.     

Preparation and properties of p-type transparent conductive Cu-doped NiO films

The NiO-Cu composite films with various Cu contents of 0-18.17 at.% are deposited on a glass substrate. An ultra high electrical resistivity (ρ) is obtained and cannot be detected by a four point probe measurement when the Cu content in the films is lower than 6.97 at.%. The ρ value is reduced significantly to 35.8 Ω-cm as Cu content is increased to 9.18 at.%, and it further decreases to 0.02 Ω-cm when the Cu content further increases to 18.17 at.%. The Hall measurement for all Cu-doped NiO films shows p-type conduction. In addition, the transmittance of NiO films also decreases continuously from 96% to 43% as Cu content increases from 0 to 18.17 at.%. The XRD patterns of Cu-doped NiO films show that only NiO peaks appear and the crystallinity of NiO films degrades as Cu content exceeds 6.97 at.%. A large amount of lattice sites of Ni²⁺ ions in a NiO crystallite is replaced by the Cu⁺ ions that lead to p-type conduction and result in the degradation of crystallinity for NiO-Cu composite films that have a higher Cu content.     

Electrical and optical properties of Zn-In-Sn-O transparent conducting thin films

Indium tin oxide (ITO) is one of the widely used transparent conductive oxides (TCO) for application as transparent electrode in thin film silicon solar cells or thin film transistors owing to its low resistivity and high transparency. Nevertheless, indium is a scarce and expensive element and ITO films require high deposition temperature to achieve good electrical and optical properties. On the other hand, although not competing as ITO, doped Zinc Oxide (ZnO) is a promising and cheaper alternative. Therefore, our strategy has been to deposit ITO and ZnO multicomponent thin films at room temperature by radiofrequency (RF) magnetron co-sputtering in order to achieve TCOs with reduced indium content. Thin films of the quaternary system Zn-In-Sn-O (ZITO) with improved electrical and optical properties have been achieved.The samples were deposited by applying different RF powers to ZnO target while keeping a constant RF power to ITO target. This led to ZITO films with zinc content ratio varying between 0 and 67%. The optical, electrical and morphological properties have been thoroughly studied. The film composition was analysed by X-ray Photoelectron Spectroscopy. The films with 17% zinc content ratio showed the lowest resistivity (6.6 × 10^− 4 Ω cm) and the highest transmittance (above 80% in the visible range). Though X-ray Diffraction studies showed amorphous nature for the films, using High Resolution Transmission Electron Microscopy we found that the microstructure of the films consisted of nanometric crystals embedded in a compact amorphous matrix. The effect of post deposition annealing on the films in both reducing and oxidizing atmospheres were studied. The changes were found to strongly depend on the zinc content ratio in the films.     

Photochemical properties of CeO2-coated ZnO nanorods

Well-aligned ZnO nanorods were deposited by a mild hydrothermal process and coated with nanosized CeO2 particles (approximately 5 nm) by an oxidative-soak-coating method at 45 degrees C. The low growth temperature proved useful in avoiding interfacial reaction between the two phases. Correlation of photoluminescence results indicated that the defects responsible for the deep level emission (DLE) from ZnO were largely located at the surface. The CeO2 coating reduced the DLE but also the photocatalytic activity as surficial hydroxyl groups were involved in the nucleation of the CeO2 phase and thus not available for absorption of the methylene blue species for degradation. Still, CeO2 coated ZnO nanorods retained their photocatalytic ability and could be useful as bifunctional catalyst to treat multiple contaminants simultaneously.     

溅射功率和氧分压对ITO薄膜光电性能的影响研究

采用直流反应磁控溅射法制备了氧化铟锡(ITO)透明导电薄膜,通过四探针、紫外可见分光光度计、X射线衍射(XRD)、霍尔效应仪、扫描电镜(SEM)等对薄膜样品进行了表征,研究了溅射功率和氧分压对ITO薄膜微观结构和光电性能的影响,结果表明:溅射功率对ITO的光电性能影响较小,沉积速率随着溅射功率的增大而加快;随着氧分压的升高,载流子浓度降低,霍尔迁移率先增大后减小,电阻率逐渐增大。在优化的工艺条件下,制备了在可见光区平均透过率达85%、电阻率为1×10-4Ω.cm的光电性能优良的ITO薄膜。     

Effects of annealing temperature and heat-treatment duration on electrical properties of sol-gel derived indium-tin-oxide thin films

Transparent indium tin oxide (ITO) thin films have been deposited by the dip-coating process on silica substrates using solutions of 2,4-pentanedione, ethanol, indium and tin salts. The films have been first dried in air at 260 °C for 10 min and then annealed in a reducing atmosphere at different temperatures for various durations. The resistivity of ITO layers was found to decrease with increasing the metal concentration of the starting solution or the annealing temperature. Hence, by adjusting both metal concentration in the coating solution and heat-treatment, resistivities lower than 5 × 10^− 3 Ω cm for an annealing temperature of 550 °C and lower than 2 × 10^− 2 Ω cm for an annealing temperature of 300 °C, were obtained. These results are correlated with the density and the size of ITO grains in the films.     

