Transparent Indium Tin Oxide Films Research Articles

Genetic algorithm-enabled on-demand co-design of optically transparent metamaterial for multispectral stealth applications

This paper proposes a genetic algorithm (GA)-enabled co-design method for the development of metamaterials with on-demand microwave reflectivity and infrared (IR) emissivity. First, we proposed a multilayered metamaterial based on metasurface with hexagonal patch and ring patterns. An equivalent circuit model (ECM) was then established to model the microwave reflectivity of the metamaterial. To achieve broadband low microwave reflectivity, a GA based on this ECM was adopted to optimize the structural parameters of the metamaterial. A co-design task was accomplished by setting a judgment condition in the algorithm for low IR emissivity. With the help of GA, a metamaterial with broadband low microwave reflectivity and low IR emissivity was designed. Subsequently, a prototype metamaterial was fabricated by patterning optically transparent indium tin oxide films. The calculated, simulated, and measured results agreed well. The co-designed metamaterial had an IR emissivity of 0.15 within the spectral range of 3–14 µm, −10 dB microwave reflectivity at frequencies of 3.1–32.2 GHz, and transparency in the visible band. The proposed co-design method will benefit the design and application of multispectral stealth metamaterials.

Role of plasma parameters on the characteristics properties of flexible transparent ITO films deposited by 3D facing and planar facing magnetron sources

A rectangular closed and hollow three-dimensionally confined large area magnetron source (3-DCLAMS) and a conventional moderate area facing target magnetron source (FTMS) have been used to study the plasma characteristics using different diagnostics at different working pressures. Flexible indium tin oxide (ITO) films deposited at similar operating conditions using these sources were characterized by numerous standard analyses to study their film properties. The 3-DCLAMS with high discharge current at a low-discharge voltage is capable of generating high plasma density, which assists a high ion flux and energy density on the substrate that is necessary for the high growth rate deposition of highly conductive crystalline ITO films with smooth surface morphology. Utilizing suitable plasma characteristics, highly conductive and transparent ITO films of 30 nm with the minimum resistivity ρ ∼ 4.1 × 10−4 Ω cm and ∼9.3 × 10−4 Ω cm and average transmittance T ∼ 84% and 82%, respectively, were deposited in the 3-DCLAMS and the FTMS system. The presented result shows that the 3-DCLAMS system could be useful for making high-quality, flexible ITO films at a very high deposition rate of ∼250 nm/min.

Structural optical and electrical properties of a transparent conductive ITO/Al-Ag/ITO multilayer contact.

Indium tin oxide (ITO) is a widely used material for transparent conductive oxide (TCO) films due to its good optical and electrical properties. Improving the optoelectronic properties of ITO films with reduced thickness is crucial and quite challenging. ITO-based multilayer films with an aluminium–silver (Al–Ag) interlayer (ITO/Al–Ag/ITO) and a pure ITO layer (as reference) were prepared by RF and DC sputtering. The microstructural, optical and electrical properties of the ITO/Al–Ag/ITO (IAAI) films were investigated before and after annealing at 400 °C. X-ray diffraction measurements show that the insertion of the Al–Ag intermediate bilayer led to the crystallization of an Ag interlayer even at the as-deposited stage. Peaks attributed to ITO(222), Ag(111) and Al(200) were observed after annealing, indicating an enhancement in crystallinity of the multilayer films. The annealed IAAI film exhibited a remarkable improvement in optical transmittance (86.1%) with a very low sheet resistance of 2.93 Ω/sq. The carrier concentration increased more than twice when the Al–Ag layer was inserted between the ITO layers. The figure of merit of the IAAI multilayer contact has been found to be high at 76.4 × 10−3 Ω−1 compared to a pure ITO contact (69.4 × 10−3 Ω−1). These highly conductive and transparent ITO films with Al–Ag interlayer can be a promising contact for low-resistance optoelectronics devices.

2-bit amplitude-modulated coding metasurfaces based on indium tin oxide films

Metasurfaces exhibit some extraordinary phenomena, resulting in their wide applications in controlling electromagnetic (EM) waves. Recently, the introduction of digital coding metasurfaces has greatly improved the design and broadened the application scope of metasurfaces. However, in most previous studies, the control of EM waves was achieved based on the phase distribution. Here, we present 2-bit amplitude-modulated coding metasurfaces based on optically transparent indium tin oxide films in the microwave frequency regime. The proposed coding metasurfaces are composed of coding unit cells with multiring structures with specific coding sequences, allowing the dramatic control of reflected amplitudes under the normal incidence while keeping other states unchanged. Using this method, almost continuous amplitude modulation can be easily realized with different coding sequences without the need to redesign the structure. The results of simulations and experiments show precise agreement, thereby validating the feasibility of our design. In addition, the optical transparency of the metasurface indicates its promise in a variety of microwave and visible-light applications.

