Backside opening
a) b) c)
d) e) f)
Au
shell
2. 5
1.07
µm
39 nm
x
z
y
x
z
y
x
z
y
2.0
1. 5
1.0
0.5
0.0
120
100
80
60
40
20
0
g)
1000
1000
100
10
1
500 600 700 800
Campanile
Bow-tie antenna
Sharp tip
900
Incident wavelength (nm)
Normalized feld (|E|) enhancement
SiO2
core
OPTICAL ANTENNAS continued
the nanowire shifted the resonant peak
from 1300 to 1530 nm, attractive for
communication applications. 6
Halas’s group took a different ap-
proach, capturing the energy produced
when surface plasmons in an optical an-
tenna decay to hot electron-hole pairs.
They fabricated an array of 300 rectan-
gular gold nanorods on the surface of n-
doped silicon, forming a Schottky barrier
between the two materials. Hot electrons
generated in the gold nanoantenna had
enough energy to cross the Schottky
barrier and produce a photocurrent in
the silicon. The wavelength response
FIGURE 2. More elaborate dipole-type
antennas concentrate power at their central
feed gap in the same way as the bow-tie.
This campanile-type antenna concentrated
light energy into a 10 nm zone for probe
measurements at Stanford.
