Yttria-stabilized zirconia thin film electrolyte produced by RF sputtering for solid oxide fuel cell applications

Thin film (40-600 nm) yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC) were deposited on NiO-YSZ anodes and fused silica substrates by RF sputtering, using low applied power without the use of post deposition annealing heat treatment. YSZ film showed a nanocrystalline structure and consisted of the Zr_.85Y_.15O_1.93 (fcc) phase. The film was dense and the YSZ/anode interface was continuous and crack free. According to preliminary in-plane conductivity measurements (temperature range 550-750 °C) on the YSZ film, the activation energy for ionic conduction was found to be 1.18 ± 0.01 eV.     

Synthesis and characterization of electrolyte-grade 10%Gd-doped ceria thin film/ceramic substrate structures for solid oxide fuel cells

In the present research, spray pyrolysis technique is employed to synthesize 10%Gd-doped ceria (GDC) thin films on ceramic substrates with an intention to use the "film/substrate" structure in solid oxide fuel cells. GDC films deposited on GDC substrate showed enhanced crystallite formation. In case of NiO-GDC composite substrate, the thickness of film was higher (~ 13 μm) as compared to the film thickness on GDC substrate (~ 2 μm). The relative density of the films deposited on both the substrates was of the order of 95%. The impedance measurements revealed that ionic conductivity of GDC/NiO-GDC structure was of the order of 0.10 S/cm at 500 °C, which is a desirable property for its prospective application.     

Ion conducting properties of hydrogen-containing Ta2O5 thin films prepared by reactive sputtering

Hydrogen-containing Ta₂O₅ (Ta₂O₅:H) thin films are considered to be a candidate for a proton-conducting solid-oxide electrolyte. In this study, Ta₂O₅:H thin films were prepared by reactively sputtering a Ta metal target in an O₂ + H₂O mixed gas. The effects of sputtering power and post-deposition heat treatment on the ion conducting properties of the Ta₂O₅:H thin films were studied. The ionic conductivity of the films was improved by decreasing the RF power and a maximum conductivity of 2 × 10⁻⁹ S/cm was obtained at an RF power of 20 W. The ionic conductivity decreased by heat-treatment in air, and no ion-conduction was observed after treatment at 300 °C due to the decrease in hydrogen content in the films.     

Morphology and growth of e-beam deposited YSZ thin films

Yttria-stabilized zirconium (YSZ) thin films were grown from the tetragonal phase of ZrO₂ stabilized by 8 wt% of Y₂O₃ (8% of YSZ) ceramic powders using e-beam deposition technique (EB-PVD). The influence of the type of substrate on the microstructure of deposited YSZ thin films was analysed. YSZ thin films (2-3 μm of thickness) were deposited on three different types of substrates: optical quartz (SiO₂), porous Ni-YSZ substrates and Alloy 600 (Fe-Ni-Cr). The dependence of the substrate temperature (from 20 to 600 °C) on the thin film structure and the surface morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that (i) the substrate temperature has an influence on the crystallite size, which varied between 12 and 50 nm, (ii) the substrate type has an influence on the growth mechanism of YSZ thin films, and (iii) a bias voltage applied to the substrate during the deposition of thin films has an influence on the densification of YSZ layers.     

On the green density, sintering behavior and electrical property of tape cast Ce0.9Gd0.1O1.95 electrolyte films

Gadolinia doped ceria (Ce_0.9Gd_0.1O_1.95, GDC) electrolyte films were tape cast from oxalate coprecipitated GDC powders, gelcast GDC powders and their mixtures, respectively, to evaluate the effects of the original particle size and distribution on the properties of the green and sintered GDC cast tapes. The apparent density of different original powders, as well as the green density, sintered behavior, and electrical conductivity of tapes cast from the various starting powders were investigated. Mixing the coprecipitated and the gelcast GDC powders not only results in a higher packing efficiency of particles in the loose powders, but also results in higher green and sintered densities of cast tapes. Furthermore, tapes cast from the 50/50 powder mixtures can be sintered to 96.2% of theoretical density at relatively low sintering temperature of 1400°C, whereas those from the oxalate coprecipitated and from the gelcast powders were only 89.7 and 94.1% dense, respectively. The ac impedance measurement shows that GDC films cast from the 50/50 powder mixture exhibit good electrical conductivity (4.2 and 6.0 S m⁻¹ at 700 and 800°C in air, respectively). The test results have revealed that high-density GDC films can be fabricated by tape casting technique at relatively low sintering temperature by optimizing the particle size distribution of the starting powders.     

