Precise control of thermal conductivity at the nanoscale through individual phonon-scattering barriers

Abstract

The ability to precisely control the thermal conductivity (kappa) of a material is fundamental in the development of on-chip heat management or energy conversion applications. Nanostructuring permits a marked reduction of kappa of single-crystalline materials, as recently demonstrated for silicon nanowires. However, silicon-based nanostructured materials with extremely low kappa are not limited to nanowires. By engineering a set of individual phonon-scattering nanodot barriers we have accurately tailored the thermal conductivity of a single-crystalline SiGe material in spatially defined regions as short as approximately 15 nm. Single-barrier thermal resistances between 2 and 4 x 10(-9) m(2) K W(-1) were attained, resulting in a room-temperature kappa down to about 0.9 W m(-1) K(-1), in multilayered structures with as little as five barriers. Such low thermal conductivity is compatible with a totally diffuse mismatch model for the barriers, and it is well below the amorphous limit. The results are in agreement with atomistic Green's function simulations.

Lorenz Function of Bi2Te3/Sb2Te3 Superlattices

“…1. The latter is obtained by phonon-blocking at superlattice (SL) interfaces or grain boundaries [5][6][7][8] and leads to a reduced lattice thermal conductivity κ ph . Here, the Lorenz function is particularly important for thermoelectrics, providing a measure to separate the electronic and lattice contribution to the thermal conductivity [9].…”

Determining Phonon Mean Free Paths from Observations of Quasiballistic Thermal Transport

“…Thermal transport at length scales comparable to phonon wavelengths and mean free paths (MFPs) is presently a topic of considerable interest [1][2][3][4]. Size effects caused by the macroscopic dimensions of a bulk sample were first considered by Casimir [5].…”

Radial quasiballistic transport in time-domain thermoreflectance studied using Monte Carlo simulations

“…6 Reduced thermal conductivity due to phonon scattering at boundaries and interfaces has been demonstrated in numerous material systems, and many of these nanostructured materials are under investigation as thermoelectrics. [7][8][9][10][11][12] Engineering thermal conductivity using classical size effects requires knowledge of phonon MFPs. 13 Recently, there have been various efforts to measure MFP spectra experimentally using observations of quasiballistic heat conduction.…”