Properties of ion assisted deposited titania films

Thin films of titanium dioxide have been deposited using ion assisted deposition with oxygen ions in the energy range 100�500 eV and current densities up to 100 ?A/cm2. It has been observed that the refractive index of the films increases up to 300 eV and the extinction coefficient increased only nominally up to 300 eV. Optical band gap calculations have shown a strong dependence of the gap on the energy of incident ions. Beyond a critical energy and current density of the ions the refractive index and extinction coefficient of the films start deteriorating. It has also been found that beyond the critical values the optical band gap value decreases. The maximum refractive index obtained was 2.49 at an energy of 300 eV and 50 ?A/cm2 current density. Post?deposition annealing of the films at 500?°C resulted in a slight increase in refractive index without affecting the extinction coefficient. X?ray diffraction studies revealed a monophasic anatase structure in these films. ?

Study of electrical properties of pulsed excimer laser deposited strontium titanate films

Polycrystalline SrTiO3 films were prepared by pulsed excimer laser ablation on Si and Pt coated Si substrates. Several growth parameters were varied including ablation fluence, pressure, and substrate temperature. The structural studies indicated the presence of [100] and [110] oriented growth after annealing by rapid thermal annealing at 600-degrees-C for 60 s. Deposition at either lower pressures or at higher energy densities encouraged film growth with slightly preferred orientation. The scanning electron microscopy studies showed the absence of any significant particulates on the film surface. Dielectric studies indicated a dielectric constant of 225, a capacitance density of 3.2 fF/mum2, and a charge density of 40 fC/mum for films of 1000 nm thick. The dc conductivity studies on these films suggested a bulk limited space charge conduction in the high field regime, while the low electric fields induced an ohmic conduction. Brief time dependent dielectric breakdown studies on these films, under a field of 250 kV/cm for 2 h, did not exhibit any breakdown, indicating good dielectric strength.

Metal-insulator transitions in metal clusters: a high-energy spectroscopy study of palladium and silver clusters

Bremsstrahlung isochromat spectroscopy (BIS) along with ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) has been employed to investigate the electron states of Pd and Ag deposited on amorphous graphite at different coverages. The metal core level binding energies increase with decreasing cluster size while the UPS valence bands show a decrease in the 4d states at E(F) accompanied by a shift in the intensity maximum to higher binding energies. BIS measurements show the emergence of new states closer to E(F) with increase in the cluster size. It is pointed out that the observed spectral shifts cannot be accounted for by final-state effects alone and that initial-state effects have a significant role. It therefore appears that a decrease in cluster size is accompanied by a metal-insulator transition.

Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 x 10(-2) Omega cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide. (C) 2011 Elsevier B.V. All rights reserved.

Optical and structural properties of reactive ion beam sputter deposited CeO2 films

Optical and structural properties of reactive ion beam sputter deposited CeO2 films as a function of oxygen partial pressures (P-O2) and substrate temperatures (T-s) have been investigated. The films deposited at ambient temperature with P-O2 of 0.01 Pa have shown a refractive index of 2.36 which increased to 2.44 at 400 degrees C. Refractive index and extinction coefficient are sensitive up to a T-s of similar to 200 degrees C. Raman spectroscopy and X-ray diffraction (XRD) have been used to characterise the structural properties. A preferential orientation of (220) was observed up to a T-s of 200 degrees C and it changed to (200) at 400 degrees C: and above. Raman line broadening, peak shift and XRD broadening indicate the formation of nanocrystalline phase for the films deposited up to a substrate temperature of 300 degrees C. However, crystallinity of the films were better for T-s values above 300 degrees C. In general both optical and structural properties were unusual compared to the films deposited by conventional electron beam evaporation, but were similar in some aspects to those deposited by ion-assisted deposition. Apart from thermal effects, this behavior is also attributed to the bombardment of backscattered ions/neutrals on the growing film as well as the higher kinetic energy of the condensing species, together resulting in increased packing density. (C) 1997 Elsevier Science S.A.

Electrochemical studies of polyaniline in a gel polymer electrolyte - High energy and high power characteristics of a solid-state redox supercapacitor

Studies on redox supercapacitors employing electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In the present study, polyaniline (PANI) has been potentiodynamically deposited on stainless steel substrate and characterized in a gel polymer electrolyte (GPE). Use of the GPE facilitates a voltage limit of the capacitor to 1 V, instead of 0.75 V in aqueous electrolytes. From charge-discharge studies of the solid-state PANI capacitors, a specific capacitance of 250 F g(-1) has been obtained at a specific power of 7.5 kW kg(-1) of PANI. The values of specific capacitance and specific power are considerably higher than those reported in the literature. High energy and high power characteristics of the PANI are presented. (C) 2002 The Electrochemical Society.