Efficient phase matching algorithm for measurements of ultrathin indium tin oxide film thickness in white light interferometry

A novel method is proposed to measure the thickness of the indium tin oxide (ITO) film, which is less than 20 nm, using valid Fourier’s phase information of white light correlogram and curve matching algorithm. Based on the Fourier transform amplitude information, the valid phase distribution function that contains the thin transparent electrode ITO film thickness information has been successfully extracted. A curve matching algorithm based on standard deviation is employed to accurately calculate the thickness of such thin ITO films. The experimental results show that the thickness values were consistent with that determined using the stylus instruments, indicating that this method can be applied to measure the ITO film thickness ranging from 5 to 100 nm.

Highly conductive and transparent ITO films deposited at low temperatures by pulsed DC magnetron sputtering from ceramic and metallic rotary targets

The fabrication of complex device structures often requires deposition of Indium tin oxide (ITO) thin films on temperature sensitive substrates. For example, substrates containing electronic components or organic materials used in displays, touch panels, and electroluminescent devices often restrict process temperatures to below 100°C. Currently the best ITO quality is attained for films deposited with magnetron sputtering using ceramic targets at substrate temperatures above 200°C. In the present study, ITO layers with thicknesses ranging from 25nm to 200nm were deposited on glass substrates by pulsed DC magnetron sputtering using rotary ceramic ITO targets and reactive sputtering from rotary indium-tin targets. Optical and electrical properties were measured and compared for both types of ITO layers. The as-deposited layers were treated post-growth to enhance electrical conductivity and optical transmission. A standard thermal treatment is compared to flash lamp annealing (FLA) with the goal of keeping substrate temperature below 100°C. The enhancement of both electrical and optical properties has been determined by sheet resistance measurements and optical spectroscopy. ITO coatings with optical transmissions higher than 87% and resistivity lower than 2.5×10−4Ωcm could be achieved. A strong influence of the oxygen flow during deposition has been observed for the electrical and optical properties after post-treatment.

Manufacture of sub-μm thin, particulate-based ITO layers by roller coating

This paper presents the development of nanoparticulate indium tin oxide (ITO) inks for the continuous manufacture of ultrathin (∼280nm) ITO layers on PET substrates by roller coating at very high coating speeds. Ethanol- and water-based ITO inks containing polyvinylpyrrolidone as binder were prepared and rheologically characterized. The influence of different ink compositions on coating properties was evaluated by the concept of the dimensionless capillary number Ca. The ITO films were characterized concerning optical and electrical properties in dependence on ink composition and coating parameters. The organic solvent ethanol could be replaced by water, being cheap and environmental friendly. These inks allow the manufacture of sub-μm thin ITO layers with high layer quality and low specific electrical resistance of 3Ωcm. Flexible and highly transparent ITO films with an inline-transmission of 88% in the regime of visible light which absorbed simultaneously up to 96% in the NIR region were produced.

Highly transparent RF magnetron-sputtered indium tin oxide films for a-Si:H/c-Si heterojunction solar cells amorphous/crystalline silicon

We prepared highly transparent magnetron-sputtered indium tin oxide (ITO) films deposited at various RF powers for a-Si:H(p)/c-Si heterojunction solar cell applications. The surface morphology of ITO films improved in terms of an increase in grain size as the RF power increased. Rapid growth of the (400) plane was observed with increasing RF power, while the (222) plane remain unchanged. The ITO film deposited at 100W showed the lowest resistivity of 3.8×10−4Ωcm and highest visible transmittance of 90.19%. The deposition rate and optical bandgap of ITO films were varied from 20 to 100nm/min and from 3.68 to 3.77eV for RF power from 50 to 250W, respectively. Highly transparent ITO films were utilized as the front anti-reflection layer in heterojunctions with intrinsic thin-layer (HIT) solar cells showed the efficiency of 16.3% for RF power of 100W. The HIT solar cells deposited at RF power of 100W also exhibited higher carrier lifetime and implied voltage.

