146
Y. Min et al.
et al. found that using the one-phase route to produce self-assemblies, short-ranged
FCC crystals can be formed from the cross-linked network for specific dithiol linkerlength and NP size [75]. The stability of the lattices was evaluated based on geometrical considerations and numerical simulations as a function of ligand length and
number of connected nearest neighbors, and a phase diagram of super-lattice formation was provided. The methods employed provide perspective in further exploration
for well-crystallized lattices. Further management of Au NP assemblies was investigated, and an interesting electric device was constructed, consisting of an electric
platform of nano-electrode–molecule–NP bridge, showing a significant improvement
of reproducibility of electrical measurements (Fig. 5.13) [36]. The Au NP (5 nm)
situated between the nano-electrode (19 nm) were connected with 1,8-octanedithiol,
where the outer thiol groups are protected by triphenylmethyl (ω-trityl), which lead
to reproducible and stable metal–molecule bonds replacing the physisorbed metal–
molecule junction. Correspondingly, the conductivity increased and the spread of
the resistance histogram reduced by one order of magnitude, which demonstrated
that the use of this platform can be a potential method for characterization of Au NP
networks and furthermore molecule levels current transport application.
Langmuir–Blodgett (LB) Method
The LB method makes use of the surface pressure to initiate NP crosslinking deposited onto substrate. One example reported by Chen uses 4,4
-
thiobisbenzenethiol as bifunctional linker that facilitated cross-linking of monolayerprotected Au NP [37]. Two-dimensional NP networks were prepared by using the LB
method, where neighboring NP were chemically bridged by the bifunctional linker
at the air/water interface. The fluctuations of surface pressure were studied during
the formation of the assembly, showing that high surface pressures help to activate
cross-linking, which resulted in long-range ordered and robust NP networks. The
typical surface plasmon band of Au NP redshifted by 30 nm, which was attributed
to the electronic coupling interactions between neighboring NP. Ordered arrays of
quantum dots can also be produced by photo-oxidation to remove the organic part in
the network [76].
Light-Triggered Self-assemblies
A light adjustable Au NP network was produced by using azobenzene-thiol derivatives as inter-particle linkers. It was shown that the spacing between NP can be
reversibly controlled by trans-cis isomerization of the azobenzene moiety induced by
UV and visible light (Fig. 5.14) [77]. Analogously, another photoactive trans-ligand
4,4
-bis(11-mercaptoundecanoxy)azobenzene (ADT) containing a photoswitchable
azobenzene unit was used to assemble metal NP into assembly triggered by UV
irradiation modified by light of different wavelengths [78, 79]. In that case, the selfassembly was irreversible for high ligand surface concentrations, resulting in NP
organized into permanently cross-linked structures by dithiols.
Y. Min et al.
et al. found that using the one-phase route to produce self-assemblies, short-ranged
FCC crystals can be formed from the cross-linked network for specific dithiol linkerlength and NP size [75]. The stability of the lattices was evaluated based on geometrical considerations and numerical simulations as a function of ligand length and
number of connected nearest neighbors, and a phase diagram of super-lattice formation was provided. The methods employed provide perspective in further exploration
for well-crystallized lattices. Further management of Au NP assemblies was investigated, and an interesting electric device was constructed, consisting of an electric
platform of nano-electrode–molecule–NP bridge, showing a significant improvement
of reproducibility of electrical measurements (Fig. 5.13) [36]. The Au NP (5 nm)
situated between the nano-electrode (19 nm) were connected with 1,8-octanedithiol,
where the outer thiol groups are protected by triphenylmethyl (ω-trityl), which lead
to reproducible and stable metal–molecule bonds replacing the physisorbed metal–
molecule junction. Correspondingly, the conductivity increased and the spread of
the resistance histogram reduced by one order of magnitude, which demonstrated
that the use of this platform can be a potential method for characterization of Au NP
networks and furthermore molecule levels current transport application.
Langmuir–Blodgett (LB) Method
The LB method makes use of the surface pressure to initiate NP crosslinking deposited onto substrate. One example reported by Chen uses 4,4
-
thiobisbenzenethiol as bifunctional linker that facilitated cross-linking of monolayerprotected Au NP [37]. Two-dimensional NP networks were prepared by using the LB
method, where neighboring NP were chemically bridged by the bifunctional linker
at the air/water interface. The fluctuations of surface pressure were studied during
the formation of the assembly, showing that high surface pressures help to activate
cross-linking, which resulted in long-range ordered and robust NP networks. The
typical surface plasmon band of Au NP redshifted by 30 nm, which was attributed
to the electronic coupling interactions between neighboring NP. Ordered arrays of
quantum dots can also be produced by photo-oxidation to remove the organic part in
the network [76].
Light-Triggered Self-assemblies
A light adjustable Au NP network was produced by using azobenzene-thiol derivatives as inter-particle linkers. It was shown that the spacing between NP can be
reversibly controlled by trans-cis isomerization of the azobenzene moiety induced by
UV and visible light (Fig. 5.14) [77]. Analogously, another photoactive trans-ligand
4,4
-bis(11-mercaptoundecanoxy)azobenzene (ADT) containing a photoswitchable
azobenzene unit was used to assemble metal NP into assembly triggered by UV
irradiation modified by light of different wavelengths [78, 79]. In that case, the selfassembly was irreversible for high ligand surface concentrations, resulting in NP
organized into permanently cross-linked structures by dithiols.