J Mater Sci: Mater Electron (2017) 28:13176–13184
Plasmon- exciton induced circular dichroism in Gold/PMMA
S. M. Hamidi
· F. Jafari
· S. Behjati
· F. Sohrabi
Received: 7 February 2017 / Accepted: 15 May 2017 / Published online: 26 May 2017
© Springer Science+Business Media New York 2017
light because a chiral molecule has a sense of rotation
(clockwise or counterclockwise) . From quantum view-
point, the interactions of electronic excited states result in
delocalization of electronic excitation (exciton) which sub-
sequently modify the absorption spectrum and CD signal
. Also, the ﬂuorescent nature of dyes [e.g. rhodamine
B (RB)] originates from the ﬂuorescent resonant energy
transfer between diﬀerent molecules due to this delocaliza-
tion eﬀect .
On the other hand, pure plasmonic chirality can take
place via plasmon–plasmon interactions in metallic
nanocrystal assemblies (geometry asymmetry) or chiral
shape of individual nanocrystals (shape asymmetry) [5–7].
In the ﬁrst case (i.e. nanoassemblies), a chiral system can
consist of chiral or nonchiral individual nanocrystals in an
asymmetrical, chiral geometry like helix conﬁguration .
The physical interpretation of plasmonic-induced chirality
is based on the interacting dipoles and diﬀerent modiﬁca-
tion of the electron cloud due to incident circularly-polar-
ized light .
By combining exciton- and plasmon-induced chiral-
ity, plasmon-exciton induced chirality comes to existence.
Plasmonic structures can inﬂuence the electromagnetic
ﬁeld distribution inside the chiral molecule apart from their
participation in optical absorption of nanocrystal-molecule
composite . In addition to the possibility of enhancing
CD signal of molecules via plasmonic structures, the com-
binatory characteristics bring the possibility of observing
the CD signal in visible range while in exciton-induced chi-
rality, this signal is mostly in UV range [3, 5]. These advan-
tages pave the way for the design of new optical materials
and devices .
In this paper, we beneﬁt from exciton-plasmon coupling
with this modiﬁcation that we introduce a thin gold ﬁlm
and on top of this plasmonic layer, we spin-coated PMMA
Abstract We have investigated the strong coupling
between exciton-plasmon by the aid of reﬂectance spectros-
copy under diﬀerent dye molecules weight in the samples.
For this purpose, we have prepared ﬁve diﬀerent samples as
); in which the weight of RB has
been changed from 0 to 4 mg. The spectroscopy of the sam-
ples has been done under angular modulation and also the
dispersion relation of the samples has been extracted from
this measurement. These measurements revealed the forma-
tion of two split polaritonic extreme in reﬂectance spectra
as a function of wavelength. Then we have shown exciton–
plasmon coupling in dispersiondiagram which presented
an extra allowed mode between the polaritonic branches.
After that, the circular dichroism spectra of samples have
been measured to see the strong coupling circular dichro-
ism. Our results show that, we have signiﬁcant change in
the dichroism of gold thin ﬁlm due to strong coupling in all
of visible region.
A molecule possesses chirality eﬀect if it has neither mir-
ror-symmetry planes nor a center of symmetry . Using
two chiral states of light, chirality can be measured via the
circular dichroism (CD) spectroscopy which is the diﬀer-
ence between the absorbance of right- and left-handed inci-
dent light . The physical origin of CD signal is that a
molecule behaves diﬀerently towards right- and left-handed
* S. M. Hamidi
Magneto-plasmonic Lab, Laser and Plasma Research
Institute, Shahid Beheshti University, Tehran, Iran