Nanoscale heat transfer – from computation to experiment

Abstract

Heat transfer can differ distinctly at the nanoscale from that at the macroscale. Recent advancement in computational and experimental techniques has enabled a large number of interesting observations and 5 understanding of heat transfer processes at the nanoscale. In this review, we will first discuss recent advances in computational and experimental methods used in nanoscale thermal transport studies, followed by reviews of novel thermal transport phenomena at the nanoscale observed in both computational and experimental studies, and discussion on current understanding of these novel phenomena. Our perspectives on challenges and opportunities on computational and experimental 10 methods are also presented. IntroductionHeat transfer at the nanoscale can differ distinctly from that predicted by classical laws.1 Understanding nanoscale heat transfer will help thermal management of electronic, optical, and 15 optoelectronic devices, and design new materials with different thermal transport properties for energy conversion and utilization. Research on nanoscale heat transfer has advanced significantly over the past two decades, and a large number of interesting phenomena have been observed. 20The record-high thermal conductivities were computationally calculated (6600 W/mK at room temperature) 2 and experimentally measured (3500 W/mK at room temperature) 3 in a single-walled carbon nanotube (CNT), a one-dimensional system with thermal conductivity exceeding that of diamond -25 the best known heat conductor in bulk form. The thermal conductivities of CNTs are not only high but could also be diverging due to the one-dimensional nature of thermal transport. [4][5][6] Graphene 7 has also been reported to have exceptionally high thermal conductivity (5800 W/mK). Polymers, such as polyethylene, are usually regarded as thermal insulators in the amorphous phase (~0.3 W/mK). 9 However, simulations suggest that along a polyethylene molecular chain, thermal conductivity is high and could even be divergent.10 Ultradrawn polyethylene nanofibers are found to have thermal 35 conductivities (~100 W/mK) hundreds of times higher than their amorphous counterparts. 11 In fluids suspended with nanoparticles, thermal conductivity enhancement way beyond the amount predicted by traditional effective medium theory has been reported. 12,13 This observation has inspired a large amount of 40 research both theoretically and experimentally to explore the mechanism and applications of the enhanced thermal transport in nanofluids. [14][15][16][17][18][19] Theories have predicted that radiative heat transfer between objects separated at small distances increase significantly with decreasing separations, supported by a few 45 prior experiments performed at micrometer or larger separations. [20][21][22] Recent experiments have pushed the separations between surfaces to tens of nanometers, and radiative heat transfer many orders of magnitude higher than that predicted by Planck's blackbody radiation law has been reported. Besides the high and inc...

Superdiffusive heat conduction in semiconductor alloys. II. Truncated Lévy formalism for experimental analysis

“…the distribution of the average distance phonons travel ballistically between consecutive scattering events, governs key aspects of the thermal behavior. Even at room temperature, a significant portion of heat in commonly used semiconductors is found to be carried by phonons with MFPs well into the micron range [2,3]. Thermal transport over these length scales is of crucial importance for nanoscale devices [4].…”

First-principles study of thermal transport inFeSb2

“…In this paper, we apply a first-principles formalism for the thermal conductivity calculation based on DFT and real-space lattice dynamics, recently developed [31,32] and verified for several realistic materials [33][34][35][36][37][38], to FeSb 2 to understand its intrinsic phonon-phonon interactions and, more importantly, provide the information of the phonon mean free path distribution, which is important in guiding the nanostructuring strategy for effectively reducing its thermal conductivity [3,9,11,39]. The detailed calculation procedures can be found in the references [31,32] and will only be briefly outlined here.…”

Electron transfer across a thermal gradient

“…Such studies have been motivated by the use of inelastic tunneling spectroscopy, and more recently Raman spectroscopy, as diagnostic tools on one hand, and by considerations of junction stability on the other. In parallel, there has been an increasing interest in vibrational heat transport in nanostructures and their interfaces with bulk substrates (3)(4)(5)(6)(7)(8)(9)(10)(11) focusing on structure-transport correlations (12)(13)(14)(15), moleculesubstrate coupling (16)(17)(18), ballistic and diffusive transport processes (11,19), and rectification (20)(21)(22). More recently, noise (23)(24)(25)(26), nonlinear response (e.g., negative differential heat conductance), and control by external stimuli (27,28) have been examined.…”