Conductivity Of Metal Films Research Articles

Influence of the quantum size effect for grazing electrons on the electronic conductivity of metal films

The thickness dependence of the electronic conductivity of thin (5–150 nm) single-crystal (100) films of refractory metals is investigated at different temperatures ranging from 4.2 K to room temperature. Regions of square-root, quasilinear, and quadratic dependences are observed. The quasilinear thickness dependence is explained by the influence of quantum effects on the transverse motion of electrons in the case when electron scattering by the film surfaces dominates. For macroscopic film thicknesses 30–50 nm, much greater than the Fermi wavelength of an electron, quantum corrections to the electronic conductivity reach values of the order of 50%. This is a consequence of the quantum size effect for grazing electrons, which leads to an anomaly in electron scattering by the film surfaces. The region of the quadratic thickness dependence corresponds to the quantum limit, and the square-root region corresponds to the classical limit. The effect is explained in a quasiclassical two-parameter model (the effective angle α* for small-angle electrons and the parameter γ, equal to the ratio of this angle to the diffraction angle) that takes into account the diffraction angular limits for grazing electrons. The effect occurs for parameters α*≪1 and γ∼1 and differs from the “ordinary” quantum size effect.

Epitaxial SrRuO3 thin films on (001) SrTiO3

Highly conductive metallic oxide thin films of SrRuO3 with single crystalline quality have been grown on (001) SrTiO3 by using pulsed laser deposition. The films have a [00l] orientation with an in-plane relationship of [110]SrRuO3 // [100]SrTiO3. They have excellent metallic behavior with room temperature resistivity of ∼310 μΩ cm and a residual resistance ratio of about 7 at 4.2 K, the largest reported to date. A clear ferromagnetic transition at ∼147 K was detected by resistivity and magnetic measurements. However, the transition becomes blurred as the density-of-point defects increases in the films following a 400 keV proton irradiation with an accumulative dose up to ∼6.0×1016 ions/cm2.

Wavelength dependences of the dielectric constant of thermally evaporated aluminum films

An in situ observation of the dielectric constant ε m of thermally evaporated continuous aluminum (Al) thin films has been made in the wavelength range 500–1000 nm by excitation of surface plasmon polaritons in the attenuated total reflection configuration. Such a dependence of the Al films fabricated in an ultrahigh vacuum environment has been modeled with Ashcroft and Sturm's theory on an optical conductivity, Fuchs and Sondheimer's theory and Mayadas and Shatzkes' theory on an electrical conductivity of metal films. By analysing ε m as the sum of an interband and Drude free-electron component, we have shown that electrons are scattered by a grain boundary and a surface. For oxide-contaminated films, the dielectric constant has been measured as a function of wavelength and the results have been interpreted by considering the ε m of films free from oxide contamination.

The wave characteristics of thermal conduction in metallic films irradiated by ultra-short laser pulses

The behaviour of conduction heat transfer in a metallic film irradiated by a laser pulse with Gaussian temporal profile is investigated by using the thermal wave model. Calculations are performed to describe the propagation and reflection of a temperature wave and heat flux through the film. The temperature response at the front surface obtained from the thermal wave model is compared with that from the microscopic two-step conduction model by considering a real situation that a Cu film is irradiated by a picosecond laser pulse.

Nanocrystalline metallic powders and films produced by the polyol method

Abstract The polyol method has been extended to synthesize metallic powders of Ru, Rh, Sn, Re, W, Pt, Au, Fe-Cu, Co-Cu, Ni-Cu, in addition to powders of Fe, Co, Ni, Cu, Pd and Ag which were previously prepared by others using this method. This method can also be used to deposit nanocrystalline metallic films on a variety of substrates, including PyrexTM, KaptonTM, TeflonTM, aluminum nitride, carbon fibers and alumina fibers. This can be a viable catalyst-free method for the deposition of conductive metallic films on non-conductive substrates.

Conductivity of metallic films and multilayers.

We examine the quantum and semiclassical approaches to the calculation of the electrical conductivity using a model of free electrons with a finite lifetime. We evaluate the Kubo formula exactly for the free-electron model for homogeneous conductors, thin films, and multilayers. We use these results to explicitly demonstrate the relationships among the exact quantum approach, semiclassical approaches, and an approximate quantum approach. One popular semiclassical approach uses a specularity parameter to describe the fraction of electrons that scatter coherently at boundaries. We show that this parameter should depend on the angle at which the electrons are incident on the boundary. Another semiclassical theory employs the concept of a local mean free path. We show that this approximation works surprisingly well; the error in the calculated conductivity being significant only for very thin layers. A third approach uses an approximate solution to the Kubo formula. We show that this approximation works well for thick layers and extremely thin layers but not for intermediate layer thicknesses. We discuss the implication of these results to the study of the giant magnetoresistance.

