Mean Free Path Of Conduction Electrons Research Articles

Base pressure effect on electrical properties of chromium nanofilms

The thickness dependence of chromium films deposited onto a glass substrate is studied in the range 3.5–70 nm. Their electrical resistance grows with the base pressure during the deposition due to the scattering of electrons from impurities. The conduction electron mean free path is determined in the frameworks of Mayadas–Shatzkes theory.

Impact of substrates on the electrical properties of thin chromium films [Online First

Objective: We studied the impact of substrates on the electrical properties of thin chromium films. Substrates may serve many purposes, such as to define orientation, to conduct electrical current in vertical devices, as a gate in transistors, etc. The thickness range of the chromium films grown on both substrates was (3.5-70) nm. Methods and materials: We used Fuchs-Sondheimer(FS) and Mayadas-Shatzkes(MS) theories to analyze electrical resistivity data for chromium(Cr) films grown on both substrates simultaneously by thermal evaporation in vacuum, under identical deposition conditions. Results and discussion: The infinitely thick film resistivity (ρ0), conduction electron mean free path(l), specularity parameter(p), scattering power of the grain boundary(α') and grain boundary reflection coefficient(R') were found to depend upon the nature of the substrate and the binding force between them and evaporated chromium atoms. The growth and microstructure of the chromium films were examined using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Conclusions: Our experimental data exactly fits with the MS theory in the entire thickness range grown for the chromium films deposited on both the substrates. Examination of film structure by SEM indicated that the films consist of grains of relatively pure chromium of different sizes, and depends upon deposition conditions and parameters, which are important factors that dictate the structural properties of the films.

Influence of thickness on micro-structural characterizationof Silver films

Thin silver(Ag) films have found many applications in different optical devices such as solar cells, light emitting diodes, to improve the properties of organic semiconductors and to launch new materials. The primary objective of this paper is to explore the micro-structural characterization of thin silver films, that is, their responses to film thicknesses. We here start with the phenomenon of electrical conduction in bulk silver metal by estimating the conduction electron mean free path in order to select the thickness range of the films to be grown. Hence, we have selected the range of thickness 10-90 nm as the conduction electron mean free path in bulk silver is 57 nm. Scanning Electron Microscopy (SEM) techniques have been employed to reveal the physical processes of nucleation and growth. Vacuum deposited are usually polycrystalline islands, during the initial stages of growth are single crystals.

Optical, magnetic, and charge-carriers transport properties of a transition metal: bulk palladium.

Three parametric models of Drude-Lorentz (DL) are used to describe the spectral variation of the dielectric function of bulk palladium. An improved version of the acceptance-probability-controlled simulated annealing method is applied to optimize the values of the parameters involved in the models: high-frequency dielectric constant, free-electron collision frequency and corresponding relaxation time, oscillation strengths, nominal resonance frequencies, and Lorentzian widths. Normalization of the oscillation strengths allows the introduction of a new parameter in the context of the original DL model: the number density ratio, which is the ratio between the number density of conduction electrons and the number density of metal atoms. Inclusion of this parameter in the optimization procedure allows us to evaluate additional parameters related to the charge-carriers transport: the number density of conduction electrons, average effective mass of conduction electrons and holes, Fermi energy and electronic density of states at the Fermi energy, electrical resistivity, intrinsic mean-free path of conduction electrons, electronic heat capacity, Hall coefficient, as well as the mobilities of conduction electrons and holes. The paramagnetic and diamagnetic susceptibilities are also included as derived parameters. A parametric form of the bulk Pd dielectric function, with incorporation of the average local electric field effect in the Lorentz contribution, is reported.

Transition of expanded liquid iron to the nonmetallic state under supercritical pressure

A transition of expanded liquid iron to the nonmetallic state under high pressures (30–100 kbar) at high temperatures (of about 1 eV) is discovered. The result is obtained by direct measurement of the dependence of resistivity on the specific internal energy and volume. Measurements are taken in the specific volume range from the melting curve to values six times higher than the normal specific volume V 0 in the solid state. It is shown that iron remains in the metallic state up to a relative volume of V/V 0 = 3–4, at which the resistivity attains a value of about 3–4 μΩ m and becomes almost independent of temperature, while the conduction electron mean free path decreases to the atomic spacing. For V/V 0 = 4–5, a transition to the nonmetallic state takes place, for which the temperature coefficient of resistance becomes negative and its absolute value becomes much higher than in the metallic state.

