Interlayer Interactions in Anisotropic Atomically-thin Rhenium Diselenide

TL;DR

This study investigates the anisotropic interlayer interactions in atomically thin ReSe2, revealing layer-dependent optical and vibrational properties, and providing insights into its potential for anisotropic electronic and optoelectronic applications.

Contribution

First comprehensive analysis of interlayer phonon modes, optical bandgap, and polarization-resolved photoluminescence in ReSe2, highlighting its weak van der Waals interactions and anisotropic properties.

Findings

Layer-dependent optical bandgap increases from 1.26 eV to 1.32 eV from bulk to monolayer.

Ultralow frequency interlayer Raman modes enable layer number and orientation identification.

ReSe2 exhibits weak van der Waals interactions and strong in-plane anisotropy.

Abstract

Recently, two-dimensional (2D) materials with strong in-plane anisotropic properties such as black phosphorus have demonstrated great potential for developing new devices that can take advantage of its reduced lattice symmetry with potential applications in electronics, optoelectronics and thermoelectrics. However, the selection of 2D material with strong in-plane anisotropy has so far been very limited and only sporadic studies have been devoted to transition metal dichalcogenides (TMDC) materials with reduced lattice symmetry, which is yet to convey the full picture of their optical and phonon properties, and the anisotropy in their interlayer interactions. Here, we study the anisotropic interlayer interactions in an important TMDC 2D material with reduced in-plane symmetry - atomically thin rhenium diselenide (ReSe2) - by investigating its ultralow frequency interlayer phonon vibration modes, the layer dependent optical bandgap, and the anisotropic photoluminescence (PL) spectra for the first time. The ultralow frequency interlayer Raman spectra combined with the first study of polarization-resolved high frequency Raman spectra in mono- and bi-layer ReSe2 allows deterministic identification of its layer number and crystal orientation. PL measurements show anisotropic optical emission intensity with bandgap increasing from 1.26 eV in the bulk to 1.32 eV in monolayer, consistent with the theoretical results based on first-principle calculations. The study of the layer-number dependence of the Raman modes and the PL spectra reveals the relatively weak van der Waals interaction and 2D quantum confinement in atomically-thin ReSe2.