Transport theory in metallic films: Crossover from the classical to the quantum regime.

Using the quantum-statistical approach, we have developed a unified transport theory of metallic films. A general description for the conductivity in metallic films has been rigorously formulated in the presence of both impurity scattering and surface roughness. An explicit connection between the quasiclassical and present quantum approaches is also presented. We show that the quasiclassical theory by Fuchs [Proc. Cambridge Philos. Soc. 34, 100 (1938)] and Sondheimer [Adv. PHys. 1, 1 (1952)] can be reformed to be applicable to ultrathin metallic films by introducing a treatment of the surface via angle-dependent specularity parameters and including the quantum size effect. Moreover, to the lowest-order approximation in the theory, the previous quantum-approach results and discussions have naturally been recovered.

Optical reflectivity of Cu and Ag films on Si(100) 2*1 surfaces

The interest of measuring the DC and optical conductivity of metallic films on Si surfaces is discussed. Experiments on the reflectivity of Cu and Ag deposits on Si(100) 2*1 surfaces are summarized.

Comparison of ion beam sputtered chromium and iridium films for electron microscopy applications

AbstractThe structure and composition of thin, conductive metallic films of chromium and iridium that are typical of the coatings used for electron microscopy is described. The purpose of this study was to determine the grain size and composition of the films deposited, with thicknesses of 1 nm, 2.5 nm, and 5 nm, onto amorphous carbon films using ion beam sputtering with argon as the sputtering gas. A comparison between chromium films deposited under conditions of liquid nitrogen (LN) trapping or of no trapping revealed slight differences in their microstructure. As expected, the grain size of the films increased with the thickness, and the average grain sizes varied between 10 and 25 nm. Grain size was also found to depend on the source of ion beam energy; the correlation between grain size and beam energy was more pronounced in the iridium films than in the chromium films. This effect was greater when the deposition chamber was not LN trapped. As the ion beam energy increased from 18 W to 24 W, there was a corresponding increase in grain size in some of the films. Although transmission electron diffraction analysis indicated the presence of about 5% chromium oxide in the chromium films, no oxide was detected in the iridium films.

Inexpensive conductance measurement device for low-temperature thermometry

The authors have built an inexpensive AC synchronous detector for measuring conductances between 5 mu S and 1 S. This allows the measurement and control of low temperatures using carbon glass, Ge or similar resistors with precision to within the standard temperature calibration resolution (+or-0.1%). Simple modifications that improve stability and response time are presented, which enable the instrument to be used to measure changes in the conductivity of metallic films during deposition and of polymers under ion bombardment.

Microstructurally engineered, optically transmissive, electrically conductive metal films

Using standard multilayer and effective medium models, we determine microstructures that optimize the near-IR-visible normal-incidence optical transmittance of electrically conducting metal films intended for use as semitransparent contacts for semiconductor devices such as photodetectors or photoelectrochemical converters. Various conditions are considered, including unpolarized and linearly polarized light and electrical conduction both parallel and perpendicular to the surface. For linearly polarized light, the optimum microstructure consists of parallel metal lines of nominally square cross section oriented perpendicular to the polarization vector of the incident light, regardless of the direction of electrical conduction. The line separation and cross-sectional dimensions must both be small compared to the wavelength λ. For unpolarized radiation, the optimum microstructure depends on the direction of electrical conduction. For conduction parallel to the surface, the optimum microstructure again consists of parallel lines with the lines oriented perpendicular to the residual linear polarization, if any, of the incident flux. For conduction perpendicular to the surface, the optimum microstructure consists of cylindrical metal posts of dimension small compared to λ. Expressions are derived that allow the thicknesses and refractive indices of protective antireflection coatings to be calculated to first order in the thicknesses of the metal films. The more general case of antireflection coatings for anisotropic structures is briefly discussed.

Experimental determination of the surface roughness parameter in metal films

New approximate equations for the conductivity of metal films are derived from the theoretical predictions of the surface roughness model previously proposed to describe the effect of the rms surface roughness on the film conductivity. Comparison between exact and approximate values of the film conductivity shows good agreement in well defined thickness and roughness parameters ranges. It is found that these approximate equations are convenient tools for a systematic study of the influence of annealing temperature or condensation conditions on the film surface properties. On the basis of the present model previously published data are reinterpreted giving experimental values for the fractional change in the surface roughness due to the nucleation of a metal overlayer.

