Anisotropic magnetic properties of obliquely deposited Ni films

Magnetic properties of evaporated nickel films, deposited onto 75 m thick 300 H Kapton substrates by evaporation at oblique off-normal angles of incidence, were investigated by SQUID magnetometry. We found that, in the film plane, the direction of easy magnetization lay perpendicular to the incidence plane for films deposited at < 50°. At large s, the easy axis changed to the direction parallel to the incidence plane. The anisotropy, coercivity and squareness of the hysteresis loops increased with an increase in . The results may be qualitatively understood from the presence of an inclined columnar structure with shape anisotropy governing the demagnetization of the magnetic fields.     

Preparation and optical characterization of e-beam deposited cerium oxide films

Cerium oxide films, of 0.3–1 μm thickness, were reactively deposited in the oxygen atmosphere onto quartz plates by the PVD method. An electron gun was used as an evaporation source. Films were characterized with the AFM method, Raman spectroscopy and spectrophotometrically. Optical properties of these films were examined for the wavelength range 0.2–2.5 μm. Films were characterized by high transparency, between 0.38 and 2.5 μm. The complex refractive index, n^*=n − jk, was evaluated. The dispersion characteristics for n(λ) and k(λ) were presented. We found that the refractive index strongly depends on the temperature of substrates (300 K ⩽ T_s ⩽ 673 K) during film deposition. Estimated values of the refractive index (at λ = 0.55 μm) were in the range 1.91–2.34.     

Residual stress in obliquely deposited MgF2 thin films

MgF(2) films with a columnar microstructure are obliquely deposited on glass substrates by resistive heating evaporation. The columnar angles of the films increases with the deposition angle. Anisotropic stress does not develop in the films with tilted columns. The residual stresses in the films depend on the deposition and columnar angles in a columnar microstructure.     

Electrical properties and morphology of obliquely deposited electrochromic WO3 films

A thin film of WO₃ deposited obliquely (θ≈50°) improves the electro-optical response times of an electrochromic display device based on a proton insertion-extraction mechanism. The difference in the response times is attributed to morphological differences as revealed by electron microscope observations. WO₃ films were deposited normally and obliquely, by electron beam gun deposition technique so as to have comparable resistivities in vacuum of about 10^-4 Torr. The resistivity of these films was varied in different ways by exposure to atmospheric air in a controlled manner. Systematic and comparative investigations of the variation in resistivity of these films showed that the resistivity increased in the first stage (10^-4 Torr to atmospheric pressure), attained a maximum value and decreased thereafter in the second stage on long exposure to the atmosphere. The initial increase was explained as the result of oxidation leading to better stoichiometry, limited by the process of uptake of water vapour (hydration). The latter effect was much less for normally deposited film; however, for obliquely deposited film it was much greater and resulted in a decrease in resistivity by three orders of magnitude more than for normally deposited film. The large degree of hydration in an obliquely deposited film was ascribed to its more porous nature, leading to faster electro-optical response times. It was concluded that the microstructure, the stoichiometry and the water content control the electro-optical response of WO₃ films.     

Empirical equations for the principal refractive indices and column angle of obliquely deposited films of tantalum oxide, titanium oxide, and zirconium oxide

Values of the transmittance T(s) and the phaseretardation D were recorded in situ at two angles duringthe growth of thin films of tantalum oxide, titanium oxide, andzirconium oxide for deposition angles theta(nu) in the range40 degrees -70 degrees . Column angles for the same films were determinedex situ from scanning electron microscopy photographs ofdeposition-plane fractures. We show that the experimental columnangles are smaller than the corresponding values predicted by thetangent-rule equation psi = tan(-1)(0.5 tan theta(nu)) and that the experimental values fit a modifiedform of the equation psi = tan(-1)(E(1) tan theta(nu)) where E(1) is less than 0.5. We also show that theprincipal refractive indices are represented well by quadraticfunctions of the deposition angle, for example, n(1)(theta(nu)) = A(0) + A(2) theta(nu)(2).     

