Biomedical Engineering Reference
In-Depth Information
12.2.4
Summary
In summary, we have seen that the key results in nanoplasmonics
can be found by considering a cylindrical wire. In particular, these
results are:
•
Metal dielectric waveguides support guided modes;
•
As their size is reduced, these modes become confined
to the extreme subwavelength scale and both their group
velocity and phase velocity slow down;
•
Localized plasmons can be thought of as standing wave
Fabry-Perot resonances, where the end reflection is in-
cluded in the analysis;and,
•
By wrapping the wire in a loop, a magnetic response can be
obtained,butithasbeenarguedthatthiscanonlybestrong
for the large permittivity limit.
In the next section, we will describe how fast electrons can be used
as a nanoplasmonicprobe.
12.3 Electron Energy Loss Spectroscopy
Among the first predictions of observing plasmons considered the
use of EELS (Blackstock, A.W. and Ritchie, R.H. and Birkhoff, R.D.,
1955). Since that time, there have been significant advances in the
use of EELS to map out plasmons on nanostructured metals. Here,
wewillfocusonthetheoryofEELSanddiscussapplicationsofEELS
to nanoplasmonics.
12.3.1
Theory
An electron traveling past a metal nanostructure is essentially a
delta-like current source that induces an electric field. The electron
then loses energy,
E
through this self-induced field via the
relation:
E
=
e
∞
∞
0
ω
(
ω
)
d
ω
−∞
v
·
E
ind
(
r
e
(
t
),
t
)
dt
=
(12.6)
