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Register a new userStretching graphene using polymeric micro-muscles
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Added by
Francesco Colangelo
Publication date
2017
fields
Physics
and research's language is
English
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The control of strain in two-dimensional materials opens exciting perspectives for the engineering of their electronic properties. While this expectation has been validated by artificial-lattice studies, it remains elusive in the case of atomic lattices. Remarkable results were obtained on nanobubbles and nano-wrinkles, or using scanning probes; microscale strain devices were implemented exploiting deformable substrates or external loads. These devices lack, however, the flexibility required to fully control and investigate arbitrary strain profiles. Here, we demonstrate a novel approach making it possible to induce strain in graphene using polymeric micrometric artificial muscles (MAMs) that contract in a controllable and reversible way under an electronic stimulus. Our method exploits the mechanical response of poly-methyl-methacrylate (PMMA) to electron-beam irradiation. Inhomogeneous anisotropic strain and out-of-plane deformation are demonstrated and studied by Raman, scanning-electron and atomic-force microscopy. These can all be easily combined with the present device architecture. The flexibility of the present method opens new opportunities for the investigation of strain and nanomechanics in two-dimensional materials.
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The control of the local strain profile in 2D materials offers an invaluable tool for tailoring the electronic and photonic properties of solid-state devices. In this paper, we demonstrate a local engineering of the exciton photoluminescence (PL) energy of monolayer tungsten disulfide (WS2) by means of strain. We apply a local uniaxial stress to WS2 by exploiting electron-beam patterned and actuated polymeric micrometric artificial muscles (MAMs), which we implement onto monolithic synthetic WS2/graphene heterostructures. We show that MAMs are able to induce an in-plane stress to the top WS2 layer of the van der Waals heterostructure and that the latter can slide on the graphene underneath with negligible friction. As a proof of concept for the local strain-induced PL shift experiments, we exploit a two-MAM configuration in order to apply uniaxial tensile stress on well-defined micrometric regions of WS2. Remarkably, our architecture does not require the adoption of fragile suspended microstructures. We observe a spatial modulation of the excitonic PL energy of the WS2 monolayers under stress, which agrees with the expected strain profile and attains a maximum redshift of about 40 meV at the maximum strain intensity point. After the actuation, a time-dependent PL blueshift is observed in agreement with the viscoelastic properties of the polymeric MAMs. Our approach enables inducing local and arbitrary deformation profiles and circumvents some key limitations and technical challenges of alternative strain engineering methods requiring the 2D material transfer and production of suspended membranes.
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