Comparative study of the two-phonon Raman bands of silicene and graphene

TL;DR

This study computationally compares the two-phonon Raman spectra of silicene and graphene, revealing a crossover behavior near the c-plasmon energy and predicting distinctive Raman bands for structural analysis.

Contribution

It introduces a detailed computational analysis of two-phonon Raman spectra in silicene and graphene, highlighting resonance effects and spectral features related to electronic and phononic structures.

Findings

Raman spectra show a crossover near the c-plasmon energy.

Resonant Raman scattering paths change beyond this energy.

Predicted Raman bands can aid in structural characterization.

Abstract

We present a computational study of the two-phonon Raman spectra of silicene and graphene within a density-functional non-orthogonal tight-binding model. Due to the presence of linear bands close to the Fermi energy in the electronic structure of both structures, the Raman scattering by phonons is resonant. We find that the Raman spectra exhibit a crossover behavior for laser excitation close to the \pi-plasmon energy. This phenomenon is explained by the disappearance of certain paths for resonant Raman scattering and the appearance of other paths beyond this energy. Besides that, the electronic joint density of states is divergent at this energy, which is reflected on the behavior of the Raman bands of the two structures in a qualitatively different way. Additionally, a number of Raman bands, originating from divergent phonon density of states at the M point and at points, inside the Brillouin zone, is also predicted. The calculated spectra for graphene are in excellent agreement with available experimental data. The obtained Raman bands can be used for structural characterization of silicene and graphene samples by Raman spectroscopy.