scholarly journals Phonons and Thermal Transport in Si/SiO2 Multishell Nanotubes: Atomistic Study

2021 ◽  
Vol 11 (8) ◽  
pp. 3419
Author(s):  
Calina Isacova ◽  
Alexandr Cocemasov ◽  
Denis L. Nika ◽  
Vladimir M. Fomin
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Geometrical Parameters ◽  
Boltzmann Transport ◽  
Si Nanowires ◽  
Relaxation Time Approximation ◽  
Atomistic Lattice ◽  
Key Factor ◽  
Atomistic Study

Thermal transport in the Si/SiO2 multishell nanotubes is investigated theoretically. The phonon energy spectra are obtained using the atomistic lattice dynamics approach. Thermal conductivity is calculated using the Boltzmann transport equation within the relaxation time approximation. Redistribution of the vibrational spectra in multishell nanotubes leads to a decrease of the phonon group velocity and the thermal conductivity as compared to homogeneous Si nanowires. Phonon scattering on the Si/SiO2 interfaces is another key factor of strong reduction of the thermal conductivity in these structures (down to 0.2 Wm−1K−1 at room temperature). We demonstrate that phonon thermal transport in Si/SiO2 nanotubes can be efficiently suppressed by a proper choice of nanotube geometrical parameters: lateral cross section, thickness and number of shells. We argue that such nanotubes have prospective applications in modern electronics, in cases when low heat conduction is required.

Phonon Transport in SiGe-Based Nanocomposites and Nanowires for Thermoelectric Applications

2015 ◽  
Vol 1735 ◽  
Author(s):  
M. Upadhyaya ◽  
Z. Aksamija
Keyword(s):  
Thermal Conductivity ◽  
Silicon Germanium ◽  
Thermal Transport ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Voronoi Tessellation ◽  
Phonon Transport ◽  
Interface Properties ◽  
Boltzmann Transport ◽  
Rough Interfaces

ABSTRACTSilicon-germanium (SiGe) superlattices (SLs) have been proposed for application as efficient thermoelectrics because of their low thermal conductivity, below that of bulk SiGe alloys. However, the cost of growing SLs is prohibitive, so nanocomposites, made by a ball-milling and sintering, have been proposed as a cost-effective replacement with similar properties. Lattice thermal conductivity in SiGe SLs is reduced by scattering from the rough interfaces between layers. Therefore, it is expected that interface properties, such as roughness, orientation, and composition, will play a significant role in thermal transport in nanocomposites and offer many additional degrees of freedom to control the thermal conductivity in nanocomposites by tailoring grain size, shape, and crystal angle distributions. We previously demonstrated the sensitivity of the lattice thermal conductivity in SLs to the interface properties, based on solving the phonon Boltzmann transport equation under the relaxation time approximation. Here we adapt the model to a broad range of SiGe nanocomposites. We model nanocomposite structures using a Voronoi tessellation to mimic the grains and their distribution in the nanocomposite and show excellent agreement with experimentally observed structures, while for nanowires we use the Monte Carlo method to solve the phonon Boltzmann equation. In order to accurately treat phonon scattering from a series of atomically rough interfaces between the grains in the nanocomposite and at the boundaries of nanowires, we employ a momentum-dependent specularity parameter. Our results show thermal transport in SiGe nanocomposites and nanowires is reduced significantly below their bulk alloy counterparts.

Thermal Conductivity Reduction in Few-Layer Graphene

2011 ◽  
Author(s):  
Dhruv Singh ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Thermal Conductivity ◽  
Weak Coupling ◽  
Phonon Scattering ◽  
Single Layer ◽  
Acoustic Mode ◽  
Single Layer Graphene ◽  
Boltzmann Transport ◽  
Layer Graphene ◽  
Out Of Plane ◽  
Few Layer Graphene

Using the linearized Boltzmann transport equation and perturbation theory, we analyze the reduction in the intrinsic thermal conductivity of few-layer graphene sheets accounting for all possible three-phonon scattering events. Even with weak coupling between layers, a significant reduction in the thermal conductivity of the out-of-plane acoustic modes is apparent. The main effect of this weak coupling is to open many new three-phonon scattering channels that are otherwise absent in graphene. The highly restrictive selection rule that leads to a high thermal conductivity of ZA phonons in single-layer graphene is only weakly broken with the addition of multiple layers, and ZA phonons still dominate thermal conductivity. We also find that the decrease in thermal conductivity is mainly caused by decreased contributions of the higher-order overtones of the fundamental out-of-plane acoustic mode. Moreover, the extent of reduction is largest when going from single to bilayer graphene and saturates for four layers. The results compare remarkably well over the entire temperature range with measurements of of graphene and graphite.

Theory of Thermal Conductivity of Micro- and Nano-structured Materials

2009 ◽  
Vol 1172 ◽  
Author(s):  
Gyaneshwar P. Srivastava
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Polycrystalline Diamond ◽  
Comprehensive Treatment ◽  
Si Nanowires ◽  
Quantitative Investigation ◽  
Debye Relaxation ◽  
Structured Materials ◽  
20 Nm

AbstractWe provide a brief discussion of the Boltzmann equation derived Callaway-Debye relaxation time theory of lattice thermal conductivity of micro- and nano-structured materials (of size greater than 20 nm. Incorporated in the theory is a comprehensive treatment of three-phonon scattering events. Using numerical results from this theory, we present a quantitative investigation of the magnitude and temperature variation of the conductivity of CVD polycrystalline diamond films, suspended GaAs nanostructures, Si nanowires, and AlN micro- and nano-ceramics.

