Mechanochemically Controlled Functionalization of Graphene Microdrums

Mechanochemical reactions involve the use of applied mechanical distortions to reactants to drive chemical reactions. In this work, we demonstrate the use of mechanical force to direct location-specific reactions on suspended bilayer graphene microdrums, by manipulating their geometric landscape, through the introduction of standing-wave oscillations using an atomic force microscope (AFM) probe. By introducing these oscillations into the suspended membrane while it is held in contact with an underlying reactant medium (e.g. water), the mechanically induced oxidation of graphene is observed, whereby the greatest reactivity is seen to occur at the peaks of the induced standing waves, which correspond to the regions of highest local strain in the graphene bilayers. Mapping these reactive regions using Raman microspectroscopy reveals that the radial position of the highest regions of reactivity depends on the applied oscillation frequency, beginning at the center of the microdrums at low frequencies (ca. 1-20 kHz), and then expanding outward at frequencies above 100 kHz. From finite element modeling (FEM) of the frequency-dependent mechanics of the membranes, this change in shown to be consistent with the radial redistribution of the regions of the highest local curvature of the graphene. The ability to use mechanical distortions to drive location-specific functionalization of 2D materials such as graphene provides a new route to the design of nanoscale devices and site-directed catalysis on such materials.