142
Y. Min et al.
Fig. 5.9 Silver NP linked by a Pt-containing organometallic dithiol bridge. Reproduced with
permission from Ref. [63]
thiol-containing Pt(II) centers bridge the Ag NP. The 2-D networks were obtained
through –SH derivatives covalently bound to Ag NP surface without Pt–S bond
cleavage. Employing an accurate synchrotron radiation-induced XPS experiment, a
semi-quantitative analysis of the chemical interactions between Ag and the complex
was performed. The percentage of completely and partially covalent thiols was 54.6%
(direct covalent bond) and 45.4% (one terminal grafting involving non-covalent interactions between NP), respectively. A subsequent work was performed to characterize
the material by X-ray absorption fine structure spectroscopy (XAFS) and XPS techniques, providing deeper insight at the atomic level into the physicochemical properties of the material [63]. XAS (S and Ag K-edges) analysis supply further support
for the interaction of the dithiol with Ag atoms on the surface of the NP (Fig. 5.9).
Dithiol organic molecules with different chain lengths and various middle
groups have been used to tune the structure and optical and electric properties of Au NP networks. For instance, Au NP networks were produced
from 9,9-didodecyl-2,7-bis(acetylthio)fluorene (Au NP-1) and 9,9-didodecyl-2,7bis(acetylthiophenylethynyl)fluorene (Au NP-2) playing the role of linkers [33]. A
red shift of the emission band for Au NP-1 in emission spectroscopy was observed
compared to the free thioester, suggesting an electron density flow to the gold center
through the S-bridge, whereas the effect was quenched in Au NP-2, probably due
to the increased distance of the fluorenyl chromophore from the gold core. The
same type of molecule (π–π conjugated 9,9-didodecyl-2,7-bis-thiofluorene, FL) was
reported to give a structural reorganization of the Au NP assembly after thermal
treatments (Fig. 5.10) [38].
With the help of grazing incidence X-ray diffraction technique, a proposition was
put forward that a partial transition from a hexagonal-like to a cubic-like packing of
Au NP occurred during the thermal annealing (up to 100 °C with a rate of 10 °C/min).
The electric properties of the Au NP assemblies and deposited films were also probed
[64]. Current–voltage (I/V ) response curve follows a non-ohmic relation for Au
NP few layer thin films, with a conduction mechanism that strongly depends on
polarons and bipolarons along π bridges of the carbon chain of the fluorene bridge.
For multilayer thick films, the properties followed approximately an ohmic law. In
contrast, Au NP few layer thin film possesses a resistance two orders of magnitude
smaller. The overall resistance decreases upon illumination thanks to the organic
linkers in the network, and optoelectronic properties appeared.
Y. Min et al.
Fig. 5.9 Silver NP linked by a Pt-containing organometallic dithiol bridge. Reproduced with
permission from Ref. [63]
thiol-containing Pt(II) centers bridge the Ag NP. The 2-D networks were obtained
through –SH derivatives covalently bound to Ag NP surface without Pt–S bond
cleavage. Employing an accurate synchrotron radiation-induced XPS experiment, a
semi-quantitative analysis of the chemical interactions between Ag and the complex
was performed. The percentage of completely and partially covalent thiols was 54.6%
(direct covalent bond) and 45.4% (one terminal grafting involving non-covalent interactions between NP), respectively. A subsequent work was performed to characterize
the material by X-ray absorption fine structure spectroscopy (XAFS) and XPS techniques, providing deeper insight at the atomic level into the physicochemical properties of the material [63]. XAS (S and Ag K-edges) analysis supply further support
for the interaction of the dithiol with Ag atoms on the surface of the NP (Fig. 5.9).
Dithiol organic molecules with different chain lengths and various middle
groups have been used to tune the structure and optical and electric properties of Au NP networks. For instance, Au NP networks were produced
from 9,9-didodecyl-2,7-bis(acetylthio)fluorene (Au NP-1) and 9,9-didodecyl-2,7bis(acetylthiophenylethynyl)fluorene (Au NP-2) playing the role of linkers [33]. A
red shift of the emission band for Au NP-1 in emission spectroscopy was observed
compared to the free thioester, suggesting an electron density flow to the gold center
through the S-bridge, whereas the effect was quenched in Au NP-2, probably due
to the increased distance of the fluorenyl chromophore from the gold core. The
same type of molecule (π–π conjugated 9,9-didodecyl-2,7-bis-thiofluorene, FL) was
reported to give a structural reorganization of the Au NP assembly after thermal
treatments (Fig. 5.10) [38].
With the help of grazing incidence X-ray diffraction technique, a proposition was
put forward that a partial transition from a hexagonal-like to a cubic-like packing of
Au NP occurred during the thermal annealing (up to 100 °C with a rate of 10 °C/min).
The electric properties of the Au NP assemblies and deposited films were also probed
[64]. Current–voltage (I/V ) response curve follows a non-ohmic relation for Au
NP few layer thin films, with a conduction mechanism that strongly depends on
polarons and bipolarons along π bridges of the carbon chain of the fluorene bridge.
For multilayer thick films, the properties followed approximately an ohmic law. In
contrast, Au NP few layer thin film possesses a resistance two orders of magnitude
smaller. The overall resistance decreases upon illumination thanks to the organic
linkers in the network, and optoelectronic properties appeared.