scholarly journals Reduction of Lattice Thermal Conductivity in PbTe Induced by Artificially Generated Pores

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Jae-Yeol Hwang ◽  
Eun Sung Kim ◽  
Syed Waqar Hasan ◽  
Soon-Mok Choi ◽  
Kyu Hyoung Lee ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Pore Structure ◽  
Transport Properties ◽  
Thermoelectric Materials ◽  
Thermal Transport ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Phonon Modes ◽  
Thermal Transport Properties

Highly dense pore structure was generated by simple sequential routes using NaCl and PVA as porogens in conventional PbTe thermoelectric materials, and the effect of pores on thermal transport properties was investigated. Compared with the pristine PbTe, the lattice thermal conductivity values of pore-generated PbTe polycrystalline bulks were significantly reduced due to the enhanced phonon scattering by mismatched phonon modes in the presence of pores (200 nm–2 μm) in the PbTe matrix. We obtained extremely low lattice thermal conductivity (~0.56 W m−1 K−1at 773 K) in pore-embedded PbTe bulk after sonication for the elimination of NaCl residue.

scholarly journals Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Lina Yang ◽  
Austin J. Minnich
Keyword(s):  
Thermal Conductivity ◽  
Monte Carlo ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Computational Study ◽  
Phonon Transport ◽  
Nanocrystalline Si

Abstract Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.

scholarly journals Effect of Phase Transition on the Thermal Transport in Isoreticular DUT Materials

2021 ◽  
Author(s):  
Penghua Ying ◽  
Jin Zhang ◽  
Zheng Zhong
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Transport Property ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Transition Process ◽  
Thermal Transport Property ◽  
Potential Applications ◽  
Flexible Metal ◽  
Dynamics Simulations

<p></p><p>Soft porous crystals (SPCs) or flexible metal-organic frameworks have great potential applications in gas storage and separation, in which SPCs can undergo phase transition due to external stimuli. Thus, understanding the effect of phase transition on the thermal transport in SPCs becomes extremely crucial, because the latent heat generated in aforementioned applications is needed to be effectively removed. In this paper, taking the isorecticular DUT series as an example, the thermal transport property of SPCs during the phase transition from the large pore (lp) phase to the narrow pore (np) phase is comprehensively investigated by molecular dynamics simulations together with the Green-Kubo method. According to our calculations, all DUT structures exhibit an ultralow thermal conductivity smaller than 0.2 Wm<sup>-1</sup>K<sup>-1</sup>. In addition, we find that the effect of phase transition on the thermal transport property of different DUT materials considered here strongly depends on their porosity. As for DUT-48, its lp phase has a thermal conductivity larger than that of its np phase. However, in other DUT materials, i.e, DUT-47, DUT-49, DUT-50, and DUT-151 the thermal transport property of their lp phase is found to be weaker than that of their np phase. This complicated effect of phase transition on the thermal transport in SPCs can be explained by a porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process.</p><p></p>

Optimized Design of Composite Materials for Heat Transport Applications

2011 ◽  
Author(s):  
Babak Kouchmeshky ◽  
Peter Kroll ◽  
Ibukun Olubanjo
Keyword(s):  
Thermal Conductivity ◽  
Composite Materials ◽  
Thermal Transport ◽  
Elevated Temperatures ◽  
Phonon Scattering ◽  
Optimized Design ◽  
Individual Contributions ◽  
Non Equilibrium Molecular Dynamics ◽  
Dynamics Simulations ◽  
The Individual

Careful design of composite materials offers a chance for engineering phonon band gaps and controlling phonon scattering. Taking advantage of this strategy, we study properties of SiC composite materials for engineering applications in which the control of thermal transport is important. In particular, knowledge of the individual contributions of phonons on thermal transport provides us the necessary information to focus on most significant phonon frequencies. In our study, we select a series of candidate model geometries and use a virtual testing method for elevated temperatures to support the design process. Integrating atomistic non-equilibrium molecular dynamics simulations to determine thermal conductivity we provide a proof-of-concept study and deliver best design scenarios of SiC composite materials with very low-thermal conductivity.

Spectral Detail of Phonon Conduction and Scattering in Graphene

2011 ◽  
Author(s):  
Dhruv Singh ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Thermal Conductivity ◽  
Phonon Scattering ◽  
Interatomic Potential ◽  
Phonon Dispersion ◽  
Transition Probabilities ◽  
Transition Probability ◽  
Phonon Transport ◽  
Temperature Perturbation ◽  
Boltzmann Transport ◽  
Wide Range

This paper examines the thermodynamic and thermal transport properties of the 2D graphene lattice. The interatomic interactions are modeled using the Tersoff interatomic potential and are used to evaluate phonon dispersion curves, density of states and thermodynamic properties of graphene as functions of temperature. Perturbation theory is applied to calculate the transition probabilities for three-phonon scattering. The matrix elements of the perturbing Hamiltonian are calculated using the anharmonic interatomic force constants obtained from the interatomic potential as well. An algorithm to accurately quantify the contours of energy balance for three-phonon scattering events is presented and applied to calculate the net transition probability from a given phonon mode. Under the linear approximation, the Boltzmann transport equation (BTE) is applied to compute the thermal conductivity of graphene, giving spectral and polarization-resolved information. Predictions of thermal conductivity for a wide range of parameters elucidate the behavior of diffusive phonon transport. The complete spectral detail of selection rules, important phonon scattering pathways, and phonon relaxation times in graphene are provided, contrasting graphene with other materials, along with implications for graphene electronics. We also highlight the specific scattering processes that are important in Raman spectroscopy based measurements of graphene thermal conductivity, and provide a plausible explanation for the observed dependence on laser spot size.

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