Variation Of Mean Free Path Research Articles

Temperature-Dependent Circuit Modeling and Performance Evaluation Due to Crosstalk in Capacitively Coupled Interconnects of Intercalation-Doped Multilayer Graphene Nanoribbon

The present work explores the temperature-dependent performance evaluation due to crosstalk in coupled interconnects of intercalation-doped multilayer graphene nanoribbons (ID-MLGNR). A temperature-dependent equivalent single conductor (ESC) model of arsenic pentafluoride (AsF5) ID-MLGNR is considered and is employed to analyze its crosstalk performance (i.e., crosstalk-induced noise and crosstalk-induced delay). Other metallic interconnect materials viz. mixed carbon nanotube bundles (MCB) and copper (Cu) are also analyzed in a similar manner. The temperature-dependent crosstalk performance of ID-MLGNR is compared with that of MCB and Cu, at different temperatures from 300 to 500 K. For the specified temperature range, in case of crosstalk-induced noise, the AsF5 ID-MLGNR-based long interconnects demonstrate superior performance to its MCBs and Cu counterparts. Moreover, the temperature-dependent crosstalk-induced delay is less with ID-MLGNR in comparison with both MCB and Cu interconnects. The large values of the mean free path (MFP) and conductivity of AsF5 ID-MLGNR contribute to its improved performance. In addition, the impact of variation in MFP, interlayer spacing and Fermi level is studied on the crosstalk delay performance of ID-MLGNR. From the obtained results, it is revealed that variation in these parameters results in the significant variation of 62 ps, 51 ps and 169 ps, respectively, in the odd mode (OM) crosstalk delay. Hence, for emerging nano-technology nodes (e.g., 14 nm), ID-MLGNR interconnects with its improved crosstalk performance are proposed as a potential alternative to its MCBs and Cu counterparts.

Remarkable effects of dirty limit on superconducting condensate

Using heterostructures that combine a two superconductor (Nb-Pb). We demonstrate the modulation of the superconducting condensate at the nanoscale via variation of mean-free path. The modulation of superconductivity can be obtained not only for chosing smaller superconducting lengths comparing with bulk superconducting length or considering several geometric shapes, but also whether strong local dopping effect can be produced over the superficial area of the superconductor. Through this mechanism, a nanoscale pattern of two condensates regions can be created in the superconductor. This yields a magenetization curves that has no counterpart in the literature. We show that this form of modulation based on the possibity of change mean-free path represent a groundbreaking prospects in the study of the effects that might exploit unique superconducting properties, due to allows the manipulation of magnetic flux quanta.

Molecular free paths in nanoscale gas flows

Average distance traveled by gas molecules between intermolecular collisions, known as the mean free path (MFP), is a key parameter for characterizing gas flows in the entire Knudsen regime. Recent literature presents variations in MFP as a function of the surface confinement, which is in disagreement with the kinetic theory and leads to wrong physical interpretations of nanoscale gas flows. This controversy occurs due to erroneous definition and calculation practices, such as consideration of gas wall collisions, using local bins smaller than a MFP, and utilizing time frames shorter than a mean collision time in the MFP calculations. This study reports proper molecular MFP calculations in nanoscale confinements by using realistic molecular surfaces. We utilize molecular dynamics (MD) simulations to calculate gas MFP in three-dimensional periodic systems of various sizes and for force-driven gas flows confined in nano-channels. Studies performed in the transition flow regime in various size nano-channels and under a range of gas–surface interaction strengths have shown isotropic mean travelled distance and MFP values in agreement with the kinetic theory regardless of the surface forces and surface adsorption effects. Comparison of the velocity profiles obtained in MD simulations with the linearized Boltzmann solutions at predicted Knudsen values shows good agreement in the bulk of the channels, while deviations in the near wall region due to the influence of surface forces are reported.

Theory of the longitudinal and Hall conductivities of the cuprate superconductors

We establish the applicability to transport phenomena in the cuprate superconductors of a nearly antiferromagnetic Fermi liquid (NAFL) description of the magnetic interaction between planar quasiparticles by using it to obtain the temperature dependent resistivity and Hall conductivity seen experimentally in the normal state. Following a perturbative calculation of the anisotropic (as one goes around the Fermi surface) quasiparticle lifetimes which are the hallmark of a NAFL, we obtain simple approximate expressions for the longitudinal, $\sigma_{xx}$, and Hall, $\sigma_{xy}$, conductivities which reflect the magnetic crossovers seen experimentally as one varies the doping level and temperature. We present a simple phenomenological model for the variation in mean free path around the Fermi surface, and use this to extract from experiments on $\sigma_{xx}$ and $\sigma_{xy}$ quasiparticle lifetimes in the hot (strongly coupled quasiparticle) and cold (weakly coupled quasiparticle) regions of the Fermi surface which are consistent with the perturbation theory estimates. We improve upon the latter by carrying out direct numerical (non-variational) solutions of the Boltzmann equation for representative members of the YBa$_2$Cu$_3$O$_{6+x}$ and La$_{2-x}$Sr$_x$CuO$_4$ systems, with results for transport properties in quantitative agreement with experiment. Using the same numerical approach we study the influence of CuO chains on the a-b plane anisotropy and find results in agreement with experimental findings in YBa$_2$Cu$_4$O$_8$.

