Stress driven phase transformation in ZrO2 film

Zirconia thin layers (250 nm) were deposited on stainless steel substrates using organo-metallic injection chemical vapour deposition (MOCVD) process with zirconium beta-diketonate as precursor at low oxygen pressure and 900 °C. Low roughness zirconia films were made up of a mixture of tetragonal and monoclinic phases depending on the process conditions. As the zirconia tetragonal phase is known to be stabilized by small grain size and/or internal compressive stresses, tensile and/or compressive external stress fields were applied at room temperature using a bending test device. Then, XRD measurements were used to determine tetragonal/monoclinic phase ratio and also residual stresses in the films before and after the tests. The film surface was observed at the various stages of the experiments by field electron gun-scanning electron microscopy (FEG-SEM).Under these stress fields, phase transformation occurs in the film, from tetragonal structure to a monoclinic one. Some preferential tetragonal planes give rise to monoclinic ones. The external stress field is also likely to redistribute the internal stresses within the films.     

Synthesis, structure, microstructure and mechanical characteristics of MOCVD deposited zirconia films

Zirconia (ZrO₂) thin films were deposited by metal organic chemical vapor deposition (MOCVD) on (1 0 0) Si over temperature and pressure ranges from 700 to 900 °C and 100 to 2000 Pa, respectively. The oxide films were characterized by field emission microscopy and X-ray diffraction so that microstructure and ratios of monoclinic and tetragonal phases could be estimated according to the process conditions. The mechanical behaviour of the substrate-film systems was investigated using Vickers micro-indentation and Berkovitch nano-indentation tests. The characteristics of silicon are not modified by the presence of a thin film of silicon oxide (10 nm), formed in the reactor during heating. Young's modulus and the hardness of tetragonal zirconia phase, 220 and 15 GPa, respectively, are greater than values obtained for monoclinic phase, 160 and 7 GPa, respectively. The zirconia films are well adherent and the toughness of tetragonal zirconia phase is greater than that of monoclinic phase.     

Effects of annealing temperature on the structural and photoluminescence properties of nanocrystalline ZrO2 thin films prepared by sol-gel route

Highly transparent nanocrystalline zirconia thin films were prepared by the sol-gel dip coating technique. XRD pattern of ZrO₂ thin film annealed at 400 °C shows the formation of tetragonal phase with a particle size of 13.6 nm. FT-IR spectra reveal the formation of Zr-O-Zr and the reduction of OH and other functional groups as the temperature increases. The transmittance spectra give an average transmittance greater than 80% in the film of thickness 262 nm. Photoluminescence (PL) spectra give intense band at 391 nm and a broad band centered at 300 nm. The increase of PL intensity with elevation of annealing temperature is related to reduction of OH groups, increase in the crystallinity and reduction in the non-radiative related defects. The luminescence dependence on defects in the film makes it suitable for luminescent oxygen-sensor development. The “Red shift” of excitation peak is related to an increase in the oxygen content of films with annealing temperature. The “Blue shift” of PL spectra originates from the change of stress of the film due to lattice distortion. The defect states in the nanocrystalline zirconia thin films play an important role in the energy transfer process.     

W doped SnO2 growth via sol–gel routes and characterization: Nanocubes

The effects of W doping on the characteristical properties of SnO₂ thin films prepared by sol–gel spin coating method were investigated. The SnO₂ thin films were deposited at various W doping ratios and characterized by various measurements. XRD studies indicated that the undoped and W doped SnO₂ films had cubic and tetragonal phases. The SEM images of WTO thin films showed cubic shaped nanocubes corresponding to cubic phase and the smaller particles corresponding to tetragonal phase were formed on the film surfaces, and their distributions and sizes were dependent on the W doping ratio. EDX spectroscopy analyses showed that the calculated and participated atomic ratios of W/(W + Sn) (at.%) in the starting solution and in the WTO thin films were almost close. It was found that the sheet resistance depended on W doping ratio and 2.0 at.% W doped SnO₂ (WTO) exhibited lowest value of sheet resistance (7.11 × 10³ Ω/cm²).     

