A novel solvothermal route to benzene ring-capped oxide nanocrystals

A novel solvothermal synthesis based on the reaction between nitrate and benzene for metal oxide nanocrystals including ZrO₂ and SnO₂ is introduced. The as-prepared nanocrystals are characterized by TEM, XRD and IR techniques in detail, and the possible mechanism of this solvothermal reaction is discussed. Benzene molecules used as capping agent, instead of long-carbon chain molecules, are chemically adsorbed to the surface of the as-prepared oxide nanocrystals, making nanocrystals with long-term stability and good dispersibility in hydrocarbons.     

Transparent heaters based on solution-processed indium tin oxide nanoparticles

We demonstrate transparent heaters constructed on glass substrates using solution-processed indium tin oxide (ITO) nanoparticles (NPs) and their heating capability. The heat-generating characteristics of the heaters depended significantly on the sintering temperature at which the ITO NPs deposited on a glass substrate by spin-coating were transformed thermally into a solid film. The steady-state temperature of the ITO NP film sintered at 400 °C was 163 °C at a bias voltage of 20 V, and the defrosting capability of the film was confirmed by using dry-ice.     

Colloidal indium tin oxide nanoparticles for transparent and conductive films

Nanosized colloidal indium tin oxide (ITO) dispersion was prepared for electrically conductive and transparent coating materials. A titanate coupling agent, isopropyl tri(N-ethylenediamino)ethyl titanate, was chosen as a dispersant for the stabilization of ITO nanoparticles in organic solvent. ITO sol was deposited on a cathode ray tube panel for antistatic or electromagnetic shielding purposes, and alkyl silicate was used for the formation of an antireflective over-coat layer. The resulting double-layered coating showed low sheet resistance, which satisfied semi-TCO regulation and low reflectance of visible light. To control the electrical and optical properties of the coating layer, the effects of secondary particle size of ITO aggregates and the dispersant concentration of ITO sol were studied. The stability of ITO sol was estimated by measuring the particle size as a function of the storage days and the aggregation of colloidal ITO dispersion with storage day was explained by depletion flocculation.     

Refractive indices of textured indium tin oxide and zinc oxide thin films

The refractive indices of textured indium tin oxide (ITO) and zinc oxide (ZnO) thin films were measured and compared. The ITO thin film grown on glass and ZnO buffered glass substrates by sputtering showed distinct differences; the refractive index of ITO on glass was about 0.05 higher than that of ITO on ZnO buffered glass in the whole visible spectrum. The ZnO thin film grown on glass and ITO buffered glass substrates by filtered vacuum arc also showed distinct differences; the refractive index of ZnO on glass was higher than that of ZnO on ITO buffered glass in the red and green region, but lower in the blue region. The largest refractive index difference of ZnO on glass and ITO buffered glass was about 0.1 in the visible spectrum. The refractive index variation was correlated with the crystal quality, surface morphology and conductivity of the thin films.     

Ultraflat indium tin oxide films prepared by ion beam sputtering

Indium tin oxide (ITO) films with a smooth surface (root-mean-square roughness; R_rms=0.40 nm) were made using a combination of the deposition conditions in the ion beam-sputtering method. Sheet resistance was 13.8 Ω/sq for a 150-nm-thick film grown at 150 °C. Oxygen was fed into the growth chamber during film growth up to 15 nm, after which, the oxygen was turned off throughout the rest of the deposition. The surface of the films became smooth with the addition of ambient oxygen but electrical resistance increased. In films grown at 150 °C with no oxygen present, a rough surface (R_rms=2.1 nm) and low sheet resistance (14.4 Ω/sq) were observed. A flat surface (R_rms=0.5 nm) with high sheet resistance (41 Ω/sq) was obtained in the films grown with ambient oxygen throughout the film growth. Surface morphology and microstructure of the films were determined by the deposition conditions at the beginning of the growth. Therefore, fabrication of ITO films with a smooth surface and high electrical conductivity was possible by combining experimental conditions.     

Properties of indium tin oxide films deposited using High Target Utilisation Sputtering

Indium tin oxide (ITO) films were deposited on soda lime glass and polyimide substrates using an innovative process known as High Target Utilisation Sputtering (HiTUS). The influence of the oxygen flow rate, substrate temperature and sputtering pressure, on the electrical, optical and thermal stability properties of the films was investigated. High substrate temperature, medium oxygen flow rate and moderate pressure gave the best compromise of low resistivity and high transmittance. The lowest resistivity was 1.6 × 10^− 4 Ω cm on glass while that on the polyimide was 1.9 × 10^− 4 Ω cm. Substrate temperatures above 100 °C were required to obtain visible light transmittance exceeding 85% for ITO films on glass. The thermal stability of the films was mainly influenced by the oxygen flow rate and thus the initial degree of oxidation. The film resistivity was either unaffected or reduced after heating in vacuum but generally increased for oxygen deficient films when heated in air. The greatest increase in transmittance of oxygen deficient films occurred for heat treatment in air while that of the highly oxidised films was largely unaffected by heating in both media. This study has demonstrated the potential of HiTUS as a favourable deposition method for high quality ITO suitable for use in thin film solar cells.     

