Graphite edge controlled registration of monolayer MoS2 crystal orientation

Abstract

Transition metal dichalcogenides such as the semiconductor MoS2 are a class of two-dimensional crystals. The surface morphology and quality of MoS2 grown by chemical vapor deposition are examined using atomic force and scanning tunneling microscopy techniques. By analyzing the moiré patterns from several triangular MoS2 islands, we find that there exist at least five different superstructures and that the relative rotational angles between the MoS2 adlayer and graphite substrate lattices are typically less than 3°. We conclude that since MoS2 grows at graphite step-edges, it is the edge structure which controls the orientation of the islands, with those growing from zig-zag (or armchair) edges tending to orient with one lattice vector parallel (perpendicular) to the step-edge.

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS2

“…Atomic resolution STM image taken on the substrate is shown in Fig. 2(c) where the lattice constant is determined to be 2.46 ± 0.02 Å in good agreement with the lattice parameter of HOPG3136. Figure 2(d) shows an atomic resolution image acquired on monolayer MoS 2 where the lattice constant is 3.13 ± 0.03 Å, in agreement with literature values3136.…”

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

“…This case is rare since the rotational angles of CVD grown MoS 2 on HOPG, tend to be small. [23][24][25][26] The corresponding ball model is drawn in Fig. 4b.…”

“…40 In our experience, the underlying HOPG substrate can be imaged directly, by using an atypically large set-point current of 50 nA. 24 Thus, not only the surface's information, but also that of the underlying layer can be detected using STM. 31 On the other hand, first-principles investigations have revealed that there may be a weak but clear charge redistribution in the space between MoS 2 and graphene.…”

“…12,13,[19][20][21] The heterojunction of twisted MoS 2 deposited on graphene or graphite is also noteworthy. The band profile and morphology have been revealed in previous STM/STS investigations, [22][23][24][25][26] and the opening of a band gap in graphene by overlaying a MoS 2 monolayer has been observed using angle-resolved photoemission spectroscopy. 27,28 However, the detailed connection between the atomic structure of the twisted heterojunction and the corresponding electronic structure is still lacking.…”

“…Generally, adjacent apparent moiré peaks are seen to have a small difference upon close inspection, and a larger periodicity is necessary for finding another point of exactly commensurate stacking. 24 We performed a series of STS measurements in the vicinity of this intersection, using a measurement frame of size 40 × 8 nm 2 spanning the boundary. The frame consists of 200 × 40 pixels, each with one tunneling spectrum.…”