Acoustic Phonon Spectrum and Thermal Transport in Nanoporous Alumina Arrays

TL;DR

This study investigates how nanopore size in alumina membranes influences acoustic phonon spectra and thermal conductivity, revealing boundary scattering and spatial confinement effects at pore sizes below 40 nm.

Contribution

It provides experimental and theoretical insights into phonon behavior and heat transport in nanoporous alumina with varying pore sizes, highlighting size-dependent effects.

Findings

Bulk-like phonon spectra at 180 nm pores

Spectral confinement features at 25-40 nm pores

Reduced phonon velocity in smaller pores

Abstract

We report results of a combined investigation of thermal conductivity and acoustic phonon spectra in nanoporous alumina membranes with the pore diameter decreasing from D=180 nm to 25 nm. The samples with the hexagonally arranged pores were selected to have the same porosity of ~13%. The Brillouin-Mandelstam spectroscopy measurements revealed bulk-like phonon spectrum in the samples with D=180-nm pores and spectral features, which were attributed to spatial confinement, in the samples with 25-nm and 40-nm pores. The velocity of the longitudinal acoustic phonons was reduced in the samples with smaller pores. Analysis of the experimental data and calculated phonon dispersion suggests that both phonon-boundary scattering and phonon spatial confinement affect heat conduction in membranes with the feature sizes D<40 nm.