Chemistry Reference
In-Depth Information
because of their extreme toxicity. The earliest routes to TOPO-capped lead
chalcogenide nanoparticles were single-source based, where monomeric
lead(
II
) diseleno- or dithiocarbamates were thermolysed to give the required
particles.
97,98
Again, in a similar manner to the cadmium dithiocarbamate
system,
nal product. The use of
symmetrical lead diselenocarbamates such as Pb(Se
2
CNEt
2
)
2
resulted in the
generation of micrometre-sized selenium particles as well as PbSe nano-
particles, whereas the use of Pb(Se
2
CNMe(
n
-hex))
2
resulted solely in the
formation of PbSe nanoparticles with as cubic crystal core as determined by
X-ray powder di
the alkyl constituents dictated the
d
n
1
y
4
n
g
|
4
raction. The thermolysis of the symmetrical thiocarbamate
system, Pb(S
2
CNEt
2
)
2
resulted in the formation of PbS particles with either
a hexagonal or cubic morphology, and later studies also revealed quasi-
spherical particles when prepared at low temperatures (60
C), and cubic at
higher temperatures (80
C).
99
The PbE (E
S, Se) particles produced were
crystalline, relatively large and polydispersed, displaying various shapes from
spherical to cubic structures, despite the relatively low temperature of
synthesis (
ca.
150
C for PbS, 180
C for PbSe). The band edges of the
resulting particles did not display any sharp features, but were signi
¼
cantly
shi
ed from their bulk values. In these cases no emission was reported, but
what is important, in this case and at the time of publication, is that the
single-source precursors provided a synthetic pathway to these otherwise
unavailable technologically important materials. Later publications also
reported the thermolysis of Pb(S
2
CNEt
2
)
2
in diphenylether using thiols and
amines as capping agents, giving PbS exhibiting a wide range of shapes.
100
Other precursors used for the synthesis of PbS include Pb(SCOC
6
H
5
)
2
, which
was dissolved in long-chain amines which catalysed the decomposition of
the precursor, giving a range of materials, although no optical properties
were reported.
101
The dithio/diselenocarbamate precursors have been extended to other
semiconducting systems. Indium chalcogenide nanoparticles may
.
nd use
in solar cell applications as the copper indium gallium selenide (CIGS)-based
materials are radiation-hard and are the focus of much research. The simple,
symmetrical diethyl dithio- and diselenocarbamates were prepared using the
standard techniques, and thermolysed in either TOPO or 4-ethylpyridine.
Although TOPO might at
rst appear the more suitable surfactant system due
to the higher temperature, isolation of the nanoparticles proved di
cult and
better-de
ned particles were obtained from 4-ethylpyridine.
102
Dithiocarbamates are also applicable to other more unusual systems.
Europium sul
de (EuS) is a ferromagnetic semiconductor, with a bandgap of
1.7 eV (
ca.
730 nm)
103
and a small exciton diameter of
ca.
0.5 nm.
104
A range of
lanthanide dithiocarbamates (including Nd, Sm, Gd, Ho and Er dithiocar-
bamates) were prepared as potential precursors for rare-earth sul
des, with
EuS being the main material of interest.
105
The precursor Eu(S
2
CNEt
2
)
3
:co-
ligand was used in the synthesis of EuS nanoparticle with a cubic crystalline
core, exhibiting various morphologies between 5 and 50 nm, with the larger
particles exhibiting a cubic shape.
106
Due to the large coordination sphere of
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