Photon-Induced Near Field Electron Microscopy - California Institute ...

Q x
8
6
4
2
0
0E+0
x
2E+4
y
cap
4E+4
center
6E+4
side
8E+4
0 1 2 3 4 5
photon energy (eV)
Figure 7. Optical and electric excitation efficiencies of a silver nanorod.
|E| 2 Re[E Im[F 0 ] |F 0 | 2
// ]
Q x
x
y
Figure 8. Scattered electric fields ( E), ⃗ field integral ( ˜F 0), and transition probabilities ( ˛ ˜F 0˛˛˛2
) for a silver nanorod at ŷ and
ˆx polarized 519 nm excitations. Note that electric fields were Gaussian-filtered (σ = 1 pixel) to reduce DDA artifact.
∣
with much stronger intensities in the middle. Furthermore, ∣Ẽ ∣ is dominated by Ẽx at ends, but by Ẽy in
∣
the middle, which results in different numbers of nodes between ∣Ẽ ∣ 2 ]
and Re
[Ẽx , and the PINEM image is
correlated to ∣E
⃗ ∣ 2 .
Figs. 9 and 10 show scattering intensities and PINEM images at various resonance energies, respectively.
Good correlations between scattering intensities and PINEM images are readily seen. Perpendicular excitations
all show PINEM images similar to that at 519 nm, which is a dipole excitation in a cylinder. Parallel excitations
show a strong wavelength dependence. In particular, 400 nm shows (linear) hexapole (l = 5) behavior, and the
PINEM image shows six maxima along the rod axis. 342 nm corresponds to 3.6 eV peak in Fig. 7, which shows a
strong excitation for perpendicular polarization and almost no excitation for parallel polarization. Consequently,
the PINEM image for 342 nm parallel polarization shows non-resonant behavior, namely a weak dipole excitation.
489 nm 400 nm
342 nm 250 nm
x
y
Figure 9. Scattering intensities of a silver nanorod at 489, 400, 342, and 250 nm. Note that electric fields were Gaussianfiltered
(σ = 1 pixel) to reduce DDA artifact.
489 nm 400 nm
342 nm 250 nm
x
y
Figure 10. Transition probabilities of a silver nanorod at 489, 400, 342, and 250 nm.
Proc. of SPIE Vol. 8845 884506-7