Different effects of grain boundary scattering on charge and heat transport in polycrystalline platinum and gold nanofilms

The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen （77K） and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann-Franz law. We build an electron relaxation model based on Matthiessen＇s rule to analyse the thermal conductivity and employ the Mayadas ＆ Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann-Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.

Excellent thermoelectric performance of boron-doped n-type Mg_(3)Sb_(2)-based materials via the manipulation of grain boundary scattering and control of Mg content

Thermoelectric devices require thermoelectric materials with high figure-of-merit(ZT)values in the operating temperature range.In recent years,the Zintl phase compound,n-Mg_(3)Sb_(2),has received much attention owing to its rich chemistry and structural complexity.However,it hardly achieves high ZT values throughout the medium temperature range.Herein,by increasing the sintering temperature as much as possible,we successfully increased the average grain size of the compound by 15 times,and the grain boundary scattering was manipulated to obtain high carrier mobility of up to 180 cm^(2)V^(-1)s^(-1).Simultaneously,we optimized the Mg content for ultralow lattice thermal conductivity.We first doped the Mg_(3)Sb_(2)-based materials with boron for higher sintering temperature,good thermal stability,and higher hardness.The synergistic optimization of electrical and thermal transport resulted in excellent ZT values(0.62 at 300 K,1.81 at 773 K)and an average ZT of 1.4(from300 to 773 K),which are higher than the state-of-the-art values for n-type thermoelectric materials,demonstrating a high potential in device applications.

Effects of Interface and Grain Boundary on the Electrical Resistivity of Cu/Ta Multilayers

The electrical resistivity of Cu/Ta multilayers deposited by radio-frequency magnetron sputtering on a polyimide substrate was investigated as a function of monolayer thickness. It is found that the resistivity of the multilayer increases with decreasing monolayer thickness from 500 nm to 10 nm. Two significant effects of layer interface scattering and grain boundary scattering were identified to dominate electronic transportation behavior in the Cu/Ta multilayers at different length scales. The electrical resistivity of the multilayer with monolayer thickness ranging from nanometer to submicron scales can be well described by a newly-proposed Fuchs-Sandheimair （F-S） and Mayadas-Shatzkes （M-S） combined model.

An Alternative Method to Study Wave Scattering by Semi-infinite Inertial Surfaces

A new method to solve the boundary value problem arising in the study of scattering of two-dimensional surface water waves by a discontinuity in the surface boundary conditions is presented in this paper. The discontinuity arises due to the floating of two semi-infinite inertial surfaces of different surface densities. Applying Green＇s second identity to the potential functions and appropriate Green＇s functions, this problem is reduced to solving two coupled Fredholm integral equations with regular kernels. The solutions to these integral equations are used to determine the reflection and the transmission coefficients. The results for the reflection coefficient are presented graphically and are compared to those obtained earlier using other research methods. It is observed from the graphs that the results computed from the present analysis match exactly with the previous results.

Scaling behavior of thermal conductivity in single-crystallineα-Fe2O3 nanowires

Unveiling the thermal transport properties of various one-dimensional(1D)or quasi-1D materials like nanowires,nanotubes,and nanorods is of great importance both theoretically and experimentally.The dimension or size dependence of thermal conductivity is crucial in understanding the phonon-phonon interaction in the low-dimensional systems.In this paper,we experimentally investigate the size-dependent thermal conductivity of individual single crystallineα-Fe2O3 nanowires collaborating the suspended thermal bridge method and the focused electron-beam self-heating technique,with the sample diameter(d)ranging from 180 nm to 661 nm and length(L)changing from 4.84μm to 20.73μm.An empirical relationship for diameter-/length-dependent thermal conductivity is obtained,which shows an approximately linear dependence on the aspect ratio(L/(1+Cd))at T=300 K,where C is a fitting parameter.This is related to the boundary scattering and diameter effect ofα-Fe2O3 nanowires although rigorous calculations are needed to confirm the result.

Enhancement in Thermoelectrical Power Factor of N-Type Si80Ge20 Alloys

Influences of the carrier concentration and mobility of heavily doped n-type Si80 Ge20 alloys on the thermoelectrical power factor are investigated. The experimental results indicate that thermoeleetrieal power factors of 32- 36μWem-1K^-2 eouM be consistently achieved with carrier concentrations of 2.1-2.9 × 10^20cm^-3 and carrier mobilities of 36-40 cm^2 V^-1s^-1. However, many samples with suitable carrier concentrations do not always have high mobilities and high power factors. Some possible explanations for this behaviour are discussed.

Factors affecting the spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium

The spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium is discussed within the accuracy of the first-order Born approximation. It is shown that spectral shifts and spectral switches are affected both by the polarization of the incident light wave and by the characters of the scat-tering medium. Moreover, numerical results show that the direction at which the spectral switch occurs is governed by the characters of the scattering medium, whereas the magnitude of the spectral switch is affected by the polarization of the incident light wave.

An application of radiation boundary condition to scattering problem of acoustic waves in fluids

A numerical method of solving acoustic wave scattering pnblem in fluids is described. Radiation boundary condition (RBC) obtained by factorization method of Helmholtz equation is applied to transforming the exterior boundary value problem in unbounded region into one in a finite region. Combined with RBC and scatterer surface boundary condition, Helmholtz equation is solved numerically by the finite difference method. Computational results for sphere and prolate spheroidal scatterers are in excellent agreement with eigenfunction solutions and much better than the results of OSRC method.