Transverse hot-electron focusing.

Transverse electron focusing is reported for hot electrons. Differential transresistance measurements show anomalous behavior at high electron energies. Corresponding dc electron focusing data reveal that the differential characteristics arise from the electron energy dependences of the mean free path and specularity coefficient. The variation of mean free path with energy is derived from the experimental data.

Microwave response of thin-film superconductors

The interaction of microwaves with superconductors was explored via extensive measurements of the surface resistance Rs and reactance Xs at 10 GHz of superconducting Sn. The measurements were carried out as functions of thickness d and temperature T for Sn films ranging in thickness from 190 Å to bulk. By varying the thickness with accompanied variation of mean free path, we were able to examine the wave-vector dependence of the microwave-superconductor interaction. An analysis, based on the Bardeen–Cooper–Schrieffer electrodynamical kernel, was developed for calculating Rs and Xs as functions of d, T, and frequency. Details of the measurement techniques and analysis are presented. Experiment and theory agree excellently, with no adjustable parameters. For films with d<800 Å we find that the electrodynamics is local because of impurity scattering, while for thicker films nonlocal effects are important. The results imply that superconducting films with microwave response that agrees with theoretical expectations can be fabricated for potential applications in a variety of superconducting structures.

Reciprocal of the Mean Free Path

The geometry of a rectangular enclosure is examined from the viewpoint of the absorption of reverberant energy. For diffuse sound, the significant quantity is not what is implied by the term mean free path but rather the mean reciprocal of the pathlengths. For particular modes, the reciprocal of the pathlengths can vary widely from its mean value and introduce a corresponding uncertainty in the relation of decay rate to absorption coefficient. Although no simple expressions have been found for enclosures of general shape, the range of variation from mode to mode seems to be nearly as great as for rectangular enclosures. This paper was written independently of a related one by F. V. Hunt [J. Acoust. Soc. Am. 36, 556-564 (1964)] and their simultaneous appearance is purely a coincidence. Hunt's paper is concerned primarily with reconciling the various formulations of the mean free path, whereas this paper stresses the variation of mean free path and the inversely related collision frequency for isolated normal modes.

Theory of Space-Charge-Limited Emission in High-Pressure Gas Diodes

A theory for space-charge-limited current in gas-filled thermionic diodes has been developed which takes into consideration the variation of mean free path with electronic energy. The theory is applied to experimental data obtained on gas-filled diodes containing helium, neon, argon, and krypton, in the pressure range 1–700 Torr, and is shown to be in reasonable agreement with experiment.

Cosmic ray investigations with an airborne neutron monitor

A neutron monitor has been in operation aboard a magnetic survey aircraft. During a cruise in November, 1958, the latitude effect of the nucleonic component was measured over the same route between Tokyo and the Aleutian Islands as that covered by Sandstrom in February, 1957. Although the two sets of data normalized at Tokyo are in agreement up to approximately 43° N (modified geomagnetic latitude), a change in the shape of the curve had occurred at higher latitudes. The intensity at 55° N had decreased by 13%, and the « knee » had shifted from 47° N to 43° N. The latitude variation of the absorption mean free path was determined from intensityvs. altitude curves at geomagnetic latitudes 50° N, 37° N, 25° N, and 13° N. A change of roughly 10% over a range of primary cut-off rigidity from 2 GV to 15 GV was indicated. Comparison with earlier results of others revealed no appreciable variation of the mean free path during the solar cycle.

The electrical properties of graphite

The Hall coefficient and resistivity of a range of polycrystalline graphites with different crystal sizes and a single crystal of Travancore graphite have been measured over a wide range of temperature. The number of free electrons has been found to be approximately 6x10 18 per cm 3 at room temperature; the variation with temperature cannot be accurately determined. The deficit of electrons in poorly crystalline graphite gives rise to positive Hall coefficients. Quenching removes electrons, and a study of this process has enabled the ratio of the mobilities of positive holes and electrons to be estimated at 0·80. An interesting effect has been observed in the variation of the Hall coefficient of the single crystal with field; no satisfactory explanation has been found for this phenomenon. The resistivity of polycrystalline graphite depends on the density and on the orientation and size of the crystals. From the variation of resistivity with temperature and the size of the crystals, the mean free path due to thermal scattering, has been found to be 2350 Å at 273° K; the variation of mean free path with temperature has been deduced. The product of effective mass and velocity of the free electrons has been determined as a function of temperature; the accuracy is limited by uncertainties in the number of free electrons.

Gas Temperatures and Elastic Losses in Low Pressure Mercury-Argon Discharges

The increase ΔT in average gas temperature for ac and dc has been determined from measurements of the increase in pressure. A small McLeod gauge was used. Wall temperature was regulated. Corrections for end effects were made by comparing results for long and short tubes of 3.6 cm diameter. Assuming the radial variation of heat input to be parabolic, the temperature distribution was calculated using published values of heat conductivity K. From the results the heat input Pm per centimeter length was calculated. This value was compared with the elastic loss Pc computed from electron temperature Te and number of electrons Ne per centimeter column, taking into account the variation of mean free path with electron velocity. Good agreement was obtained for mercury pressures ranging from 1 to 25 microns, with the arc current 0.2–0.6 ampere and the argon filling pressure 3.5 mm (Hg).