Room temperature indium tin oxide by XeCl excimer laser annealing for flexible display

A XeCl excimer laser (λ=308 nm) has been used to anneal Indium Tin Oxide (ITO) films deposited at 25 °C using DC magnetron sputtering. With increasing laser fluence, the film crystallinity was improved while retaining the as-deposited 111 texture. As a result of laser irradiation, the sheet resistance of 100 nm ITO films decreased from 191 Ω/□ (1.91×10⁻³ Ω cm) to 25 Ω/□ (2.5×10⁻⁴ Ω cm), while the optical transmittance in the visible range increased from 70% to more than 85%. Surface roughness and etching properties were also significantly improved following laser annealing.     

Effects of thermal treatment on the electrical and optical properties of silver-based indium tin oxide/metal/indium tin oxide structures

In this article, we report the results of the study of thermal treatment effects on the electrical and optical properties of silver-based indium tin oxide/metal/indium tin oxide (IMI) multilayer films. Heat treatment conditions such as temperature and gaseous atmosphere was varied to obtain better electrical and optical properties. We obtained improved electrical properties and observed considerable shift in the transmittance curves after heat treatment. Several analytical tools such as X-ray diffraction, spectroscopic ellipsometer and spectrophotometer were used to explore the causes of the changes in electrical and optical properties. The sheet resistance of the structure was severely influenced by deposition conditions of the indium tin oxide (ITO) layer at the top. Moreover, the shift of optical transmittance could be explained on the basis of the change in refractive indices of ITO layers during heat treatment. The properties of Ag-alloy-based IMI films were compared with those of pure Ag-based ones. Some defects originating from Ag layer corrosion were observed on the surface of ITO-pure Ag–ITO structures, however, their number decreased significantly in the cases of Ag-alloys containing Pd, Au and Cu, though the resistivity values of Ag-alloys were slightly higher than those of silver. Atomic force microscopy measurement results revealed that the surface of the IMI multilayer was so smooth that it meets the required qualifications as the bottom electrode of organic light emitting diodes.     

Investigation on indium concentration dependence of solution processed indium tin oxide thin film transistors

The effect of the indium content in indium tin oxide (ITO) films fabricated using a solution-based process and ITO channel thin film transistors (TFTs) was examined as a function of the indium mole ratio. The carrier concentration and resistivity of the ITO films could be controlled by the appropriate treatments. The TFTs showed an increase in the off-current due to the enhanced conductivity of the ITO channel layer with increasing indium mole ratios, producing an increase in the field effect mobility. The characteristics of the a-ITO channel TFT showed the best performance (μ_FE of 3.0 cm² V^− 1 s^− 1, V_th of 2.0 V, and S value of 0.4 V/decade) at In:Sn = 5:1.     

Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method

Indium tin oxide (ITO) thin films with well-controlled layer thickness were produced by dip-coating method. The ITO was synthesized by a sol-gel technique involving the use of aqueous InCl₃, SnCl₄ and NH₃ solutions. To obtain stable sols for thin film preparation, as-prepared Sn-doped indium hydroxide was dialyzed, aged, and dispersed in ethanol. Polyvinylpyrrolidone (PVP) was applied to enhance the stability of the resulting ethanolic sols. The transparent, conductive ITO films on glass substrates were characterized by X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The ITO layer thickness increased linearly during the dipping cycles, which permits excellent controllability of the film thickness in the range ~ 40-1160 nm. After calcination at 550 °C, the initial indium tin hydroxide films were transformed completely to nanocrystalline ITO with cubic and rhombohedral structure. The effects of PVP on the optical, morphological and electrical properties of ITO are discussed.     

Deposition of indium tin oxide by atmospheric pressure chemical vapour deposition

We report the deposition of indium tin oxide (ITO) by atmospheric pressure chemical vapour deposition (APCVD). This process is potentially scalable for high throughput, large area production. We utilised a previously unreported precursor combination; dimethylindium acetylacetonate, [Me₂In(acac)] and monobutyltintrichloride, MBTC.[Me₂In(acac)] is a volatile solid. It is more stable and easier to handle than traditional indium oxide precursors such as pyrophoric trialkylindium compounds. Monobutyltintrichloride (MBTC) is also easily handled and can be readily vaporised. It is compatible with the process conditions required for using [Me₂In(acac)].Cubic ITO was deposited at a substrate temperature of 550 °C with growth rates exceeding 15 nm/s and growth efficiencies of between 20 and 30%. Resistivity was 3.5 × 10^− 4 Ω cm and transmission for a 200 nm film was > 85% with less than 2% haze.     

