Monolayer behaviour in bulk ReS2 due to electronic and vibrational decoupling

Abstract

Semiconducting transition metal dichalcogenides consist of monolayers held together by weak forces where the layers are electronically and vibrationally coupled. Isolated monolayers show changes in electronic structure and lattice vibration energies, including a transition from indirect to direct bandgap. Here we present a new member of the family, rhenium disulphide (ReS 2 ), where such variation is absent and bulk behaves as electronically and vibrationally decoupled monolayers stacked together. From bulk to monolayers, ReS 2 remains direct bandgap and its Raman spectrum shows no dependence on the number of layers. Interlayer decoupling is further demonstrated by the insensitivity of the optical absorption and Raman spectrum to interlayer distance modulated by hydrostatic pressure. Theoretical calculations attribute the decoupling to Peierls distortion of the 1T structure of ReS 2 , which prevents ordered stacking and minimizes the interlayer overlap of wavefunctions. Such vanishing interlayer coupling enables probing of two-dimensional-like systems without the need for monolayers.

Electronic and Optoelectronic Applications Based on 2D Novel Anisotropic Transition Metal Dichalcogenides

“…The interlayer decoupling originates from the Peierls distortion of the initial 1T ReS 2 revealed by Zhong et al As a result of the disordered stacking and minimized wavefunction overlap, this interlayer decoupling provides an ideal platform to characterize unique phenomena in few‐layered ReX 2 while circumventing the challenge of preparing monolayer samples 65. Tongay et al also confirmed that because of the weak interlayer interactions between the distorted Re atoms, the van der Waals forces and the binding energy between the ReS 2 layers are very weak 40. Therefore, both bulk crystal and monolayer ReS 2 exhibit unique anisotropic optical and electronic properties 40, 97.…”

“…In this special 1T′ crystalline structure, the extra electron in the d orbital of the rhenium atom promotes the construction of a strong metallic Re—Re bond (Figure 1b) 32, 38, 66, 96. The distance between these dimerized Re atoms can be even shorter than that in rhenium single crystals97; thus, the total energy and symmetry of the system are reduced 40. This is a major origin of the strong anisotropic properties of ReSe 2 and ReS 2 validated by Liu et al67 The in‐plane anisotropic properties of monolayer and few‐layered ReS 2 are shown in Figure 1c, ReS 2 has two principal axes, ( a axis, 118.97°; b axis, 61.03°).…”

Two-dimensional inorganic analogues of graphene: transition metal dichalcogenides

“…The value of α for the A 1g mode in monolayer MoSe 2 is much smaller (−0.0045 × 10 −2 cm −1 K −1 ) than that of monolayer MoS 2 due to difference in the strain-phonon modes as revealed by first-principles calculations [77]. When exposed to shockwaves, few-layer MoS 2 and other TMDCs undergo morphological changes with [73], (c) adapted with permission from Tongay et al [74], (d) adapted with permission from Gupta et al [31] and (e, f ) adapted with permission from Jana et al [75]. (Online version in colour.)…”

Progress on Crystal Growth of Two-Dimensional Semiconductors for Optoelectronic Applications

“…For most TMDC materials like MoX2 and WX2, the band gap shows a similar indirect-to-direct transformation with decreasing thickness. One exception is ReS2 which possesses a direct band gap for both monolayer and multilayer/bulk ( Figure 1c) [22]. Therefore, TMDCs can be expected to exhibit good optoelectronic response in the near-infrared to visible spectral region.…”

“…In this paper, we review the development of approaches to synthesize thin films of 2D semiconductors, while presenting further strategies to extend their applications in future high-performance optoelectronic devices. [31]; (b) Atomic structure of black phosphorous [24]; (c) Comparison of normalized PL intensity of RS 2 with other transition metal dichalcogenide (TMDC) materials [22]; (d) Calculated band alignment of different monolayer TMDC materials [32]; (e) Calculated layer dependence of band edge positions of TMDC materials [32]. …”