Transport Properties Of Films Research Articles

Tunneling measurements of fluctuation effects near the superconductor to insulator transition

We present measurements of the temperature dependence of the tunneling density of states near the Fermi energy, G 0 (T), and resistive transitions, R(T), of ultrathin PbBi films. Both R(T) and G 0 (T) broaden substantially near the superconductor to insulator transition (SIT). The broadening in R(T) is not affected by the proximity of a ground plane suggesting that long range Coulomb interactions are not important to the SIT. The results suggest that the transport properties of films near the SIT are influenced by fluctuations in both the phase and the amplitude of the order parameter. We discuss the data in terms of recent theories of the superconducting transition in low superfluid density systems.

Influence of the deposition parameters on the structural and transport properties of YBaCuO thin films prepared by pulsed laser deposition

YBCO superconducting films were deposited by (XeCl=308 nm) pulsed laser deposition (PLD) on (100)-oriented SrTiO 3, MgO and Si single crystal substrates. Control of the YBCO thin film epitaxial growth and microstructure quality are important factors for superconducting electronic device applications. In this aim, we studied the influence of the oxygen pressure during the growth, the distance between target–substrate and substrate structure on the degree of structural orientation and surface quality of the films. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were used to make comparative studies of microstructure with transport properties of the films.

Transport properties of layered cuprate films with multiple fluorite-type blocks (Pb-32 n2 phase) and of Pb-3212 phase films

A layered cuprate having a multiple fluorite-type block, (Pb 2Cu)Sr 2(Eu,Ce) 5Cu 2O y , and a superconductor, (Pb 2Cu)Sr 2Ca 0.5Eu 0.5Cu 2O 8+δ (Pb-3212 phase), have been grown by the molecular beam epitaxy technique. Crystal structure and transport properties of the films have been investigated with special attention to the oxygenation conditions during the growth and during the cooling process after growth. Different layered cuprates were obtained depending on the former conditions, while the latter conditions affected the transport properties.

Post-annealing effect on transport properties of CoPd alloy films

A series of Co 100− x Pd x (χ=25–85 at.% Pd) alloy films were made by the vapour deposition method. The film thickness t was set at 400 Å. Some of the films were isothermally annealed for 1 h at various temperatures T u in the range 240–400 °C. The average grain size D of each film was checked by an X-ray diffractometer and an atomic force microscope. The zero-field resistivity ρ 0, and the anisotropic magnetoresistance ratio Δρ ρ 0 were measured for each film at room temperature. We have obtained data for D, ρ 0, and Δρ ρ 0 as a function of T u. It is concluded that the 1 h anneals of these films can be divided into two stages: the recovery and the grain growth. It is also found that although the average grain size is enlarged continuously by increasing T u, the transport properties of the films for a fixed thickness approach their saturated values long before the grains stop to grow.

Superconducting properties of YBaCuO thin films obtained by thermocycling

YBaCuO films fabricated by laser ablation method were subjected to a thermocycling. Our investigations showed that the degradation process of the current transport properties of films is accompanied by the appearance of a maximum on the curve of the critical current density, depending on the number of thermocycles. This effect manifests itself most strongly in the films with degraded superconducting properties. The critical temperature and the transition width vary only slightly in this case.

Gas transport through integral‐asymmetric membranes: A comparison to isotropic film transport properties

AbstractPressure‐normalized gas fluxes for defect‐free integral‐asymmetric membranes prepared according to a dry/wet phase inversion process were measured as a function of temperature and pressure and compared to measurements on thick isotropic films. Asymmetric membranes were prepared from polysulfone, polycarbonate, and poly(ester carbonate). The activation energies of permeation for O2 and N2 in the range of 25–55°C were higher for the asymmetric polysulfone membranes than for a thick isotropic film. O2/N2 selectivities of the asymmetric membranes are higher than those for isotropic films. The asymmetric membranes did not show the typical dualmode behavior for the CO2 flux as a function of pressure as determined for thick films. Differences in the free volume and its distribution in the ultrathin skin layer of the asymmetric membranes compared to isotropic films may be responsible for these results. © 1993 John Wiley & Sons, Inc.

An investigation into the mechanical and transport properties of aqueous latex films: a new hypothesis for the film-forming mechanism of aqueous dispersion system.

