ICFO-The Institute of Photonic Sciences, The Barcelona Institute of Science and Technology , 08860 Barcelona, Spain.
Center for Graphene Science, College of Engineering Mathematical and Physical Sciences, University of Exeter , Exeter EX4 4PU, United Kingdom.
Nano Lett. 2017 Oct 11;17(10):5908-5913. doi: 10.1021/acs.nanolett.7b01603. Epub 2017 Sep 5.
As a two-dimensional semimetal, graphene offers clear advantages for plasmonic applications over conventional metals, such as stronger optical field confinement, in situ tunability, and relatively low intrinsic losses. However, the operational frequencies at which plasmons can be excited in graphene are limited by the Fermi energy E, which in practice can be controlled electrostatically only up to a few tenths of an electronvolt. Higher Fermi energies open the door to novel plasmonic devices with unprecedented capabilities, particularly at mid-infrared and shorter-wave infrared frequencies. In addition, this grants us a better understanding of the interaction physics of intrinsic graphene phonons with graphene plasmons. Here, we present FeCl-intercalated graphene as a new plasmonic material with high stability under environmental conditions and carrier concentrations corresponding to E > 1 eV. Near-field imaging of this highly doped form of graphene allows us to characterize plasmons, including their corresponding lifetimes, over a broad frequency range. For bilayer graphene, in contrast to the monolayer system, a phonon-induced dipole moment results in increased plasmon damping around the intrinsic phonon frequency. Strong coupling between intrinsic graphene phonons and plasmons is found, supported by ab initio calculations of the coupling strength, which are in good agreement with the experimental data.
作为一种二维半导体，石墨烯在等离子体应用方面相对于传统金属具有明显的优势，例如更强的光场限制、原位可调性和相对较低的固有损耗。然而，能够在石墨烯中激发等离子体的工作频率受到费米能 E 的限制，在实际中，费米能只能通过静电控制在几十分之一电子伏特的范围内。更高的费米能为具有前所未有的性能的新型等离子体器件打开了大门，特别是在中红外和更短的红外波长频率下。此外，这使我们能够更好地理解本征石墨烯声子与石墨烯等离子体的相互作用物理。在这里，我们提出了 FeCl 插层石墨烯作为一种新的等离子体材料，它在环境条件下具有很高的稳定性，载流子浓度对应于 E > 1 eV。这种高掺杂形式的石墨烯的近场成像使我们能够在很宽的频率范围内对等离子体进行表征，包括它们的相应寿命。与单层系统相比，对于双层石墨烯，声子诱导的偶极矩导致本征声子频率周围的等离子体阻尼增加。通过对耦合强度的从头计算，发现本征石墨烯声子与等离子体之间存在强耦合，这与实验数据非常吻合。
