Free Path Length Research Articles

Classical Size Effects in Sb Doped SnTe Thin Films

The possibility of obtaining strongly degenerate (> 4×1020 сm-3) SnTe thin films (d = 200 - 2000 nm) with p-type conductivity by thermal evaporation in vacuum of SnTe crystals doped with Sb, with subsequent condensation onto as (0001) mica and sytal substrates, was established. The thickness dependences of electro-physical properties of thin films were obtained. In this region of thickness there was growth of the carrier mobility with thickness, which is attributable to manifestation of classical size effect and interpreted in the framework of Fuchs-Sondheimer theory. These measurements show little correlation between the length of free path of charge cattiers and the lateral diameter of surface objects.

Analytical solution of the problem of heat transfer in rarefied gas between two coaxial cylinders

The method of characteristics was used within the framework of the kinetic approach to construct an analytical solution of the problem of heat transfer in a channel whose walls were formed by two coaxial cylinders. The main equation was the Williams kinetic equation, and the boundary condition on the channel walls was the diffusion reflection model. The vector field of the heat flux in the channel was determined, and the specific heat flux through the cross section of the channel was calculated. It was shown that the results obtained for a limiting case, in which the cylinder radii were significantly greater than the mean length of free path of gas molecules, were in good agreement with the results obtained for a plane channel with infinite parallel walls.

Primary physical mechanism of different magnetic fields action on roots of some plants

Background: Though the magnetic field action on biological object is proved now by many experiments it cannot be explained. The counterarguments are the small value of magnetic induction, that is effective for static magnetic field and the small value of ions free path length for ion cyclotron resonance presence. Objectives of the article were to generalize all the results that had been obtained before in static, alternative and combined magnetic fields and to explain all results by one and the same primary physical mechanism. Materials and methods that were used to obtain experimental results were based on the using of well reproducible magnetic conditions. For this purpose 3 lays µ-metal shield and superconductive shield with warm volume were used. The artificial magnetic field was created in the shield. The objects of the investigation were roots of cress, maize and pea. Their gravitropic reaction was studied. Results and discussion: All experimental results were compared with the theories and calculations maid before and following from the three mechanisms proposed below. It was shown that there were three physical primary mechanisms that could lead to effect of low frequency alternative and combined magnetic fields and permanent magnetic field on gravitropic reaction in plants. All of them depended on the relative location of roots, gravity and components of permanent and alternative magnetic fields between themselves. The first mechanism is based on the classic model of the rotation of ions in the plane that is perpendicular to the magnetic field direction or precession of magnetic moments round the direction of magnetic field vector. The second mechanism is connected with the piezoelectric properties of starch grain (porous piezoelectricity). This property of starch may create the change in the moving of starch grains in alternative and combined magnetic fields, and even in static one. The third mechanism is caused by the phase transition in water created by weak combined or alternative magnetic fields. Conclusions: The comparison of effects of these three mechanisms between themselves allowed choosing the most possible one. It was shown that the first mechanism was preferred. Only the first mechanism can explain the dependence of observed effects on magnetic field direction.

Clean superconductivity in electron doped Pr2−xCexCuO4+δthin films hetero-epitaxially grown on SrTiO3by reactive molecular beam epitaxy

Abstract

Atypical thermal transport in Cu nanorods in the diffusive–ballistic crossover

We propose a simple theoretical calculation scheme based on the phenomenological Fourier heat-flow formalism to study thermal transport behaviors in nanoscale copper rods. The axial heat transport is characterized by a new super-oscillatory feature along with small-amplitude heat spikes. It is anticipated that these atypical spikes are generated by accumulation of localized “hotspots” that have low heat dissipation characteristics. In the case of radial transport, we witness the existence of three distinct heat regimes owing to buildup of hot electrons after experiencing ballistic scattering events. It is important to note that, even though the nanorod diameter is comparable to or smaller than the electron mean free path length, λmfp ∼ 30 nm; multiple ballistic electronic scattering from the outer surface of the nanorods and subsequent accrual into several layers through secondary collisional events has led to concentric heat zones. The hotspots disappear when the nanorod diameter exceeds λmfp.

The distributed thermal model of fin field effect transistor

This paper demonstrates the thermal analysis of the modern Fin-FET transistor manufactured in 12nm technology node. The analyzed structure is based on the microchip which was developed by Samsung Group and which was applied in modern electronic structures using the 14nm Samsung Low Power Early technology. The investigated structure consists of the fourfold Fin-FET transistor and contains its ambient. Moreover, the different dynamics of the temperature changing is demonstrated what is the significant issue in power management. The explanation of the character of the crystal lattice, in which distances between nodes are smaller than the average length of the phonon free path, is included. The technical specification of the investigated structure as well as die layers and their material parameters are described. Furthermore, the description of the prepared thermal model is demonstrated. The temperature simulations are carried out using the Finite Difference Method. The simulation results are presented and discussed in detail.

