Raman vibrational spectra of bulk to monolayer ReS2 with lower symmetry

TL;DR

This study uses Raman spectroscopy and LDA calculations to identify all Raman active modes in ReS2, revealing its low symmetry and structural properties from bulk to monolayer, with implications for 2D material analysis.

Contribution

It demonstrates a combined experimental and computational approach to fully characterize Raman modes in low-symmetry 2D materials like ReS2 without vdW corrections.

Findings

All 18 first-order Raman modes identified for bulk and monolayer ReS2.

LDA calculations accurately reproduce Raman spectra without vdW correction.

No surface reconstruction or low-frequency rigid-layer modes below 100 cm-1 observed.

Abstract

Lattice structure and symmetry of two-dimensional (2D) layered materials are of key importance to their fundamental mechanical, thermal, electronic and optical properties. Raman spectroscopy, as a convenient and nondestructive tool, however has its limitations on identifying all symmetry allowing Raman modes and determining the corresponding crystal structure of 2D layered materials with high symmetry like graphene and MoS2. Due to lower structural symmetry and extraordinary weak interlayer coupling of ReS2, we successfully identified all 18 first-order Raman active modes for bulk and monolayer ReS2. Without van der Waals (vdW) correction, our local density approximation (LDA) calculations successfully reproduce all the Raman modes. Our calculations also suggest no surface reconstruction effect and the absence of low frequency rigid-layer Raman modes below 100 cm-1. Combining with Raman and LDA thus provides a general approach for studying the vibrational and structural properties of 2D layered materials with lower symmetry.