title: Far-field nanoscale infrared spectroscopy of vibrational fingerprints of molecules with graphene plasmons.
abstract: Infrared spectroscopy, especially for molecular vibrations in the fingerprint region between 600 and 1,500 cm(-1), is a powerful characterization method for bulk materials. However, molecular fingerprinting at the nanoscale level still remains a significant challenge, due to weak light-matter interaction between micron-wavelengthed infrared light and nano-sized molecules. Here we demonstrate molecular fingerprinting at the nanoscale level using our specially designed graphene plasmonic structure on CaF2 nanofilm. This structure not only avoids the plasmon-phonon hybridization, but also provides in situ electrically-tunable graphene plasmon covering the entire molecular fingerprint region, which was previously unattainable. In addition, undisturbed and highly confined graphene plasmon offers simultaneous detection of in-plane and out-of-plane vibrational modes with ultrahigh detection sensitivity down to the sub-monolayer level, significantly pushing the current detection limit of far-field mid-infrared spectroscopies. Our results provide a platform, fulfilling the long-awaited expectation of high sensitivity and selectivity far-field fingerprint detection of nano-scale molecules for numerous applications.
authors.affiliation: National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Hai
authors.initials: H
authors.lastname: Hu
authors.affiliation: National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Xiaoxia
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Physics, Zhejiang Normal University, Jinhua 321004, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhai
authors.affiliation: National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Debo
authors.initials: D
authors.lastname: Hu
authors.affiliation: National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Ruina
authors.initials: R
authors.lastname: Liu
authors.affiliation: School of Physics, Center for Nanochemistry, Collaborative Innovation Center of Quantum Matter, Peking University, Beijing 100871, China.
authors.forename: Kaihui
authors.identifier: http://orcid.org/0000-0002-8781-2495
authors.initials: K
authors.lastname: Liu
authors.affiliation: Department of Micro- and Nanosciences, Aalto University, Tietotie 3, FI-02150 Espoo, Finland.
authors.forename: Zhipei
authors.initials: Z
authors.lastname: Sun
authors.affiliation: National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Dai