Abstract
Electron tomography in combination with electron energy-loss spectroscopy (EELS) experiments and simulations was used to unravel the interplay between structure and plasmonic properties of a silver nanocuboid dimer. The precise 3D geometry of the particles fabricated by means of electron beam lithography was reconstructed through electron tomography, and the full three-dimensional information was used as an input for simulations of energy-loss spectra and plasmon resonance maps. Excellent agreement between experiment and theory was found throughout, bringing the comparison between EELS imaging and simulations to a quantitative and correlative level. In addition, interface mode patterns, normally masked by the projection nature of a transmission microscopy investigation, could be unambiguously identified through tomographic reconstruction. This work overcomes the need for geometrical assumptions or symmetry restrictions of the sample in simulations and paves the way for detailed investigations of realistic and complex plasmonic nanostructures.
Highlights
Electron tomography in combination with electron energy-loss spectroscopy (EELS) experiments and simulations was used to unravel the interplay between structure and plasmonic properties of a silver nanocuboid dimer
The precise 3D geometry of the particles fabricated by means of electron beam lithography was reconstructed through electron tomography, and the full three-dimensional information was used as an input for simulations of energy-loss spectra and plasmon resonance maps
By tailoring shape and alignment of metallic nanoparticles, it becomes possible to control properties of localized surface plasmon resoncances (LSPRs), such as spectral peak positions or nearfield couplings and enhancements.[1,2,4−6] In particular the topdown approach of electron beam lithography plays an important role in the quest of versatile nanoparticle manufacturing,[7−11] but the technique usually suffers from imperfections, surface roughness, and limited spatial resolution, which leads to nanoparticle shapes that deviate from the design objectives
Summary
Figure 1. 3D reconstruction of the silver nanocuboids seen (a) from the top side and (b) from the bottom (substrate) side. Instead of attempting a tomographic reconstruction of the plasmon fields (with exception of two interface modes to be discussed at the end), we used the precise 3D geometry of the particles as an input for EELS simulations[14,31−33] and computed EEL spectra and maps for direct comparison with experiment. Simulated EEL spectra and maps of coupled silver nanocuboids agree extremely well with experimental data, except for small deviations originating from incomplete information about the actual material composition and crystallinity. These differences could be eliminated if pure monocrystalline materials were used, or simulation tools would consider the exact material properties. Image acquisition, and data processing, plasmon resonance maps under several tilt angles, details about simulations, and considerations about sample aging (PDF)
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