The Structure And Mechanics Of Atomically-Thin Graphene Membranes

Abstract

Graphene is an exciting new atomically-thin two dimensional system with applications ranging from next generation transistors, to transparent and flexible electrodes, to nanomechanical systems. We study the structure, electronic, and mechanical properties of suspended graphene membranes, and use them to produce mechanical resonators. We first showed that it was possible to produce suspended graphene membranes even down to one atom thick using exfoliated graphene, and resonate the membranes using optical interferometry. The resonators had frequencies in the MHz and quality factors from 20-850, but showed no reproducibility. In order to produce predictable and reproducible graphene resonators we developed methods for making large arrays of single-layer graphene membranes of controlled size, shape and tension using chemical vapor deposition (CVD) grown graphene. We used transmission electron microscopy to study the polycrystalline structure of the graphene, we found that the different grains stitched together by disordered lines of 5-7 defects. Using electron transport and scanned probe techniques, we found that the polycrystalline grain structure reduces the ultimate strength of the graphene, but did not as strongly affect the electrical properties. We systematically studied the mechanical resonance of the single-layer CVD graphene membranes as a function of the size, clamping geometry, temperature and electrostatic tensioning. We found that the CVD graphene produces tensioned, electrically conducting, highly-tunable resonators. In addition we found that clamping the graphene membrane on all sides reduces the variation in the resonance frequency, and makes the behavior more predictable.