Deposition of Conducting Oxide Thin Films as Anode for Solar Cell Device

Transparent Conducting Indium Tin Oxide (ITO) and Zinc Oxide (ZnO) thin films were deposited with Pulsed Laser Deposition PLD at 300°C. The ITO films have small grain size of 5-10 nm and a high value transmission (95%) in the wavelength range from 300 to 700 nm with a low resistivity of 2.25 × 10 Ω.cm. While Zinc Oxide (ZnO) films have grain size of 15 nm and a transmission of 85% with a resistivity of 2.10 × 10 Ω.cm. A lower resistivity and better spectra selectivity is a measurement of the quality and potential use of transparent ITO and ZnO films for the application as anode electrodes for optoelectronic devices. The optimized ITO film was then used individually as anode in a solar cell based on organic conjugated polymer BEH-co-MEH-PPV. The cell fabricated in this study with an active layer made by solution-processed polymer. It was also found that the surface roughness and work function of oxide films are very important to enhance the stability and efficiency of electrode thin films used for solar cells. The solar cell structure ITO/BEHP-co-MEH-PPV/Al has shown a photovoltaic performance with open circuit voltages (Voc) of the cell being 0.45 V and power conversion efficiency of 6.4% and a fill factor of 40%. Original Research Article Article British Journal of Applied Science & Technology, 4(5): 739-748, 2014 740

A plasmonic mercury sensor based on silver–gold alloy nanoparticles electrodeposited on indium tin oxide glass

We construct silver–gold alloy nanoparticles (Ag–AuNPs) as the basis of a reagentless, sensitive and simple mercury sensor. Ag–AuNPs were electrodeposited directly on transparent indium tin oxide film coated glass. Hg(II) ions in aqueous solution could be reduced by Ag atoms existing in Ag–AuNPs; the deposition/amalgamation of Hg on the nanoparticles resulted in a blue shift of the localized surface plasmon resonance peak. Therefore, Hg2+ can be detected quantitatively by using a spectrophotometer. The sensor response is linear in the range from 0.05 to 500ppb of Hg(II) concentration. No sample separation or preconcentration is required for detection of ultralow levels of mercury in water samples. The results shown herein have potential applications in the development of a new optical sensor for the detection of low concentrations of mercury.

RF magnetron sputtered indium tin oxide films with high transmittance and work function for a-Si:H/c-Si heterojunction solar cells

The RF magnetron sputtered indium tin oxide (ITO) films were deposited on glass substrates with low resistivity, high transmittance and work function for various oxygen (O2) flow rates. The addition of small O2 contents during the sputtering process increased the Hall mobility of ITO films while carrier concentration was decreased. The work function of ITO films was enhanced from 4.31 to 4.81 eV through the growth of (222) plane having relatively low surface energy. The highly transparent ITO films were employed as front anti-reflection layer in heterojunction with intrinsic thin layer (HIT) solar cells and the best photo-voltage parameters were found to be; Voc = 665 mV, Jsc = 35.1 mA/cm2, FF = 73.2% and η = 17.1% for the O2 flow rate of 0.1 sccm. The high work function ITO films play an important role for barrier height modification in HIT solar cell.

Improved performance mechanism of III–V compound triple-junction solar cell using hybrid electrode structure

To improve the conversion efficiency of InGaP/InGaAs/Ge compound triple-junction solar cells, the hybrid electrode structure consisting of the metal contact pads and the transparent indium–tin-oxide (ITO) film was designed. The metal contact pad was used to form good ohmic contact. The current extraction capability of the resulting solar cells was enhanced by reducing the interval of the metal contact pads. In addition, transparent ITO films were used to replace the conventional bus-bar metal electrodes to avoid shadow loss. To study the improvement mechanisms of the conversion efficiency, the designed electrodes with various intervals among the metal contact pads were fabricated on solar cells, and the performances were evaluated for comparison.

In-situ preparation of metal oxide thin films by inkjet printing acetates solutions

ABSTRACTDirect printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method of producing stable inks for ‘in-situ’ deposition of oxide thin films by inkjet printing. The inks were prepared from metal-acetates solutions and printed on a variety of substrates. The acetate precursors were decomposed into oxide films during the subsequent calcination process to achieve the ‘in-situ’ deposition of the desired oxide films directly on the substrate. By this procedure we have obtained room temperature contamination free ferromagnetic spintronic materials like Fe doped MgO and ZnO films from their acetate(s) solutions. We find that the origin of magnetism in ZnO, MgO and their Fe-doped films to be intrinsic. For a 28 nm thick film of Fe-doped ZnO we observe an enhanced magnetic moment of 16.0 emu/cm3 while it is 5.5 emu/cm3 for the doped MgO film of single pass printed. The origin of magnetism is attributed to cat-ion vacancies. We have also fabricated highly transparent indium tin oxide films with a transparency >95% both in the visible and IR range which is rather unique compared to films grown by any other technique. The films have a nano-porous structure, an added bonus from inkjetting that makes such films advantageous for a broad range of applications.