MOCVD of zirconium oxide thin films: Synthesis and characterization

The synthesis of thin films of zirconia often produces tetragonal or cubic phases, which are stable at high temperatures, but that can be transformed into the monoclinic form by cooling. In the present study, we report the deposition of thin zirconium dioxide films by metalorganic chemical vapor deposition using zirconium (IV)-acetylacetonate as precursor. Colorless, porous, homogeneous and well adherent ZrO₂ thin films in the cubic phase were obtained within the temperature range going from 873 to 973 K. The deposits presented a preferential orientation towards the (1 1 1) and (2 2 0) planes as the substrate temperature was increased, and a crystal size ranging between 20 and 25 nm. The kinetics is believed to result from film growth involving the deposition and aggregation of nanosized primary particles produced during the CVD process. A mismatch between the experimental results obtained here and the thermodynamic prediction was found, which can be associated with the intrinsic nature of the nanostructured materials, which present a high density of interfaces.     

Growth of oxide thin films for optical gas sensor applications

Tungsten trioxide and titanium dioxide thin films were synthesised by pulsed laser deposition. We used for irradiations of oxide targets an UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser source, at 2 J/cm² incident fluence value. The experiments were performed in low oxygen pressure. The (0 0 1) SiO₂ substrates were heated during the thin film deposition process at temperature values within the 300-500 °C range. The structure and crystalline status of the obtained oxide thin films were investigated by high resolution transmission electron microscopy. Our analyses show that the films are composed by nanoparticles with average diameters from a few to a few tens of nm. Moreover, the films deposited at substrate temperatures higher than 300 °C are crystalline. The tungsten trioxide films consist of a mixture of triclinic and monoclinic phases, while the titanium dioxide films structure corresponds to the tetragonal anatase phase. The oxide films average transmittance in the visible-infrared spectral range is higher than 80%, which makes them suitable for sensor applications.     

Structural and optical properties of YSZ thin films grown by PLD technique

We report on the structural and optical properties of yttria stabilized zirconia (YSZ) thin films grown by pulsed laser deposition (PLD) technique and in situ crystallized at different substrate temperatures (T_s = 400 °C, 500 °C and 600 °C). Yttria-stabilized zirconia target of ∼1 in. diameter (∼95% density) was fabricated by solid state reaction method for thin film deposition by PLD. The YSZ thin films were grown on an optically polished quartz substrates and the deposition time was 30 min for all the films. XRD analysis shows cubic crystalline phase of YSZ films with preferred orientation along 〈1 1 1〉. The surface roughness was determined by AFM for the films deposited at different substrate temperatures. The nano-sized surface roughness is found to increase with the increase of deposition temperatures. For the optical analysis, a UV-vis-NIR spectrophotometer was used and the optical band gap of ∼5.7 eV was calculated from transmittance curves.     

Composition, structure and magnetic properties of sputter deposited Ni-Mn-Ga ferromagnetic shape memory thin films

Polycrystalline Ni-Mn-Ga thin films were deposited by the d.c. magnetron sputtering on well-cleaned substrates of Si(1 0 0) and glass at a constant sputtering power of 36 W. We report the influence of sputtering pressure on the composition, structure and magnetic properties of the sputtered thin films. These films display ferromagnetic behaviour only after annealing at an elevated temperature and a maximum saturation magnetization of 335 emu/cc was obtained for the films investigated. Evolution of martensitic microstructure was observed in the annealed thin films with the increase of sputtering pressure. The thermo-magnetic curves exhibited only magnetic transition in the temperature range of 339-374 K. The thin film deposited at high sputtering pressure of 0.025 mbar was found to be ordered L2₁ austenitic phase.     

