Thermal transport in Si/Ge nanocomposites

This study examines the nature of thermal transport properties of single layer twodimensional honeycomb structures of silicon-germanene nanoribbon (SiGeNR), silicene nanoribbon (SiNR) and germanene nanoribbon (GeNR) which have not yet been characterized experimentally.

Nano Letters, 2011

Vertically aligned single-crystal silicon nanowire arrays (SiNWs) with various lengths, surface roughnesses and porosities were fabricated with the metal-assisted chemical etching method. Using the laser flash technique and differential scanning calorimetry, we characterized the thermal conductivities of bulk SiNWs/Si/SiNWs sandwich-structured composites (SSCs) at room temperature (300 K). The results demonstrate that the thermal conductivities of SSCs notably decrease with increases in the length, surface roughness and porosity of SiNWs. Furthermore, based on the series thermal-resistance model, we calculated the thermal conductivity of porous SiNWs to be as low as 1.68 W m −1 K −1 at 300 K. Considering the remarkable phonon scattering from the diameter, surface roughness and porosity of SiNWs, leading to a significant reduction of the thermal conductivity, SSCs and SiNWs could be applied to high-performance thermoelectric devices.

Sadhana, 2010

The effects of nanoscale size dependent parameters on lattice thermal conductivity are calculated using the Debye-Callaway model including transverse and longitudinal modes explicitly for Si nanowire with diameters of 115, 56, 37 and 22 nm. A direct method is used to calculate the group velocity for different size nanowire from their related calculated melting point. For all diameters considered, the effects of surface roughness, defects and transverse and longitudinal Gruneisen parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the reported experimental curve. The obtained fitting value for mean Gruneisen parameter has a systematic dependence on all Si nanowire diameters changing from 0•791 for 115 nm diameter to 1•515 for the 22 nm nanowire diameter. The dependence also gave a suggested surface thickness of about 5-6 nm. The other two parameters were found to have partially systematic dependence for diameters 115, 56, and 37 nm for defects and 56, 37 and 22 nm for the roughness. When the diameters go down from 115 to 22 nm, the concentration of dislocation increased from 1•16 × 10 19 cm −3 to 5•20 × 10 19 cm −3 while the surface roughness P found to increase from 0•475 to 0•130 and the rms height deviation from the surface changes by about 1•66 in this range of diameter. The diameter dependence also indicates a strong control of surface effect in surface to bulk ratio for the 22 nm wire diameter.

This study examines the nature of thermal transport properties of single layer twodimensional honeycomb structures of silicon-germanene nanoribbon (SiGeNR), silicene nanoribbon (SiNR) and germanene nanoribbon (GeNR) which have not yet been characterized experimentally.

American Institute of Physics, 2019

Silicon germanium nanowire has varieties of applications in nanoelectronics and optoelectronics due to technological advances. Nowadays, Computational Material Science is evolving because computer simulation is a tool to get insight about the properties of materials at atomic or molecular level which is used to predict and/or verify experiments. This is considered as a bridge between theory and experiment. In this paper, silicon germanium square nanowire having simulation length of 97.74 A0 is simulated by Nonequilibrium molecular dynamics simulation. Empirical interatomic potential used is Stillinger Weber potential. For canonical ensemble, effect of temperatures on thermal conductivity of silicon germanium square nanowire is studied

Nanotechnology, 2017

We report on structural, compositional, and thermal characterization of self-assembled in-plane epitaxial Si1-xGex alloy nanowires grown by molecular beam epitaxy on Si (001) substrates. The thermal properties were studied by means of scanning thermal microscopy, while the microstructural characteristics, the spatial distribution of the elemental composition of the alloy nanowires and the sample surface were investigated by transmission electron microscopy and energy dispersive x-ray microanalysis. We provide new insights regarding the morphology of the in-plane nanostructures, their size-dependent gradient chemical composition, and the formation of a 5 nm thick wetting layer on the Si substrate surface. In addition, we directly probe heat transfer between a heated scanning probe sensor and Si1-xGex alloy nanowires of different morphological characteristics and we quantify their thermal resistance variations. We correlate the variations of the thermal signal to the dependence of the...

American Journal of Nanoscience and Nanotechnology, 2014

Theoretical investigation of the alloy concentration and temperature dependences of the lattice thermal conductivity of silicon-germanium nanowires is performed using the Steigmeier and Abeles model. Phonon scattering processes are represented by frequency-dependent relaxation time approximation. In addition to the commonly considered acoustic three-phonon umklapp processes, phonon-boundary and point-defect scattering mechanisms are assumed. No distinction is made between longitudinal and transverse phonons. The importance of all the mechanisms involved in the model is clearly demonstrated. Analysis of the results shows that: (1) alloy scattering is the dominant scattering mechanism at intermediate and high temperatures; (2) thermal conductivity is mainly depends on the alloy concentration across the full range of temperatures; (3) weak diameter dependence of thermal conductivity is observed in Si 1 x Ge x alloy nanowires; (4) the roughness of nanowires depends on the alloy concentration and has a major role in decreasing thermal conductivity at low temperatures; (5) the anharmonicity parameter is not size-dependent, as compared to Si and Ge nanowires. These findings provide new insights into the fundamental understanding of high-performance nanostructural semiconductors of relevance to optoelectronic and thermoelectric devices.

We present a calculation of the lattice thermal conductivity of Si-Ge nanowires (NWs), based on solving the Boltzmann transport equation by the Monte Carlo method of sampling the phonon mean free paths. We augment the previous work with the full phonon dispersion and a partially diffuse momentum-dependent specularity model for boundary roughness scattering. We find that phonon flights are comprised of a mix of long free-flights over several µm interrupted by bursts of short flights, resulting in a heavy tailed distribution of flight lengths, typically encountered in Lévy walk dynamics. Consequently, phonon transport in Si-Ge NWs is neither entirely ballistic nor diffusive; instead, it falls into an intermediate regime called superdiffusion where thermal conductivity scales with the length of the NW as κ ∝ L α with the exponent of length dependence α ≈ 0.33 over a broad range of wire lengths 10 nm< L <10 µm regardless of diameter and roughness. We conclude that thermal conductivity in Si-Ge alloy NWs is length-dependent up to 10 µm and therefore can be tuned for thermoelectric applications. arXiv:1610.08477v1 [cond-mat.mes-hall]

Journal of Applied Physics, 2005

A simple model of thermal conductivity, based on the harmonic theory of solids, is used to study the heat transfer in nanostructures. The thermal conductivity is obtained by summing the contribution of all the vibration modes of the system. All the vibrational properties ͑dispersion curves and relaxation time͒ that are used in the model are obtained using the data for bulk samples. The size effect is taken into account through the sampling of the Brillouin zone and the distance that a wave vector can travel between two boundaries in the structure. The model is used to predict the thermal conductivity of silicon nanowires and nanofilms, and demonstrates a good agreement with experimental results. Finally, using this model, the quality of the silicon interatomic potential, used for molecular-dynamics simulations of heat transfer, is evaluated.

Thermal Transport Measurement of Silicon-Germanium Nanowires.