Iwamoto M., Kwon Y.-S., Lee T. (Eds.) Nanoscale Interface for Organic Electronics
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Training and Fatigue of Conducting Polymer Artificial Muscles 239
π-electron system could be lowered by straighten of polymer chains,
resulting in the shift of oxidation and reduction potential to lower energy.
The remarkable shift of reduction peak by the stress in CV of Fig. 7(a)
may be related to this energy shift. The oxidation attacks the lowered
π-electrons and degrades the electrochemical activity of the films. The
detailed mechanism of degradation by electrochemical cycle under
tensile stress is not known in detail, however, the thermodynamical
behavior of ion diffusion is also taken into account.
8. Prospect of Soft Actuators
Soft actuators based on conducting polymers are being developed with
respect to the strain, contraction force and response time, which are more
than those of skeletal muscle. However, there are still some problems,
such as cycle life and stability as well as using liquid electrolyte. The soft
actuators are a new candidate for human friendly machine to drive robots.
Mostly present conducting polymers being studied for soft actuators are
existing materials, and new materials aimed for soft actuators are needed.
Also novel applications of soft actuators has to be considered.
References
1. K. Kaneto, Oyo Butsuri, 76 (12), 1356 (2007) [In Japanese].
2. Ed. Y. Osada, Frontier of Soft Actuators, N.T.S. (2004) [In Japanese].
3. T. Mirfakhrai, J. D. W. Madden and R. H. Baughman, Materials Today, 10, 30
(2007).
4. K. Oguro, Kagaku to Kogyou, 72, 162 (1998) [In Japanese].
5. K. Kaneto, M. Kaneko, Y.-G. Min and A. G. MacDiarmid, Synthetic Metals, 71,
2211 (1995).
6. Q. Pei, M. Rosethal, S. Stanford, H. Prahlad and R. Pelrine, Smart Mater. Struct., 13,
N86-N92 (2004).
7. Toshiro, Zairyou Kagaku, 32, 59 (1995) [In Japanese].
8. Y. Osada, H. Okuzaki and H. Hori, Nature, 355, 242 (1992).
9. T. Fukushima, K. Asaka, A. Kosaka and T. Aida, Agrew Chem. Int. Ed., 44, 2410
(2005).
10. Y. Nakabo, T. Mukai, K. Asaka and K. Ogawa, WW-EAP Newsletter, 7, 22 (2005).
11. W. Yim, J. Lee and K. J. Kim, Bioinspiration and Biomimetics, 2, 531 (2007).
12. K. Kaneto and M. Kaneko, Applied Biochemistry and Biotechnology, 96, 13 (2001).
K. Kaneto 240
13. S. Hara, T. Zama, A. Ametani, W. Takashima and K. Kaneto, J. Mater. Chem., 14,
1516 (2004).
14. S. Hara, T. Zama, W. Takashima and K. Kaneto, Synth. Met., 146, 199 (2004).
15. K. Kaneto, Oyo Butsuri, 75, 318 (2006).
16. S. Hara, T. Zama, W. Takashima and K. Kaneto, Polym. J., 36, 933 (2004).
17. S. Hara, T. Zama, W. Takashima and K. Kaneto, Smart Mater. Struct., 14, 1501
(2005) .
18. S. Hara, T. Zama, W. Takashima and K. Kaneto, Polym. J., 36, 151 (2005).
19. K. Kaneto, H. Fujisue, M. Kunifusa and W. Takashima, J. Smart Mat. and Struct.,
16, S250 (2006).
20. K. Kaneto, H. Fujisue, K. Yamato and W. Takashima, Thin Solid Film, 516, 2808
(2008).
21. H. Fujisue, T. Sendai, K. Yamato, W. Takashima and K. Kaneto, Bioinsp. Biomim.,
2, S1 (2007).
22. K. Kaneto, H. Suematsu and K. Yamato, Bioinsp. Biomim., 3, 035005 (2008) (6pp).
23. W. Takashima, M. Nakashima, S. S. Pandey and K. Kaneto, Electrochimica Acta,
49, 4239 (2004).
24. M. Fuchiwaki, W. Takashima and K. Kaneto, Mol. Crys. Liq. Crys., 374, 523 (2002).
25. K. Kaneto, H. Suematsu and K. Yamato, Advances in Science and Technology, 61,
122 (2008).
