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proved to be an e
ective route to high-quality nanoparticles. The air-stable
adduct compound [Zn(SePh)
2
][(CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
] has been used in
the preparation of TOPO-capped ZnSe nanoparticles by injection of a TOP
solution of the precursor into the solvent at temperatures between 320 and
385
C. The particles formed were 2.7
4.9 nm in diameter, with emission
between 2.75 eV (
ca.
450 nm) and 3.20 eV (
ca.
390 nm) dependent on the
temperature of synthesis. Excitonic shoulders were clearly observed in the
absorption spectra of particles prepared at lower temperatures, and all
emission was band edge with only slight trap emission observed.
55,56
Ther-
molysis of the tellurium analogue, [Zn(TePh)
2
][(CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
]in
dodecylamine (DDA) and TOP at the lower temperature of 180
-
d
n
1
y
4
n
g
|
4
240
C
resulted in the formation of spherical particles of ZnTe with a cubic crys-
talline core. The substitution of DDA for a mixture of trioctyl amine (TOA)
and dimethylhexylamine resulted in the formation of spherical particles,
which quickly grew into rods and bulk ZnTe. Higher synthesis temperatures
resulted in particles with a band edge of 3.57 eV (
ca.
350 nm), whereas
particles prepared at the lower temperature exhibited a bandgap of 2.79 eV
(
ca.
450 nm), a shi
-
from the bulk value of 2.26 eV (
ca.
550 nm). These results
appear counter-intuitive, as they indicate that the higher-temperature
synthesis yielded smaller particles. The emission was, again, close to band
edge with no evidence of trap emission.
57
Metal xanthate complexes, structurally similar to dithiocarbamates, have
found use in the preparation of metal sul
de nanoparticles. In initial work,
the precursor cadmium diethylxanthate was easily prepared by the reaction
between cadmium chloride and potassium ethylxanthate. The resulting
precursor was dissolved in TOP and injected into TOPO at 180
C. Particle
formation was observed a
.
er 5 minutes, with growth of an hour resulting in
only a small red shi
in the absorption spectra, an indication of slow particle
growth. The routes yielded spherical CdS particles of
ca.
4 nm diameter with
a hexagonal crystalline core, which exhibited band edge luminescence.
58
An
investigation into varying reaction concentrations, times and temperatures
using HDA as a solvent instead of TOPO resulted in the controllable synthesis
of anisotropic particles.
59
Using high monomer (precursor) concentrations,
long reaction times and temperatures of not more than 200
C, multiarm
particles formed with rods being the preferred morphology at synthesis
temperatures above 200
C. Increasing the monomer concentration also
increased the aspect ratio of the resulting particles, and prolonged reaction
times resulted in the bent and high-aspect-ratio particles forming spherical
particles.
Similar results were obtained in work reported by Pradhan
et al.
, who
prepared particles
60
and rods of CdS from ethylxanthate precursors by altering
the monomer concentration.
61
-
63
Pb, Zn,
Hg, Ni, Mn, Cu) were also prepared by alkylxanthate precursors, as were core/
shell particles of CdS/ZnS and ZnS/CdS. Notably, lead and mercury ethyl-
xanthates decomposed at room temperature, making preparation of high-
quality particles di
In this work, particles of MS (M
¼
cult (although in other studies, lead hexadecylxanthate
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