• nanodevices
• 2D materials
• strain engineering

Recently, the study of the influence mechanical deformation on the properties of two-dimensional materials revealed many interesting results, such as photoluminescence (PL) tuning in monolayer transition metal dichalcogenides (TMD) and pseudo-magnetic field appearance in graphene. Controlling local strain allows to better exploit these properties and to design strain-based devices. Micrometric artificial muscles (MAM) are polymer-based actuators activated by electrons exposure and they represent a valuable method to induce local strain. Experiments with polymethil methacrylate (PMMA) have already demonstrated the correct operation of MAMs but a proper PMMA calibration relating the induced strain to the electron dose is still lacking. We provide a first study of the dependence of PMMA shrinkage on the electron dose and energy. Secondly, we explore metallic actuator as alternative to PMMA MAMs, which typically display strain relaxation over time preventing the design of permanent strain-based devices. We exploit the stress that thin metallic films acquire after deposition by evaporation to realize permanent actuators. The residual stresses of titanium and vanadium were estimated by depositing thin films on silicon nitride cantilevers and by studying their deformation. Vanadium revealed to be the best choice and was used to induce strain in tungsten disulfide (WS2) flakes on bilayer graphene (BLG). WS2 displays a strong strain-tunable PL peak around 2 eV together with superlubricity at WS2/BLG interface, permitting to induce strain while avoiding membrane suspension. A variety of actuators based on vanadium were designed and realized on triangular WS2 flakes. At present, we have not been able to detect any induced strain, possibly due to the insufficient adhesion between actuators and two-dimensional material in the current design.