Epitaxial growth of YSZ buffer layer for YBa2Cu3O7−δ coated conductor by reel-to-reel pulsed laser deposition

Yttria-stabilized zirconia (YSZ) buffer layers were deposited on CeO₂ buffered biaxially textured Ni-W substrate by reel-to-reel pulsed laser deposition (PLD) for the application of YBa₂Cu₃O_7−δ (YBCO) coated conductor and the influence of substrate temperature and laser energy on their crystallinity and microstructure were studied. YSZ thin films were prepared with substrate temperature ranging from 600 to 800 °C and laser energy ranging from 120 to 350 mJ. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin film structure and surface morphology depend on these parameters. It was found that the YSZ films grown at substrate temperature below 600 °C or laser energy above 300 mJ showed amorphous phase, the (0 0 1) preferred orientation and the crystallinity of the YSZ films were improved with increasing the temperature, but the surface roughness increased simultaneously, the SEM images of YSZ films on CeO₂/NiW tapes showed surface morphologies without micro-cracks. Based on these results, we developed the epitaxial PLD-YSZ buffer layer process at the tape transfer speed of 3-4 m/h by the reel-to-reel system for 100 m class long YBCO tapes.     

Microstructural and compositional studies of liquid-phase deposition derived PbTiO3 thin films on LaNiO3 substrates

PbTiO₃ thin films were successfully deposited on the LaNiO₃ (LNO) substrates by the liquid-phase deposition (LPD) method and post-annealing at various temperatures. The structure, morphology and composition of the films were investigated by some analytical techniques. The as-deposited films are amorphous and composed of densely packed spherical particles. The films with the grain size of 180 nm start to decompose and crystallize into perovskite structure at 450 °C and show a perovskite single phase with tetragonal structure after annealing at 650 °C. X-ray photoelectron spectroscopy (XPS) analysis reveals that the as-deposited film contains fluorine and carbon as major impurities. Fluorine could be completely eliminated by annealing at 650 °C in air.     

Structure and photoluminescence properties of epitaxial SnO2 films grown on α-Al2O3 (0 1 2) by MOCVD

SnO₂ thin films have been successfully deposited on α-Al₂O₃ (0 1 2) substrates by metalorganic chemical vapor deposition (MOCVD) in the temperature range 500-700 °C. The films were epitaxially grown in the tetragonal SnO₂ phase and were (1 0 1) oriented. In-plane orientation relationship [0 1 0]SnO₂||[1 0 0]Al₂O₃ and [1 0 1?]SnO₂||[1? 2? 1]Al₂O₃ was determined between the film and substrate. Photoluminescence (PL) spectra measured at room temperature revealed that the film grown at 700 °C showed an intense ultra-violet (UV) PL peak at 333 nm, which was a band-edge emission peak in SnO₂ films. At a temperature of 13 K, a new broad PL band centered at about 480 nm was observed. The corresponding PL mechanisms are discussed in detail.     

The role of target-to-substrate distance on the DC magnetron sputtered zirconia thin films’ bioactivity

Zirconium dioxide thin films were deposited on 316L-stainless steel type substrates using DC unbalanced magnetron sputtering. The process parameter of this work was the target-to-substrate distance (d_t-s), which was varied from 60 to 120 mm. The crystal structure and surface topography of zirconium dioxide thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The results demonstrate that all of the ZrO₂ thin films are composed monoclinic phase. The film sputtered at short d_t-s (60 mm) shows a rather heterogeneous, uneven surface. The grain size, roughness, and thickness of thin films were decreased by increasing d_t-s. The bioactivity was assessed by investigating the formation of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) on the thin film surface soaked in simulated body fluids (SBF) for 7 days. XRD and scanning electron microscopy (SEM) were used to verify the formation of apatite layers on the samples. Bone-like apatites were formed on the surface of the ZrO₂ thin film in SBF immersion experiments. A nanocrystalline hydroxyapatite (HA) with a particle size of 2-4 μm was deposited. Higher crystallinity of HA on the surface was observed when the distance d_t-s increased to more than 80 mm. Therefore, it seems that a d_t-s greater than 80 mm is an important sputtering condition for inducing HA on the zirconia film.     

