Chemistry Reference
In-Depth Information
substituents on the
b
-carbon (Figure 7.1c) which imparted greater stability
to the subsequent decomposition product (3-ethyl-5-phenyl-2,3-dihydro-1,3-
selenazole),
to enhance elimination.
24,25
Compounds of
the formula
[M(S
2
CNHR)
2
](M
ec-
tive single-source precursors to CdS and ZnS nanoparticles of varying
morphologies.
26
Lazell and O
¼
Cd, Zn; R
¼
alkyl chain) have also shown to be e
d
n
1
y
4
n
g
|
4
Brien reported an interesting synthetic route to CdS nano-
particles
27
using an unusual asymmetric dithiocarbamate, which was
inspired by
'
silver particles.
28
The novel precursor,
[Cd(S
2
CNMe(C
18
H
37
))
2
]
2
, was prepared which possessed a signi
'
self-capping
'
cantly
longer side group than normally used. The material was then thermolysed
in vacuo
inside a metal
-
organic chemical vapour deposition (MOCVD)
chamber at 200
C and the resulting material extracted using pyridine.
Fourier transform infrared (FTIR) spectroscopy suggested that one of the
decomposition products, HNMe(C
18
H
37
), passivated the particles. The QDs
produced were crystalline,
ca.
4
-
5 nm in diameter and displayed the expected
shi
in band edge. Emission was broad with a slight low-energy tail, but
predominantly band edge in origin. This was extended to the preparation of
self-capped Bi
2
S
3
particles using the precursor Bi(S
2
CN(C
18
H
37
)(CH
3
))
3
using
similar conditions.
29
Bismuth sul
de, Bi
2
S
3
, has also been prepared by
asymmetric dithiocarbamates. Initially investigations used Bi(S
2
CNMe(
n
-
hex))
3
in 2-ethoxyethanol yielding nano
bres,
30
but this was extended to
a wider range of complexes and solvents.
31
The thermolysis of Bi(S
2
CNMe(
n
-
hex))
3
in TOPO led to a mixture of Bi
2
S
3
and elemental bismuth, while
4-ethylpyridine and ethylene glycol resulted in the pure nanostructured
semiconductor as required, although 2-ethoxyethanol gave the largest
product yield. Bi
2
S
3
prepared in ethylene glycol gave very distinct rods that
appeared to be hundreds of nanometres long, and gave a distinct feature in
the absorption spectra at
ca.
550 nm, unlike material prepared in 4-ethyl-
pyridine or 2-ethoxyethanol which gave featureless spectra, although all were
clearly blue-shi
.
ed from the bulk bandgap of 1.3 eV (
ca.
950 nm). Use of the
adduct complex Bi(S
2
CNMe(
n
-hex))
3
(C
12
H
8
N
2
) resulted in slightly longer
bres of the same morphology. Again, the asymmetric M(S
2
CNMe(
n
-hex))
x
system was used to prepare nanoparticles of PtS (3 nm) and PdS (5 nm) using
the compounds Pt(S
2
CNMe(
n
-hex))
2
and Pd(S
2
CNMe(
n
-hex))
2
respectively in
TOPO at 250
C.
32
Both sets of particles gave broad emission pro
les at
ca.
490 nm, the origin of which was unclear, but may be related to the ther-
molysis of the capping agent. Nanoparticles of PtS had a clear absorption
feature at
ca.
360 nm.
The potential application of ZnE (E
S, Se) particles in optoelectronics has
been covered in Chapter 1 and single-source routes based on zinc dithio/
selenocarbamates have been developed. The compound EtZnSe
2
CNEt
2
was
used to prepare particles of ZnSe 3
¼
6 nm in diameter with a hexagonal
crystalline core, by injecting a TOP solution of the precursor into TOPO at
between 200
-
250
C.
33
The particles showed a band edge shi
-
ed from the
bulk value by between 0.15
-
0.25 eV and exhibited band edge emission,
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