Development of higher performance indium tin oxide films at a very low temperature (< 80 °C) by the neutral beam-assisted sputtering process

At very low temperatures (< 80 °C), improved performance indium tin oxide (ITO) thin films with a low resistivity of 4.22 × 10⁻⁴ Ωcm and high transmittance > 90% at 550 nm were developed using the neutral beam-assisted sputtering (NBAS) technique, which included a cyclic inter-treatment process with an Ar neutral beam. Transmission electron microscopy and electron diffraction showed that the neutral particles with hyper-thermal energy was able to enhance the formation of the nano-crystalline phase and activate the dopant without additional heating or plasma damage during ITO thin film deposition.     

Transparent, amorphous and organics-free ZnO thin films produced by chemical solution deposition at 150 °C

We have studied the low-temperature processing of ZnO by chemical solution deposition. A transparent, stable precursor solution prepared from zinc acetate dihydrate dissolved in 2-methoxyethanol was spin-coated on SiO_x/Si, soda-lime glass and polymer substrates and heated at 150 °C. Selected thin films deposited on SiO_x/Si were additionally heated at 450 °C.Microstructural and chemical analyses showed that the thin films heated at 150 °C in air were amorphous, contained no organic residues and had a root mean square roughness of 0.7 nm. The films deposited on SiO_x/Si and heated at 450 °C were crystallised and consisted of randomly oriented grains with a diameter of about 20 nm. All thin films were transparent, exhibiting a transmission of over 80% in the visible range. The resistivity of the 120-nm thick ZnO films processed at 150 °C was 57 MΩ cm and upon heating at 450 °C it decreased to 1.9 kΩ cm.     

Effects of oxygen flow ratios and annealing temperatures on Raman and photoluminescence of titanium oxide thin films deposited by reactive magnetron sputtering

Titanium oxide (TiO_x) thin films were deposited on the Si(100) substrates by direct-current reactive magnetron sputtering at 3-15 % oxygen flow ratios (FO₂% = FO₂/(FO₂ + FAr) × 100%), and then annealed by rapid thermal annealing (RTA) at 350-750 °C for 2 min in air. The phase, bonding and luminescence behaviors of the as-deposited and annealed TiO_x thin films were analyzed by X-ray diffraction (XRD), Raman spectroscopy and photoluminescence (PL) spectroscopy, respectively. The as-deposited TiO_x films were amorphous from XRD and showed weak Raman intensity. In contrast, the distinct crystalline peaks of anatase and rutile phases were detected after RTA at 550-750 °C from both XRD and Raman spectra. A mixture of anatase and rutile phases was obtained by RTA at 3 FO₂% and its amount increased with annealing temperature. Only the anatase phase was detected in the 6-15 FO₂% specimens after RTA. The PL spectra of all post-annealed TiO_x films showed a broad peak in visible light region. The PL peak of TiO_x film at 3 FO₂% at 750 °C annealing can be fitted into two Gaussian peaks at ~ 486 nm (2.55 eV) and ~ 588 nm (2.11 eV) which were attributed to deep-level emissions of oxygen vacancies in the rutile and anatase phases, respectively. The peak around 550 nm was observed at 6-15 FO₂% which is attributed to electron-hole pair recombination from oxygen vacancy state in anatase phase to valence band. The variation of intensity of PL peaks is concerned with the formation of the rutile and anatase phases at different FO₂% and annealing temperatures.     

Property variations of direct-current reactive magnetron sputtered copper oxide thin films deposited at different oxygen partial pressures

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were deposited on glass substrates at different oxygen partial pressures by direct-current reactive magnetron sputtering of pure copper target in a mixture of argon and oxygen gases. Oxygen partial pressure was found to be a crucial parameter in controlling the phases and, thus, the physical properties of the deposited copper oxide thin films. Single-phase Cu₂O thin films with cubic structure were obtained at low oxygen partial pressure between 0.147 Pa and 0.200 Pa while higher oxygen partial pressure promoted the formation of CuO thin films with base-centered monoclinic structure. Polycrystalline Cu₂O thin films deposited with oxygen partial pressure at 0.147 Pa possessed the lowest p-type resistivity of 1.76 Ω cm as well as an optical band gap of 2.01 eV. On the other hand, polycrystalline CuO thin films deposited with oxygen partial pressure at 0.320 Pa were also single phase but showed a n-type resistivity of 0.19 Ω cm along with an optical band gap of 1.58 eV.     

