Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

Vladimir M Fomin,Alexander A Balandin

doi:10.3390/app5040728

Abstract

We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.

Highlights

Spatial confinement of acoustic and optical phonons in semiconductor thin films, superlattices, and nanowires changes their properties in comparison with bulk materials [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
The lowest phonon dispersion curves are shown for axially symmetric waves n = 0, NL = 4 in
We established a possibility of efficient engineering of the acoustic phonon energy dispersion in multishell tubular structures produced by a novel method of self-assembly of micro- and nano-architectures

Summary

Introduction

Spatial confinement of acoustic and optical phonons in semiconductor thin films, superlattices, and nanowires changes their properties in comparison with bulk materials [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. The experimentally-measured reduction of the phonon thermal conductivity in thin films and nanowires usually results from the increased phonon-rough boundary scattering. Another mechanism of the thermal conductivity reduction is related to the phonon spectrum modification and decrease of the phonon group velocity in thin films [10,29,34] and nanowires [12,13,14,30,31,34]. The acoustic phonon confinement effects theoretically predicted for thin films and nanowires [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34] have been directly observed experimentally using the Brillouin light scattering technique using suspended silicon thin films with the thickness H ≈ 7 nm [36] and gallium nitride nanowires with the diameters D ≈ 150 nm [37]

Objectives

Results

Conclusion