Confinement of Vibrational Modes in Nanocrystalline Silicon

TL;DR

This paper demonstrates that vibrational modes can be confined within silicon nanocrystals by encapsulating them in hydrogenated amorphous silicon, leveraging higher order property distributions rather than impedance mismatch.

Contribution

It introduces a novel mechanism for vibrational confinement based on material substructure and higher order moments, supported by idealized and realistic models.

Findings

Vibrational modes can be confined by amorphous encapsulation.

Higher order moments in material properties enable phonon management.

The approach can be used to engineer phononic properties in nanostructures.

Abstract

It is possible to confine vibrational modes to silicon nanocrystals by encapsulating them within hydrogenated amorphous silicon. This is not because of the small impedance mismatch between materials but, rather, is due to higher order moments in the distribution of density and stiffness in the amorphous phase--i.e. it is a result of material substructure. The concept is elucidated using an idealized one-dimensional setting and then demonstrated for a realistic nanocrystalline geometry. Beyond the immediate focus on amorphous encapsulation, this offers the prospect of specifically engineering higher order property distributions as an alternate means of managing phonons. The approach could be applied, for instance, to design deterministically ordered materials which exploit this means of control.