Changes of Interatomic Force Constants Caused by Quantum Confinement Effects: Study on the Calculations for the First-order Raman Spectrum of Si Nanocrystals in Comparison with Experiments

TL;DR

This study investigates how quantum confinement affects interatomic force constants and Raman spectra in silicon nanocrystals, showing that quantum effects mainly cause peak shifts while local heating influences broadening.

Contribution

It demonstrates that proper assignment of interatomic force constants within a bond polarizability model accurately reproduces experimental Raman peak shifts in Si nanocrystals.

Findings

Quantum confinement causes significant 1LO peak shifts.

Local heating mainly affects spectral broadening.

Adjusted force constants match experimental Raman spectra.

Abstract

The redshifts and asymmetric broadening observed in nanocrystal Raman Spectra are attributed to the quantum confinement effects by some authors. But others show that they may come from the local heating caused by the incident laser as well. In this study we demonstrate that in the Si nanocrystal case the latter at most has obvious effects on the broadening but has negligible effects on the 1LO peak shift, while the former contributes most of the 1LO peak shift. We also demonstrate that after assigning appropriate interatomic force constants in the calculation of Raman Spectrum by bond polarizability approximation model within the regime of free boundary condition, we may acquire the matching 1LO peak shift with experiments.