Jiawei Zhang, Xinzhong Chen, Scott Mills, Thomas Ciavatti, Ziheng Yao, Ryan Mescall, Hai Hu, Vyacheslav Semenenko, Zhe Fei, Hua Li, Vasili Perebeinos, Hu Tao, Qing Dai, Xu Du, Mengkun Liu,
https://pubs.acs.org/doi/abs/10.1021/acsphotonics.8b00190?mi=aayia761&af=R&AllField=nano&target=default&targetTab=std
Accessing the non-radiative near-field electromagnetic interactions with high in-plane momentum (q) is the key to achieve super resolution imaging far beyond the diffraction limit. At far infrared and terahertz (THz) wavelengths (e.g. 300 μm = 1 terahertz = 4 meV), the study of high q response and nanoscale near-field imaging is still a nascent research field. In this work, we report on THz nanoimaging of exfoliated single and multi-layer graphene flakes by using the state-of-the-art scattering-type near-field optical microscope (s-SNOM). We experimentally demonstrated that the single layer graphene is close to a perfect near-field reflector at ambient environment, comparable to that of the noble metals at the same frequency range. Further modeling and analysis considering the nonlocal graphene conductivity indicate that the high near-field reflectivity of graphene is a rather universal behavior: graphene operates as a perfect high-q reflector at room temperature. Our work uncovers the unique high-q THz response of graphene, which is essential for future applications of graphene in nano-optics or tip-enhanced technologies.
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