The effects of plasticizer, physical aging, and film-forming temperature on the mechanical and transport properties of films formed from aqueous dispersions of ethylcellulose latex were investigated. The water vapor permeability of latex films was found to decrease with diethyl phthalate to a minimum value and then to increase with diethyl phthalate at higher concentrations. Because of the decrease in free volume and the further coalescence of particles of latex polymer films in the physical aging range, the creep compliance of latex films decreased with physical aging time. Within 60 to 100 degrees C, the film-forming temperature was found to have no effect on the mechanical and transport properties of Aquacoat films. However, since many pinholes formed in the latex films when the film-forming temperature was above 100 degrees C, the water vapor permeability of latex films was higher than that of latex films formed between 60 and 100 degrees C. The formation of films from aqueous latex dispersions is suggested to proceed gradually from the top to the bottom of the latex dispersion in this study.

A method for the determination of the thermal transport properties of submicron-thick dielectric films with the use of an analytical expression

In this article we describe a method for the determination of the thermal transport properties of submicron-thick dielectric films with the use of an analytical expression for metal line temperature change. A microfabricated metal line was placed on the dielectric film to be tested, and the film was etched to the same width as the metal line. Since the heat flow from the metal line to the dielectric film becomes one dimensional in such a structure, the necessary calculations are simplified sufficiently for an analytical expression for temperature change in the metal line to be obtained. With this expression, it is possible to understand the relationship between the thermal transport properties of the film and temperature change in the metal line. The study show that reducing the thickness of the metal line is crucial to permitting measurements regarding the heat capacity of the film. With the use of an 84 nm thick aluminium line, the thermal conductivity and heat capacity of 294 nm thick ZnSSiO 2 were determined to be respectively 0.58 W m −1 K −1 and 2.6 × 10 6 J m −3 K −1.

Effect of oxygen pressure on properties of BiSrCaCuO thin films grown by laser deposition

We present the results of a study of the effect of oxygen pressure on the properties of BiSrCaCuO (BSCCO) thin films grown by laser ablation. Films of the same phase, which were deposited at different oxygen pressures, show quite different properties. Here, we define the phases of BSCCO films from their c-axis lattice constants calculated from the 2θ X-ray diffraction angle of the 002 peak. In-situ films deposited at high oxygen pressure (≥ 100 mTorr) show higher critical temperatures and critical current densities. However, by post annealing, transport properties of films deposited at low oxygen pressure (several 10 mTorr) are improved significantly. With respect to this difference, the results of X-ray diffraction and energy dispersive X-ray spectroscopy studies, and Hall effect measurements are discussed.

Transport properties of vacuum deposited indium-antimony alloy films

In xSb (1−x) (0<x<1) alloy films have been grown by flash evaporation technique onto glass substrates in a vacuum of 10 −5 torr. The effect of composition on the electron transport properties of films is reported. It has been observed that films with composition around x = 0.6 show minimum resistivity, maximum carrier mobility and more order in structure. The charge carriers appear to be holes for all compositions except x = 0.3.

Conducting polypyrrole films containing [Ru(2,2'-bipyridine) 2(3-{pyrrol-1-ylmethyl} pyridine)Cl] +: Electrochemistry, spectroelectrochemistry, electronic conductivity, and ionic conductivity

Electronically conducting copolymer films of pyrrole and [Ru(bp) 2(pmp)Cl] + (bp = 2,2'-bipyridine, pmp = 3-(pyrrol-1-ylmethyl)pyridine) have been prepared by anodic polymerization. Voltammograms of these copolymer films exhibit reversible electrochemistry of the Ru complex at a formal potential of +0.82 5 V vs. SSCE, superimposed on a broad flat wave due to the polypyrrole backbone. The electrochemistry of the polypyrrole backbone is similar to that of polypyrrole films grown under similar conditions. The Ru content of the films, which has been estimated by cyclic voltammetry and by visible region spectroelectrochemistry, can be increased both by increasing the [Ru(bp) 2(pmp)Cl] +: pyrrole ratio in the polymerization solution and by increasing the polymerization potential. The electron and ion transport properties of films prepared under a variety of conditions have been measured in order to assess the potential value of copolymers of this type in electrocatalysis. The incorporation of the Ru complex into polypyrrole increases its ionic conductivity but decreases its electronic conductivity. However, the conditions required for incorporating a significant quantity of the Ru complex, produce a polypyrrole matrix with less than optimal transport properties.

