Giant anisotropy in nanoscale cutting of multilayer MoS2.

We report the nanostructuring of multilayer MoS2 surfaces caused by diamond tips indenting and cutting through a few tens of monolayers (ML) in ambient air. The resulting wear damage increases by an order of magnitude or more when the cutting alignment is rotated from the zigzag (ZZ) to the armchair (AC) crystallographic direction, while keeping the loading conditions unchanged. This pronounced anisotropy is attributed to the formation of secondary microcracks along the adjacent ZZ directions during AC-cutting, which promote surface cleavage and the detachment of compact MoS2 fragments. Such secondary cracking is not observed during ZZ-cutting. Furthermore, the scratch grooves exhibited a stepped morphology with terrace heights of about 20 nm. This value, comparable to the minimum thickness of the removed chips, defines a threshold for the exfoliation of the otherwise curved MoS2 chips produced at lower indentation depths. These observations provide new insights into the nanoscale fracture and wear mechanisms of transition metal dichalcogenide (TMD) materials. They also have implications for the micromachining of MoS2-based devices, for which ZZ-cutting provides more uniform and localized surface modification while substantially reducing wear.