Electrical Conductivity Of Thin Films Research Articles

High-pressure low-temperature electrical properties of template-synthesized polypyrrole at low synthesis temperature: dimensional crossover under pressure

We have measured the pressure and temperature dependence of the electrical conductivity of thin films composed of doped polypyrrole microtubules with a diameter of 400 nm. The microtubules have been synthesized at 0°C in a host membrane. The wall thickness of these microtubules can be controlled by a variation of the synthesis time. The results of these measurements are interpreted using the Mott Variable Range Hopping model. Samples composed of thin wall microtubules show a higher characteristic dimension of the conduction process than samples composed of thick wall microtubules. Under pressure, the dimension of the hopping process increases and three-dimensional behavior prevails for all investigated wall thicknesses of the microtubules. Under pressure samples composed of thin wall microtubules show also a change of the temperature dependence of the pre-exponential factor in the Mott law. The results suggest that the microtubules are not homogeneous but are composed of layers with different electrical conductivity behavior.

CONDUCTIVITY OF LAYERED STRUCTURES WITH A STRONGLY DEGENERATE ELECTRON GAS

The study of the effect of the boundaries on the electrical conductivity of thin films is a well-known problem of solid state physics. An interest in it is aroused due to the latest intense investigations of multilayer periodical structures with the conductivity of a metallic type. When considering the conductivity of spatially restricted systems on the basis of the Boltzman equation, the problem of correct boundary conditions for distribution functions is of essential importance. We consider a structure consisting of many layers of the same material with a degenerate electron gas, divided either by thin tunnelly transparent barriers or by planes with randomly distributed scattering centres on them. This role can be played by any defects of the interface. A similar situation is observed, for example, in metallic superlattices or semiconductor structures with delta-doped layers. The width of the conducting layers z0 is assumed to be large enough comparing to the electron wavelength λ, so that the effect of size quantization could be neglected. To calculate the conductivity of the structure we use a method based on the solution of a kinetic equation in the layer with periodical boundary conditions. At the interface the boundary conditions for the distribution functions are determined by joining the electron wave functions. Let the electric field E = (E,0,0) be directed along the conducting layers plane which is perpendicular to the z-axis of the structure. The kinetic equation for distribution functions inside each layer under a weak electric field has the form

New aromatic benzazole polymers, 3. Synthesis of rigid-rod benzobisazole polymers with main-chain 2,2'-bipyridine-5,5'-diyl units

SUMMARY: Rigid-rod benzobisthiazole (Bipy-PBZT), benzobisoxazole (Bipy-PBO) and benzobisimidazole (Bipy-PyBI) polymers containing 2,2'-bipyridine-5,5'-diyl moieties were synthesized from 2,2'-bipyridine-5,5'-dicarbonyl dichloride and one of the following monomers: 2,5-diamino-1,4-benzenedithiol, 4,6-diamino-1,3-benzenediol, and 2,3,5,6-tetraaminopyridine. Bipy-PyBI is the first rigid-rod benzobisimidazole polymer without any solubilizing pendants that exhibits lyotropic behavior. These polymers displayed thin-film electrical conductivity of ≈10–10–10–8 S/cm in pristine state; 10–5–10–4 S/cm upon infiltration with AgNO3; 25–42 S/cm after Ag+ → Ag0 reduction by NaBH4.

Surface roughness and grain boundary scattering effects on the electrical conductivity of thin films

In this work, we investigate surface/interface roughness and grain boundary scattering effects on the electrical conductivity of polycrystalline thin films in the Born approximation. We assume for simplicity a random Gaussian roughness convoluted with a domain size distribution $\ensuremath{\sim}{e}^{\ensuremath{-}\ensuremath{\pi}{r}^{2}/{\ensuremath{\zeta}}^{2}}$ to account for finite grain size effects with \ensuremath{\zeta}, the average domain size. For semiconducting quantum wells a peculiar interplay takes place between quantum mechanical and roughness-grain boundary scattering effects as a function of the domain size \ensuremath{\zeta} and the roughness correlation length \ensuremath{\xi}. For metallic films grain boundary scattering becomes significant for domain sizes comparable to the roughness correlation length \ensuremath{\xi}.

“Vapoconductivity”. Sorption of Organic Vapors Causes Large Increases in the Conductivity of a Dendrimer

Dendrimers peripherally modified with oligothiophene cation radicals were prepared. The electrical conductivity of thin films showed rapid, dramatic (up to 800×), and reversible increases in conductivity when exposed to certain organic vapors.

Raman scattering spectra and electrical conductivity of thin silicon films with a mixed amorphous-nanocrystalline phase composition: Determination of the nanocrystalline volume fraction

Raman spectra and electrical conductivity of thin films of hydrogenated silicon with mixed amorphous-nanocrystalline phase composition have been studied. It is shown that interpretation of experimental data in terms of percolation theory permits one to determine the integrated Raman-scattering cross-section ratio of the nanocrystalline to amorphous phase and to obtain a quantitative estimate of the volume fraction of each phase.