Effect of annealing on molybdenum doped indium oxide thin films RF sputtered at room temperature

Thin films of molybdenum doped indium oxide (IMO) were deposited on glass at room temperature using an in-built three-source RF magnetron sputtering. The films were studied as a function of oxygen volume percentage (O₂ vol. %; ranging from 0.0 to 17.5%) in the sputtering chamber. The as-deposited amorphous films were crystallized on post-annealing. The as-deposited films are low conducting and Hall coefficients were undetectable; whereas post-annealed films possess fairly high conductivity. The lowest transmittance (11.96% at 600 nm) observed from the films deposited without oxygen increased to a maximum of 88.01% (3.5 O₂ vol. %); whereas this transmittance was decreased with the increasing O₂ vol. % to as low as 81.04% (15.6 O₂ vol. %); a maximum of 89.80% was obtained from the films annealed at 500 °C in open air (3.5 O₂ vol. %). The optical band gap of 3.80 eV obtained from the films deposited without oxygen increased with increasing O₂ vol. % to as high as 3.91 eV (17.5 O₂ vol. %). A maximum of 3.92 eV was obtained from the films annealed at 300 °C in N₂:H₂ gas atmosphere (17.5 O₂ vol. %).     

Characteristics of highly orientated BiFeO3 thin films on a LaNiO3-coated Si substrate by RF sputtering

BiFeO₃ (BFO) films were grown on LaNiO₃-coated Si substrate by a RF magnetron sputtering system at temperatures in the range of 300-700 °C. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. For a substrate temperature below 300 °C and at 700 °C only partially crystalline films and completely randomly polycrystalline films were grown, whereas highly (001)-orientated BFO film was obtained for a substrate temperature in the range of 400-600 °C. The crystalline quality of BFO thin films increase as the deposition temperature increase except for the film deposited at 700 °C. The fitted result from X-ray reflectivity curves show that the densities of the BFO films are slightly less than their bulk values. For the BFO films deposited at 300-600 °C, the higher the deposition temperature, the larger the remnant polarization and surface roughness of the films present.     

Thin films of tetragonal zirconia (3Y-TZ) deposited by reactive sputtering

Thin films of tetragonal zirconia (TZ), comprised of 3 mol% Y₂O₃ (3Y-TZ), were deposited onto silicon, oxide-coated silicon, slide glass and aluminum oxide substrates by reactive sputtering of metallic targets in mixtures of oxygen and argon. The texture of deposited films varied with oxygen-to-argon flow ratios with which the target surface altered between metal and oxide compound constituents. Thin films of TZP with (2 0 0) preferred orientation were obtained from sputter deposition in the metallic mode whereas (1 1 1) texture was obtained in the compound mode at ambient temperature. The film texture tends to align along the 〈1 1 1〉 direction while the substrate was heated to 300 °C during the deposition. The texture of all these films was stable upon annealing at 900 °C in air. The reasons for the texture development are discussed.     

La1−xSrxCuO2.5−δ as new cathode materials for intermediate temperature solid oxide fuel cells

La_1−xSr_xCuO_2.5−δ (LSCu), which exhibit excellent electrical conductivity and oxygen vacancies were investigated as potential cathode materials for solid oxide fuel cell (SOFC) applications. The structure stability, electrical conductivity, cathodic overpotential, and the reactivity with yttria-stabilized zirconia (YSZ) were examined in this study. It was found that the LSCu perovskite was obtained only when the addition of strontium fell in the range between 15 and 30%. With more than 20% of strontium addition, this material showed excellent electrical property and immunity to the reaction with YSZ at 800 °C. The conductivities of LSCu were as high as 900 S/cm at 600 °C, and 800 S/cm at 800 °C. The cathodic overpotential of this material was approximately 3.8 and 10.6 mV at a current density of 100 mA/cm² at 850 and 750 °C, respectively. These properties are superior to Sr-doped lanthanum manganite (LSM), which is the state-of-the-art cathode material of SOFCs.     