Evaluation of metal/indium-tin-oxide for transparent low-resistance contacts to p-type GaN

In search of a better transparent contact to p-GaN, we analyze various metal/indium-tin-oxide (ITO) (Ag/ITO, AgCu/ITO, Ni/ITO, and NiZn/ITO) contact schemes and compare to Ni/Au, NiZn/Ag, and ITO. The metal layer boosts conductivity while the ITO thickness can be adjusted to constructive transmission interference on GaN that exceeds extraction from bare GaN. We find a best compromise for an Ag/ITO (3 nm/67 nm) ohmic contact with a relative transmittance of 97% of the bare GaN near 530?nm and a specific contact resistance of 0.03 Ω·cm². The contact proves suitable for green light-emitting diodes in epi-up geometry.     

Annealing effect on properties of transparent and conducting ZnO thin films

This work presents the effect of postdeposition annealing on the structural, electrical and optical properties of undoped ZnO (zinc oxide) thin films, prepared by radio-frequency sputtering method. Two samples, 0.17 and 0.32 µm-thick, were annealed in vacuum from room temperature to 350 °C while another 0.32 µm-thick sample was annealed in air at 300 °C for 1 h. X-ray diffraction analysis revealed that all the films had a c-axis orientation of the wurtzite structure normal to the substrate. Electrical measurements showed that the resistivity of samples annealed in vacuum decreased gradually with the increase of annealing temperature. For the 0.32 µm-thick sample, the gradual decrease of the resistivity was essentially due to a gradual increase in the mobility. On the other hand, the resistivity of the sample annealed in air increased strongly. The average transmission within the visible wavelength region for all films was higher than 80%. The band gap of samples annealed in vacuum increased whereas the band gap of the one annealed in air decreased. The main changes observed in all samples of this study were explained in terms of the effect of oxygen chemisorption and microstructural properties.     

Preparation and wettability examinations of transparent SiO2 binder-added MgF2 nanoparticle coatings covered with fluoro-alkyl silane self-assembled monolayer

SiO2-added MgF2 nanoparticle coatings with various surface roughness properties were formed on fused silica-glass substrates from autoclaved sols prepared at 100-180 °C. To give it hydrophobicity, we treated the samples with fluoro-alkyl silane (FAS) vapor to form self-assembled monolayers on the nanoparticle coating and we examined the wettability of the samples. The samples preserved good transparency even after the FAS treatment. The wettability examination revealed that higher autoclave temperatures produced a larger average MgF2 nanoparticle particle size, a larger surface roughness, and a higher contact angle and the roll-off angle.     

Structure and thermal properties of transparent conductive nanoporous F:SnO2 films

The nanoporous F:SnO₂ materials prepared for the purpose of dye-sensitized solar cells (DSCs) application are composed of SnCl₄ (98.0%) and HF (48-51%), produce with a NH₄OH aqueous solution with sol-gel method as a catalyst. Acetylene black is needed to make nano-porous from FTO heated until 120 °C that will change it from sol to gel and with that 2 phase sintering with 500 °C and 550 °C can be predicted to produce nano-materials. The preferred orientation indicates (110), (101), (211) for SnO₂ and (200) for fluorine, respectively. The main IR features include resonances at 660, 620 and 540 cm^− 1. From the FE-SEM results, the mean pore size of the sample is range of 16-38 nm. Finally, the nanoporous F:SnO₂ film used for TCO layer of dye-sensitized solar cells (DSCs) exhibited an energy conversion efficiency of about 1.83% at light intensity of 100 mW/cm².     

Preparation and properties of transparent conductive N-doped CuAlO2 films using N2O as the N source

N-doped CuAlO₂ films were prepared by RF magnetron sputtering on quartz substrates using N₂O as the N source. N concentration in the films is detected by Auger electron spectroscopy in detail, which confirms that N is indeed incorporated into the films. The optical and electrical properties of transparent conductive N-doped CuAlO₂ films are modulated by the N₂O flow ratio in sputtering gas. The N-doped films have a visible transmittance of 60–70 % and a high infrared transmittance of ~85 %. The film deposited by using 15 % N₂O flow ratio with the optimal crystalline is provided with a conductivity of 3.75 × 10^?2 S cm^?1 at room temperature, which improves over one order of magnitude compared with the undoped film. The enhanced conductive property is mainly originated from the ionization of acceptor impurities.