反応性スパッタ法によるNbCxN1-x超伝導薄膜の作成

NbCxN1-x thin films were prepared on glass substrates by reactive sputtering in a mixture gases of Ar, CH4 and N2 using Niobium plate as a target. The substrate temperature was varied in the high temperature range from 500 to 900°C. Structural properties were investigated by X-ray diffraction. Preferred orientation was observed for the thin films deposited at the substrate temperature of 800°C. Thin films had smooth surface and high mechanical hardness. The Vickers hardness of NbC and NbCxN1-x thin film was about 1150 and from 600 to 700, respectively. The electrical conductivity of thin film was 1.0×104[S/cm]. The highest turn on temperature of 16.2 [K] was observed for the NbCxN1-x thin film. These properties are of importance for the fabrication of NbCxN1-x superconducting devices.

A study on the influence of the cations and anions on the electrical conductivity in thin films of potassium and rubidium halides

Thin films of rubidium chloride and rubidium iodide have been studied with respect to their transient and AC electrical behaviour at room temperature. The transient current was measured in the time range 10-5 s to 104 s, following the application of a step voltage for different amplitudes between 0.4 V and 2.0 V. The AC current was measured over the frequency range 1 Hz to 200 kHz for harmonically varying voltages with amplitudes in the range 0.4-1.2 V. Analysis of the results shows that the AC conductivity is due to anions, whereas the transient conductivity is due only to anions in the time interval from the onset of the applied step voltage up to 10-2 s. For times greater than 10-2 s the transient conductivity is due not only to anions, but also to the release of trapped electrons by the Poole-Frenkel mechanism alone or assisted by tunnelling. The results are compared with previous studies on potassium halides and rubidium bromide. Finally, the observed behaviour is correlated with the electronic polarizabilities of the ions and the effective charge of the salts.

New conducting polymers, 3. Doping, stability, electrical, and optical characteristics of poly-(P-phenylphosphoethynediyl)

Studies on direct-current electrical conductivity and optical properties of a new solution of processable conducting polymer are reported. Electrical conductivity of thin films of the polymer on glass plate at room temperature was 6×10−6 S/cm. Study of conductivity with variation of temperature does not provide any definite thermal activation energy, which is in accordance with the amorphous nature of polymer. Optical absorption data adopting the Bardeen equation showed that maximum ‘optical gap’ (Eg) is 3.30 eV. Doping with Br2-vapor was found to be only partially effective in decreasingEg by 0.43 eV. The polymer was found to be quite stable under normal atmospheric conditions. Environmental stability of both undoped and doped polymer has been discussed.

Theory of electrical transport and scattering at a metal-metal interface

The Schrodinger equation for an electron near a randomly rough metal-metal (or metal-vacuum) interface is approximately solved. The wavefunction and probability currents are averaged over all realisations of the interface characterised by its root-mean-square departure from flatness and the extent of its lateral correlation, and the results are used to set up simple boundary conditions for the Boltzmann transport equation. These are in the form of angle-dependent transmission and reflection coefficients, generalising Fuch's reflectivity parameter, but given as explicit functions of observable properties of the interface. These results are further applied to the calculation of the electrical conductivity of thin films and foils, and of double-layer metallic films.

Electrical conduction in thin films of CeOz/Cd

Abstract AC and DC conduction in metal-insulator-metal (MFM) sandwich samples based on CeOz/Cd as a dielectric prepared by the co-evaporation technique has been investigated and the results are in agreement with the behaviour expected of amorphous thin dielectric films.

薄膜酸化物の電気伝導度測定法に関する二，三の検討

薄膜酸化物の電気伝導度測定法に関する二，三の検討

Electrical conduction in thin films of CeO2/GeO2

A.c. and d.c. conduction in MIM sandwich structures based on CeO2/GeO2 as a dielectric prepared by the co-evaporation technique has been investigated for samples having different compositions. A transition of electrical conductivity from amorphous semiconductor to metallic behaviour as the temperature increased is reported. The electroformed samples show a voltage-controlled negative resistance (VCNR) at high values of bias voltage.

In situ electrical conductivity and the amorphous-crystalline transition in vacuum deposited thin films of Se80Te20 alloy

The electrical conductivity of thin films of Se80Te20 polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied duringin situ heating and cooling cycles. From the electron diffraction of as-grown films it is seen that the studied films are amorphous at room temperature. The electrical conductivity and electron diffraction studies showed that the as-grown amorphous thin films undergo an amorphous-crystalline transition in the temperature range 340 to 360 K. Upon cooling, the films appear to undergo a crystalline crystalline transition around the same temperatures. There does not appear to be any dependence of the amorphous-crystalline transition temperature on the thickness of the films. However, high-resistance films (thinner films) have a well-defined transition temperature while the low-resistance films (thicker films) have a broader transition. The electrical conductivity of polycrystalline Se80Te20 films above 360 K appears to be an exponential function of reciprocal temperature.