26. T. F. Otero, Advances in Science and Technology, 61, 112 (2008).
27. T. Sendai, H. Suematsu and K. Kaneto, Jpn. J. Appl. Phys., 48, 051506 (2009) (4p).
28. E. Smela, W. Lu and B. R. Mattes, Synthetic Metals, 151, 25 (2005).
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Part 3
Polymer
Electronics
243
CHAPTER 12
SURFACE PLASMON EXCITATIONS AND EMISSION LIGHTS
IN NANOSTRUCTURED ORGANIC FILMS
Keizo Kato
Graduate School of Science and Technology, Niigata University,
2-8050 Ikarashi, Nishi-ku, Niigata 950-2181, Japan
E-mail: keikato@eng.niigata-u.ac.jp
The research is reviewed on the attenuated total reflection (ATR)
method utilizing surface plasmon (SP) excitations at the interface
between metal and dielectric ultrathin films, that is, the surface plasmon
resonance (SPR) method. The ATR method is quite useful for
evaluation of the dielectric ultrathin films and applications to sensors
and plasmonic devices. Emission lights due to SP excitations are
observed through the prism in the Kretschmann configuration for the
ATR method, when metal films on the prism or organic films with
metal films on the prism are directly irradiated from air by a laser beam,
that is, reverse irradiation. The emission lights depend on the surface
roughness of the films and are also related to the photoluminescence of
organic molecules. The properties and applications of the SP emission
lights are described. Among the SP excitation methods, one of the most
well known techniques is a prism coupling technique based on the ATR
configuration, while a grating coupling technique can be widely used
for the sensing or plasmonic devices. The grating coupling excitation
method is also described.
1. Introduction
The investigation of properties in organic ultrathin films is very
important and many studies on the electrical and optical devices have
been carried out. For the development of organic ultrathin film devices
with high efficiency, it is quite important particularly to evaluate the
K. Kato 244
structure and optical functions of the ultrathin films. The attenuated total
reflection (ATR) method utilizing surface plasmon (SP) excitation at the
interface between metal and dielectric ultrathin films is one of very
useful techniques for evaluation of dielectric properties of the ultrathin
films and sensing.
1,2
SPs are a coupling mode of free electrons and light,
and they can be resonantly excited on metal surfaces in the Kretschmann
and the Otto configurations by electromagnetic waves due to the total
reflection of a p-polarized laser beam.
1
SPs are two-dimensional optical
waves and propagate along the surfaces with strong electromagnetic
waves, that is, evanescent waves, which decay exponentially away
from the surfaces. SPs are also utilized in near-field optics where
electromagnetic waves with light frequency are localized in structures
smaller than the light wavelength.
3
It is considered that SPs are very
important and useful for the application to optical nano-devices.
3
Recently, emission lights have been observed through the prism in the
Kretschmann configuration for the ATR method, when metal ultrathin
films on the prism or organic ultrathin films with metal ultrathin films on
the prism were directly irradiated from air by a laser beam, that is,
reverse irradiation.
3-6
The emission lights depend on the surface
roughness of the films.
6
The intensities and the spectra of the emission
lights strongly depend on the emission angles and the emission lights are
also related to the photoluminescence of organic molecules.
7-9
The
relation between the peak wavelengths of the spectra and the emission
angles corresponded to the dispersion property of the resonant
excitations of SPs in the ATR configuration.
7
From the dispersion
properties, it was estimated that the light emission was caused by
multiple excitations of SPs.
7-9
The SP emission light property also
depended on the nanostructures and the strongest emission was observed
at some separation of the dye molecule from the metal surface.
8
The
intensity of SP emission light was found to depend on the amount of
dyes and nano-spacing between the metal and dyes.
8,9
The SP emission
light also depended on the polarization direction of excitation light,
which was due to the molecular shape of the dyes.
10
Among the SP excitation methods, one of the most well-known
techniques is the prism coupling technique based on the ATR
configuration. The grating coupling technique has not been widely used
Surface Plasmon Excitations and Emission Lights in Organic Films 245
for SPR sensors or plasmonic devices.
11-14
One major advantage of using
the grating-coupling excitation method is the fact that a prism is not
necessary; hence, inexpensive and disposable plastics can be used as the
substrates, allowing for more flexible configurations.
15,16
2. SP Excitation and ATR Method
2.1. SP Excitation
Figure 1(a) shows the reflection of the p-polarized light at the interface
at the interface between a prism and air. The condition of the total
reflection of the incident light is given by
-1
i c 1 2
sin ( / )
n n
θ θ
> = (1)
where
θ
i
is the incident angle of the incident light,
θ
c
is the critical angle
of the total reflection, and
n
1
and n
2
indicate the reflective indices of the
prism and air, respectively. Figure 1(b) shows the electric field pattern of
the p-polarized incident light at the interface and the evanescent wave
produced at the interface.
Figure 2 shows the SP excitation at the interfaces of metal thin films.
The electric fields of p-polarized incident light generate vibration of free
electrons of the metal thin film and excite the SP. The SP excitations at
the interfaces between the metal thin film and air and between the metal
thin film and organic ultrathin film are shown in Figs. 2(a) and 2(b),
(a) (b)
Fig. 1. Reflection of p-polarized incident light and the evanescent wave produced at the
interface between prism and air. (a) indicates the total reflection at the interface and
(b) indicates the electric field pattern of the p-polarized incident light at the interface and
the produced evanescent wave.
prism
air
θ
i
p-polarized
incident light
n
1
> n
2
n
2
reflected light
prism
air
θ
i
p-polarized
incident light
n
1
> n
2
n
2
reflected light
prism
air
evanescent wave
electric field
prism
air
evanescent wave
prism
air
evanescent wave
electric field
K. Kato 246
respectively. You can find that the electric fields of the metal interface
are enhanced by the SP excitation.
