Nano-Plasmonic Phenomena in Graphene
| Date/Time: | Monday, 16 Feb 2015 from 4:10 pm to 5:00 pm |
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| Location: | Physics 0003 |
| Phone: | 515-294-5441 |
| Channel: | College of Liberal Arts and Sciences |
| Actions: | Download iCal/vCal | Email Reminder |
Abstract: Graphene plasmons, which are collective oscillations of Dirac fermions in graphene, are of broad interests in both fundamental research and technological applications. In this talk, we present the first nano-imaging and nano-spectroscopy studies of graphene plasmons using the scattering-type scanning near-field optical microscopy - a unique technique allowing efficient excitation and high-resolution imaging of graphene plasmons. With this technique, we were able to show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons in the infrared frequencies. The observed plasmons are highly confined surface modes with a wavelength around 200 nm that are conveniently tunable by the back gate voltages [Nature 487, 82-85 (2012)]. In addition, we performed nano-spectroscopy of graphene over a broad range of mid-infrared frequencies, which provides evidence of strong coupling between graphene plasmons and SiO2 optical phonons [Nano Lett. 11(11), 4701-4705 (2011)]. Furthermore, we were able to map and characterize grain boundaries inside CVD graphene film by examining the distinct plasmonic interference patterns triggered by these line defects. Our modeling and analysis unveiled unique electronic properties associated with grain boundaries [Nature Nanotech. 8, 821-825 (2013)]. Finally, we investigate the plasmonic properties of Bernal-stacking bilayer graphene (BLG) and find that BLG supports gate-tunable infrared plasmons with higher confinement compared to graphene and randomly stacked graphene layers. Moreover, BLG plasmons can be turned off completely in a wide voltage range close to the charge neutrality point. Those unique plasmonic properties are attributed to both interlayer quantum tunneling and bandgap opening in BLG.
Bio: Zhe Fei is a staff scientist in Center for Nanoscale Materials, Argonne National Laboratory. He received his Ph.D. in Physics (2014) at UC San Diego, B.S. in Physics (2006) and M.S. in Physics (2009) at Nanjing University. He has been working on optical physics of novel two-dimensional layered materials since 2006.