Phase transformation and semiconductor-metal transition in thin films of VO2 deposited by low-pressure metalorganic chemical vapor deposition

Thin films of the semiconducting, monoclinic vanadium dioxide, VO2(M) have been prepared on ordinary glass by two methods: directly by low-pressure metalorganic chemical vapor deposition (MOCVD), and by argon-annealing films of the VO2(B) phase deposited by MOCVD. The composition and microstructure of the films have been examined by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Films made predominantly of either the B or the M phase, as deposited, can only be obtained over a narrow range of deposition temperatures. At the lower end of this temperature range, the as-deposited films are strongly oriented, although the substrate is glass. This can be understood from the drive to minimize surface energy. Films of the B phase have a platelet morphology, which leads to an unusual microstructure at the lower-deposition temperatures. Those grown at similar to370 degreesC convert to the metallic, rutile (R) phase when annealed at 550 degreesC, whereas those deposited at 420 degreesC transform to the R phase only at 580 degreesC. (When cooled to room temperature, the annealed films convert reversibly from the R phase to the M phase.) Electron microscopy shows that annealing leads to disintegration of the single crystalline VO2(B) platelets into small crystallites of VO2(R), although the platelet morphology is retained. When the annealing temperature is relatively low, these crystallites are nanometer sized. At a higher-annealing temperature, the transformation leads to well-connected and similarly oriented large grains of VO2(R), enveloped in the original platelet. The semiconductor-metal transition near 68 degreesC leads to a large jump in resistivity in all the VO2(M) films, nearly as large as in epitaxial films on single-crystal substrates. When the annealed films contain well-connected large grains, the transition is very sharp. Even when preferred orientation is present, the transition is not as sharp in as-deposited VO2(M), because the crystallites are not densely packed as in annealed VO2(B). However, the high degree of orientation in these films leads to a narrow temperature hysteresis. (C) 2002 American Institute of Physics.

Stresses in Ion Assisted Deposited Oxide Thih Films

Thin films of Ceria, Titania and Ziroonia have been prepared using Ion Assisted Deposition(IAD). The energy of ions was varied between 0 and 1 keV and current densities up to 220 μA/cm were used. It was found that the stress behaviour is dependent on ion species, i.e. Argon or Oxygen, ion energy and current density and substrate temperature apart from the material. While oeria files showed tensile stresses under the influence of argon ion bombardment at ambient temperature, they showed a sharp transition from tensile to compressive stress with increase in substrate temperature. When bombarded with oxygen ions they showed a transition from tensile to compressive stress with increase in energy. The titania films deposited with oxygen ions, on the other hand showed purely tensile stresses. Zirconia films deposited with oxygen ions, however, showed a transition from tensile to compressive stress.

Electrical properties of ferroelectric YMnO3 films deposited on n-type Si(111) substrates

YMnO3 thin films were grown on an n-type Si substrate by nebulized spray pyrolysis in the metal-ferroelectric-semiconductor (MFS) configuration. The capacitance-voltage characteristics of the film in the MFS structure exhibit hysteretic behaviour consistent with the polarization charge switching direction, with the memory window decreasing with increase in temperature. The density of the interface states decreases with increasing annealing temperature. Mapping of the silicon energy band gap with the interface states has been carried out. The leakage current, measured in the accumulation region, is lower in well-crystallized thin films and obeys a space-charge limited conduction mechanism. The calculated activation energy from the dc leakage current characteristics of the Arrhenius plot reveals that the activation energy corresponds to oxygen vacancy motion.

Enhancement of charge and energy storage in sol-gel derived pure and La-modified PbZrO3 thin films

Antiferroelectric lanthanum-modified PbZrO3 thin films with La contents between 0 and 6 at. % have been deposited on Pt(111)/Ti/SiO2/Si substrate by sol-gel route. On the extent of La-modification, maximum polarization (Pmax) and recoverable energy density (W) have been enhanced followed by their subsequent reduction. A maximum Pmax ( ∼ 0.54 C/m2 at ∼ 60 MV/m) as well as a maximum W ( ∼ 14.9 J/cc at ∼ 60 MV/m) have been achieved on 5% La modification. Both Pmax and W have been found to be strongly dependent on La-induced crystallographic orientations.

