Nanoscale Imaging of Plasmonic Coupling in Nanorod Dimers/Trimers by UEM

Replacing electronic signals with light pulses as information carriers is a prime motivation behind research on photonic circuits. Plasmonics based on surface plasmon polaritons, charge collectivly oscillating at the interface or surface, is attracting extensive interests because it enables concentration and manipulation of electric fields well beyond diffraction limit via nanoscale structures.[1] Therefore, direct imaging of the plasmonic field and its coupling at the nanoscale between photonics circuit components or plasmonic nanostructures is critical for nanophotonics applications, while scientists in this field mainly rely on theoretical simulation of the plasmonic field by FDTD or other programs. Noble metals such as Au or Ag are among the most popular plasmonic materials because of their strong coupling with light from visible to near-infrared (NIR) wavelengths. The anisotropic optical properties of the Au or Ag nanorods between the long and short axis provide tunable plasmonic energies and alternate ways to manipulate the plasmonic couplings between their dimer or trimer nanostructures depending on their mutual orientations and light polarizations. Photon-Induced Near Field Electron Microscopy (PINEM) developed in ultrafast electron microscopy (UEM) enables scientists to capture the evanescent electromagnetic field on its intrinsic time scale and with nanometer resolution.[2] To gain deeper insights regarding the plasmonic coupling mechanism at the nanometer scale, the dependences of the plasmonic coupling within the dimer/trimer on laser polarizations and fluences, time, and nanorod mutual orientations were investigated at high spatiotemporal resolution on the newly established scientific UEM platform at Center for Nanoscale Materials, Argonne National Laboratory.<br/><br/>[1] Gramotnev, D.K.; Bozhevolnyi, S.I, Plasmonics beyond the diffraction limit. Nature Photonics 2010, 4, 83-91.<br/>[2]. Barwick, B.; Flannigan, D.J.; Zewail, A.H. Photon-induced near field electron microscopy. Nature 2009, 462,902-906.<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.