Characterization of copper oxide thin films deposited by the thermal evaporation of cuprous oxide (Cu2O)

Thin films of copper oxide were deposited by thermal evaporation of cuprous oxide (Cu₂O) powder. The substrates were either unheated or heated to a temperature of 300 °C. The films were also annealed in air at a temperature of 500 °C for 3 h. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and UV-visible spectrophotometry. The effects of the substrate temperature and post-deposition annealing on the chemical, structural and optical properties of the films were investigated. As-deposited films on unheated substrates consisted of mixed cupric oxide (CuO) and Cu₂O phases, with a higher concentration of the Cu₂O phase. However, the films deposited on heated substrates and the annealed films were predominantly of the CuO phase.     

Pulsed laser deposition synthesis of superconducting (Cu,C)-Ba-O thin films

(Cu,C)-Ba-O thin films have been epitaxially grown on (100) SrTiO₃ at 500 °C by pulsed laser deposition. Their crystallinity and transport properties have been investigated in order to clarify dominate deposition parameters for carbon-incorporation and superconductivity. The present study has revealed that the growth rate positively correlates with CO₃ content and superconducting properties. In addition, the results suggest that suppression of the radiation damage from energetic particles during deposition is an important factor in obtaining a high and sharp superconducting transition temperature. The work has shown that process parameters can be optimized for growth rate, CO₃ content and minimal radiation damage allowing a superconducting onset temperature of 50 K and zero resistance temperature above 40 K to be realized.     

Low temperature (< 100 °C) fabrication of thin film silicon solar cells by HWCVD

Amorphous silicon films have been made by HWCVD at a very low substrate temperature of ≤ 100 °C (in a dynamic substrate heating mode) without artificial substrate cooling, through a substantial increase of the filament-substrate distance (∼ 80 mm) and using one straight tantalum filament. The material is made at a reasonable deposition rate of 0.11 nm/s. Optimized films made this way have device quality, as confirmed by the photosensitivity of > 10⁵. Furthermore, they possess a low structural disorder, manifested by the small Γ/2 value (half width at half maximum) of the transverse optic (TO) Si-Si vibration peak (at 480 cm^− 1) in the Raman spectrum of ∼ 30.4 cm^− 1, which translates into a bond angle variation of only ∼ 6.4°. The evidence gathered from the studies on the structure of the HWCVD grown film by three different techniques, Raman spectroscopy, spectroscopic ellipsometry and transmission electron microscopy, indicate that we have been able to make a photosensitive material with a structural disorder that is smaller than that expected at such a low deposition temperature.Tested in a p-i-n solar cell on Asahi SnO₂:F coated glass (without ZnO at the back reflector), this i-layer gave an efficiency of 3.4%. To our knowledge, this is the first report of a HWCVD thin film silicon solar cell made at such a low temperature.     

Structural and surface property study of sputter deposited transparent conductive Nb-doped titanium oxide films

We have investigated structural and surface property of transparent conductive Nb-doped titanium oxides (TNO) thin film with high conductivity of 10⁻⁴ Ω cm order which were made by RF-magnetron sputtering at high deposition rates followed by an annealing in vacuum. The grain sizes of TNO evaluated by atomic force microscope were found to become larger by annealing at temperature higher than 500 °C. The measured work functions of the TNO films using ultra-violet light photoelectron spectroscopy were 5.02-5.47 eV, and depended on TNO grain size and on the amount of surface weakly bound oxygen that was estimated from peak area intensities of O(1 s) X-ray photoelectron spectra.     

Preparation and magnetic properties of SrFeO3−x (x = 0.25 ∼ 0.5) using RF magnetron sputtering optimized through sputtering plasma analysis

We investigated the preparation and the magnetic properties of SrFeO_3−x using conventional RF magnetron sputtering. Photoluminescence spectrum analyses of the sputtering plasma revealed that the film composition was changed even using the stoichiometry target. After fixing the composition of the targets from an intensity ratio of the Sr and Fe plasma, the polycrystalline SrFeO_3−x films with different oxygen deficiencies were able to prepare using the various sputtering gas ratio. The magnetic properties of the samples were also changed with changing the sputtering gas ratio. This magnetic property change was likely due to the suppression of the oxygen deficiency in the film.     