X-Ray Photoelectron Spectroscopy of Core (Silver)-Shell (Polydiacetylene) Type Hybridized Nanocrystals

In the core-shell type hybridized nanocrystals composed of silver (Ag)-core and polydiacetylene (PDA)-shell, the localized surface plasmon (LSP) from Ag-core disappeared during solid-state polymerization in the coreprecipitation method. From high-energy X-ray photoelectron spectroscopy measured with synchrotron radiation X-ray in SPring-8, it has become apparent that a Ag-core is composed of nano-sized conductive domains. Domain boundaries may cause the reduction of the conduction electron mean free path in a Ag-core, and may be responsible for LSP damping without changing the plasmon frequency. [DOI: 10.1380/ejssnt.2009.711]

Surface plasmon broadening for arbitrary shape nanoparticles: A geometrical probability approach

A geometrical probability measure is proposed for calculating the effective conduction electron mean free path of an arbitrary shape convex particle. It is shown that the plasmon widths determined from this mean free path are consistent with exact quantum mechanical widths for simple particle shapes. We use the mean free path formula to evaluate size and shape dependent dielectric functions and extinction spectra for silver spheroids, square prisms, truncated tetrahedrons, and cylinders.

Influence of the Ar-ion irradiation on the giant magnetoresistance in Fe/Cr multilayers

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in Fe/Cr multilayers exhibiting the giant magnetoresistance (GMR) effect is studied by the conversion electron Mössbauer spectroscopy (CEMS), vibrating sample magnetometer hysteresis loops, magnetoresistivity, and electric resistivity measurements and supplemented by the small-angle x-ray diffraction. The increase of Ar-ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step sites detected by CEMS. The modification of microstructure induces changes in magnetization reversal indicating a gradual loss of antiferromagnetic (AF) coupling correlated with the degradation of the GMR effect. Distinctly weaker degradation of AF coupling and the GMR effect observed for irradiated samples with a thicker Cr layer thickness suggest that observed effects are caused by pinholes creation. The measurements of temperature dependence of remanence magnetization confirm increase of pinhole density and sizes during implantation. Other effects which can influence spin dependent contribution to the resistance, such as interface roughness as well as shortening of mean-free path of conduction electrons, are also discussed.

The influence of boundary scattering on transport phenomena in ferromagnetic metal—dielectric nanocomposites

It is the rather common for metal-dielectric composites to have metallic grains with size about 10–100Å. This dimension is of the order of the bulk mean-free path of conduction electrons. Then the electron scattering at the boundaries between the adjacent grains (intergranular contacts) and at the interfaces between metallic grains and dielectric matrix would give a significant contribution to the total scattering and thus to the transport phenomena. We consider a simple model for intergranular contact and interface scattering and calculate the extraordinary Hall effect (EHE) in ferromagnetic nanocomposites taking into account the boundary scattering. The results of these calculations are in qualitative agreement with the recent experimental data on giant EHE in nanocomposites (NiFe) x (SiO 2) 1− x .

Magnetization and magnetoresistance of Co/Cu layered films

Multilayer Co/Cu and sandwich layer Co/Cu/Co films made by magnetron sputtering using no special layering elements give the oscillatory magnetic coupling and magnetoresistance (MR) previously reported. The largest value with MR 80% is for a Co(10 AA)/Cu(10 AA) multilayer 340 AA thick. The increase of resistivity in small magnetic fields is the source of the MR. The MR is small in the sandwich layer films until Cu thicknesses above 23 AA where values of MR are 11% and the magnetic hysteresis loops show structure. The MR is isotropic within +or-1% except for demagnetization. The authors prefer a model where the interface disorder is responsible for the large change in resistivity by restricting the conduction electron mean free path.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Band-edge detection in insulators by tunneling spectroscopy

Tunneling spectroscopy on a thin metal film, having a thickness less than a conduction-electron mean free path, can reveal band-structure features of an insulating substrate upon which the film has been overlaid. Virtual transitions which couple energy-band states of the substrate with conduction-band states of the metal create subsidiary structure in the metal’s density of states. It is shown that band edges of the insulator should cause sharp peaks in the (differential) tunneling conductance (versus bias voltage) between the metal and, for example, the tip of a scanning tunneling microscope.

Conduction Electron Scattering in Alloys

The aim of this review is to present a simple physical picture which shows how the electrical resistivity of a system depends upon the spatial extent and lifetime of the scattering disturbance measured in relation to the conduction electron mean free path and relaxation time. The contribution from spin fluctuations associated with isolated magnetic impurities is discussed on the basis of this model and it is shown that at temperatures below the characteristic spin fluctuation temperature the impurity acts as though it were nonmagnetic. Some results are given for both 'Kondo' (Anderson) and exchange enhanced (Wolfi) systems. Spin glasses are also discussed and the resistivity behaviour is shown to result from a competition between the RKKY interaction and spin fluctuation effects. Ordered magnetic clusters are shown to be static for periods comparable with the conduction electron relaxation time, so that there is no resistivity anomaly expected at the superparamagnetic blocking temperature. The observed temperature dependence of the resistivity then follows simply from the change in magnetic correlations within the cluster.

