Chemistry Reference
In-Depth Information
excess thiol and TOAB in methanol to form Au(I)-SR polymers. NaBH
4
aqueous
solution is then added to produce polydispersed Au nano-clusters. After size-
focusing processes, only two monodispersed components Au
144
(SR)
60
(major
product) and Au
25
(SR)
18
(side product) are present in the product (see Fig.
8
). By
taking the advantage of large solubility difference in acetone, pure Au
144
(SR)
60
can
be separated with a yield of 10-20% [
81
,
106
,
107
]. By controlling the size range of
the initial polydispersed clusters, pure Au
25
(SR)
18
or Au
144
(SR)
60
clusters without
the need of the above isolation have also been achieved by Jin and co-workers.
Topochemical polymerisation of diynes attached to the surface of gold has been
neatly used to encapsulate the gold particles. Gold nanoparticles (AuNPs) coated
with the diacetylene henicosa-10,12-diyn-1-yl (DS9) disulfide were made by the
direct synthesis in toluene solutions. The average size of the nano-hybrid metal core
was finely adjusted by manipulation of the preparative conditions in the diameter
range from 1.6 to 7.5 nm using transmission electron microscopy. The
topochemical polymerisation of DS9 was carried out in colloidal suspensions
using UV radiation. The results showed that in these assemblies the monomer
undergoes an intra-particle polymerisation and that the dominant polydiacetylene
phase present is ruled by the core size. The deposition of the photo-irradiated
colloids onto different substrates was found to leave the polydiacetylene conjuga-
tion unaltered [
108
].
An important characteristic of thiol-stabilised gold colloids is that on evapora-
tion of the organic solvent they spontaneously form highly ordered 2D and 3D thin-
film arrays on suitable substrates. This makes it possible to tune the optical and
electrical properties of the thin films by varying the sizes of the metal particles and
the inter-particle spacings. The protecting groups and capping molecules on the
surface of the metal particles are modified using standard organic chemistry pro-
cedures. Pelka [
109
] has shown that varying the chain length of the hydrocarbon of
linking thiolato ligands on 4-5 nm gold nanoparticles self-assembled on glass has a
dramatic effect on their dc conductivities. Measurements made down to 4.2 K show
a strong relationship between the dc conductivity and the spacer length. Corbierre
[
110
] has recently combined electron beam lithography and controlled nanoparticle
nucleation and growth to create precisely patterned 1D arrays of gold particles. The
inter-particle distances and the patterns of nanoparticles are precisely tuned by
varying the electron beam parameters.
2.3 Metal Vapour Syntheses, Radiolysis
and Sonolysis Techniques
Metal vapour synthesis techniques have been used to synthesise molecular gold
clusters with 5-11 metal atoms and gold colloids. The former are favoured if the
organic solutions contain strongly binding phosphine ligands, whereas the latter are
favoured when these ligands are absent [
111
-
113
]. Gold colloid particles with
