Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

Abstract

This report presents a series of low-temperature (4.5 K) scanning tunneling microscopy and spectroscopy experimental results on monolayer MoS 2 deposited on highly oriented pyrolytic graphite using chemical vapor deposition. To reveal the detailed connection between atomic morphology and conductivity in twisted MoS 2 /graphite heterojunctions, we employ high-sensitivity tunneling spectroscopy measurements by choosing a reduced tip-sample distance. We discern previously unobserved conductance peaks within the band gap range of MoS 2 , and by comparing the tunneling spectra from MoS 2 grains of varying rotation with respect to the substrate, show that these features have small but non-negligible dependence on the moiré superstructure. Furthermore, within a single moiré supercell, atomically resolved tunneling spectroscopy measurements show that the spectra between the moiré high and low areas are also distinct. These in-gap states are shown to have an energy shift attributed to their local lattice strain, matching corresponding behavior of the conduction band edge, and we therefore infer that these features are intrinsic to the density of states, rather than experimental artifacts, and attribute them to the twisted stacking and local strain energy of the MoS 2 /graphite heterointerface.

Moiré-pattern-modulated electronic structures in Sb2Te3/graphene heterostructure

“…The difference of dI/dV curves between two epitaxial orientations is mainly ascribed to a combined effect of lattice mismatch difference and charge transfer. Similar phenomenon was observed in the system of MoS2/graphite [21]. Moiré pattern of three rotation angles 1° (R(37/61)), 14° (R(19/31)) and 20° (R(4/7))were observed.…”

“…Generally, commensurate moiré patterns can be described as linear integer combinations of the lattice vectors of both the substrate and overlayer. The supercell is labeled as a rhombus consisted of white and black triangles and noted as R(7, 12) [21]. The notation R (7,12) denotes that the overlayer Sb2Te3 unit cell length of 0.426 nm multiplied by 7, and the substrate graphene unit cell length of 0.246 nm multiplied by 12.…”

“…where as and ae are the lattice constant of the substrate and the overlayer, respectively [21]. The mismatch can take on either sign.…”

Spin-orbit interaction induced in graphene by transition metal dichalcogenides

“…Experimentally, however, due to a large lattice mismatch between graphene and TMDs (∼28 %) such a perfect periodicity does not exist 37 . Absence of perfect periodicity is also confirmed by the observations of pseudoperiodic faint Moiré pattern 53,54 . Therefore graphene/TMD superlattices are never perfectly periodic 55 unless the relative rotational angle between two lattices (graphene and TMD) is carefully selected.…”

“…The dominant Elliot-Yafet (EY) mechanism around the Dirac point indicates the importance of KM SOI in this low doping region. We also discuss the possibility of VZ SOI and the reason for the suppressed Rashba SOI, taking into account recent reports on band structures of graphene/TMD systems measured by angleresolved photoemission spectroscopy (ARPES) [50][51][52] and scanning tunneling microscopy (STM) studies on Moiré patterns [53][54][55] .…”