Substrate temperature effect on the SiC passivation layer synthesized by an RF magnetron sputtering method

This paper describes amorphous silicon carbide (a-SiC) film as an alternative material to silicon nitride (SiN) and silicon oxide (SiO₂) for the passivation layer of solar cells. We deposited the film on p-type silicon (100) wafers and glass substrates by RF magnetron sputtering using a SiC (99%) target. Structural and optical properties of the films were investigated according to the process temperature (room temperature, 300 °C, 400 °C, 500 °C and 600 °C). The structural properties were analyzed by Raman microscopy and XPS (X-ray Photoelectron Spectroscopy). The XPS showed that the content of SiC in the film is increased when the substrate temperature is higher. The optical properties of the films were examined by UV-visible spectroscopy and Ellipsometer. The optical characteristic measurement showed that the lowest refractive index of the film is 2.65. Also, using carrier lifetime measurement, we investigated the performance of SiC as the passivation layer. At the substrate temperature of 600 °C, we obtained a highest carrier lifetime of 7.5 μs.     

Fabrication of TiO2 nanotubes by anodization of Ti thin films for VOC sensing

Ti thin films were anodized in aqueous HF (0.5 wt.%) and in polar organic (0.5 wt.% NH₄F + ethylene glycol) electrolytes to form TiO₂ nanotube arrays. Ti thin films were deposited on microscope glass substrates and then anodized. Anodization was performed at potentials ranging from 5 V to 20 V for the aqueous HF and from 20 V to 60 V for the polar organic electrolytes over the temperatures range from 0 to 20 °C. The TiO₂ nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). It has been observed that anodization of the deposited Ti thin films with aqueous HF solution at 0 °C resulted in nanotube-type structures with diameters in the range of 30-80 nm for an applied voltage of 10 V. In addition, the nanotube-type structure is observed for polar organic electrolyte at room temperature at the anodization voltage higher than 40 V. The volatile organic compound (VOC) sensing properties of TiO₂ nanotubes fabricated using different electrolytes were investigated at 200 °C. The maximum sensor response is obtained for carbon tetrachloride. The sensor response is dependent on porosity of TiO₂. The highest sensor response is observed for TiO₂ nanotubes which are synthesized using aqueous HF electrolyte and have very high porosity.     

Optical and electrical properties of heat-resistant Sb-doped Sn1 − xHfxO2 transparent conducting films

To examine variations in the transparent conducting properties after annealing at high temperatures, 300-nm thick Sb-doped Sn_1 − xHf_xO₂ (x = 0.00-0.10) films were deposited onto silica glass substrates by the RF sputtering method and annealed in air up to 1000 °C at 200 °C increments. After annealing, all the Sb-doped SnO₂ films were transparent and electrically conductive, but large cracks, which decreased the electrical conductivity, were generated in several films due to crystallization or the thermal expansion difference between the film and substrate. Only the film deposited at room temperature in an Ar and O₂ mixed atmosphere did not crack after annealing, and its electrical conductivity exceeded 100 S cm^− 1 even after annealing at 1000 °C in air. Hf-doping blue shifted the fundamental absorption edges in the UV region in the Sb-doped Sn_1 − xHf_xO₂ films. Additionally, the optical transmission at 310 nm, T₃₁₀, increased as the Hf concentration increased, whereas the electrical conductivity was inversely proportional to the Hf concentration. On the other hand, thinner films (150-nm thick) with x = 0.00 showed both a high electrical conductivity over 100 S cm^− 1 and a high transparency T₃₁₀ = 65% after high temperature annealing.     

