Thermal Conductivity of Phonon Modes in Graphene Nanoribbon at Localized High Heating

2015 ◽  
Author(s):  
Tatiana Zolotoukhina
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Single Layer ◽  
Phonon Transport ◽  
Graphene Nanoribbon ◽  
Single Layer Graphene ◽  
Quasi Equilibrium ◽  
Phonon Modes ◽  
Limited Region ◽  
Small Areas

The spectral components of the phonon transport in the locally thermally excited graphene samples were studied by molecular dynamics (MD) method. In order to be able to select and analyze separate phonon modes in the time of propagation, the transient Green-Kubo approach to the definitions of density of states (DOS) and thermal conductivity was tested in quasi-equilibrium regimes for limited region of the graphene sample studied. Propagation of single modes at the background of diffusional phonon distribution and energy decay of such modes are studied by calculation of the DOS and dispersion relations, their dependence on the heating condition and temperature is studied. Similar conditions can be generated at localized heating of small areas of graphene structures in electronic devices. In transient regime, many issues of thermal transport evaluation still remain not sufficiently tested, especially phonon dynamics. Thermal conductivity of graphene samples related to transport of separate phonon modes is still not completely investigated, however, recent result give indication on the difference in the contribution of phonon modes. In the study, we consider mostly high temperature transport modes that are generated at the heated spot in order to be able to define their velocities and lifetimes in the limit of transient MD sampling. The single-layer graphene nanoribbon of 150 nm to 40 nm was relaxed and prepared in equilibrium in zigzag and armchair orientations. REBO potential for graphene was utilized. Our calculation has shown that at the heating to high temperatures of 1000K and higher, the G mode of graphene remains stationary and has a minimal contribution into thermal transport by coherent modes. The coherent phonon mode or modes that contribute the most into thermal transport were confined in the vicinity of 30 THz and can possibly be attributed to the D modes of graphene.

Thermal Conductance and Constriction Resistance of Single-Layer Graphene Nano Ribbons

2010 ◽  
Author(s):  
Zhen Huang ◽  
Jayathi Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Function Method ◽  
Graphene Nanoribbons ◽  
Thermal Conductance ◽  
Transmission Function ◽  
Single Layer ◽  
Phonon Transport ◽  
Single Layer Graphene ◽  
Phonon Modes ◽  
Layer Graphene ◽  
Wave Effects

This paper considers phonon transport behavior in graphene nanoribbons (GNRs) that bridge semi-infinite graphene contacts. The work employs an atomistic Green’s function method to investigate phonon wave effects in zigzag and armchair edge ribbons. Phonon transmission functions and thermal conductances are found to be sensitive to the edge shape of structures. The thermal conductances of GNRs with different widths are normalized by the quantum of thermal conductance to reveal the relation between number of phonon modes and conductance as a function of temperature. In addition, the phonon transmission functions of nano ribbons with defects are evaluated by artificially creating mismatches at interfaces. By comparing the transmission function of different defect patterns and the corresponding thermal conductances, the reduction of phonon transport is quantified. The length of defects is found to be important to phonon transport. Constriction effects are also studied at abrupt mismatched interfaces, and the reduction of thermal conductance is found to be moderately high.

Thermal Transport at Carbon Nanotube-Graphene Junction

2013 ◽  
Author(s):  
Jungkyu Park ◽  
Vikas Prakash
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Carbon Nanotube ◽  
Thermal Resistance ◽  
Thermal Transport ◽  
Single Layer ◽  
Single Layer Graphene ◽  
Interfacial Thermal Resistance ◽  
Interfacial Resistance ◽  
Pillar Height

We present results of a molecular dynamics study to analyze thermal transport at carbon nanotube (CNT)-graphene junctions comprising of single layer graphene and (6,6) armchair single-walled carbon nanotubes (SWCNTs). Two possible junction types with different degrees of sp2 and sp3 hybridization are investigated. Reverse Non-Equilibrium Molecular Dynamics (RNEMD) simulations are used to obtain the thermal conductivities in these hybrid structures and also analyze the role of the interfacial thermal resistance at the SWCNT-graphene junctions in limiting thermal transport. The highest out-of-plane (along the SWCNT axis) thermal conductivity of a hybrid structure with a CNT-graphene junction was obtained to be 158.9±1.2 W/m-K when the junction comprised of only sp2 bonds with an interpillar distance of 15 nm and a pillar height of 200 nm. The highest in-plane thermal conductivity (along the graphene layer plane) with two CNT-graphene junctions was found to be 392.2±9.9 W/m-K with junctions comprising of only sp2 bonds and an interpillar distance of 20 nm and a pillar height of 25 nm. In all cases, junctions with mixed sp2/sp3 hybridization showed higher interfacial thermal resistance than junctions with pure sp2 bonds, and the thermal interfacial resistance was found to be weakly dependent on the length of CNT and the interpillar distance. The highest interfacial thermal resistance measured across the CNT-graphene junction was 3.10×10−6 K-cm2/W when the junction comprised of mixed sp2/sp3 bonds and with 15 nm interpillar distance and 50 nm pillar height.

