13 Creation of Organic-Metal Hybridized Nanocrystals …
253
(NLO) materials having high third-order NLO susceptibility and ultra high speed
optical response [14, 15].
As a result, one can successfully obtain well-defined PDA NCs dispersed in an
aqueous medium [10–12]. The morphology such as crystal size and shape of organic
NCs is controlled experimentally by changing reprecipitation conditions: selection
of good and poor solvents, concentration and injected amount, injection rate, temperature and stirring rate of poor medium, addition of surfactant, and so on. Organic NCs
provide some interesting linear optical properties and function [10–12]. For example,
the excitonic absorption peak (EAP) positions are continuously blue-shifted with
decreasing crystal size in the case PDA NCs [16], whereas the fluorescence emission peak positions measured with near-field scanning optical microspectroscopy
(NSOM) are also blue-shifted in the case of perylene NCs as the crystal size is
reduced [17]. These kinds of optical shift are due to thermally soften nanocrystal
lattice induced by the increase in specific surface area in small-sized organic NCs,
i.e., reduction of optoelectronically inter-molecular interaction in nanocrystal lattice
[18]. In addition, the layered thin films have been finely prepared by utilizing negative
surface potential of PDA NCs, and then the third-order NLO susceptibility was multiplied apparently with the number of layers toward optoelectronic and/or photonic
device applications [10, 11].
13.1.3 Organic-Metal Hybridized Nanocrystals
So far, PDA core-silver (Ag) shell-type hybridized NCs have been fabricated successfully by establishing visible-light-driven photocatalytic reduction method [19], and
were characterized carefully with scanning electron microscope (SEM), transmission electron microscope (TEM) with electron diffraction (ED) pattern, powder X-ray
diffraction (XRD) pattern, and electron probe X-ray microanalyzer (EPMA).
In fact, the aqueous solution of AgNO 3 and NH 3 was added into PDA NCs dispersion liquids, and then visible (Vis) light was irradiated at a given interval. As a result, it
was confirmed that Ag NPs (ca. 10 nm in size) as Ag shell were selectively deposited
only on the surface of PDA NCs as a core. The extinction spectrum showed the interesting features, that is, the red-shift and broadening of LSPR peaks from Ag shell,
and also red-shifted EAP of PDA core. The former is caused by imhomogeneous
distribution in size and the dephasing effect of LSPR, and the later is due to changes
of dielectric environment in the surrounding PDA core. The necessitated condition is
that the redox potential of metal ion should be located between conduction band (CB)
and valence band (VB) of PDA core [18]. Probably, the excited electron at CB would
reduce metal ion effectively, and the formed metal NPs are selectively adsorbed only
on the surface of PDA core with negative surface potential. In addition, the size and
deposition density of the resulting metal NPs were influenced considerably by the
relationship between redox potential of metal ion and work function of metal NPs [18,
19]. Actually, one can deposit Ag NPs on the surface of PDA core, being independent
of morphology (size and shape) of PDA core [19]. The present concept of formation
253
(NLO) materials having high third-order NLO susceptibility and ultra high speed
optical response [14, 15].
As a result, one can successfully obtain well-defined PDA NCs dispersed in an
aqueous medium [10–12]. The morphology such as crystal size and shape of organic
NCs is controlled experimentally by changing reprecipitation conditions: selection
of good and poor solvents, concentration and injected amount, injection rate, temperature and stirring rate of poor medium, addition of surfactant, and so on. Organic NCs
provide some interesting linear optical properties and function [10–12]. For example,
the excitonic absorption peak (EAP) positions are continuously blue-shifted with
decreasing crystal size in the case PDA NCs [16], whereas the fluorescence emission peak positions measured with near-field scanning optical microspectroscopy
(NSOM) are also blue-shifted in the case of perylene NCs as the crystal size is
reduced [17]. These kinds of optical shift are due to thermally soften nanocrystal
lattice induced by the increase in specific surface area in small-sized organic NCs,
i.e., reduction of optoelectronically inter-molecular interaction in nanocrystal lattice
[18]. In addition, the layered thin films have been finely prepared by utilizing negative
surface potential of PDA NCs, and then the third-order NLO susceptibility was multiplied apparently with the number of layers toward optoelectronic and/or photonic
device applications [10, 11].
13.1.3 Organic-Metal Hybridized Nanocrystals
So far, PDA core-silver (Ag) shell-type hybridized NCs have been fabricated successfully by establishing visible-light-driven photocatalytic reduction method [19], and
were characterized carefully with scanning electron microscope (SEM), transmission electron microscope (TEM) with electron diffraction (ED) pattern, powder X-ray
diffraction (XRD) pattern, and electron probe X-ray microanalyzer (EPMA).
In fact, the aqueous solution of AgNO 3 and NH 3 was added into PDA NCs dispersion liquids, and then visible (Vis) light was irradiated at a given interval. As a result, it
was confirmed that Ag NPs (ca. 10 nm in size) as Ag shell were selectively deposited
only on the surface of PDA NCs as a core. The extinction spectrum showed the interesting features, that is, the red-shift and broadening of LSPR peaks from Ag shell,
and also red-shifted EAP of PDA core. The former is caused by imhomogeneous
distribution in size and the dephasing effect of LSPR, and the later is due to changes
of dielectric environment in the surrounding PDA core. The necessitated condition is
that the redox potential of metal ion should be located between conduction band (CB)
and valence band (VB) of PDA core [18]. Probably, the excited electron at CB would
reduce metal ion effectively, and the formed metal NPs are selectively adsorbed only
on the surface of PDA core with negative surface potential. In addition, the size and
deposition density of the resulting metal NPs were influenced considerably by the
relationship between redox potential of metal ion and work function of metal NPs [18,
19]. Actually, one can deposit Ag NPs on the surface of PDA core, being independent
of morphology (size and shape) of PDA core [19]. The present concept of formation