Interplay of crystal thickness and in-plane anisotropy and evolution of quasi-one-dimensional electronic character inReSe2

Abstract

We study the valence band structure of ReSe 2 crystals with varying thickness down to a single layer using nanoscale angle-resolved photoemission spectroscopy and density functional theory. The width of the top valence band in the direction perpendicular to the rhenium chains decreases with decreasing number of layers, from ∼200 meV for the bulk to ∼80 meV for monolayer. This demonstrates increase of in-plane anisotropy induced by changes in the interlayer coupling and suggests progressively more one-dimensional character of electronic states in few-layer rhenium dichalcogenides.

Using in-plane anisotropy to engineer Janus monolayers of rhenium dichalcogenides

“…Also, within our computational framework, both are indirect band gap semiconductors: the conduction band minimum (CBM) is found at Γ whereas the valence band maximum (VBM) is located slightly away from it. This is in agreement with other works using similar methodology [42,48] although a direct band gap has been predicted at the GW level [49] (interestingly, the latter also predicts direct band gaps in the bulk while experiments suggest this is not the case [50][51][52][53]). All of the Janus monolayers inherit the CBM location as well as the shape of the valence band around Γ from the pristine structures and remain indirect band gap semiconductors.…”

“…In the former study, four different Raman bands arising from the local vibrational modes of sulfur atoms were observed, corresponding to substitutions occupying each of the sites. Interestingly, because in ReX 2 the valence band maximum is predominantly built from in-plane rhenium d-orbitals [13,41], a unique coupling develops between the crystal thickness and in-plane anisotropy of the electronic dispersion: the anisotropy increases as the crystal is thinned down and reaches maximum in the monolayer [42]. This suggests that rhenium TMD monolayers are an ideal platform to explore how in-plane anisotropy of 2D crystals can be used to engineer novel atomically thin Janus materials.…”

Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T‐TaSe2

“…[ 31 ] Comparison of different exchange‐correlation functional choices showed that this was likely to be an adequate level of approximation, especially for the lattice dynamics. [ 32 ] Full details of the DFT calculations are reported in the Supporting Information.…”

“…We used the QUANTUM ESPRESSO package [28] with ultrasoft [29] or projector augmented-wave [30] pseudopotentials, and the local density approximation (LDA) was used with a Perdew-Zunger exchange-correlation functional [31] . Comparison of different exchange-correlation functional choices shows that this is likely to be an adequate level of approximation, especially for the lattice dynamics [32] . Full details of the DFT calculations are reported in the SI.…”

A single-atom vanadium-doped 2D semiconductor platform for attomolar-level molecular sensing

“…The measured thickness is consistent with that of a previously reported monolayer ReSe 2 sample. 23 The AFM image also reveals a smooth and at surface prole of the as-synthesized TMDs regardless of the vanadium single-atomic doping. Aer the substitutional single-atom doping with vanadium, the shape, size, and thickness of the 1T 0 ReSe 2 sample remained almost unchanged owing to the low dopant concentration (Fig.…”