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In-Depth Information
changed particle size and prolonged heating at relatively elevated tempera-
tures (193
C) again resulted in cubic particles being formed, with a sphere/
cube transition occurring at approximately 9.3 nm. Importantly, the emis-
sion spectra of small (2.9 nm diameter) PbTe particles were also measured for
the
rst time, and found to be band edge with quantum yields of up to 52%,
signi
cantly higher than PbS, although not as high as some reports for PbSe.
Although most synthetic routes resulted in either quasi-spherical, cubic or
octahedral particles, PbTe rods could also be prepared by solution
synthesis.
68
In this example, PbCO
3
and NaHTe were reacted together in
water, the product isolated, dispersed in TOP and injected into HDA at
190
d
n
1
y
4
n
g
|
7
270
C. The precursor was found to contain PbTe, the carbonate salt and
tellurium which resulted in further growth once injected into the amine.
-
3.2 Other Group IV Chalcogenides
Other group IV
VI nanoscale compounds have been prepared by similar
chemistries; GeTe nanowires have been prepared using Ge(OCH(CH
3
)
2
)
4
as
a precursor.
69
In this case, the germanium precursor was dissolved in TOP,
and placed in a
-
ask containing ODE as the reaction solvent, oleic acid and
OAm in the presence of a
uorine-doped tin oxide glass slide covered with
ask was then heated to 220
C, resulting in the
formation of bismuth particles in solution. Injection of TOPTe into the
a thin
lm of bismuth. The
ask
then resulted in the formation of GeTe nanowires, using the bismuth
particles as nucleation sites. Interestingly, the wires, 50
-
100 nm in diam-
.
eter and up to 2
m long, had no trace of bismuth in the structure, sug-
gesting that the usual solution
m
solid (SLS) growth mentioned in
Chapter 1 was not the growth mechanism. The presence of tellurium
particles 200
-
liquid
-
400nmindiameterwerealsodetected.
A similar method, using a GeI
2
-
-
TOP complex as a precursor (with no
bismuth particles), and using TOPO and dodecanethiol as capping agents
has been reported.
70
The dodecanethiol and TOPTe were injected rapidly and
sequentially, resulting in amorphous GeTe particles. The dodecanethiol was
found to be essential, as no germanium particles formed unless the ligand
was present. It was deduced by NMR that the thiol displaced TOP, forming
aGe
-
thiol precursor, which reacted with TOPTe to yield GeTe particles
2.5
4.5 nm in diameter. The amorphous particles could be crystallised by
heating to 240
C. Larger nanoparticles of GeTe have also been reported
using bis[bis(trimethylsilyl)-amino]Ge(
II
) as a germanium precursor.
71
Tin(
II
) sul
-
-SnS) has also been synthesised by heating a mixture of
Sn[N[(CH
3
)
3
Si]
2
]
2
, TOP, oleic acid and ODE to 170
C.
72
It is noteworthy that
the use of Sn(CO
2
CH
3
)
2
did not yield the oleate complex, hence the need for
the silylated precursor. To the hot precursor solution was injected a solution
de (
a
PbTe particles. Reprinted with permission from W. Lu, J. Fang, K. L.
Stokes and J. Lin,
J. Am. Chem. Soc.
, 2004,
126
, 11798. Copyright 2004
American Chemical Society.
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