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Curvature matters: new study shows how graphene adheres over underlying trench

Continued miniaturisation of technologies is opening up exciting new possibilities in areas such as chemical sensors, signal processing and accelerometers, using nanoelectromechanical systems (NEMS), which are nanoscale devices that integrate electrical and mechanical functionalities. These devices promise high sensitivity and ultralow power consumption, which are essential features for future technologies. One important class of NEMS is the graphene resonator, in which an atomically thin layer of carbon atoms is suspended over a trench. Experiments have shown these resonators are pulled tight, like a drumhead, but until now researchers have not been able to explain how this tensioning occurs.

Now, new simulations by ISI Researcher Zoe Budrikis and ISI Research Leader Stefano Zapperi, whose results have been recently published on NanoLetters, show that although interactions between graphene and the trench are relatively weak, even a slight curvature of the rim of the underlying trench is enough to make the graphene adhere to the trench sidewalls, pulling the graphene sheet tight. This effect persists even at high temperatures, where one might expect adhesion to break down.

“We had tried all sorts of tricks to get the graphene to adhere in simulations with sharp edges but none of them were very satisfying,” says Zoe Budrikis. “The importance of a bit of rounding was almost an accidental discovery.” Calculations on a simplified model show how the effect works, by balancing stretching, adhesion and bending effects. These calculations also suggest new ideas for experiments using deliberately controlled trench shapes to make resonators with desired properties.

Temperature-Dependent Adhesion of Graphene Suspended on a Trench, Zoe Budrikis and Stefano Zapperi, NanoLetters, December 14, 2015.