Studies of solution deposited cerium oxide thin films on textured Ni-alloy substrates for YBCO superconductor

Cerium oxide (CeO₂) buffer layers play an important role for the development of YBa₂Cu₃O_7−x (YBCO) based superconducting tapes using the rolling assisted biaxially textured substrates (RABiTS) approach. The chemical solution deposition (CSD) approach has been used to grow epitaxial CeO₂ films on textured Ni–3 at.% W alloy substrates with various starting precursors of ceria. Precursors such as cerium acetate, cerium acetylacetonate, cerium 2-ethylhexanoate, cerium nitrate, and cerium trifluoroacetate were prepared in suitable solvents. The optimum growth conditions for these cerium precursors were Ar–4% H₂ gas processing atmosphere, solution concentration levels of 0.2–0.5 M, a dwell time of 15 min, and a process temperature range of 1050–1150 °C. X-ray diffraction, AFM, SEM, and optical microscopy were used to characterize the CeO₂ films. Highly textured CeO₂ layers were obtained on Ni–W substrates with both cerium acetate and cerium acetylacetonate as starting precursors. YBCO films with a J_c of 1.5 MA/cm² were obtained on cerium acetylacetonate-based CeO₂ films with sputtered YSZ and CeO₂ cap layers.     

TEM observation of gold nanoparticles deposited on cerium oxide

The structure of Au nanoparticles supported on CeO₂ using the deposition precipitation method was observed using a transmission electron microscope (TEM). The shape of Au nanoparticles and the fine structure of contact interface between the Au nanoparticles and CeO₂ supports were carefully examined. It was found that there was a preferential orientation relationship between Au nanoparticles and the CeO₂ support. It was also observed that small and thin Au nanoparticles disappeared during TEM observation, shrinking layer by layer down to a mono-atomic layer.     

Stripe domains in NiCo obliquely deposited films potentialcandidates for information storage

An investigation is conducted of strong and weak stripe domains which appear in obliquely deposited NiCo films above a critical thickness for various compositions and angles of deposition in order to test the ability of such structures for information storage. It is shown that a modulation of this structure is possible, especially for the applied field perpendicular to the stripe direction. Materials with higher coercivity are needed for application. For this purpose it is desirable to modify the preparation conditions (e.g. use of Cr sublayer), which could result in a less continuous media. The question is whether in such a media the stripe domains would still exist. New ideas developed in the course of this work are the opportunity to use weak stripe domains of alternate polarity for Ni-rich alloys and the ability of the isolated bubblelike domain obtained at high field for cobalt-rich films to be used as information storage     

Thermal expansion coefficients of obliquely deposited MgF2 thin films and their intrinsic stress

This study elucidates the effects of columnar angles and deposition angles on the thermal expansion coefficients and intrinsic stress behaviors of MgF2 films with columnar microstructures. The behaviors associated with temperature-dependent stresses in the MgF2 films are measured using a phase-shifting Twyman-Green interferometer with a heating stage and the application of a phase reduction algorithm. The thermal expansion coefficients of MgF2 films at various columnar angles were larger than those of glass substrates. The intrinsic stress in the MgF2 films with columnar microstructures was compressive, while the thermal stress was tensile. The thermal expansion coefficients of MgF2 films with columnar microstructures and their intrinsic stress evidently depended on the deposition angle and the columnar angle.     

Enhanced catalytic activity of nanostructured cerium oxide films

We study the catalytic activity and structure, density and morphology of nanostructured ceria (CeO_2−x, 0.15<x<0.05, grain size 4–28 nm) films using X-ray diffraction (XRD) and reflectivity (XRR). The voids content of the films was determined by XRR and was found to vary between 7% and 40%. The catalytic efficiency of the films is investigated using temperature programmed reaction (TPR) and monitoring the oxidation products. The TPR results are correlated with the density and grain size of the CeO_2−x films and show that smaller grain size may reduce the activation temperature of C combustion as low as ∼200 °C.     

