Electron Energy Loss and One- and Two-Photon Excited SERS Probing of “Hot” Plasmonic Silver Nanoaggregates
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We report electron energy loss spectroscopy (EELS) and one- and two-photon excited surface-enhanced Raman scattering (SERS) and hyper Raman studies on plasmonic silver nanoaggregates. By comparison with computations, EELS imaging reveals an inverse relationship between local field intensity in an optical experiment and electron energy loss intensity at energies corresponding to excitation wavelengths used for optical probing. This inverse relation exists independent on specific nanoaggregate geometries and is mainly controlled by the gap size between the particles forming the aggregate. The ratio between two- and one-photon excited SERS measured at different excitation wavelengths provides information about local fields in the hottest spots and their dependence on the photon energy. Our data verify experimentally the predicted increase of local optical fields in the hot spots with increasing wave lengths. The reported findings show new experimental ways to characterize local fields of plasmonic nanostructures. This is of particular importance for complex structures which are not easily approachable by computations.
KeywordsSurface-enhanced Raman scattering (SERS) Electron energy loss spectroscopy (EELS) Plasmonic nanoatructures Silver nanoaggregates Plasmonic dimers Two-photon excitation
We thank the Director of the Center for Electron Nanoscopy, Andrew Burrows, for supporting the project. We also would like to thank Mildred Dresselhaus, Massachusetts Institute of Technology, for reading the manuscript and for valuable comments.
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