Electrical and thermoelectrical properties of Zn3P2 films grown by the hot wall epitaxy technique

Zinc phosphide thin films were prepared by the hot wall epitaxy technique. The transport properties of films grown at different substrate temperatures from 200 to 350 °C were studied from room temperature up to 600 °C. Films were also grown in pure oxygen and nitrogen atmospheres at a pressure of 10−6 Torr, and the conductivity of the films was measured in situ. Thermoelectric measurements on films grown on mica were also done at various temperatures ranging from 300 to 800 K. Arrhenius plots of electrical conductivity yielded an electronic band gap of 1.32 eV and acceptor levels of 0.21 and 0.49 eV corresponding to interstitial phosphorus and absorbed oxygen levels, respectively. Variation of growth temperature, pressure, and nature of the gas present inside the chamber during growth are shown to result in a range of electrical resistivities and to be responsible for changes in carrier concentration. The sign of Seebeck coefficient was found to change from positive to negative at a temperature of 240 °C for a film grown on mica at a substrate temperature of 350 °C.

Electrical transport, optical properties, and structure of TiN films synthesized by low-energy ion assisted deposition

Thin films of TiN, covering a narrow range around stoichiometric composition, were synthesized by low-energy ion assisted growth at deposition temperatures TD=100, 300, 500, and 700 °C. The deposition apparatus consisted of an unbalanced dc magnetron sputter source which allowed high rate deposition from a titanium target with simultaneous bombardment of the growing film by a beam of mixed Ar+ and N+2 ion species at an ion-to-condensing atom arrival rate ratio of five. For each deposition temperature, films were prepared at various ion energies in the range Ei =2–100 eV. The presence of reactive N+2 ions and the effects of ion bombardment facilitate increased incorporation of nitrogen and decrease the overall defect density in the structure of TiN. Electrical transport properties of films were investigated by measurements of the temperature dependence of resistivity ρ(T) in the range T=4–300 K, and superconducting transition temperature Tc. These measurements were complemented by measurement of optical reflectance, x-ray diffraction, and scanning electron microscopy investigations to determine the structure and composition of films. Collectively the film properties have a strong dependence on ion energy and deposition temperature. Films deposited at optimum conditions (TD =500 °C and Ei =30–50 eV) possess a high degree of crystalline perfection with a strong (200) texture and a high optical reflectance (82% at λ=800 nm). These properties correlate with the following optimum electrical properties: room-temperature resistivity ρ300∼26 μΩ cm, resistivity ratio RR=2.13, temperature coefficient of resistivity TCR=2.43×10−3 K−1, and Tc =5.35 K. These results represent the best results yet reported for microcrystalline TiN films. The temperature dependence of resistivity has a normal-metal behavior and it obeys Matthiessen’s rule. The phonon contribution to resistivity at room temperature, ρthermal, is about 14 μΩ cm and is in agreement with that of single-crystal TiN. As the disorder in the structure of TiN increases, TCR is found to decrease and zero TCR is predicted for limiting values of resistivity ρ300=300–400 μΩ cm.

Electron localisation in nonstoichiometric films of aluminium nitride produced by reactive sputtering

Thin films of nonstoichiometric aluminium nitride of various compositions (AINx, with 0<or=x<or=1) were fabricated using planar magnetron sputtering. Three different transport regimes have been observed. The transport properties of films with room temperature conductivity above 104 Omega -1 cm-1 are found to be well described by the semi-classical Boltzmann equations. In films with room temperature conductivity between 104 Omega -1 cm-1 and 100 Omega -1 cm-1 the conductivity is found to be dominated by electron localisation effects while the thermoelectric power remains free-electron like. This is seen as indicating that the density of states remains unaffected as localisation effects set in. The temperature dependence of films with room temperature conductivity between 0.5 Omega -1 cm-1 and 10-3 Omega -1 cm-1 is found to be well described by the equation sigma (T)= sigma 0T-pexp(T0/T)-s, with s=1/4, thus suggesting that the conduction proceeds by variable-range hopping. Limits on the value of p are established and are used to show that only one theory of variable-range-hopping is consistent with such a temperature dependence.