Crystallographic texture and morphology of obliquely deposited Co-Cr magnetic thin films on flexible polymeric substrates

Thin magnetic films of Co-Cr have been obliquely deposited by evaporation and sputtering at a fixed incidence angle of 45° using tilted sample holders. The layers exhibit a columnar microstructure with the column axes at an angle in the range 15°–35° with respect to the film normal. The tilt angle strongly depends on the type of substrate used, the deposition temperature and the substrate pretreatment. The c axes of the h.c.p. crystallites always coincide with the column axes. A Ti underlayer forces the columns and crystallites of the Co-Cr film to grow vertically to the film plane despite the oblique incidence deposition process.     

Electrochromism of the electroless deposited cuprous oxide films

Thin cuprous oxide films were prepared by a low cost, chemical deposition (electroless) method onto glass substrates pre-coated with fluorine doped tin oxide. The X-ray diffraction pattern confirmed the Cu₂O composition of the films. Visible transmittance spectra of the cuprous oxide films were studied for the as-prepared, colored and bleached films. The cyclic voltammetry study showed that those films exhibited cathode coloring electrochromism, i.e. the films showed change of color from yellowish to black upon application of an electric field. The transmittance across the films for laser light of 670 nm was found to change due to the voltage change for about 50%. The coloration memory of those films was also studied during 6 h, ex-situ. The coloration efficiency at 670 nm was calculated to be 37 cm²/C.     

Properties of spray deposited niobium oxide thin films

Niobium Oxide (Nb₂O₅) thin films were deposited on the glass substrates, using spray pyrolysis technique. During deposition the preparative parameters like nozzle to substrate distance, spray rate, concentration of the sprayed solution were kept constant at optimized values. The effect of substrate (deposition) temperature (varied between 250 to 450°C) and post annealing treatment (at temperature 500°C) on the structural, optical and electrical properties of thin films were studied. Using scanning electron microscopy and X-ray diffraction technique morphological and structural characterizations of the films were carried out. For optical and electrical properties of thin films, optical absorption and two probe electrical resistivity techniques were used. It has been observed that with increase in the substrate temperature films become micro or polycrystalline. Annealed films exhibit higher crystallinity. Other parameters like thickness, electrical resistivity and band gap energy value decrease with increase in substrate temperature.     

Enhanced electrochromism in cerium doped molybdenum oxide thin films

Cerium (5-15% by weight) doped molybdenum oxide thin films have been prepared on FTO coated glass substrate at 250 °C using sol-gel dip coating method. The structural and morphological changes were observed with the help of XRD, SEM and EDS analysis. The amorphous structure of the Ce doped samples, favours easy intercalation and deintercalation processes. Mo oxide films with 10 wt.% of Ce exhibit maximum anodic diffusion coefficient of 24.99 × 10⁻¹¹ cm²/s and the change in optical transmittance of (ΔT at 550 nm) of 79.28% between coloured and bleached state with the optical density of (ΔOD) 1.15.     

Optical and electrical properties of obliquely deposited a-GeSe<Subscript>2</Subscript> films

Oblique deposition and exposure to photons of energy greater than the bandgap have a marked effect on the structure and consequently on electrical and optical properties of amorphous chalcogenides. This paper presents a detailed study of photoinduced effect and oblique deposition effect on electrical and optical properties of a-GeSe₂ films deposited at different angles (0°–80°). The indirect-optical bandgap energy (2.18 eV) was found to be independent of angle of incidence. The spectral response of refractive index and extinction coefficient has been determined in the wavelength range of 0.6–1 μm using the transmission spectra. Refractive index decreases with the increase in angle of incidence. The value of refractive index was observed to be 2.28 for 0° and 2.00 for 80° films at 0.646 μm. An increase in bandgap was also observed on exposure to the UV light for ∼120 min. The change in bandgap became more significant with the increase in angle of incidence (∼ 2.3% for 0° and ∼10.6% for 80°). The temperature dependence of conductivity along with time dependence and spectral response of photocurrent has also been investigated.