Nanoscale eengineering of infrared plasmons in graphene.

摘要

Surface plasmons are collective oscillations of free charge carriers confined in interface between two dielectrics, where the real part of the dielectric changes sign (e.g a metal-insulator interface such as gold film and air). The study of surface plasmon has been a popular research theme with potential applications utilizing the fact that the wavelength of plasmons can be many order smaller than that of the incident lights. The potential applications include transfer of information in hundreds of terahertz instead of upper limit of gigahertz in traditional wires, photodetectors with frequency range from terahertz to mid-IR, and nano-imaging. In our experiment, we use an IR near-field microscopy with resolution as low as 10nm but energy scale of micron range. This is achieved by shinning an AFM tip with infrared laser on top of the sample and collecting the scattered light from the sample. The spatial resolution proportional to where a is the size of the tip and the resolution can reach 10nm. This technique beats the diffraction limit of near-IR (10um) by over 1000x. The wavelength and amplitude damping of plasmon greatly depends on the property of free carriers in the material. While metals such as gold had been widely studied and shown promising results, a better platform with longer propagation length and shorter wavelength is needed for application. Graphenes supreme electronic transport property makes it apiii pears to be an excellent candidate for plasmonic. Graphene plasmon across a p-n junction will be discussed. Oxygen doping of graphene with different dosage via UV ozone is studied. Oxygen doping has shown promising results for graphene plasmon guide. Plasmon fringes are developed in the interior breaking the limit of boundary condition. The UV ozone treatment can be fine controlled and without damaging the graphene sheet. One can, in theory, mask and selectively dope to create a robust graphene plasmon circuit that is stable in room temperature.