Amorphous silicon thin film solar cells deposited entirely by hot-wire chemical vapour deposition at low temperature (< 150 °C)

Amorphous silicon n-i-p solar cells have been fabricated entirely by Hot-Wire Chemical Vapour Deposition (HW-CVD) at low process temperature < 150 °C. A textured-Ag/ZnO back reflector deposited on Corning 1737F by rf magnetron sputtering was used as the substrate. Doped layers with very good conductivity and a very less defective intrinsic a-Si:H layer were used for the cell fabrication. A double n-layer (µc-Si:H/a-Si:H) and µc-Si:H p-layer were used for the cell. In this paper, we report the characterization of these layers and the integration of these layers in a solar cell fabricated at low temperature. An initial efficiency of 4.62% has been achieved for the n-i-p cell deposited at temperatures below 150 °C over glass/Ag/ZnO textured back reflector.     

Structure and dielectric properties of highly (100)-oriented PST thin films deposited on MgO substrates

High-quality Pb_0.4Sr_0.6TiO₃ (PST) thin films have been epitaxially grown on MgO (100) substrates at various substrate temperatures by the pulsed laser deposition (PLD) technique. Their crystalline phase structures and surface morphology were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their in-plane orientation was observed by the Phi scans on the (111) plane. Their dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in PST thin film. The crystalline phase formation of the thin film depended on the deposition temperature. The phase formation ability and (100)-orientation of these films were increased with increasing deposition temperature. Both of the high tunabilities and low dielectric loss of the thin films show that the (100)-oriented PST is a potential material that can be used for tunable applications.     

Effects of oxygen pressure on the growth of pulsed laser deposited ZnO films on Si(0 0 1)

ZnO thin films were prepared on Si(0 0 1) substrates using a pulsed laser deposition (PLD) technique and then their growth and properties were investigated particularly as a function of ambient O₂ pressure during film growth. It was found that the microstructure, crystallinity, orientation and optical properties of the films grown are strongly dependent on the O₂ pressures used. Completely c-axis oriented ZnO films are grown in a low O₂ pressure regime (5×10⁻⁴-5×10⁻² Torr), whereas a randomly oriented film with a much lower crystallinity and a rougher grained-surface is grown at an O₂ pressure of 5×10⁻¹ Torr. This deterioration in film quality may be associated with the kinetics of atomic arrangements during deposition. Our results suggest that ambient O₂ pressure is an important processing parameter and should be optimized in a narrow regime in order to grow a ZnO film of good properties in PLD process.     

Deposition of ultrathin parylene C films in the range of 18 nm to 142 nm: Controlling the layer thickness and assessing the closeness of the deposited films

In this work we describe the deposition of ultrathin parylene C films in the range of 18 nm to 142 nm. Experimental results were obtained from measurements with a commercially available parylene deposition system which was equipped with a quartz crystal microbalance in order to monitor the thickness of the applied layers as well as the deposition rate in real time during the deposition process. This paper will supply the data required to conveniently reproduce the deposition of ultrathin films in the range of well below 100 nm. Furthermore we describe a simple and robust method to test if the applied parylene layers are closed which may be an important aspect to consider if ultrathin layers are to be used as protective coatings or the like. For an exemplary planar electrode structure, we have found a parylene layer of 35 nm to be the thinnest possible closed layer.     

Structural and electrical properties of amorphous GaAs sputtered at high substrate temperature (220 and 400 °C)

The influence of deposition conditions on structural and electrical properties of amorphous gallium arsenide (a-GaAs) thin films, deposited by RF sputtering at two substrate temperatures (glass substrates) and (Mo and ITO/glass substrates), is studied by both X-ray diffraction and electrical dark conductivity σ measurements, in the range (−150 °C to +150 °C) of temperature.The increase of sputtering argon pressure, P_Ar, leads to the growth of an amorphous structure and reduces the room-temperature dark conductivity, σ_RT, which suggests a reduction in the density of defects. Similar results are obtained with a decrease of the dc self-bias voltage, V_p, of RF electrodes. These results suggest that the density of defects is reduced with the energy decrease of the bombarding species while increasing P_Ar or decreasing V_p. The product of the target-to-substrate distance by the argon pressure, (d×P_Ar), representing the number of particles free path, confirms some results of the literature which indicate that the density of defects can be reduced significantly by reducing the energy of the bombarding species while increasing P_Ar or decreasing V_p. Materials of great resistivity (≈10⁸ Ω cm) are obtained either for low V_p or for great d×P_Ar. In addition, the thermal annealing reduces considerably the room-temperature dark conductivity.     

