Probing the Role of Interlayer Coupling and Coulomb Interactions on Electronic Structure in Few-Layer MoSe₂ Nanostructures

Abstract

Despite the weak nature of interlayer forces in transition metal dichalcogenide (TMD) materials, their properties are highly dependent on the number of layers in the few-layer two-dimensional (2D) limit. Here, we present a combined scanning tunneling microscopy/spectroscopy and GW theoretical study of the electronic structure of high quality single- and few-layer MoSe2 grown on bilayer graphene. We find that the electronic (quasiparticle) bandgap, a fundamental parameter for transport and optical phenomena, decreases by nearly one electronvolt when going from one layer to three due to interlayer coupling and screening effects. Our results paint a clear picture of the evolution of the electronic wave function hybridization in the valleys of both the valence and conduction bands as the number of layers is changed. This demonstrates the importance of layer number and electron–electron interactions on van der Waals heterostructures and helps to clarify how their electronic properties might be tuned in future 2D nanodevices.

Exciton states in monolayer MoSe 2 : impact on interband transitions

“…Interestingly the spin-up and spin-down minima are not positioned at the same k-value. Note that the appearance of this local minimum has also been predicted recently in [47].…”

Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2

“…The transition energies for monolayer MoS 2 are shown to be in excellent agreement with available absorption and photoluminescence measurements. Similar conclusions were derived also from the study of many-body effects and diversity of exciton states and their role in the formation of the optical spectrum of MoS 2 by Qiu et al [79] and in recently performed STS and PL studies of MoSe 2 layers on graphene substrate, supported by GW and Bethe-Salpeter calculations of exciton binding energies [80,81]). …”

Excitons in atomically thin transition-metal dichalcogenides

“…3a). The reported values, as summarized in the Table II, range from 0.22 eV for MoS 2 to 0.55 eV for MoSe 2 (Ugeda et al, 2014); further reports include (Bradley et al, 2015;Chiu et al, 2015;Rigosi et al, 2016;Zhang et al, 2015a). The differences can be related to (i) the overall precision in extracting the onsets of the tunneling current and (ii) to the use of different conducting substrates required for the STS, i.e., the influence of different dielectric environments and related proximity effects.…”