Characterization of nanomechanical graphene drum structures

Abstract

Characterization of nanomechanical graphene drum structures is presented in this paper. The structures were fabricated by mechanical exfoliation of graphite onto pre-etched circular trenches in silicon dioxide on a silicon substrate. Drum structures with diameters ranging from 3.8 to 5.7 µm and thicknesses down to 8 nm were achieved. Mechanical characterization of the devices was then carried out by using atomic force microscopy (AFM) to measure their electrostatic deflection. The structures were found to have linear spring constants ranging from 3.24 to 37.4 N m−1 and could be actuated to about 18–34% of their thickness before exhibiting nonlinear deflection. An analytical framework was formulated to model the deflection behaviour which was verified through finite element simulations (FEM). The experimental measurements agree well with analytical and finite element results using Young's modulus of 1 TPa. The resonance characteristics of the structures were derived by both plate theory and FEM simulations. It was found that our drum structures could potentially vibrate at frequencies in excess of 25 MHz. The small size and high operating frequencies of our nanomechanical graphene devices make them very promising for resonant mass sensing applications with 10−20 g Hz−1 sensitivity, a two order of magnitude improvement over other reported silicon structures.