Positive magnetoconductance and dephasing in strongly localized black phosphorus

We study the magnetoconductance and dephasing in a strongly localized regime in black phosphorus (BP) devices. The phase coherence length, lφ obtained from the magnetoconductance follows a temperature dependence of T–1/3 in the strongly localized regime with kFle < 1 (ξ < lφ) based on the Ioffe–Regel criterion. Here kF, le and ξ are the Fermi wave vector, mean free path and localization length, respectively. The conductance behavior as a function of temperature confirms that the transport regime of our BP is in a variable‐range‐hopping regime, which results in the strongly localized regime.

Low Energy Gamma Radiation Induced Effects on Ultrasonic Velocity and Acoustic Parameters in Polyvinylidene Fluoride Solution

The modification of polyvinylidene fluoride (PVDF) polymer properties with irradiation is of interest as it possesses unique piezo-, pyro-, and ferroelectric properties. In this paper, we report the results of acoustic parameters of irradiated PVDF mixed with dimethylacetamide (DMAC) solution with low energy γ-source (Cs-137). The polymer solution covered with mica film assures only γ-ray passage and the duration was increased from 18 to 50 hours to achieve the higher dose rate. The dose rate was estimated using the strength of the radioactive source and the duration of the exposure. The ultrasonic velocity (v), density (ρ), and viscosity (η) of 0.2 wt% and 0.5 wt% PVDF dissolved in pure DMAC solution, irradiated with different dose rate were measured using ultrasonic interferometer (Mittal make), Pyknometer, and Oswald’s viscometer, respectively. It is observed that the values of v, ρ, and η change with dose rate. The acoustic parameters such as adiabatic compressibility (β), intermolecular free path length (Lf), acoustic impedance (Z), relative association (RA), ultrasonic attenuation (α/f2), and relaxation time (τ) are calculated using the experimental data. These results are interpreted in terms of the solute-solvent interaction in a polymer solution and scissoring chain damage.

Intersection of Paschen's curves for argon

The intersection of Paschen's curves for argon with a same gap length but a different electrode radius was observed. While the breakdown voltage increases with the increase of the nonuniformity in the electric field of the gap at lower pressures, it decreases at higher pressures. The reason for the intersection of Paschen's curves was given based on the mean free path length of the electrons inversely proportional to the gas pressure and the electron impact ionization coefficient exponentially increasing with the electric field. The intersection of the Paschen's curves was qualitatively reproduced by a numerical simulation.

Ultrasonic behavior of various chalcones in some solvents at different temperatures

La velocidad ultrasónica, la densidad y la viscosidad de soluciones de algunas chalconas sintéticas se midieron en N, N-dimetilformamida y cloroformo a diferentes temperaturas (desde 298,15 hasta 318,15 K). A partir de estos datos experimentales, se calcularon diversos parámetros acústicos tales como la impedancia específica (Z), la compresibilidad adiabática (ks), la función de sonido molar de Rao (Rm), la longitud de trayecto libre intermolecular (Lf), el número de solvatación (Sn) y la presión interna (Π), para comprender las interacciones moleculares en las soluciones estudiadas. Los resultados se interpretan en términos de las posibles interacciones moleculares que ocurren en las soluciones.

Quantitative determination of elastic and inelastic attenuation coefficients by off-axis electron holography

Off-axis electron holography is a well-established transmission electron microscopy technique, typically employed to investigate electric and magnetic fields in and around nanoscale materials, which modify the phase of the reconstructed electron wave function. Here, we elaborate on a detailed analysis of the two characteristic intensity terms that are completing the electron hologram, the conventional image intensity and the interference fringe intensity. We show how both are related to elastic and inelastic scattering absorption at the sample and how they may be separated to analyze the chemical composition of the sample. Since scattering absorption is aperture dependent, a quantitative determination of the corresponding attenuation coefficients (reciprocal mean free path lengths) requires the use of holographic image modi with well-defined objective aperture stops in the back-focal plane of the objective lens. The proposed method extends quantitative electron holography to a correlated three-in-one characterization of electric and magnetic fields, Z-contrast and dielectric losses in materials.

Spherical averages in the space of marked lattices

A marked lattice is a d-dimensional Euclidean lattice, where each lattice point is assigned a mark via a given random field on {mathbb {Z}}^d. We prove that, if the field is strongly mixing with a faster-than-logarithmic rate, then for every given lattice and almost every marking, large spheres become equidistributed in the space of marked lattices. A key aspect of our study is that the space of marked lattices is not a homogeneous space, but rather a non-trivial fiber bundle over such a space. As an application, we prove that the free path length in a crystal with random defects has a limiting distribution in the Boltzmann-Grad limit.

Effect of Solvents on the Ultrasonic Velocity and Acoustic Parameters of Polyvinylidene Fluoride Solutions

Ultrasonic studies provide a wealth of information in understanding the molecular behavior and intermolecular interaction of polymer solvent mixtures. Attempts were made to measure ultrasonic velocity, density, and viscosity for the mixture of polyvinylidene fluoride (PVDF) in acetone and dimethylformamide (DMF) of various stoichiometric ratios at 300 K using crystal controlled ultrasonic interferometer (Mittal make), pyknometer (specific gravity bottle), and Ostwald viscometer, respectively. The acoustic parameters adiabatic compressibility (β), intermolecular free path length (Lf), acoustic impedance (Z), relative association (RA), ultrasonic attenuation (α/f2), and relaxation time (τ) have been estimated using experimental data with well-known techniques. The variation of these acoustic parameters is explained in terms of solute-solvent molecular interaction in a polymer solution.