Viscoplastic behavior of a FeCrAl alloy for high temperature steam electrolysis (HTSE) sealing applications between 700 °C and 900 °C

High temperature steam electrolysis (HTSE) is one of the most promising technologies for the industrial production of hydrogen. However one of the remaining problems lies in sealing at high temperature. The reference solution is based on glass seals which presents several drawbacks. That explains why metallic seals are under development. The expected seal will be submitted to creep under low stresses between 700 °C and 900 °C, possibly involving complex loading and thermal history. The candidate material investigated in this work is a FeCrAl (OC404, Sandvik) supplied as a 0.3 mm thick sheet. The ability of this material to develop a protective layer of alumina was studied first, as well as grain size growth during thermal ageing. Creep and tensile tests were performed between 700 °C and 900 °C to determine its mechanical properties. This database was used to propose and identify an elasto-viscoplastic behavior for the material. Creep was described by the Sellars-Tegart law. This law was then used to simulate and predict creep indentation tests performed in the same range of temperatures.     

Structural and optical properties of rock-salt Cd1 − xZnxO thin films prepared by thermal decomposition of electrodeposited Cd1 − xZnxO2

Cd_1 − xZn_xO nanocrystalline thin films with rock-salt structure were obtained through thermal decomposition of Cd_1 − xZn_xO₂ (x = 0, 0.37, 0.57, 1) thin films which were electrodeposited from aqueous solution at room temperature. X-ray diffraction results showed that the Zn ions were incorporated into rock salt-structure of CdO and the crystal lattice parameters decreased with the increase of Zn contents. The bandgaps of the Cd_1 − xZn_xO thin films were obtained from optical transmission and were 2.40, 2.51, 2.63 and 3.25 eV, respectively.     

Characterisation of thin film silicon films deposited by plasma enhanced chemical vapour deposition at 162 MHz, using a large area, scalable, multi-tile-electrode plasma source

Large area (600 × 720 mm) depositions of hydrogenated microcrystalline silicon (μc-Si:H) have been achieved at high deposition rates using a scalable, multi-tile electrode topology. Depositions have shown local results of μc-Si:H deposited with SiH₄ concentrations of up to 20% and at rates of up to 15 Å/s. Of particular interest for this electrode topology is the material across the inter-tile gap. Here we present measurements of the deposition uniformity across the inter-tile gap as well as the material characteristics of the layers. The behaviour of the crystalline fraction, χ_c is observed using Raman spectroscopy, x-ray diffractometry, and dark/light conductivity measurements. A qualitative interpretation of these results is presented, relating them to depletion of SiH₄ in the plasma.     

Atomic layer deposition of iron(III) oxide on zirconia nanoparticles in a fluidized bed reactor using ferrocene and oxygen

Conformal films of amorphous iron(III) oxide and α-Fe₂O₃ have been coated on zirconia nanoparticles (26 nm) in a fluidized bed reactor by atomic layer deposition. Ferrocene and oxygen were alternately dosed into the reactor at temperatures between 367 °C and 534 °C. Self-limiting chemistry was observed via in situ mass spectrometry, and by means of induced coupled plasma-atomic emission spectroscopy analysis. Film conformality and uniformity were verified by high resolution transmission electron microscopy, and the growth rate was determined to be 0.15 Å per cycle. Energy dispersive spectroscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy were utilized as a means to determine film composition at each deposition temperature. Over all of the deposition temperatures investigated, films were deposited as amorphous iron(III) oxide. However, after heat treatment at 850 °C in air and N₂ atmospheres, α-Fe₂O₃ was the predominant species.     

Sol-gel synthesis and luminescence property of ZnO:(La,Eu)Cl nanocomposite thin films

A kind of ZnO:(La, Eu)Cl nanocomposite thin film phosphor with strong red emission was synthesized by the sol-gel process. X-ray diffraction and scanning electron microscopy characterization indicate that the films were composed of nano-sized grains and a LaOCl phase appeared accompanying with (100) oriented ZnO phase after annealed at 600 °C in oxygen. The photoluminescence properties were investigated by measuring the excitation and emission spectra. These luminescence results suggested that Eu³⁺ ions could incorporate into the LaOCl lattice and charge transfer occurred between LaOCl phase and Eu³⁺ ions. La co-doping with Eu-Cl leads to the improvement of the red luminescence of Eu³⁺ and also suppressed the broad green emission of ZnO host.