Synthesis and Optical Properties of Noble Metal Nanoparticles for Biodetection - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 7

In this section, we present the model predictions for the overall
absorption spectra of different metal nanorods with 50 nm in
length and 20 nm in diameter (see Fig. 1.1). The calculations were
conducted including size correction for the effective mean free path
of free electrons. It gives better descriptions to the experimental
observations. In terms of the clearly resolved characteristic surface
plasmon bands for longitudinal and transverse modes, we found
no particular trend by considering the free electron density. Well-
resolved surface plasmon bands were observed in the cases of Na,
Cu, Ag, Au, Al, and Ga. In addition, absorption spectra for either
longitudinal or transverse mode are given in Fig. 1.2 and Fig. 1.3,
respectively.

400 50 40

Cu

Na Ni Al

800

40

300 30

600

30

200 20

400

20

100 10

200

10

0 0 0 0

200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200

50 100 3

Ti Pd Ag Ga

40 40 80

2

30 60

20

20 40

1

10 20

0 0 0 0

200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200

20 30 30 40

Mn Pt Au Co

16

30

20 20

12

20

8

10 10

10

4

0 0 0

0

200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200

50 50

Re Fe Os Rh 60

40 40 40

30 30

40

20 20 20

20

10 10

0 0 0 0

200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200 200 400 600 800 1000 1200

Wavelength (nm)

Figure 1 . 3 Simulated absorption spectra for the transverse surface
plasmon mode of metallic nanorods, a component to the full
spectra shown in Fig. 1.1.

1 . 3 . 3 Scattering Spectra of Noble Metal Nanorods

In the model descriptions, the deinitions and originalities for the
surface plasmon associated absorption and scattering are different.
Basically, the imaginary part of the mean polarizability contributes
to the dipole absorption while square of the mean polarizability is
responsible for the scattering. 13,46 The results mainly conirm the
dominating role of the surface plasmon to both spectra. Peak positions