Engineered Creation of Periodic Giant, Nonuniform Strains in MoS2 Monolayers

The realization of ordered strain fields in 2D crystals is an intriguing perspective in many respects, including the instauration of novel transport regimes and enhanced device performances. However, the current straining techniques hardly allow to reach strains higher than approximate to 3% and in most cases there is no control over the strain distribution. In this work, a method is demonstrated to subject micrometric regions of atomically thin molybdenum disulfide (MoS2) to giant strains with the desired ordering. Selective hydrogen-irradiation of bulk flakes allows the creation of arrays of size/position-controlled monolayer domes containing pressurized hydrogen. However, the gas pressure is ruled by energy minimization, limiting the extent and geometry of the mechanical deformation of the 2D membrane. Here, a protocol is developed to create a mechanical constraint, that alters remarkably the morphology of the domes, otherwise subject to universal scaling laws, as demonstrated by atomic force microscopy. This enables the realization of unprecedented periodic configurations of large strain gradients-estimated by numerical simulations-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 toward the strain engineering of 2D crystals.