Two-Dimensional Mechanics of Atomically Thin Solids on Water

Abstract

Movement of a three-dimensional solid at an air−water interface is strongly influenced by the extrinsic interactions between the solid and the water. The finite thickness and volume of a moving solid causes capillary interactions and water-induced drag. In this Letter, we report the fabrication and dynamical imaging of freely floating MoS 2 solids on water, which minimizes such extrinsic effects. For this, we delaminate a synthesized wafer-scale monolayer MoS 2 onto a water surface, which shows negligible height difference across water and MoS 2. Subsequently patterning by a laser generates arbitrarily shaped MoS 2 with negligible in-plane strain. We introduce photoswitchable surfactants to exert a lateral force to floating MoS 2 with a spatiotemporal control. Using this platform, we demonstrate a variety of two-dimensional mechanical systems that show reversible shape changes. Our experiment provides a versatile approach for designing and controlling a large array of atomically thin solids on water for intrinsically two-dimensional dynamics and mechanics.

Chemistry of Materials Nanoarchitectonics for Two-Dimensional Films: Langmuir–Blodgett, Layer-by-Layer Assembly, and Newcomers

“…As a top-down approach, Park and co-workers reported laser-induced structural fabrication of single-walled MoS 2 nanosheets on an air−water interface. 86 Wafer-scale single-walled MoS 2 was exfoliated and floated on the water surface. MoS 2 of arbitrary shape and structure was created by patterning with a laser.…”

“…In-plane structural fabrication of single layers has also been developed. As a top-down approach, Park and co-workers reported laser-induced structural fabrication of single-walled MoS 2 nanosheets on an air–water interface . Wafer-scale single-walled MoS 2 was exfoliated and floated on the water surface.…”

“…(A) Laser-induced structural fabrication of single-walled MoS 2 nanosheets for controls of mechanical motion of floating MoS 2 piece. Reproduced with permission from ref . (B) Spontaneous formation of two-dimensional maze pattern in mixed monolayer morphologies of palmitic acid (C 16 ) and behenic acid (C 22 ).…”