Nanoscale thermal transport. II. 2003–2012

TLDR

Nanoscale thermal transport research is driven by demands for improved thermal barriers, thermoelectric conversion, phase‑change memory, heat‑assisted magnetic recording, nanoscale electronics, and nanoparticle therapies, with interfaces becoming increasingly critical as length scales shrink to ~1 nm where radiative and conductive mechanisms overlap. This review surveys experimental, theoretical, and computational advances over the past decade and summarizes the current state of the field. Recent metrology advances, such as time‑domain thermoreflectance and scanning thermal microscopy, now routinely measure thin‑layer thermal conductivity with micron‑scale resolution and sub‑10 nm spatial precision, enabling heat‑flow sensitivity down to 10 pW and analysis of sub‑femtogram samples. First‑principles phonon lifetime calculations have enabled parameter‑free predictions of thermal conductivity, while ultralow conductivity below the conventional minimum has been observed in nanolaminates and disordered crystals with strong anisotropy.

Abstract

A diverse spectrum of technology drivers such as improved thermal barriers, higher efficiency thermoelectric energy conversion, phase-change memory, heat-assisted magnetic recording, thermal management of nanoscale electronics, and nanoparticles for thermal medical therapies are motivating studies of the applied physics of thermal transport at the nanoscale. This review emphasizes developments in experiment, theory, and computation in the past ten years and summarizes the present status of the field. Interfaces become increasingly important on small length scales. Research during the past decade has extended studies of interfaces between simple metals and inorganic crystals to interfaces with molecular materials and liquids with systematic control of interface chemistry and physics. At separations on the order of ∼1 nm, the science of radiative transport through nanoscale gaps overlaps with thermal conduction by the coupling of electronic and vibrational excitations across weakly bonded or rough interfaces between materials. Major advances in the physics of phonons include first principles calculation of the phonon lifetimes of simple crystals and application of the predicted scattering rates in parameter-free calculations of the thermal conductivity. Progress in the control of thermal transport at the nanoscale is critical to continued advances in the density of information that can be stored in phase change memory devices and new generations of magnetic storage that will use highly localized heat sources to reduce the coercivity of magnetic media. Ultralow thermal conductivity—thermal conductivity below the conventionally predicted minimum thermal conductivity—has been observed in nanolaminates and disordered crystals with strong anisotropy. Advances in metrology by time-domain thermoreflectance have made measurements of the thermal conductivity of a thin layer with micron-scale spatial resolution relatively routine. Scanning thermal microscopy and thermal analysis using proximal probes has achieved spatial resolution of 10 nm, temperature precision of 50 mK, sensitivity to heat flows of 10 pW, and the capability for thermal analysis of sub-femtogram samples.