Pulsed laser deposited iron fluoride thin films for lithium-ion batteries

Iron fluoride thin films were successfully grown by Pulsed Laser Deposition (PLD), and their physico-chemical properties and electrochemical behaviours were examined by adjusting the deposition conditions, such as the target nature (FeF₂ or FeF₃), the substrate temperature (T_s ≤ 600 °C), the gas pressure (under vacuum or in oxygen atmosphere) and the repetition rates (2 and 10 Hz). Irrespective of the FeF₂ or FeF₃ target nature, iron fluoride thin films, deposited at 600 °C under vacuum, showed X-ray diffraction (XRD) patterns corresponding to the FeF₂ phase. On the other hand, iron fluoride thin films deposited at room temperature (RT) from FeF₂ target were amorphous, whereas the thin films deposited from FeF₃ target consisted of a two-phase mixture of FeF₃ and FeF₂ showing sharp and broad diffraction peaks by XRD, respectively. Their electrochemical behaviour in rechargeable lithium cells was investigated in the 0.05-3.60 V voltage window. Despite a large irreversible capacity on the first discharge, good cycling life was observed up to 30 cycles. Finally, their electrochemical properties were compared to the ones of iron oxide thin films.     

Structural transition and blue emission in textured and highly transparent spray deposited Li doped WO3 thin films

The effect of Li (0-5 wt%) doping on the properties of WO₃ thin films deposited using an automated homemade spray pyrolysis unit is studied. Change in structural and optical properties is observed on doping with Li. The XRD patterns shows that undoped WO₃ film has an orthorhombic phase while the Li (1-5 wt%) doped WO₃ films have tetragonal phase. The SEM and AFM images confirm relatively smooth surface of Li doped WO₃ films compared to undoped WO₃ film. Transmission spectra reveal that the transparency of the Li-doped films is much greater than that of undoped film. From the transmission data, the direct, indirect bandgap and phonon energies were calculated. Room temperature photoluminescence spectra showed pronounced blue emission on doping with Li.     

Correlation between microstructure and optical properties of nano-crystalline TiO2 thin films prepared by sol-gel dip coating

Titanium dioxide thin films have been prepared from tetrabutyl-orthotitanate solution and methanol as a solvent by sol-gel dip coating technique. TiO₂ thin films prepared using a sol-gel process have been analyzed for different annealing temperatures. Structural properties in terms of crystal structure were investigated by Raman spectroscopy. The surface morphology and composition of the films were investigated by atomic force microscopy (AFM). The optical transmittance and reflectance spectra of TiO₂ thin films deposited on silicon substrate were also determined. Spectroscopic ellipsometry study was used to determine the annealing temperature effect on the optical properties and the optical gap of the TiO₂ thin films. The results show that the TiO₂ thin films crystallize in anatase phase between 400 and 800 °C, and into the anatase-rutile phase at 1000 °C, and further into the rutile phase at 1200 °C. We have found that the films consist of titanium dioxide nano-crystals. The AFM surface morphology results indicate that the particle size increases from 5 to 41 nm by increasing the annealing temperature. The TiO₂ thin films have high transparency in the visible range. For annealing temperatures between 1000 and 1400 °C, the transmittance of the films was reduced significantly in the wavelength range of 300-800 nm due to the change of crystallite phase and composition in the films. We have demonstrated as well the decrease of the optical band gap with the increase of the annealing temperature.     

Influence of post-deposition annealing on the structural,optical and electrical properties of Li and Mg co-doped ZnO thin films deposited by sol–gel technique

Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O_Zn), interstitial zinc (Zn_i), interstitial oxygen (O_i) and zinc vacancy (V_Zn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films.     

Low dielectric loss Ba0.6Sr0.4TiO3/MgTiO3 composite thin films prepared by a sol–gel process

The dielectric properties of Ba_0.6Sr_0.4TiO₃ (BST)/MgTiO₃ (MT) composite thin films deposited on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by the sol–gel method were investigated. The X-ray pattern analysis indicates that the thin films exhibit good crystalline quality with perovskite phase and that insertion of MT layer does not obviously affect the phase structure of BST thin films. The characterization of dielectric properties demonstrates that configuration of BST/MT/BST thin films is an effective approach to obtain low dielectric loss and dielectric tunability of BST thin films. At room temperature, the tunability of pure BST60 films and BST/MT (15 nm)/BST composite thin films is 47% and 36%, respectively, at the frequency of 1 MHz with an applied electric field of 400 kV/cm. For BST/MT/BST composite thin films, considerable reduction in the dielectric loss values is observed, which renders them attractive for tunable microwave device applications.     