Enhanced characterization of ITO films deposited on PET by RF superimposed DC magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited on polyethylene terephthalate substrates by RF superimposed DC magnetron sputtering using an ITO target composed of In₂O₃ (90 wt.%):SnO₂ (10 wt.%). The total sputtering power was maintained at 70 W and the power ratio of RF/(RF + DC) was varied from 0 to 100% in steps of 25%. The discharge voltage and deposition rate decreased with increasing RF/(RF + DC) power ratio. The ITO film deposited at a 50% RF portion of the total power showed the lowest resistivity (3.18 × 10^− 4 Ωcm), high transmittance (87.5%) and relatively good mechanical durability, which was evaluated using bending and scratch tests.     

The effect of substrate temperature on Al-doped ZnO characteristics for organic thin film transistor applications

The influence of substrate temperature on the structural, electrical, and optical properties of aluminum-doped zinc oxide (AZO) films fabricated by radio frequency (RF) magnetron sputtering was investigated. The AZO films were deposited at various substrate temperatures, and the effect of AZO gate electrode conductivity on organic thin film transistor (OTFT) performance was examined. While an increase in the substrate temperature from 100 °C to 300 °C led to an improvement in crystallinity, substrate temperatures over 300 °C caused degradation of the electrical and surface properties. We fabricated OTFTs using AZO films prepared at various substrate temperatures and obtained good device performance. Thus, the performance of an OTFT can be determined by the conductivity of the AZO gate electrode.     

Fabrication of high frequency ZnO thin film SAW devices on silicon substrate with a diamond-like carbon buffer layer using RF magnetron sputtering

Diamond-like carbon (DLC) film is a promising candidate for surface acoustic wave (SAW) device applications because of its higher acoustic velocity. A zinc oxide (ZnO) thin film has been deposited on DLC film/Si substrate by RF magnetron sputtering; the optimized parameters for the ZnO sputtering are RF power density of 0.55 W/cm², substrate temperature of 380 °C, gas flow ratio (Ar/O₂) of 5/1 and total sputter pressure of 1.33 Pa. The results showed that when the thickness of the ZnO thin films was decreased, the phase velocity of the SAW devices increased significantly.     

Preparation and characterization of La0.9Sr0.1Ga0.8Mg0.2O3−δ thin film electrolyte deposited by RF magnetron sputtering on the porous anode support for IT-SOFC

Thin films of solid electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) were deposited by RF magnetron sputtering onto porous La_0.7Sr_0.3Cr_0.5Mn_0.5O_3−δ (LSCM) anode substrates. The effects of substrate temperature, sputtering power density and sputtering Ar gas pressure on the LSGM thin film density, flatness and morphology were systematically investigated. RF sputtering power density of 7.8 W cm⁻², substrate temperature of 300 °C and sputtering Ar gas pressure of 5 Pa are identified as the best technical parameters. In addition, a three-electrode half cell configuration was selected to investigate the electrochemical performance of the thin film. The LSGM film deposited at optimum conditions exhibited a lower area specific ohmic resistance of 0.68 Ω cm⁻² at 800 °C, showing that the practicability of RF magnetron sputtering method to fabricate LSGM electrolyte thin film on porous LSCM anode substrates.     

Development of graded Ni-YSZ composite coating on Alloy 690 by Pulsed Laser Deposition technique to reduce hazardous metallic nuclear waste inventory

Alloy 690 based ‘nuclear waste vitrification furnace’ components degrade prematurely due to molten glass-alloy interactions at high temperatures and thereby increase the volume of metallic nuclear waste. In order to reduce the waste inventory, compositionally graded Ni-YSZ (Y₂O₃ stabilized ZrO₂) composite coating has been developed on Alloy 690 using Pulsed Laser Deposition technique. Five different thin-films starting with Ni80YSZ20 (Ni 80 wt% + YSZ 20 wt%), through Ni60YSZ40 (Ni 60 wt% + YSZ 40 wt%), Ni40YSZ60 (Ni 40 wt% + YSZ 60 wt%), Ni20YSZ80 (Ni 20 wt% + YSZ 80 wt%) and Ni0YSZ100 (Ni 0 wt% + YSZ 100 wt%), were deposited successively on Alloy 690 coupons. Detailed analyses of the thin-films identify them as homogeneous, uniform, pore free and crystalline in nature. A comparative study of coated and uncoated Alloy 690 coupons, exposed to sodium borosilicate melt at 1000 °C for 1-6 h suggests that the graded composite coating could substantially reduced the chemical interactions between Alloy 690 and borosilicate melt.     