There are two prism coupling configurations for the SP excitations
as shown in Fig. 3. The configurations of Figs. 3(a) and 3(b) are called
Kretschmann and Otto configurations, respectively. In the Kretschmann
configuration, the SP excitation strongly depends on the thickness of the
metal thin film. While the Otto configuration, the SP excitation strongly
depends on the thickness of the air gap. The Kretchmann configuration is
useful in the visible and ultraviolet region, while the Otto configuration
is useful in the infrared and far infrared region.
1
(a) (b)
Fig. 2. SP excitation at the interface between metal thin film and air (a) and at the
interface between metal thin film and organic ultrathin film (b).
(a) (b)
Fig. 3. Prism coupling configurations for the SP excitations. (a) and (b) represent
Kretschmann and Otto configurations, respectively. The sample is metal film or metal
film with dielectric film.
p-polarized
incident light
SP
prism
air
θ
i
sample
reflected light
p-polarized
incident light
SP
prism
air
θ
i
sample
prism
air
θ
i
sample
reflected light
prism
SP
θ
i
air gap
sample
p-polarized
incident light
reflected light
prism
SP
θ
i
air gap
sample
p-polarized
incident light
reflected light
θ
i
metal thin film
SP
prism
air
evanescent wave
+
-
+
-
+
-
+
-
+
-
p-polarized
incident light
θ
i
metal thin film
SP
prism
air
evanescent wave
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
p-polarized
incident light
organic
ultrathin film
+
-
+
-
+
-
+
-
+
-
evanescent wave
SP
θ
i
prism
air
p-polarized
incident light
metal thin film
organic
ultrathin film
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
evanescent wave
SP
θ
i
prism
air
p-polarized
incident light
metal thin film
Surface Plasmon Excitations and Emission Lights in Organic Films 247
2.2. Method of ATR, Scattered Light and Emission Light
Measurements Utilizing SP Excitations
The sample configurations for the measurements of ATR, scattered
lights and emission lights utilizing SP excitations are shown in Fig. 4.
Figure 4(a) indicates the ATR and scattered light measurements and
Fig. 4(b) indicates the emission light measurement. The glass substrates
with organic ultrathin films on metal thin films are brought into optical
contact with half-cylindrical prisms using an index matching fluid.
The sample configurations are Kretschmann configuration shown in
Fig. 3(a).
The experimental system for the measurements utilizing SP
excitations is shown in Fig. 5. The samples shown in Fig. 4 are mounted
on a computer-controlled goniostage and the incident angle
θ
i
is changed
by rotating the goniostage. For the ATR measurement, the p-polarized
light is directed on to the back surface for the metal thin films through
the prism. The intensity of the reflected light is detected as a function of
θ
i
. The reflectivity, that is, the ATR value is obtained from the ratio of
the intensities of the reflected light to the incident light. Thus you
can obtain the ATR curves as a function of
θ
i
. For the scattered light
measurement, the intensity of the scattered light is observed as a function
of the scattered angle
θ
s
when the incident angle
θ
i
is set as the resonant
angle of the ATR curve. For the emission light measurement, the
intensity of the emission light is observed as a function of the emission
(a) (b)
Fig. 4. Sample configurations for the measurements utilizing SP excitations. (a) indicates
the sample configuration for ATR and scattered right measurements and (b) indicates that
for the emission light measurement by the reverse irradiation.
half-cylindrical
prism
cover glass
metal thin film
organic ultrathin
film
θ
s
scattered light
reflected light
(ATR signal)
p-polarized
incident light
θ
i
half-cylindrical
prism
cover glass
metal thin film
organic ultrathin
film
θ
s
scattered light
reflected light
(ATR signal)
p-polarized
incident light
θ
i
θ
s
scattered light
reflected light
(ATR signal)
p-polarized
incident light
θ
i
half-cylindrical
prism
cover glass
metal thin film
organic ultrathin
film
θ
e
incident light
emission light
half-cylindrical
prism
cover glass
metal thin film
organic ultrathin
film
θ
e
incident light
emission light
K. Kato 248
angle
θ
e
when the organic ultrathin film with metal ultrathin film on the
prism is directly irradiated from air by the incident light, that is, reverse
irradiation.
3-6
Figure 6 shows the calculated ATR curves for dielectric films with
the thickness of
d nm on metal thin films. The wavelength of the incident
(a) (b)
Fig. 6. Caluculated ATR curves for dielectric ultrathin films with the thickness of d [nm]
on Ag thin film (a) and on Al thin film (b).
Fig. 5. Experimental system for the measurements utilizing SP excitations.
40 45
0
1
Ag
d=6 12 18 24
Incident angle [deg]
Reflectivity
40 45
0
1
Al
d=6
12 18
24
Incident angle [deg]
Reflectivity
Lock-in amp. 1
Lock-in amp. 2
Computer
Chopper
M
ND filter
Iris
Polarizer
BS
PD-1
PD-2
Amp.
Lens
Amp.
Sample
PM
Controller
PM
DC Power
Supply
Laser