Elastic Modulus Measurement of BaPb1-X Bi X O3 by Resonance Method

The mechanical resonance frequency and amplitude of a spherical BaPb1-X Bi X O3 specimen were measured as a function of temperature (300 K–4.2 K) and external magnetic field (0–5 T). The change in the conduction electron mean free path associated with the normal-superconducting transition was observed indirectly through the change of the mechanical resonance amplitude.

Effects of Microstructure Scale on the Temperature Coefficient of Electrical Resistivity

AbstractThe temperature coefficient of resistivity dϱ/dT is shown to contain a component which depends upon the microstructure scale R0 and the conduction electron mean free path Λ. The size of this contribution depends upon the rate of change of Λ with temperature but in general dϱ/dT will be larger when R0 &lt; Λ. The general predictions of the theory are shown to be in agreement with the limited experimental data available.

On the electrical resistivity of chevrel phases

The diverse and anomalous electrical resistivity behaviour of binary and ternary chevrel phases AxMo3X4 (A=Cu, Pb, Zn, etc; 0<or=x<or=2; X=S, Se, Te) is discussed. The saturation model is applied to analyse resistivity data obtained with Mo3Se4 and CuMoSe4, in which the high-temperature resistivity is attributed to a conduction-electron mean-free path comparable to the lattice spacing. The low-temperature resistivity of these materials shows a T2 dependence characteristic of electron-phonon scattering.

Spin-wave temperature dependence of gadolinium

Previous theoretical studies of the temperature dependence of the magnon dispersion curves of rare earth metals have usually considered only the renormalization due to spin-wave interactions and the effect of temperature variations of the magnetocrystalline anisotropy. An important consideration which has not been included in these studies is the possible temperature dependence of the exchange coupling between the localized spins. Taking into account only the shorter conduction electron mean free path and the resulting decrease in the 4f-4f coupling as T increases we can qualitatively understand the general features of the measured magnon dispersion curves. Our results are consistent with recent measurements on Gd alloys which relate the temperature dependence of the magnetic ordering temperature to the conduction electron mean free path.

Effect of annealing on the resistivity of quench-condensed Cu and Cu(Fe) thin films

Pure Cu and Cu(Fe) thin films containing ∼0.1 and ∼1.0 at % Fe were prepared by low-temperature deposition onto a liquid-helium-cooled substrate. The Cu(Fe) films were annealed sequentially at approximately 17, 70, and 270 K. After each annealing stage the resistivity was measured down to ∼1.5K. The Cu(Fe) films exhibited a region in which the resistivity was proportional to ln T; in this region the logarithmic slope of the resistivity curve was only weakly affected by annealing. Below ∼10 K annealing produced a significant decrease in the impurity (Fe) contribution to the resistivity. The results are interpreted as due to increased interactions between Fe atoms produced by an increase in conduction-electron mean free path.

A computer simulation of the electrical resistivity during pre-precipitation

Abstract A computer simulation of classical conduction electron scattering in a series of two-dimensional atomic arrays which exhibit clustering (like near neighbours) and short-range ordering (unlike near neighbours) is reported. It is found that the direction of the initial change in the residual electrical resistivity with increased order depends upon the number of conduction electrons per atom n, and that for fixed n, if the resistivity initially increases for clustering it should decrease for short-range ordering and vice versa. It is also found that if the resistivity initially increases with order, it will pass through a maximum as the size of the ordered regions approaches the conduction electron mean free path length. These results are shown to be in general agreement with theoretical predictions.

The electrical resistivity during pre-precipitation processes

Abstract The behaviour of the electrical resistivity of a binary alloy during preprecipitation is discussed on the basis of a model in which the conduction electrons are described by free wave-functions and are scattered by deviations from the average lattice potential due to localized atomic clustering. The maximum in the resistivity which appears during ageing is shown to occur when the linear dimensions of the clusters become comparable with the conduction electron mean free path length. Qualitative predictions are in agreement with the experimental observations in the cases of linear, platelet and spherical clusters, whether these are considered to arise from nucleation and growth processes or spinodal decomposition. The dependence of the resistivity on the decomposition wavelength is also discussed and the case of atomic short-range ordering (as distinct from clustering) is briefly considered. The lack of experimentally determined atomic correlation parameters, however, precludes any detailed quantit...

Quantum and classical size effects in the thermoelectric power of thin bismuth films

Abstract Anomalous behaviour of the thermoelectric power of thin Bi films has been observed and the results are consistent with those anticipated, based on both quantum and classical size effects in scattering. Mayer's theory relating thermoelectric power to film thickness can be applied to the present results provided that the bulk conduction electron mean free path is used for calculations of the thermoelectric power of thick specimens and that the conduction electron de Broglie wavelength is used for thin specimens.