C. R. Pichard

Bio: C. R. Pichard is an academic researcher. The author has contributed to research in topics: Electrical resistivity and conductivity & Scattering. The author has an hindex of 8, co-authored 17 publications receiving 146 citations.

Linear variations in conductivity with thickness of thin polycrystalline films

Abstract: Starting from a three-dimensional scattering model and from the mean free path representing the effect of electronic scattering on external surfaces, a linear analytic expression is proposed for thin film conductivity and resistivity. Good agreement with experiment is found.

Theoretical analysis of the Hall effect in thin polycrystalline metallic films

Abstract: In polycrystalline films where three types of scattering processes (background, grainboundaries and external surfaces scatterings) are taking place at the same time an effective relaxation time is defined in the light of a three-dimensional model of grain-boundaries. Analytical expressions for the Hall coefficient and conductivity in thin polycrystalline metallic films subjected to a transverse magnetic field are then derived by using the Boltzmann transport equation. Previously published data can be theoretically interpreted in terms of the proposed model.

Analytical expression for the total electrical conductivity of unannealed and annealed metal films

Abstract: Previous studies have shown that the Cottey function constitutes an alternative formulation for the Fuchs-Sondheimer size-effect function, provided that a new parameter is used. This result is used for calculating the effects of scattering at a grain boundary, and a good agreement with the Mayadas-Shatzkes model is found. When background, grain-boundary and external-surface scattering are simultaneously operative, a simple analytical expression for the electrical conductivity of polycrystalline, monocrystalline and columnar metal films can be obtained in the whole experimental domain and may conveniently replace the sophisticated expression of Mayadas and Shatzkes. This expression is similar to that obtained in the framework of the multidimensional models, previously presented. No limitation exists in the value of the electronic specular reflection coefficient, and the theoretical expression is related both to annealed and unannealed films.

Alternative analytical forms of the Fuchs-Sondheimer function

Abstract: Starting from the Cottey conduction model and its extension, it is shown that the Fuchs-Sondheimer functions can be approximated by the extended Cottey function at any reduced thickness, provided that the specular electronic reflection coefficient,p, takes values larger than 0.31. Whatever the values ofp and the film thickness be an analytical formulation (in the form of the Cottey function) is proposed for an accurate approximation of the Fuchs-Sondheimer function. Moreover, it is suggested that the scattering processes defined in the Fuchs-Sondheimer model have no interaction.

Thin polycrystalline metallic-film conductivity under the assumption of isotropic grain-boundary scattering

Abstract: The polycrystalline thin-film resistivity and its temperature coefficient of resistivity are calculated from the assumption of isotropic grain-boundary scattering. The proposed simple analytical equations allow separate determination of the transmission coefficient of the grain boundary and the specular reflection coefficient at external surfaces. Good agreement with experiment is found.

Grain-boundary flux pinning by the electron-scattering mechanism

Abstract: The pinning force exerted by an isolated grain boundary upon the flux line lattice (FLL) of a type-II superconductor has been computed, based upon the assumption that electron scattering at the bou

Unexpected size effect in the thermopower of thin-film stripes

Abstract: For low-dimensional materials, size effect of a physical property is usually expected to occur when one (or more) of the dimension sizes decreases to that comparable to or smaller than one of the intrinsic characteristic lengths, e.g., the mean free path. We report here an unexpected size effect, that in centimeter-long stripes of 100-nm-thick metallic thin films, a reduction of the absolute value of thermopower occurs when the stripe width is in the order of 30-50 μm, which is 100–1000 times larger than the intrinsic mean free path of the material. When the stripe width is reduced to 1.5 μm, a relative reduction of thermopower up to 35% is measured in some metals. We suggest that the sidewall scattering due to rough edges of these stripes may be the origin of this unexpected phenomenon. The results may be applied to construct novel thermoelectric devices, such as thermocouples made from a single metal film.

Fuchs Sondheimer-Drude Lorentz model and Drude model in the study of SPR based optical sensors: A theoretical study

Abstract: A comparative study on the sensing performance of gold coated surface plasmon resonance (SPR) based sensors has been presented wherein the dispersive nature of the gold has been accounted for by Fuchs Sondheimer–Drude Lorentz (FS–DL) and Drude models. SPR transmittance spectra have been studied with varying specularity coefficients. Further, a detailed study of detection accuracy and sensitivity with both Drude model and FS–DL model has been carried out for varying gold layer thickness, sensing medium refractive indices and with three different values of specularity coefficient for fiber-coupled sensors. Furthermore, using FS–DL model, SPR insensitive thickness of the metal layer is determined for both fiber- coupled and prism-coupled sensing probes.

Some transport properties of transition metal films

Abstract: Recent experimental measurements reported on the electrical resistivity, temperature coefficient of resistance and thermoelectric power of nineteen transition metal films have been reviewed. All the theoretical models proposed so far to analyse these experimental results have been briefly summarized. Some suggestions for further experimental study on transition metal films are outlined.

Lattice thermal conductivity in a silicon nanowire with square cross section

Abstract: We present a theoretical model of lattice thermal conductivity in a silicon nanowire with square cross section. This model takes into account the modifications of the acoustic phonon dispersion and boundary scattering on the side walls. A good approximation of exact lattice thermal conductivity is obtained by the yielded precise phonon dispersion relations under the xyz algorithm of Nishiguchi et al. [J. Phys.: Condens. Matter 9, 5751 (1997)] and the inclusion of three scattering events on the side walls from the phonon Boltzmann transport equation. Comparison is also made with the thermal conductivity of a cylindrical nanowire.