Electronic band structure of ReS2 by high-resolution angle-resolved photoemission spectroscopy

Abstract

The rhenium-based transition metal dichalcogenides (TMDs) are atypical of the TMD family due to their highly anisotropic crystalline structure and are recognized as promising materials for two-dimensional heterostructure devices. The nature of the band gap (direct or indirect) for bulk, few-, and single-layer forms of ReS 2 is of particular interest, due to its comparatively weak interplanar interaction. However, the degree of interlayer interaction and the question of whether a transition from indirect to direct gap is observed on reducing thickness (as in other TMDs) are controversial. We present a direct determination of the valence band structure of bulk ReS 2 using high-resolution angle-resolved photoemission spectroscopy. We find a clear in-plane anisotropy due to the presence of chains of Re atoms, with a strongly directional effective mass which is larger in the direction orthogonal to the Re chains (2.2m e ) than along them (1.6m e ). An appreciable interplane interaction results in an experimentally measured difference of ≈100−200 meV between the valence band maxima at the Z point (0,0, 1 2 ) and the point (0,0,0) of the three-dimensional Brillouin zone. This leads to a direct gap at Z and a close-lying but larger gap at , implying that bulk ReS 2 is marginally indirect. This may account for recent conflicting transport and photoluminescence measurements and the resulting uncertainty about the nature of the band gap in this material.

Pressure-induced structural and electronic transitions, metallization, and enhanced visible-light responsiveness in layered rhenium disulphide

“…Clearly, it has an indirect band gap at (k x , k y , 0), but the global valence band maxima (VBM) and conduction band maxima (CBM) are actually located at (0, 0, 0.5), resulting in a direct band gap of 1.288 eV at GGA level. This is in quantitative agreement with the previous studies [55]. Furthermore, the pressure tends to complicate the band distribution.…”

“…However, this was challenged by recent experiments on PL spectra and electrical transport properties that indicated the characteristics of indirect behavior. This controversy was further discussed by several groups recently [55,56]. It has been found that an appreciable interplane interaction results in an experimentally measured difference of 100−200 meV between the valence band maxima at the Z point (0, 0, 0.5) and the Γ point (0, 0, 0) of the three-dimensional (3D) Brillouin zone [54].…”

Theoretical investigations of the anisotropic optical properties of distorted 1TReS2 and ReSe2 monolayers, bilayers, and in the bulk limit

“…who have reported an unchanged indirect band gap from bulk to ML. A very recent work on ReS 2 bulk, using gated field-effect transistors, tends to confirm the indirect character of the gap 19 , when recent ARPES experiments tends to prove the contrary 20 .…”

Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2

“…S13). Synchrotron-based ARPES studies of the binary compounds and associated XPS measurements 28,29 revealed no significant impurities except for native surface oxide for samples cleaved in air. Samples cleaved in UHV did not show the presence of oxygen.…”

“…The inter-layer coupling is unusually weak compared to other TMDs, [24][25][26] though recent angle-resolved photoemission spectroscopy (ARPES) studies show that the band structure of the bulk ReX 2 family still has a three-dimensional character. [27][28][29][30] ReSe 2 is an indirect band gap semiconductor for all numbers of layers [31][32][33][34] with a band gap of 1.36 eV 34 whilst there is disagreement as to the nature of the band gap for bulk ReS 2 , with some groups reporting an indirect band gap of 1.41 eV and others claiming a direct band gap of 1.5 eV. [31][32][33][34][35][36] In this paper, we focus on the alloys of composition ReSe 2 -x S x .…”