Metallic Twin Grain Boundaries Embedded in MoSe₂ Monolayers Grown by Molecular Beam Epitaxy

Abstract

Twin grain boundaries in MoSe are metallic and undergo a metal to insulator Peierls transition at low temperature. Growth of MoSe by molecular beam epitaxy results in the spontaneous formation of a high density of these twin grain boundaries, likely as a mechanism to incorporate Se deficiency in the film. Using scanning tunneling microscopy, we study the grain boundary network that is formed in homoepitaxially grown MoSe and for MoSe grown heteroepitaxially on MoS and HOPG substrates. No statistically relevant variation of the grain boundary concentration has been found for the different substrates, indicating that the grain boundary formation is substrate independent and depends mainly on the growth conditions. Twin grain boundaries exhibit three crystallographically identical orientations, and thus they form an intersecting network. Different intersection geometries are identified that imply varying defect configurations. These intersection points act as preferential nucleation sites for vapor-deposited metal atoms, which we demonstrate on the example of selective gold cluster formation at grain boundary intersections. Scanning tunneling spectroscopy shows a band gap narrowing of MoSe in the immediate vicinity of the metallic grain boundary, which may be associated with lattice strain induced at the grain boundary. Tunneling noise spectra taken over the grain boundaries indicate random telegraphic noise, suggestive of pinning/depinning behavior of conductive channels in the metallic grain boundaries or their intersection points. Finally, indications for incommensurate and commensurate Peierls-driven charge density wave formation were observed in microprobe transport measurements at 205 and 227 K, respectively.

Metallic Twin Boundaries Boost the Hydrogen Evolution Reaction on the Basal Plane of Molybdenum Selenotellurides

“…Figure 1 reports atomic force microscopy (AFM) and scanning tunneling microscopy (STM) data of a typical molybdenum selenotelluride (sample S1) 2-3 layer thick film grown by MBE on highly oriented pyrolytic graphite (HOPG) substrates. [41] STS spectra taken in between (point "A") and on (point "B") line defects, suggest the metallic nature of such boundaries, which explains the presence of the bandgap states observed in the photoemission valence band spectra. [40][41][42][43].…”

“…[40][41][42][43] These films have a low surface area and very few morphological defects (edges, holes), so they allow shedding light on the inherent electrochemistry of the basal plane. Electrolysis is the most efficient and industrially scalable method to split water.…”

“…Electrolysis is the most efficient and industrially scalable method to split water. [40][41][42][43]. The former involves the adsorption and reduction of protons Herein, we have investigated the HER activity of MoSe 2 and MoTe 2 and their solid solutions (i.e., samples S1 (MoSe 0.32 Te 1.68 ) and S2 (MoSe 0.12 Te 1.79 ) using highly controlled model systems prepared by molecular beam epitaxy (MBE).…”

“…[40][41][42][43] These films have a low surface area and very few morphological defects (edges, holes), so they allow shedding light on the inherent electrochemistry of the basal plane. [41] These MTBs have a composition of MoTe or MoSe, that is, they are Mo-enriched compared to the dichalcogenide host material. Details about the sample synthesis and their physical properties and defect structures can be found in refs.…”

Room‐Temperature Ferromagnetism in MoTe2 by Post‐Growth Incorporation of Vanadium Impurities

“…Recently, long-range magnetic order has also been observed in both MoTe 2 and MoSe 2 , which has been suggested to be induced by intrinsic ferromagnetic defects, such as Mo antisites, that is, Mo atoms at chalcogen lattice sites. [26][27][28] These grain boundaries have shown no ferromagnetic properties. Here, we investigate a new doping mechanism for 2H-MoTe 2 that enables altering the monolayer or surface layer of a MoTe 2 crystal with transition metal impurities.…”