The effect of annealing on structural, electrical and optical properties of nanostructured ITO films prepared by e-beam evaporation

Tin doped indium oxide (ITO) thin films with composition of 9.42 wt% SnO₂ and 89.75 wt% In₂O_3, and impurities balanced on glass substrates at room temperature have been prepared by electron beam evaporation technique and then were annealed in air at different temperatures from 350 to 550 °C for 1 h. XRD pattern showed that increasing annealing temperature increased the crystallinity of thin films and at 550 °C high quality crystalline thin films with grain size of about 37 nm were obtained. Conductivity of ITO thin films was increased by increasing annealing temperature and conductivity obtained results in 350-550 °C temperature range were also excellently fitted in both Arrhenius-type and Davis-Mott variable-range hopping conductivity models. The UV-vis transmittance spectra were also confirmed that the annealing temperature has significant effect on the transparency of thin films. The highest transparency over the visible wavelength region of spectrum (93%) obtained at 550 °C on annealing temperature. It should be noted that this thin film was deposited on substrate at room temperature. This result obtained is equivalent with those values that have already been reported but with high-level (20 wt%) tin doped indium oxide thin films and also at 350 °C substrate temperature. The allowed direct band gap at the temperature range 350-550 °C was estimated to be in the range 3.85-3.97 eV. Band gap widening with an increase in annealing temperature was observed and is explained on the basis of Burstein-Moss shift. A comparison between the electron beam evaporation and other deposition techniques showed that the better figure of merit value can be obtained by the former technique. At the end we have compared our results with other techniques.     

Influence of oxygen pressure on the structural, electrical and optical properties of VO2 thin films deposited on ZnO/glass substrates by pulsed laser deposition

The influence of oxygen pressure on the structural and electrical properties of vanadium oxide thin films deposited on glass substrates by pulsed laser deposition, via a 5-nm thick ZnO buffer, was investigated. For the purposes of comparison, VO₂ thin films were also deposited on c-cut sapphire and glass substrates. During laser ablation of the V metal target, the oxygen pressure was varied between 1.33 and 6.67 Pa at 500 °C, and the interaction and reaction of the VO₂ and the ZnO buffer were studied. X-ray diffraction studies showed that the VO₂ thin film deposited on a c-axis oriented ZnO buffer layer under 1.33 Pa oxygen had (020) preferential orientation. However, VO₂ thin films deposited under 5.33 and 6.67 Pa were randomly oriented and showed (011) peaks. Crystalline orientation controlled VO₂ thin films were prepared without such expensive single crystal substrates as c-cut sapphire. The metal-insulator transition properties of the VO₂/ZnO/glass samples were investigated in terms of electrical conductivity and infrared reflectance with varying temperatures, and the surface composition was investigated by X-ray photoelectron spectroscopy.     

Al-doped ZnO (AZO) films deposited by reactive sputtering with unipolar-pulsing and plasma-emission control systems

Al-doped ZnO (AZO) films were deposited on fused silica glass substrates unheated or heated at 200 °C by reactive dc sputtering using a Zn-Al alloy target with mid-frequency pulsing (50 kHz) and the plasma control unit with a feedback system of the optical emission intensity of the atomic O* line at 777 nm to control oxygen gas flow. The stable and reproducible depositions were successfully carried out in the transition region. The deposition rates attained in this study were about 10-20 times higher than the one by conventional sputtering using oxide targets. The AZO films with the lowest resistivity of 3.8 × 10^− 4 Ω cm was deposited on the substrate heated at 200 °C with a sputter power of 4 kW, where the deposition rate was 385 nm/min.