Influence of substrate temperature on the properties of oxygen‐ion‐assisted deposited CeO2 films

Substrate temperature and ion bombardment during deposition have been observed to modify significantly the optical and structural properties of dielectric thin films. Single‐layer films of CeO2 have been deposited by electron beam evaporation with simultaneous oxygen‐ion bombardment using a Kaufman broad beam ion source and maintaining the substrates at elevated temperature. A systematic study has been made on the influence of (a) substrate temperature in the range ambient to 300 °C, (b) ion energy in the range 300–700 eV, and (c) ion current density 100–220 μA/cm2 on optical properties such as refractive index, extinction coefficient, inhomogeneity, packing density, and structural properties. The refractive index increased with in increase in substrate temperature: ion energy up to 600 eV and ion current density. Homogeneous, absorption free and high index (2.48) films have been obtained at 600 eV, 220 μA/cm2 and at substrate temperature of 300 °C. The packing density of the films was observed to be unity for the same deposition conditions. Substrate temperature with simultaneous ion bombardment modified the structure of the films from highly ordered to fine grain structure.

Leakage current behavior in pulsed laser deposited Ba(Zr0.05Ti0.95)O3 thin films

Barium zirconium titanate [Ba(Zr0.05Ti0.95)O3, BZT] thin films were prepared by pulsed laser ablation technique and dc leakage current conduction behavior was extensively studied. The dc leakage behavior study is essential, as it leads to degradation of the data storage devices. The current-voltage (I-V) of the thin films showed an Ohmic behavior for the electric field strength lower than 7.5 MV/m. Nonlinearity in the current density-voltage (J-V) behavior has been observed at an electric field above 7.5 MV/m. Different conduction mechanisms have been thought to be responsible for the overall I-V characteristics of BZT thin films. The J-V behavior of BZT thin films was found to follow Lampert’s theory of space charge limited conduction similar to what is observed in an insulator with charge trapping moiety. The Ohmic and trap filled limited regions have been explicitly observed in the J-V curves, where the saturation prevailed after a voltage of 6.5 V referring the onset of a trap-free square region. Two different activation energy values of 1.155 and 0.325 eV corresponding to two different regions have been observed in the Arrhenius plot, which was attributed to two different types of trap levels present in the film, namely, deep and shallow traps.

Hypersonic wave drag reduction in re-entry capsules using concentrated energy deposition

Experiments are carried out in a shock tunnel at a nominal Mach number of 5.75 in order to study the effect of concentrated energy deposition on the drag force experienced by a 120° blunt cone. Electrical energy was deposited along the stagnation streamline of the model using a high voltage DC discharge circuit (1.5 – 3.5KW) and the drag force was measured by a single component accelerometer balance. Numerical simulations were also carried complimenting the experiments. These simulations showed a substantial drag reduction (20% ~ 65%) whereas the experiments show no appreciable reduction in drag

The irradiation of pure CH3OH and 1:1 mixture of NH3:CH3OH ices at 30 K using low energy electrons

The results of an experimental investigation of 1 keV electron irradiation of ices (deposited at 30 K) of (i) pure methanol and (ii) of a 1:1 mixture of NH3:CH3OH are reported. Molecular products formed within the ice were detected and monitored using FTIR spectroscopy. The products observed were methyl formate (H3COHCO), methane (CH4), hydroxymethyl (CH2OH), formamide (HCONH2), formic acid (HCOOH), formaldehyde (H2CO), formyl radical (HCO), cyanate ion (OCN-), isocyanic acid (HNCO), carbon monoxide (CO) and carbon dioxide (CO2). The consequences of these results for prebiotic chemistry in the interstellar medium and star forming regions are discussed. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.

Nanoscale compositional analysis of NiTi shape memory alloy films deposited by DC magnetron sputtering

The formation of surface oxide layer as well as compositional changes along the thickness for NiTi shape memory alloy thin films deposited by direct current magnetron sputtering at substrate temperature of 300 degrees C in the as-deposited condition as well as in the postannealed (at 600 degrees C) condition have been thoroughly studied by using secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, and scanning transmission electron microscopy-energy dispersive x-ray spectroscopy techniques. Formation of titanium oxide (predominantly titanium dioxide) layer was observed in both as-deposited and postannealed NiTi films, although the oxide layer was much thinner (8 nm) in as-deposited condition. The depletion of Ti and enrichment of Ni below the oxide layer in postannealed films also resulted in the formation of a graded microstructure consisting of titanium oxide, Ni3Ti, and B2 NiTi. A uniform composition of B2 NiTi was obtained in the postannealed film only below a depth of 200-250 nm from the surface. Postannealed film also exhibited formation of a ternary silicide (NixTiySi) at the film-substrate interface, whereas no silicide was seen in the as-deposited film. The formation of silicide also caused a depletion of Ni in the film in a region similar to 250-300 nm just above the film substrate interface. (C) 2013 American Vacuum Society.