High-field electrical conduction in thin films of polyethylene

The voltage-current characteristics of thin film metal-polyethylene-copper structures in which copper is used as a top electrode are studied. The samples made with thermally vacuum-evaporated polyethylene and having a top electrode of copper show space-charge-limited conduction, whereas the samples made from blown polyethylene show the Poole-Frenkel type of high-field conduction. The observed space-charge-limited conduction is belived to be due to the copper atoms diffused into the polyethylene during the deposition process. Les caracteristiques tension-courant des couches minces de metal-polyethylene-cuivre pour les echantillons avec le cuivre en position superieure, sont etudiees. Les echantillons fabriques par evaporation sous vide du polythylene montrent un processus de conduction limite par la charge d'espace, et les echantillons fabriquees du polyethylene prepares par un processus de soufflage montrent evidence pour l'effet Poole-Frenkel aux champs eleves. La conduction limitee par la charge d'espace est montree en consequence de la diffusion des atomes de cuivre pendant le processus de deposition.

Experimental verification of new theoretical equation describing electrical conductivity of thin films

Polycrystalline thin films exhibit three kinds of electronic properties: bulk properties, that are induced by the surface, and properties that are connected with the crystal arrangement and the size of the aggregates. The first analysis of electrical measurement data for thin films was carried out by Fuchs [1 ] and developed by Sondheimer [2]. In this model, the film is considered to be of uniform thickness d and limited by plane surfaces, which introduce boundary conditions on the distribution function of the electrons. The general theory assumes that a fraction p of the electrons are reflected specutarly at the surfaces while the rest are scattered diffusely. The main objections one can find in this theory is that the film approximates a planeparallel single crystal of metal. When the electron scattering at external surfaces becomes specular (p~l), this model indicates that the film conductivity reduces to the conductivity of the bulk metal. In practice, this is not the case because evaporated or sputtered films are Composed of polycrystallites, which is ignored in the FuchsSondheimer model. The grain boundary scattering gives a resistivity which varies inversely with the sample thickness. This type of dependence on thickness is precisely the form expected from the approximate expression for Fuchs theory. The influence of grain boundaries on conductivity was first studied by Mayadas and Shatzkes [3]. In their model, Mayadas and Shatzkes consider the conductivity to be due to isotropic electron scattering (caused by point defects and phonons), to surface scattering (FS effect), and to grain boundary scattering. These authors started from the assumption that an evaporated or sputtered film is made of grains that grow in a column like fashion extending from the substrate to the top of a film. With this hypothesis, grain boundaries are represented by a series of randomly electron-reflecting parallel planes oriented

Application of the Mayadas-Shatzkes Model for Electrical Conduction in Thin Films with Unlike Surfaces

Application of the Mayadas-Shatzkes Model for Electrical Conduction in Thin Films with Unlike Surfaces

Preparation and electrical conductivity of thin films of Rb4Cu16I7Cl13

A thin film of the copper ion conductor Rb4Cu16I7Cl13 was prepared on a glass plate by vacuum evaporation. An appropriate thin film was obtained by controlling the amount of the electrolyte mounted in a boat, the evaporation time etc. and by heating the deposited film at a temperature between 130 and 210° C. The electronic and ionic conductivities of the film measured by d.c. and a.c. techniques were nearly equal to those of a dense tablet of the solid electrolyte.

An improved model for electrical conduction in thin films

An improved model for electrical conduction in thin films has been worked out within the frame-work of the Fuchs-Sondheimer formalism, replacing the artificial specularity parameter P by a memory indicator γ which describes the intermediate cases between bulk material and perfectly diffusing thin film. The ratio of the bulk conductivity σ0 to thin-film conductivity σ is computed for various values of thickness a to mean free path l for a fixed value of memory indicator γ. The predicted results are in good agreement with the experimental data of Larson and Boiko as compared with those of Fuchs-Sondheimer, yielding confidence in the equations developed.

The electrical conductivity of thin films using GeO2 as the dielectric material

Measurements are made on thin films using GeO2 as the dielectric material and for thickness ranges from 130 to 2000 Å. The electrical conductivities are measured as a function of temperature. Efforts are made to investigate the current-voltage characteristics which are interpreted in terms of a Schottky emission conduction mechanism. La conductivité électrique de couches minces du diélectrique GeO2 a été mesurée en fonction de la température. L'épaisseur du film variait entre 130 et 2000 Å. Les caractéristiques courant-voltage ont été étudiées, et elles sont interprétées sur la base du mécanisme d'émission-conduction de Schottky.