Thermal transport in suspended silicon membranes measured by laser-induced transient gratings

TL;DR

This paper reviews the use of laser-induced transient thermal grating technique to measure nanoscale thermal transport in silicon membranes, revealing non-diffusive phonon transport and boundary scattering effects at room temperature.

Contribution

It provides a comprehensive overview of TTG methodology and presents new experimental findings on thermal conductivity and phonon transport in nanostructured silicon membranes.

Findings

Observation of non-diffusive phonon transport at room temperature

Thickness-dependent thermal conductivity measurements

Diffusive transport in nanopatterned membranes with nanosized holes

Abstract

Studying thermal transport at the nanoscale poses formidable experimental challenges due both to the physics of the measurement process and to the issues of accuracy and reproducibility. The laser-induced transient thermal grating (TTG) technique permits non-contact measurements on nanostructured samples without a need for metal heaters or any other extraneous structures, offering the advantage of inherently high absolute accuracy. We present a review of recent studies of thermal transport in nanoscale silicon membranes using the TTG technique. An overview of the methodology, including an analysis of measurements errors, is followed by a discussion of new findings obtained from measurements on both solid and nanopatterned membranes. The most important results have been a direct observation of non-diffusive phonon-mediated transport at room temperature and measurements of thickness-dependent thermal conductivity of suspended membranes across a wide thickness range, showing good agreement with first-principles-based theory assuming diffuse scattering at the boundaries. Measurements on a membrane with a periodic pattern of nanosized holes indicated fully diffusive transport and yielded thermal diffusivity values in agreement with Monte Carlo simulations. Based on the results obtained to-date, we conclude that room-temperature thermal transport in membranebased silicon nanostructures is now reasonably well understood.