Two-dimensional mechanics with atomically thin solids at the air-water interface

Manipulation of micro-objects at the air-water interface brought broad interest from the micro-robotics community because of the intricate interplay between the mass and shape of the moving object and the property of the water surface. For example, a floating object induces three-dimensional curvatures to the surrounding water surface depending on its mass and shape, which leads to an attractive force to neighboring floating objects and the “Cheerios effect”. Reducing the thickness and mass of a floating object would reduce such long-range interactions, ultimately enabling two-dimensional mechanical motions without inter-object interactions. Here, we realized such two-dimensional mechanical platform made with atomically thin (~ 0.6 nm) monolayer MoS₂ films, by combining materials synthesis, precise patterning, and surface actuation. For this, we use laser patterning directly applied to MoS₂ on a water surface to generate arbitrary shapes and photoactivated surfactants to produce lateral, spatially controlled external forces. Using this platform, we study the translocation and controlled shape change of various MoS₂ films, the latter of which is related to the out-of-plane deformation of the MoS₂. Our results provide essential components for realizing programmable 2D micro-mechanical systems at the ultimate thickness limit.