Development of a label-free and reagentless plasmonic immunosensor for the detection of salbutamol

A label-free and reagentless immunosensor based on localized surface plasmon resonance (LSPR) sensing was developed for the detection of salbutamol (Sal). Silver triangular nanoparticles deposited on transparent indium tin oxide film glass were used as the sensing platform. The immunosensor was prepared by direct adsorption of antibody against Sal on the surface of silver triangular nanoparticles. LSPR bands were obtained by a basic UV-vis spectrophotometer in the transmission mode. The analytical performance of the biosensor for the detection of Sal was examined. Under the optimized conditions, a calibration plot for Sal was obtained with a linear range between 0.02 μg mL−1 and 0.8 μg mL−1 (r = 0.991). The detection limit was 0.01 μg mL−1. The proposed biosensor has been used to detect the concentration of Sal in pig complex feed and pork liver samples. It is believed that the plasmonic immunosensor is simple, cost-effective and can be easily used for the detection of Sal in cases of its abuse in animal feed for field analysis.

Unraveling the Mechanism of Catalytic Reduction of O2 by Microperoxidase-11 Adsorbed within a Transparent 3D-Nanoporous ITO Film

Nanoporous films of indium tin oxide (ITO), with thicknesses ranging from 250 nm to 2 μm, were prepared by Glancing Angle Deposition (GLAD) and used as highly sensitive transparent 3D-electrodes for quantitatively interrogating, by time-resolved spectroelectrochemistry, the reactivity of microperoxidase-11 (MP-11) adsorbed within such films. The capacitive current densities of these 3D-electrodes as well as the amount of adsorbed MP-11 were shown to be linearly correlated to the GLAD ITO film thickness, indicating a homogeneous distribution of MP-11 across the film as well as homogeneous film porosity. Under saturating adsorption conditions, MP-11 film concentration as high as 60 mM was reached. This is equivalent to a stack of 110 monolayers of MP-11 per micrometer film thickness. This high MP-11 film loading combined with the excellent ITO film conductivity has allowed the simultaneous characterization of the heterogeneous one-electron transfer dynamics of the MP-11 Fe(III)/Fe(II) redox couple by cyclic voltammetry and cyclic voltabsorptometry, up to a scan rate of few volts per second with a satisfactory single-scan signal-to-noise ratio. The potency of the method to unravel complex redox coupled chemical reactions was also demonstrated with the catalytic reduction of oxygen by MP-11. In the presence of O(2), cross-correlation of electrochemical and spectroscopic data has allowed us to determine the key kinetics and thermodynamics parameters of the redox catalysis that otherwise could not be easily extracted using conventional protein film voltammetry. On the basis of numerical simulations of cyclic voltammograms and voltabsorptograms and within the framework of different plausible catalytic reaction schemes including appropriate approximations, it was shown possible to discriminate between different possible catalytic pathways and to identify the relevant catalytic cycle. In addition, from the best fits of simulations to the experimental voltammograms and voltabsorptograms, the partition coefficient of O(2) for the ITO film as well as the values of two kinetic rate constants could be extracted. It was finally concluded that the catalytic reduction of O(2) by MP-11 adsorbed within nanoporous ITO films occurs via a 2-electron mechanism with the formation of an intermediate Fe(III)-OOH adduct characterized by a decay rate of 11 s(-1). The spectroelectroanalytical strategy presented here opens new opportunities for characterizing complex redox-coupled chemical reactions not only with redox proteins, but also with redox biomimetic systems and catalysts. It might also be of great interest for the development and optimization of new spectroelectrochemical sensors and biosensors, or eventually new photoelectrocatalytic systems or biofuel cells.

AlGaInN-based light emitting diodes with a transparent p-contact based on thin ITO films

A method for obtaining transparent conductive ITO (indium-tin oxide) films aimed for use in light emitting diodes of the blue spectral range is developed. The peak external quantum efficiency of light-emitting diodes with a p-contact based on the obtained films reaches 25%, while for similar light-emitting diodes with a standard semitransparent metal contact, it is <10%. An observed increase in the direct voltage drop from 3.15 to 3.37 V does not significantly affect the possibility of applying these films in light-emitting diodes since the optical power of light-emitting diodes with a transparent p-contact based on ITO films exceeds that of chips with metal semitransparent p-contacts with a working current of 20 mA by a factor of almost 2.5. Light-emitting diodes with p-contacts based on ITO films successfully withstand a pumping current that exceeds their calculated working current by a factor of 5 without the appearance of any signs of degradation.

