Engineered creation of periodic giant, non-uniform strains in MoS2 monolayers

TL;DR

This paper presents a novel method to create highly controlled, periodic giant strains in MoS2 monolayers using proton irradiation and patterning, enabling advanced strain engineering for 2D materials.

Contribution

It introduces a new technique combining irradiation and lithography to produce ordered, high-magnitude strain patterns in MoS2 monolayers, surpassing previous strain control methods.

Findings

Achieved giant strains close to rupture (>10%) in MoS2 monolayers.

Demonstrated control over strain pattern size and position through patterning.

Confirmed high strains via Raman spectroscopy.

Abstract

The realization of ordered strain fields in two-dimensional crystals is an intriguing perspective in many respects, including the instauration of novel transport regimes and the achievement of enhanced device performances. In this work, we demonstrate the possibility to subject micrometric regions of atomically-thin molybdenum disulphide (MoS2) to giant strains with the desired ordering. Mechanically-deformed MoS2 membranes can be obtained by proton-irradiation of bulk flakes, leading to the formation of monolayer domes containing pressurized hydrogen. By pre-patterning the flakes via deposition of polymeric masks and electron beam lithography, we show that it is possible not only to control the size and position of the domes, but also to create a mechanical constraint. Atomic force microscopy measurements reveal that this constraint alters remarkably the morphology of the domes, otherwise subject to universal scaling laws. Upon the optimization of the irradiation and patterning processes, unprecedented periodic configurations of large strain gradients -- estimated by numerical simulations -- are created, with the highest strains being close to the rupture critical values (> 10 %). The creation of such high strains is confirmed by Raman experiments. The method proposed here represents an important step towards the strain engineering of two-dimensional crystals.