Stress-corrosion cracking of indium tin oxide coated polyethylene terephthalate for flexible optoelectronic devices

Stress corrosion cracking of transparent conductive layers of indium tin oxide (ITO), sputtered on polyethylene terephthalate (PET) substrates, is an issue of paramount importance in flexible optoelectronic devices. These components, when used in flexible device stacks, can be in contact with acid containing pressure-sensitive adhesives or with conductive polymers doped in acids. Acids can corrode the brittle ITO layer, stress can cause cracking and delamination, and stress-corrosion cracking can cause more rapid failure than corrosion alone.The combined effect of an externally-applied mechanical stress to bend the device and the corrosive environment provided by the acid is investigated in this work. We show that acrylic acid which is contained in many pressure-sensitive adhesives can cause corrosion of ITO coatings on PET. We also investigate and report on the combined effect of external mechanical stress and corrosion on ITO-coated PET composite films. Also, it is shown that the combination of stress and corrosion by acrylic acid can cause ITO cracking to occur at stresses less than a quarter of those needed for failure with no corrosion. In addition, the time to failure, under ~ 1% tensile strain can reduce the total time to failure by as much as a third.     

Temperature dependence of resistance and thermopower of thin indium tin oxide films

We have measured the resistance and thermopower of a series of RF sputtered and annealed indium tin oxide (ITO) thin films from 300 K down to liquid-helium temperatures. Thermal annealing was performed to modulate the levels of disorder (i.e., resistivity) of the samples. The measured resistances are well described by the Bloch-Grüneisen law between 150 and 300 K, suggesting that our thin films are metallic. At lower temperatures, a resistance rise with decreasing temperature was observed, which can be quantitatively ascribed to the two-dimensional electron-electron interaction and weak-localization effects. The thermopowers in all samples are negative and reveal fairly linear temperature dependence over the whole measurement temperature range, strongly indicating free-electron like conduction characteristics in ITO thin films. As a result, the carrier concentration in each film can be reliably determined. This work demonstrates that ITO films as thin as 15 nm thick can already possess high metallic conductivity.     

Effect of aluminum doping on the high-temperature stability and piezoresistive response of indium tin oxide strain sensors

Ceramic strain sensors based on reactively sputtered indium tin oxide (ITO) thin films doped with aluminum are being considered to improve the high-temperature stability and response. Ceramic strain sensors were developed to monitor the structural integrity of components employed in aerospace propulsion systems operating at temperatures in excess of 1500 °C. Earlier studies using electron spectroscopy for chemical analysis (ESCA) studies indicated that interfacial reactions between ITO and aluminum oxide increase the stability of ITO at elevated temperature. The resulting ESCA depth files showed the presence of two new indium-indium peaks at 448.85 and 456.40 eV, corresponding to the indium 3d5 and 3d3 binding energies. These binding energies are significantly higher than those associated with stoichiometric indium oxide. Based on these studies, a combinatorial chemistry approach was used to screen large numbers of possible concentrations to optimize the stability and performance of Al-doped ceramic strain sensors. Scanning electron microscopy was used to analyze the combinatorial libraries in which varying amounts of aluminum were incorporated into ITO films formed by cosputtering from multiple targets. Electrical stability and piezoresistive response of these films were compared to undoped ITO films over the same temperature range.     

Deposition by magnetron sputtering and characterization of indium tin oxide thin films

In this work the properties of indium tin oxide (ITO) films deposed on glass substrates by magnetron sputtering technique in the temperature range below 200 °C are studied by various methods. The physical properties of ITO thin films have been investigated using optical transmittance, photoluminescence, atomic force microscopy, ellipsometry, Hall-effect and four point probe methods. It is established that properties of ITO layers depend drastically on the temperature and oxygen partial pressure during the deposition process and exhibit some peculiarities of the surface morphology. It is found that the band gap energy of this material varies in the energy range from 4.1 to 4.4 eV and depends on the growth conditions. It is suggested that local deviations from the stoichiometry and defects are the main physical reasons of Burstein-Moss shift of the optical band gap.     