Ferromagnetic resonance in films with a plane anisotropy of electrical resistivity

High conductivity of metallic films leads to attenuation of an ultrahigh frequency field at the depth of the skin layer and, consequently, to a nonuniform distribution of the high-frequency magnetization component over the film thickness. This feature leads to a shift in the frequency and to widening of the ferromagnetic resonance line in a metallic film. In the present work, we study the effect of the plane anisotropy of electrical resistivity on the resonance behavior of polycrystalline magnetic films (Ni, Co, permalloy). Appearance of this anisotropy is related to the presence in the film of extended structural defects such as microgaps oriented along the chosen direction of the substrate texture (Lavsan, mica). In the geometry of the perpendicular magnetization and the normal incident angle of the ultrahigh frequency wave with respect to the film there are two resonance frequencies corresponding to the two orthogonal polarizations of the high-frequency field.

Review of conductor-insulator-semiconductor (CIS) solar cells

The physics and technology of a new class of photovoltaic devices, namely the conductor-insulator-semiconductor (CIS) solar cells, are reviewed in this paper. The top layer in these diodes may be a transparent conducting metal film, an oxide or polymer semiconductor, an electrolyte or a combination of these, leading to a wide variety of metal-insulator-semiconductor (MIS), semiconductor-insulator-semiconductor (SIS) and electrolyte-insulator-semiconductor (EIS) structures. The thickness of the interfacial layer and the work function of the conductor are the important parameters in the optimization of these devices. By ensuring inversion at the interface of the base semiconductor, devices can be fabricated with properties which do not depend strongly on the surface states nor on other non-idealities of the interfacial layer. CIS solar cells with efficiencies comparable with the best p-n junction cells have been fabricated. Most of the presentation is related to single-crystal devices, and the non-crystalline (polycrystalline and amorphous) semiconductor devices are treated separately. Available stability and accelerated life test data indicate fairly stable operation of optimized devices. It is suggested that the research and development efforts have reached such a stage that a prototype production facility is viable.

On the conductivity of metal films during coalescence and the influence of an electric field on their growth

The influence of an electric field normal to the substrate during film growth on the electrical resistance of thin silver deposits is investigated. For interpretation of the results, the coalescence processes are subdivided into three stages. In the first two stages the resistance of the channels determines the resistance of the film. In the first stage the islands gather after film deposition has been interrupted; in the second stage they form bridges between one another. In the third stage the resistance is determined by that of the tracks. Owing to the interaction of dipoles, an electric field causes repulsive forces between the islands without the influence of charged particles. Accelerated charge carriers in the vapour beam increase the resistance of the channels, decrease the growth rate and the mobility of the islands and change the density of the islands.

Solar cells fabricated by ionised-cluster beam technology

It is shown that ionised-cluster beam deposition and epitaxial techniques are useful for the fabrication of photocells. A thin layer of single-crystal silicon and a very thin conductive metal film made by these techniques are used to obtain wide-spectrum sensitivity of the cells. The p-n junction diode has been made by n-type silicon epitaxy onto a p-type silicon substrate. The Schottky-barrier diode has been made by depositing a gold film onto an n-type silicon substrate. These techniques have a high potential for making an ohmic-contact electrode with good adhesion. The alloy process can be eliminated from the fabrication of a photocell. Finally, the current status of solar-cell technology in Japan is reviewed.

Solar cells fabricated by ionised-cluster beam technology

It is shown that ionised-cluster beam deposition and epitaxial techniques are useful for the fabrication of photocells. A thin layer of single-crystal silicon and a very thin conductive metal film made by these techniques are used to obtain wide-spectrum sensitivity of the cells. The p-n junction diode has been made by n-type silicon epitaxy onto a p-type silicon substrate. The Schottky-barrier diode has been made by depositing a gold film onto an n-type silicon substrate. These techniques have a high potential for making an ohmic-contact electrode with good adhesion. The alloy process can be eliminated from the fabrication of a photocell. Finally, the current status of solar-cell technology in Japan is reviewed.

Influence of superimposed dielectric layers on the electrical conductivity of metal films

The increase in the resistivity of epitaxial metal films observed when a single-crystal dielectric coating is deposited on them was interpreted in terms of a pseudomorphic deformation of the film free surface and an alteration of its electrical nature.

Size Effect in Electrical Conductivity of Metallic Films with Arbitrarily Oriented Ellipsoidal Fermi Surfaces

Size Effect in Electrical Conductivity of Metallic Films with Arbitrarily Oriented Ellipsoidal Fermi Surfaces