Phonon Confinement in Stressed Silicon Nanocluster

TL;DR

This study investigates phonon confinement effects in stressed silicon nanoclusters embedded in sapphire, revealing size-dependent stress influences on optical phonon shifts using Raman spectroscopy and modeling.

Contribution

It introduces a detailed analysis of phonon confinement and stress effects in silicon nanoclusters, combining experimental Raman data with complex frequency modeling.

Findings

Nanoparticle sizes estimated at 4 and 6 nm

Observed blue shift in optical phonons due to stress

Model fits well with experimental Raman spectra

Abstract

Confined acoustic and optical phonons in Si nanoclusters embedded in sapphire, synthesized using ion-beam implantation are investigated using Raman spectroscopy. The l = 0 and l = 2 confined acoustic phonons, found at low Raman shift, are analyzed using complex frequency model and the size of the nanoparticles are estimated as 4 and 6 nm. For the confined optical phonon, in contrast to expected red shift, the Raman line shape shows a substantial blue shift, which is attributed to size dependent compressive stress in the nanoparticles. The calculated Raman line shape for the stressed nanoparticles fits well to data. The sizes of Si nanoparticles obtained using complex frequency model are consistent with the size estimated from the fitting of confined optical phonon line shapes and those found from X-ray diffraction and TEM.