Page 211 - Principles and Applications of NanoMEMS Physics

200 Chapter 5

5.3.2.1 SP Propagation in Narrow Metal Stripes

Lamprecht et al. [214] conducted studies of SP propagation in microscale
Au and Ag metal stripes of widths in the micrometer range, and determined
the effect of film width on SP propagation length, see Fig. 5-5.

CC D D
CC
High N .A.
High N .A.
P ropagatin O bjectiv
P ropagating g
O bjective e
Surface ce
Surfa M etal Structure e
M etal Structur
Plasm on
Plasm ons s 50 nm SiO
50 nm SiO
2 2
50 nm A l l
50 nm A
G lass Substrate te
θ θ G lass Substra
E E
E xcitation R egion
Measurem ent R egio
E xcitation R egion Measurem ent R egion n
Figure 5-5. Sketch of setup for spatially confined SP excitation and measurement. (After
[214].)
In particular, they fabricated 70 nm-thick gold and silver stripes with
widths in the 54 − 1µ m range. Their experimental scheme, see Fig. 5-5,
involved localized light-SP coupling by a prism arrangement utilizing an
opaque aluminum screen to achieve well demarcated excitation and
propagation regions. The propagation lengths were observed by detecting
SP stray light with a CDD camera upon excitation with three different
wavelengths, namely, 514, 633, and 785 nm. The experiment concluded that
the SP propagation length decreased with decreasing lateral stripe width, the
rate of decrease being very dramatic below 20µ m , and increased with
wavelength. At a wavelength of 633 nm, the propagation length in a silver
stripe was about 58µ m and a few microns, for stripe widths of 54µ and
m
1µ m , respectively.

5.3.2.2 SP Propagation in Nanowires

Dickson and Lyon [212], conducted studies of SP propagation in high-
aspect-ratio metal nanostructures and 20 nm diameter, 1− 15µ m -long Au
and Ag rods, observing propagation over distances greater than 10µ m for
light wavelengths of 532 nm and 820 nm. In particular, they reported that
once the SP propagation is initiated, the SPs are guided down the length of
the wire and reemerge from the end as photons via plasmon scattering. In
addition, for specific incident excitation wavelength and waveguide
composition, they were able to demonstrate unidirectional SP propagation.