arXiv subjects

Xinwei Wang

Publications and source records attributed to Xinwei Wang.

42 records · Page 3Linked to original sources

arXiv2014

Temperature dependence of electrical and thermal conduction in single silver nanowire

Silver nanowires have great application potential in fields like flexible electronic devices, solar cells and transparent electrodes. It is critical and fundamental to study the thermal and electrical transport properties in a single silver nanowire. In this work, the thermal and electrical transport in an individual silver nanowire is characterized down to 35 K with the steady state electro-thermal technique. The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds compared from that of its bulk counterpart. After fitting the temperature dependent electrical resistivity curves with the Bloch-Grüneisen formula, the Debye temperature (151 K) of the silver nanowire is found 36% lower than that (235 K) of bulk silver, confirming strong phonon softening. The thermal conductivity is reduced by 55% compared with that of its bulk counterpart at room temperature and this reduction becomes larger as the temperature goes down. To explain the opposite trends of thermal conductivity (\k{appa}) ~ temperature (T) of silver nanowire and bulk silver, a unified thermal resistivity is used to elucidate the electron scattering mechanism. A large residual unified thermal resistivity for the silver nanowire is observed while that of the bulk silver is almost zero. The same trend of variation against T indicates that the silver nanowire and bulk silver share the same phonon-electron scattering mechanism. Additionally, due to phonon-assisted electron energy transfer across the grain boundaries, the Lorenz number of the silver nanowire is found much larger than that of bulk silver and decreases with decreasing temperature.

cond-mat.mes-hall↗

arXiv2014

Phonon Softening and Weak Temperature-dependent Lorenz Number for Bio-supported Ultra-thin Ir Film

This work reports on the first-time study of the temperature-dependent behavior of the Lorenz number of bio-supported average 3.2 nm-thin Ir film down to 10 K. Due to the strong imperfection-electron scattering, a very large residual resistivity is observed for the film that dominates the overall electron transport. The Debye temperature (221 K)of the film is found much smaller than that of bulk (308 K). This phonon softening strongly confirms the extensive surface and grain boundary electron scatterings. More than one order of magnitude reduction is observed for the thermal conductivity of the film. We find the Wiedemann-Franz Law still applies to our film even at low temperatures. The overall Lorenz number and that of imperfection structure are close to the Sommerfeld value and shows little temperature dependence. This is contrast to other studied low dimensional metallic structures that have a much larger Lorenz number. Electron tunneling and hopping in the biomaterial substrate are speculated responsible for the observed Lorenz number.

cond-mat.mes-hall↗

arXiv2014

Temperature Dependent Behavior of Thermal Conductivity of Sub-5 nm Ir film: Defect-electron Scattering Quantified by Residual Thermal Resistivity

By studying the temperature-dependent behavior of electron thermal conductivity (k) in a 3.2 nm-thin film, we quantify the extremely confined defect-electron scattering and reveal the intrinsic phonon-electron scattering that is shared by bulk Ir. At low temperatures below 50 K, the thermal conductivity of the thin film has almost two orders of magnitude reduction from that of the bulk Ir. The thermal conductivity of the film increases with increasing temperature while that of the bulk Ir has an opposite trend. We introduce a unified thermal resistivity to interpret this completely different k-T relation. This residual thermal resistivity provides an unprecedented way to quantitatively evaluating defect-electron scatterings in heat conduction. The interfacial thermal conductance across the grain boundaries is found larger than that of the Al/Cu interface. Its value is proportional to temperature largely because of the electron's specific heat. A unified interfacial thermal conductance is defined and firmly proves such relation. The electron reflection coefficient is found to be large (88%) and almost temperature independent. This means most of the electrons which scatter with the grain boundary would be reflected back and the scatterings are not affected by temperature.

cond-mat.mes-hall↗

arXiv2014

Thermophysical Properties of Lignocellulose: A Cell-scale Study down to 41K

Thermal energy transport is of great importance in lignocellulose pyrolysis for bio-fuels. The thermophysical properties of lignocellulose significantly affect the overall properties of bio-composites and the related thermal transport. In this work, cell-scale lignocellulose (mono-layer plant cells) is prepared to characterize their thermal properties from room temperature down to 41 K. The thermal conductivities of cell-scale lignocellulose along different directions show a little anisotropy due to the cell structure anisotropy. It is found that with temperature going down, the volumetric specific heat of the lignocellulose shows a slower decreasing trend against temperature than that of microcrystalline cellulose, and its value is always higher than that of microcrystalline cellulose. The thermal conductivity of lignocellulose decreases with temperature from 243 K to 317 K due to increasing phonon-phonon scatterings. From 41 K to 243 K, the thermal conductivity rises with temperature and its change mainly depends on the heat capacity's change.

physics.bio-ph↗

arXiv2013

Variability Improvement by Interface Passivation and EOT Scaling of InGaAs Nanowire MOSFETs

High performance InGaAs gate-all-around (GAA) nanowire MOSFETs with channel length (Lch) down to 20nm have been fabricated by integrating a higher-k LaAlO3-based gate stack with an equivalent oxide thickness of 1.2nm. It is found that inserting an ultrathin (0.5nm) Al2O3 interfacial layer between higher-k and InGaAs can significantly improve the interface quality and reduce device variation. As a result, a record low subthreshold swing of 63mV/dec has been demonstrated at sub-80nm Lch for the first time, making InGaAs GAA nanowire devices a strong candidate for future low-power transistors.

cond-mat.mes-hall↗

arXiv2002

Reducing the Computational Requirements of the Differential Quadrature Method

This paper shows that the weighting coefficient matrices of the differential quadrature method (DQM) are centrosymmetric or skew-centrosymmetric if the grid spacings are symmetric irrespective of whether they are equal or unequal. A new skew centrosymmetric matrix is also discussed. The application of the properties of centrosymmetric and skew centrosymmetric matrix can reduce the computational effort of the DQM for calculations of the inverse, determinant, eigenvectors and eigenvalues by 75%. This computational advantage are also demonstrated via several numerical examples.

cs.CE↗