Successive deposition of layered titanium oxide/indium tin oxide films on unheated substrates by twin direct current magnetron sputtering

Layered titanium oxide/indium tin oxide (TiO₂/ITO) films were successively deposited on unheated glass substrates in situ using a twin direct current magnetron sputtering system. The layered TiO₂/ITO films exhibited a strongly polycrystalline structure that comprises anatase and rutile phases, as revealed by X-ray diffraction and Raman spectra. The X-ray photoelectron spectrum of Ti2p also verified the stoichiometric state of titanium oxide near the surface. The photo-induced hydrophilic properties of the films were determined from changes in the water contact angles under ultra-violet (UV) irradiation. The results revealed that the layered TiO₂/ITO films possessed a dissipated rate of 30% when they were stored in the dark for 12 h. This result shows that the layered TiO₂/ITO films acted as “electron pools” with an inherent energy storage capability. This unique property is attributable to the rougher surface and nearly porosity-free columnar structure, which is responsible for increased UV energy absorption and loss-free hole or electron transportation.     

Durability study on sputtered indium tin oxide thin film on Poly Ethylene Terephthalate substrate

This paper discusses the durability of the DC-Magnetron sputtered Indium Tin Oxide (ITO) thin films on 127-μm Poly Ethylene Terephthalate substrate under harsh environmental conditions and high cyclic bending fatigue. Two sets of experiments were conducted on a 60 Ω per square ITO sheet. The first set of experiments was conducted on samples with different temperature and humidity combinations while being subjected to cyclic bending fatigue loadings. The other set of experiments was conducted on samples with the same combinations of temperature and humidity but without bending fatigue loading. Design of experiments tool was used to study the effect of temperature, humidity, bending fatigue and the interaction among them on the percent change in electrical resistance of the ITO film. It was found that bending fatigue is the dominant factor to the electrical failure of ITO thin film. The failure was also influenced by temperature and humidity, especially combined high temperature and high humidity. Therefore, it is suggested that controlling the environmental factors during the roll to roll manufacturing process is crucial on quality of the products.     

Remote plasma sputtering of indium tin oxide thin films for large area flexible electronics

Indium tin oxide (ITO) thin films with a specific resistivity of 3.5 × 10^− 4 Ω cm and average visible light transmission (VLT) of 90% have been reactively sputtered onto A4 Polyethylene terephthalate (PET), glass and silicon substrates using a remote plasma sputtering system.This system offers independent control of the plasma density and the target power enabling the effect of the plasma on ITO properties to be studied. Characterization of ITO on glass and silicon has shown that increasing the plasma density gives rise to a decrease in the specific resistivity and an increase in the optical band gap of the ITO films. Samples deposited at plasma powers of 1.5 kW, 2.0 kW and 2.5 kW and optimized oxygen flow rates exhibited specific resistivity values of 3.8 × 10^− 4 Ω cm, 3.7 × 10^− 4 Ω cm and 3.5 × 10^− 4 Ω cm and optical gaps of 3.48 eV, 3.51 eV and 3.78 eV respectively.The increase in plasma density also influenced the crystalline texture and the VLT increased from 70 to 95%, indicating that more oxygen is being incorporated into the growing film. It has been shown that the remote plasma sputter technique can be used in an in-line process to produce uniform ITO coatings on PET with specific resistivities of between 3.5 × 10^− 4 and 4.5 × 10^− 4 Ω cm and optical transmission of greater than 85% over substrate widths of up to 30 cm.     

水热法合成铟锡氧化物纳米粒子的制备及表征

采用三氧化二铟和真空蒸发法制得的纳米锡粉为原料，溶解在一定浓度的氢氧化钠溶液中，水热条件下成功的合成了纳米级的铟锡氧化物粒子，通过粉末X射线衍射（XRD），场发射扫描电子显微镜（FE-SEM），透射电子显微镜（TEM）和紫外可见光光吸收光谱（Uv-Vis）等手段对所得产物进行表征。讨论了反应时间、pH值因素对产物成分和形貌的影响。结果表明：在温度为180℃，10mol／L NaOH溶液的条件下，水热反应36h得到比较均一的产物In1.94Sn0.06O3，产物形貌为均匀的六面体，大小在100nm左右，且对波长在200-400nm的光有强烈的吸收。     

A gradual annealing of amorphous sputtered indium tin oxide: Crystalline structure and electrical characteristics

Thin films of amorphous indium tin oxide were deposited by soft sputtering. The film was gradually annealed in air at temperatures from 110 °C to 150 °C. Its structural and electrical properties were monitored in order to get a better understanding of the annealing process. Firstly, carrier density decreases by oxygen intake. Crystallization speeds up at 150 °C, with a 2.5 D growth of crystallites. The preferred orientations come from sputtering induced seeds. Then, the carrier density increases again due to tin activation. Meanwhile, the carrier mobility is more damaged by the low temperature annealing in air than by a standard annealing in a reducing atmosphere. Thus, tin oxide segregation is suspected at grain boundaries.