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The most exciting phrase to hear in science, the one that heralds
new discoveries, is not Eureka!(I found it!) but rather,
"hmm.... that's funny...."
Isaac Asimov
Nanoplasmonics is the study of localized surface plasmon resonance (LSPR), i.e. collective electron oscillations,
in nanoparticles. By using correlated single particle spectroscopy [1] and HRTEM, it is possible to study the effect
of shape and size on plasmonic properties without having to use ensemble averaged data.
This technique has been
developed as part of a collaboration with the Van Duyne (Chemistry) and Schatz (Chemistry) groups. In summary, a
nanoparticle suspension is drop-coated on a TEM grid and dried. A coordinate system is then used, in which the
center of the grid is the origin, to retrieve particles analyzed by light scattering experiments in the TEM, as
below. The figure on the left shows in (a) the optical microscope setup and in (b), the flow cell which can be used
during experiments. On the right is an example of the "mapping" system used: (a) a low magnification image of the
TEM grid in which each square is represented by a 2D coordinate, (b) a low magnification TEM image, and (c) a
dark-field Rayleight scattering image. Notice the similar pattern in both TEM and scattering images.
As an example of ongoing research, the optical properties of silver nanocubes have been determined [2], and accurate size (including corner rounding)
determination by HRTEM rendered possible to obtain an exceptionally good match between theory and experiment,
as shown on the right. This experiment was the first implementation of the correlated LSPR/HRTEM technique
developed at Northwestern University. Ongoing research include the application of this method to other structures as well
as improvement on the current method.
References
[1] Y. Wang, S. K. Eswaramoorthy, L. J. Sherry, J. A. Dieringer, J. P. Camden, G. C. Schatz, R. P Van Duyne, and L. D. Marks, Ultramicroscopy, doi:10.1016/j.ultramic.2009.04.003 (2009)
[2] J. M. McMahon, Y. Wang, L. J. Sherry, R. P. Van Duyne, L. D. Marks, S. K. Gray, and G. C. Schatz, J. Phys. Chem. C, 113, 2731-2735 (2009)
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Nanoparticles and Nanoplasmonics
