Nanomechanical cleavage of molybdenum disulphide atomic layers

Abstract

The discovery of two-dimensional materials became possible due to the mechanical cleavage technique. Despite its simplicity, the as-cleaved materials demonstrated surprising macrocontinuity, high crystalline quality and extraordinary mechanical and electrical properties that triggered global research interest. Here such cleavage processes and associated mechanical behaviours are investigated by a direct in situ transmission electron microscopy probing technique, using atomically thin molybdenum disulphide layers as a model material. Our technique demonstrates layer number selective cleavage, from a monolayer to double layer and up to 23 atomic layers. In situ observations combined with molecular dynamics simulations reveal unique layer-dependent bending behaviours, from spontaneous rippling (o5 atomic layers) to homogeneous curving (B 10 layers) and finally to kinking (20 or more layers), depending on the competition of strain energy and interfacial energy.

Peeling of multilayer graphene creates complex interlayer sliding patterns

“…We did not observe a single system where the kink would have been stable after releasing the peeling force, a situation different from multilayer molybdenum disulphide for which such stable kinks have been observed experimentally 5 . This, however, is in line with the larger corrugation energy of MoS 2 compared to multilayer graphene.…”

“…This remained the case even if the two flat layers above were removed, that is, even if no adhesion contribution was present in the simulation. This is unlike the case of molybdenum disulphide where stable, or at least metastable, kinks could be made by bending the multilayer stack with a nanoprobe 5 . This difference, however, is consistent with the much larger corrugation energy of MoS 2 layers 23,24 .…”

“…The bending-induced sliding of the graphene layers consequently affects the stacking, which is known to influence profoundly the electronic properties of multilayer graphene 4 . Interlayer shifts and registry changes are known to have significant effects also in other materials 5 , thus making the studies of peeling and the related bending-induced sliding patterns of multilayer graphene particularly relevant.…”

“…An N-layer multilayer graphene stack was peeled by displacing downwards the rightmost carbon atoms on top of the peeled stack, while letting them move freely in the xy−plane. This simulation setup was designed to mimic recent experiments that used the tip of a nanoprobe to peel multilayer molybdenum disulphide 5 . The upmost, unpeeled layer was fixed.…”

Nanoscale Inhomogeneous Superconductivity in Fe(Te1–xSex) Probed by Nanostructure Transport

“…The fact that the superconducting volume fraction does not reach 100% implies possible existence of inhomogeneous superconductivity to some extent. Atomically thin Fe(Te 0.5 Se 0.5 ) crystals can be obtained on Si/SiO 2 substrate via microexfoliation (see Methods), which is widely recognized to be able to maintain the highest quality of crystal and has been extensively used for fabricating 2D crystals of graphene and transition metal dichalcogenides [33][34][35][36] . The quality and stability of the exfoliated Fe(Te 0.5 Se 0.5 ) thin flakes were examined by using the transmission electron microscope (TEM) measurements.…”