Single and double ultrashort laser pulse scattering by spheroidal metallic nanoparticles

The theory of the ultrashort laser pulse scattered by metallic nanoparticles in the region of surface plasmon resonances is developed in the framework of kinetic approach. For the spheroidal particles, dependence of the light-scattering cross-section on the shape of the particles, the carrier wave frequency, a pulse duration, and other factors is studied. Additionally, an interaction of small metallic particles with double ultrashort pulse is considered. In this case, the energy scattered by the particles demonstrates oscillating behavior when the time delay between pulses changes. Special attention is paid to the contribution of the particle’s surface when the particle’s size is close to the length of free electron path. The difference between the kinetic approach and Mie theory for nonspherical particles has been shown.

Conductivity of laser printed copper structures limited by nano-crystal grain size and amorphous metal droplet shell

We present a study of the morphology and electrical properties of copper structures which are printed by laser induced forward transfer from bulk copper. The percentage of voids and the oxidation levels are too low to account for the high resistivities (~4 to 14 times the resistivity of bulk monocrystalline copper) of these structures. Transmission electron microscope (TEM) images of slices cut from the printed areas using a focused ion beam (FIB) show nano-sized crystal structures with grain sizes that are smaller than the electron free path length. Scattering from such grain boundaries causes a significant increase in the resistivity and can explain the measured resistivities of the structures. The TEM images also show a nano-amorphous layer (~5 nm) at the droplet boundaries which also contributes to the overall resistivity. Such morphological characteristics are best explained by the ultrafast cooling rate of the molten copper droplets during printing.

Current Sensor Based on Nanocrystalline NiFe/Cu/NiFe Thin Film

The nanocrystalline NiFe/Cu/NiFe thin films were fabricated via a facile sputtering method in order to improve the current sensor performance. Further, the resulting thin films were characterized by means of X-ray diffraction, Field emission scanning electron microscopy, Atomic force microscopy and Hysteresis techniques for their structure, morphology and magnetic properties. In the present work NiFe/Cu/NiFe thin film based current sensor device length is varied and the influence of device length on current sensor performance and sensitivity were investigated. The length of device is varied from 2 to 8mm and current sensor performance increases because of mean free path length goes on decreasing and electron may be reach the boundary of material and scattered. The highest sensitivity for the device is found to be 0.76 ΩOe1.

From diffusive to ballistic Stefan–Boltzmann heat transport in thin non-crystalline films

Today, different theoretical models exist to describe heat transport in ultra-thin films with a thickness approaching the phonon mean free path length.

Efficient algorithms for general periodic Lorentz gases in two and three dimensions

We present efficient algorithms to calculate trajectories for periodic Lorentz gases consisting of square lattices of circular obstacles in two dimensions, and simple cubic lattices of spheres in three dimensions; these become increasingly efficient as the radius of the obstacles tends to 0, the so-called Boltzmann–Grad limit. The 2D algorithm applies continued fractions to obtain the exact disc with which a particle will collide at each step, instead of using periodic boundary conditions as in the classical algorithm. The 3D version incorporates the 2D algorithm by projecting to the three coordinate planes. As an application, we calculate distributions of free path lengths close to the Boltzmann–Grad limit for certain Lorentz gases. We also show how the algorithms may be applied to deal with general crystal lattices.

Случайные блуждания по псевдоспецифическим состояниям как модель облегченной диффузии ДНК-связывающего белка

The facilitated diffusion of a regulatory protein in the process of searching for a specific target site on the DNA molecule is considered. On the basis of the hypothesis of ballistic motion of the protein between scatterings of pseudo-specific sites, we proposed a phenomenological model of one-dimensional translocation of the protein along DNA. Combining this approach with the model of discrete random walks we were able to get the relationships between the mean first passage time and such characteristics as the binding energy, the mean free path length between pseudo-specific sites, the speed of protein movement and the temperature. These dependencies allow revealing the thermal and energetic optima, at which minimum values of searching time are achieved.

Accumulation of accelerated electrons in coronal loops and time delays of solar flare nonthermal emission

The mechanisms by which accelerated electrons accumulate in flare loops with regard to the observed time delays between peaks of prolonged (≫1 s) hard X-ray pulses with different energies are considered. The focus is on an analysis of electron pitch-angle scattering by background plasma particles and/or turbulent pulsations in extreme cases of frequent and rare collisions. It was shown that it is difficult to explain the origination of time delays in the scope of a diffusion model when the electron free path length (l) in the corona is smaller than the flare loop length (L). The accumulation of energetic particles in loops at l > L is related to a trap-plus-precipitation model in which the regime of weak pitch angle diffusion of trapped electrons in the loss cone predominates.