Tightening or relaxing the tension on a drumhead will change the way the drum sounds. The same goes for drumheads made from atomically thin graphene, only instead of changing the sound, stretching graphene has a profound effect on the material’s electrical properties. We recently reported the first study to show that a scanning tunneling microscope (STM) probe tip can continuously tune the deformation of a graphene drumhead, which in turn creates a localized strain field in the graphene and leads to the formation of a spatially confined quantum dot. The graphene drumheads were created by placing the graphene over etched holes in silicon dioxide.When the graphene is strained or stretched, the charge carriers get stirred in different directions instead of going in straight lines. Mathematically, the strain can be described as a fictitious magnetic field. Just as real magnetic fields make charges go in circles, the fictitious magnetic field also makes the carriers go in curved trajectories. Our atomistic simulations showed that the graphene drumhead in this study is strained symmetrically in the proximity of the STM probe tip,and further revealed that the resulting fictitious magnetic fields point up and down with a cloverleaf symmetry. Such fields force the carriers to go in a flower type pattern, thereby confining them around the apex area similar to confinement in a quantum dot. Creating semiconducting regions like quantum dots in graphene by simply straining, instead of cutting graphene might offer the best of both worlds: high speed and the band gap crucial to computing and other applications.

 

Publication: Electro-mechanical properties of graphene drumheads, Science, 336, 1557 (2012).

 

Brief Bio: Teng Li received his Ph.D. degree in engineering science from Harvard University, Master degree in materials science from Princeton University, Ph.D and B.S. degrees in solid mechanics from Tsinghua University. He is currently an Associate Professor of Mechanical Engineering at the University of Maryland, College Park, US. He is also an affiliated faculty of Maryland NanoCenter. His research interests include mechanics of flexible electronics and nanoelectronics, mechanics of low dimensional carbon nanomaterials, deformation instability of thin films and multilayers, and biomechanics of membrane and cytoskeleton in cells.Among his awards includes US National Committee of Theoretical and Applied Mechanics Fellowship in 2012, E. Robert Kent Outstanding Teaching Award in 2012, University of Maryland GRB Summer Research Award in 2009, Ralph E. Powe Jr. Faculty Award in 2007, the Best Poster Award on Gordon Research Conference on Thin Film & Small Scale Mechanical Behavior (2004,2006) and the Outstanding Poster Award in Materials Research Society Fall Meeting (2004). He is the co-founder (with Zhigang Suo) and architect of www.iMechanica.org, the largest online community of mechanics with 37,000+ registered users from all over the world as of December 2012. He has served as the Chair of the Technical Committee of Integrated Structures in ASME Applied Mechanics Division during 2008~2012.