Visual Study of Flow Pattern Evolution of Flow Boiling in a Microtube

High-speed photography was applied to visualize the flow pattern evolution of flow boiling of liquid nitrogen in an upward quartz microtube coated with a layer of transparent indium tin oxide film as the heater. The inner diameter of the employed tube was about 1.33 mm. The characteristic of nucleation site activation, which was the beginning of the flow pattern evolution, was studied visually. In the case of low heat flux and small mass flux, only a single nucleation site was activated. The departed bubbles grew to the size of the inner diameter of the tube soon and the transition from the bubbly flow to slug and annular flow occurred earlier compared to the conventional normal-sized tubes. In the case of high mass flux and high subcooling, multiple nucleation sites were activated. The interaction between adjacent nucleation sites was considered. Slug and annular flow were found to suppress the downstream nucleation site. Bubble coalescence was one of the key factors for the flow pattern evolution, and it was found that the bubble coalescence would bring about great disturbance to the adjacent nucleation site. The characteristics of bubble condensation in the subcooled liquid nitrogen were also demonstrated. Flow pattern evolution beyond the boiling crisis was also investigated. Post-dryout regimes such as inverted bubbly, inverted slug, and inverted annular flow were observed in the microtube. Flow reversal and liquid entrainment, which were relevant to flow instability in the flow pattern evolution, were demonstrated clearly.

Structural and Optical Properties of InSnO3 Sol-Gel Coatings to Use in Windows Glass Buildings

Indium stannate (InSnO3) films doping with small amounts of copper are made highly useful as architectural window coatings. Indium-tin-oxide (ITO) has attracted intense interest due to some of its unique characteristics; it has high optical transmittance in the visible region, low electric resistivity, and chemical stability. Therefore, ITO thin films have been found to play an important role in opto-electronic applications. In this work, uniform and transparent ITO films were deposited onto glass substrates using a sol-gel process. The initial sols were prepared by mixing solutions of indium chloride prepared in anhydrous ethanol with tin chloride and mechanically stirring and refluxed 2 hours and aged 2 week, the resultant mixture until a clear and sticky coating sol was obtained. The glass substrates were spin-coated and annealed at 500 °C. Because annealing conditions affect the microstructures, the properties of the resultant ITO films can be controlled. The optical transmittance of 200 nm thick ITO film was more than 80% in the visible region. The surface morphology examined by SEM appears to be uniform over large surface areas. The structural, microstructural and optical properties of the coatings and powders made from the sols were extensively characterized by using XRD, AFM and spectrophotometer techniques

Mesoporous Indium Tin Oxide as a Novel Platform for Bioelectronics

AbstractStable immobilization and reversible electrochemistry of cytochrome c in a transparent indium tin oxide film with a well‐defined mesoporosity (mpITO) is demonstrated. The transparency and good conductivity, in combination with the large surface area of mpITO, allow the incorporation of a high amount of electroactive biomolecules and their electrochemical and spectroscopic investigation. UV/Vis and resonance Raman spectroscopy, in combination with direct protein voltammetry, are employed for the characterization of cytochrome c immobilized in the mpITO and reveal no perturbation of the structural integrity of the redox protein. The potential of this modified material as a biosensor for detection of superoxide anions is also demonstrated.

Patterning of nanoparticulate transparent conductive ITO films using UV light irradiation and UV laser beam writing

Indium tin oxide (ITO) thin film is one of the most widely used as transparent conductive electrodes in all forms of flat panel display (FPD) and microelectronic devices. Suspension of already crystalline conductive ITO nanoparticles fully dispersed in alcohol was spun, after modifying with coupling agent, on glass substrates. The low cost, simple and versatile traditional photolithography process without complication of the photoresist layer was used for patterning ITO films. Using of UV light irradiation through mask and direct UV laser beam writing resulted in an accurate linear, sharp edge and very smooth patterns. Irradiated ITO film showed a high transparency (∼85%) in the visible region. The electrical sheet resistance decrease with increasing time of exposure to UV light and UV laser. Only 5 min UV light irradiation is enough to decrease the electrical sheet resistance down to 5 kΩ□.