Nanoscale Imaging of Surface Plasmon Polaritons at Interface of Metal/Dielectric by UEM

Haihua Liu^1,*, Thomas E. Gage¹, Ilke Arslan¹<br/>¹Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL, USA<br/>^*Corresponding email: [email protected]<br/> <br/>Surface plasmon polaritons (SPPs) are collective oscillation of surface charge-density waves at the interface between a metal and a dielectric material. The SPPs that propagate along the interface and exhibits exponential decays perpendicular to the interface into an adjacent dielectric medium. With the unique properties of evanescence and surface localization, SPP’s are non-radiative and can be transversely localized and guided into subwavelength metallic structures as small as a few nanometers. A new branch of photonics called plasmonics, based on control and manipulation of light using SPPs at the nanoscale, has the potential to break diffraction limit of light and exhibit significant advantages in nanophotonics device development by replacing electronic signals with light as information carriers is a prime motivation behind research on photonic circuits.¹ Therefore, it is of great importance to image the SPPs at the nanometer scale to give one deeper understanding of the guide and localization of light below the diffraction limit for nanophotonics applications.<br/> <br/>Ultrafast Electron Microcopy (UEM) has been used to study the ultrafast dynamics of light-matter interactions in physics, chemistry and materials science with temporal resolution of hundreds of femtoseconds,² which is 10 orders better than that of conventional electron microscopy limited by the camera read-out rate. Other than light-matter interaction observed in UEM, the investigation of photon-electron interaction has been enabled by one unique technique called Photon-Induced Near Field Electron Microscopy (PINEM) developed in UEM to capture the evanescent electromagnetic field on its intrinsic time scale and nanometer scale.³We recently established one state-of-art UEM scientific platform at the Center for Nanoscale Materials (CNM), Argonne National Laboratory. Besides the capabilities of imaging and diffraction, the UEM at the CNM is equipped with one GIF spectrometer, which enables it to work in energy filtering mode and record the PINEM image.⁴ Here, we investigated the excitation and localization of extended two-dimensional surface plasmon polaritons waves at the interface of metal and dielectric material including metal/dielectric interface with simple irregular nano holes or nano slots, and metal/dielectric interface with nanofabrication of nano hole array under excitation by ultrashort laser pulses using PINEM. The dependence of the SPPs on surface roughness, propagation distance, laser wavelength, fluence, and polarization was studied at the nanometer spatial scale and femtoseconds time scale. The results reveal that UEM is one powerful tool to study the SPPs at high spatiotemporal resolution of nanometer scale and femtoseconds time scale for the development and applications of SPPs-based photonic circuits such as waveguides, near-field optics, date storage, solar cells biosensing and optical communication. <br/> <br/> <br/>1. Gramotnev, D.K.; Bozhevolnyi, S.I, Plasmonics beyond the diffraction limit. Nature Photonics, 4, 83-91 (2010).<br/>2. Zewail A. H. Four-Dimensional Electron Microscopy, Science, 328, 187-913 (2010).<br/>3. Barwick B., David J. Flannigan & Ahmed H. Zewail. Photon-induced near-field electron microscopy, <i>Nature</i>, 462, 902-904, (2009).<br/>4. Haihua Liu, Thomas E Gage, Prem Singh, Amit Jaiswal, Richard D Schaller, Jau Tang, Sang Tae Park, Stephen K Gray, Ilke Arslan, Visualization of Plasmonic Couplings Using Ultrafast Electron Microscopy, Nano Letters, 21, 13, 5842–5849 (2021).<br/> <br/>Work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.