Electrical properties of evaporated silicon films

Silicon films were deposited by electron beam evaporation onto titanium-coated stainless steel substrates held at temperatures T s ranging between 300 and 800°C. Doping was achieved by the in situ co-evaporation of antimony or aluminum. The a.c. and d.c. conductivities were measured as functions of the temperature in sandwich structures with aluminium contacts. P-n junctions and SnO 2/nSi heterojunctions were also fabricated. Conduction in amorphous silicon (a-Si) samples is interpreted as due to hopping at the Fermi level E F , the gap state density at E F being between 10 19 and 10 20 cm −3 eV −1. With regard to the electrical properties two different types of behaviour are found in microcrystalline silicon depending on the substrate temperature T s . Films deposited at 400° C < T s < 500° C are similar to a-Si. The transport properties of films deposited at T s > 500° C are explained using a model involving a mixture of amorphous and crystalline components. The electrical characteristics of the p-n junctions are consistent with this model.

Weak localization in indium oxide films

We have observed anomalous transport properties in films of conducting indium oxide in both three and two dimensions. It is found that the interplay between d, l and l in ( T) (the film's thickness, elastic and inelastic mean-free-paths, respectively) determines the system's dimensionality and the nature of the transport properties. In a previous study it was shown that experimental results on 2D samples of this material are adequately accounted for by modern localization theories. This conclusion is now being extended to the 3D range as well. At the same time we find strong evidence for the relevance of electron-electron interaction in both 2D and 3D samples below ~100K. In particular, the 3D → 2D crossover temperature as a function of d and the low-field negative magnetoresistance results agree quantitatively with a τ in ~ h ̵ /k BT law for the temperature variation of the inelastic relaxation time.

Optical and thermal properties of BeO thin films prepared by reactive ionized-cluster beam technique

Preparation of BeO thin films is successfully achieved by the reactive ionized-cluster beam technique developed by the authors. Transparent BeO films with the c-axis preferential orientation which is peculiar to a hexagonal structure are obtained on glass substrates, and single-crystal epitaxial films are formed on sapphire substrates at low substrate temperatures up to 400 °C. Optical and thermal transport properties of films are investigated in detail. A strong reststrahlen reflection peak is observed in the vicinity of wavelength 13.5 μm, from which the frequencies of the transverse and longitudinal vibration modes are determined. Anisotropic lattice thermal conductivities parallel and perpendicular to the c axis of the films are measured, and the values of κ∥ph ?2.6 W/cm deg and κ⊥ph ?0.6 W/cm deg at 300 K are obtained. It is also shown that the thermal conductivities of BeO films are proportional to T−2 below Debye temperature ϑD?1053 K of this material.

Electrical transport properties of copper-doped tellurium films

Polycrystalline films of copper-doped tellurium were grown by co-evaporating copper and tellurium from separate boats. Measurements were made of the electrical transport properties of these films. It was observed that the addition of copper decreases the activation energies of both the conductivity and the mobility. The low temperature conduction data were interpreted on the basis of a variable range hopping mechanism while the high temperature data indicate the dominance of the grain boundary scattering mechanism.

Structural and transport properties of CdS films grown on Si substrates

Epitaxial films of CdS have been grown on thermally cleaned single-crystal Si substrates. The films were grown by electron-beam evaporation of CdS powder in a UHV system. X-ray Laue and transmission electron diffraction techniques have been used to examine the structure of the films. It has been found that epitaxial growth occurred on (111) substrates at a deposition temperature of approximately 340 °C. Polycrystalline films were obtained at temperatures below 300 °C on (111) substrates. Films grown on (100) substrates were polycrystalline over the range of deposition temperatures 100–390 °C. The electron transport properties of these films have been studied. The Hall mobility measurements of films grown on (111) substrates gave a value of 320 cm2(V sec)−1 for the epitaxial films, decreasing to approximately 100 cm2(V sec)−1 for polycrystalline films grown at 200 °C. For films grown on 〈100〉 substrates the Hall mobility ranged from 60 cm2(V sec)−1 at 200 °C to approximately 90 cm2(V sec)−1 at 340 °C. The electrical resistivity of the epitaxial films was 20 Ω cm and that of the polycrystalline films ranged from 10 to 300 Ω cm. Photoconductivity measurements of these films showed a relatively high trap density extending to greater than 1 eV above the valence band edge. A peak in the response at 800 nm is thought to be due to that of the Cd vacancies.

Materials; Metals and Alloys, FCC Metals: Radiation Defect Annealing - Cu: Transport Properties in Film

Materials; Metals and Alloys, FCC Metals: Radiation Defect Annealing - Cu: Transport Properties in Film