Deposition and characterization of layer-by-layer sputtered AgGaSe2 thin films

Sputtering technique has been used for the deposition of AgGaSe₂ thin films onto soda-lime glass substrates using sequential layer-by-layer deposition of GaSe and Ag thin films. The analysis of energy dispersive analysis of X-ray (EDXA) indicated a Ga-rich composition for as-grown samples and there was a pronounce effect of post-annealing on chemical composition of AgGaSe₂ thin film. X-ray diffraction (XRD) measurements revealed that Ag metallic phase exists in the amorphous AgGaSe₂ structure up to annealing temperature 450 °C and then the structure turned to the single phase AgGaSe₂ with the preferred orientation along (1 1 2) direction with the annealing temperature at 600 °C. The surface morphology of the samples was analyzed by scanning electron microscopy (SEM) measurements. The structural parameters related to chalcopyrite compounds have been calculated. Optical properties of AgGaSe₂ thin films were studied by carrying out transmittance and reflectance measurements in the wavelength range of 325-1100 nm at room temperature. The absorption coefficient and the band gap values for as-grown and annealed samples were evaluated as 1.55 and 1.77 eV, respectively. The crystal-field and spin-orbit splitting levels were resolved. These levels (2.03 and 2.30 eV) were also detected from the photoresponse measurements almost at the same energy values. As a result of the temperature dependent resistivity and mobility measurements in the temperature range of 100-430 K, it was found that the decrease in mobility and the increase in carrier concentration following to the increasing annealing temperature attributed to the structural defects (tetragonal distortion, vacancies and interstitials).     

Improved dielectric properties of (Pb,Ca)TiO3 thin films prepared by metal-organic decomposition method

(Pb,Ca)TiO₃ (PCT) thin films have been deposited on Pt/Ti/SiO₂/Si substrate by metal-organic decomposition (MOD) technique. The film processing parameters such as drying and annealing temperatures have been optimized to obtain good-quality PCT films. Compositional analysis of the film has been studied by X-ray photoelectron spectroscopy (XPS). The effect of the annealing temperature on the crystalline structure, microstructure and electrical properties have been investigated by X-ray diffraction, atomic force microscopy (AFM) and impedance analyzer, respectively. Amorphous PCT films form at 350 °C and crystallize in the perovskite phase following the isothermal annealing at ?650 °C for 3 h in oxygen ambient. Typical tetragonal structure of the PCT film is evidenced from X-ray diffraction pattern. The grain size in the PCT films increases with an increase in annealing temperature. Significant improvement in the dielectric constant value is observed as compared to other reported work on PCT films. The observed dielectric constant and dissipation factor at 100 kHz for 650 °C annealed PCT films are 308 and 0.015, respectively. The correlation of the film microstructural features and electrical behaviors is described.     

Hydrogenation of Pd-capped Mg thin films prepared by DC magnetron sputtering

Structural and optical properties of pure Mg thin film coated with Pd have been investigated. Pd-capped Mg thin films had been prepared by DC magnetron sputtering. This work presents an ex situ study on hydrogenation and dehydrogenation kinetics of Pd/Mg films at different conditions using XRD, AFM and optical spectrophotometer. We have succeeded to load thin films of Mg to MgH₂ at normal temperature and normal pressure of hydrogen gas. In hydrogenation, α-MgH₂ phase of magnesium hydride was observed in hydrogenated films at 200 °C and γ-MgH₂ at 250 °C respectively. The desorption kinetics in vacuum also revealed the phase transformation α-MgH₂ to γ-MgH₂. A reflectance change was observed in hydrogenated films in comparison of as deposited thin film. Hydrogenated (H loaded) samples were observed partially transparent in comparison of as deposited.