Investigating the thermal transport in gold decorated graphene by Opto-thermal Raman technique

2021 ◽  
Author(s):  
Ranjuna M K ◽  
Jayakumar Balakrishnan
Keyword(s):  
Thermal Conductivity ◽  
Gold Nanoparticles ◽  
Thermal Management ◽  
Thermal Transport ◽  
Thermal Conductance ◽  
Single Layer ◽  
Thermal Conversion ◽  
Single Layer Graphene ◽  
Phonon Coupling ◽  
Au Nps

Abstract We report a systematic study on the thermal transport properties of gold nanoparticles (Au NPs) decorated single-layer graphene (SLG) on a SiO2/Si substrate by the Opto-thermal Raman technique. Our results, with moderate Au NPs coverage( <10%), demonstrate an enhancement in the thermal conductivity of graphene by ~ 55% from its pristine value and a decrement in the interface conductance by a factor of 1.5. A detailed analysis of our results shows the importance of the photo-thermal conversion efficiency of Au NPs, plasmon-phonon coupling and lattice modifications in the graphene developed after gold nanoparticles deposition in enhancing the thermal conductivity and reducing the interface thermal conductance of the system. Our study paves way for a better understanding of the thermal management in such hybrid systems, which are envisioned as excellent candidates for optoelectronics and photonics applications.

scholarly journals Decoupling electron and phonon transport in single-nanowire hybrid materials for high-performance thermoelectrics

2021 ◽  
Vol 7 (20) ◽  
pp. eabe6000
Author(s):  
Lin Yang ◽  
Madeleine P. Gordon ◽  
Akanksha K. Menon ◽  
Alexandra Bruefach ◽  
Kyle Haas ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Electrical Transport ◽  
High Performance ◽  
Figure Of Merit ◽  
Phonon Transport ◽  
Core Shell ◽  
Nanowire Diameter ◽  
High Performing ◽  
Polycrystalline Thin Films

Organic-inorganic hybrids have recently emerged as a class of high-performing thermoelectric materials that are lightweight and mechanically flexible. However, the fundamental electrical and thermal transport in these materials has remained elusive due to the heterogeneity of bulk, polycrystalline, thin films reported thus far. Here, we systematically investigate a model hybrid comprising a single core/shell nanowire of Te-PEDOT:PSS. We show that as the nanowire diameter is reduced, the electrical conductivity increases and the thermal conductivity decreases, while the Seebeck coefficient remains nearly constant—this collectively results in a figure of merit, ZT, of 0.54 at 400 K. The origin of the decoupling of charge and heat transport lies in the fact that electrical transport occurs through the organic shell, while thermal transport is driven by the inorganic core. This study establishes design principles for high-performing thermoelectrics that leverage the unique interactions occurring at the interfaces of hybrid nanowires.

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.

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.

Coupling Between Phonons and Fluid Particles in Water/Carbon Nanotube Systems

2009 ◽  
Author(s):  
A. J. H. McGaughey ◽  
J. A. Thomas ◽  
J. Turney ◽  
R. M. Iutzi
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Carbon Nanotube ◽  
Relaxation Times ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Dynamics Simulation ◽  
Spectral Energy ◽  
Total Thermal Conductivity ◽  
Phonon Modes

We investigate thermal transport in water/carbon nanotube (CNT) composite systems using molecular dynamics simulations. Carbon-carbon interactions are modeled using the second-generation REBO potential, water-water interactions are modeled using the TIP4P potential, and carbon-water interactions are modeled using a Lennard-Jones potential. The thermal conductivities of empty and water-filled CNTs with diameters between 0.83 nm and 1.66 nm are predicted using molecular dynamics simulation and a direct application of the Fourier law. For empty CNTs, the thermal conductivity decreases with increasing CNT diameter. As the CNT length approaches 1 micron, a length-independent thermal conductivity is obtained, indicative of diffusive phonon transport. When the CNTs are filled with water, the thermal conductivity decreases compared to the empty CNTs and transitions to diffusive phonon transport at shorter lengths. To understand this behavior, we calculate the spectral energy density of the empty and water-filled CNTs and calculate the mode-specific group velocities, relaxation times, and thermal conductivity. For the empty 1.10 nm diameter CNT, we show that the acoustic phonon modes account for 65 percent of the total thermal conductivity. This behavior is attributed to their long mean-free paths. When the CNT is filled with water, interactions with the water molecules shorten the acoustic mode mean-free path and lower the overall CNT thermal conductivity.

Mode dependent lattice thermal conductivity of single layer graphene

2014 ◽  
Vol 116 (15) ◽  
pp. 153503 ◽  
Author(s):  
Zhiyong Wei ◽  
Juekuan Yang ◽  
Kedong Bi ◽  
Yunfei Chen
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Single Layer ◽  
Single Layer Graphene ◽  
Layer Graphene
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