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semiconductors by metal organic chemical vapour deposition (MOCVD).
9
In
a typical MOCVD reaction, metal alkyls and arsine gas were used; precursors
that are hypothetically suitable in the preparation of nanomaterials in an
organic solvent, but realistically improbable. Although e
ective in vapour
processes, precursors designed for gaseous-phase reactions are not ideal for
use in solution chemistry because of their toxic nature, air sensitivity, and the
associated di
d
n
1
y
4
n
g
|
1
culties in handling. In addition, metal alkyls such as
dimethyl- or diethyltelluride are also too stable to be e
ective precursors at
temperatures as low as 200
C, the region of interest for solution synthesis.
Initial reports on alternative precursors described the suitability of trime-
thylphosphine (Me
3
P) as a tellurium transport agent
8,10
and as a potential
replacement for dialkyltellurides.
11
The reaction between triethylphosphine
telluride andmercurymetal was investigated, givingmercury telluride (HgTe) in
almost quantitative yields.
10
This reaction suggested the assignment of the
phosphine telluride as a single coordinate complex of Te(0). Since elemental
metals are not normally utilised as precursors, the reaction was repeated using
the metal alkyl diethylmercury (Et
2
Hg) and the less volatile diphenylmercury
(Ph
2
Hg). Re
d
n
4
.
uxing an organic solution of the metal alkyl and a phosphine
telluride complex lead to the preparation of HgTe
via
the formation of an
intermediate, Hg(TePh)
2
. It was also observed that Hg(TePh)
2
eliminated
mercury metal during the reaction, which immediately reacted with excess
phosphine telluride giving HgTe. This reaction is noteworthy due to the inser-
tion of Te atoms into a Hg
C bond and highlights the important role phos-
phines can play in the low-temperature solution synthesis of semiconductors.
Steigerwald also prepared cadmium chalcogenides using silylated precur-
sors and metal alkyls,
12
providing a solution-based organometallic route to
CdSe. The reaction between metal alkyls and hydrogen chalcogenide gases
had previously been reported,
13
but most silylated chalcogens exist as a liquid
at room temperature and are therefore easier to handle than a vapour-phase
precursor. The reaction proceeded in simple organic solvents providing an
amorphous red/brown solid, which could be converted to bulk crystalline
CdSe upon annealing at 400
C. The work was extended to cover ZnSe and
CdTe. The solvent was found to have a distinct e
-
ect on the reaction rate;
dealkylsilylation in dichloromethane proceeded almost instantaneously,
while reactions in toluene took days to complete and reactions in saturated
hydrocarbons required weeks. Interestingly, there was no reaction between
Me
2
Cd and the silylated precursor in the absence of solvent. Although the
materials resulting from these reactions were not necessarily nanometric in
size, this molecular precursor chemistry can be thought as the origin of the
solution-based organometallic routes to nanomaterials.
1.2 Inverse Micelles
Steigerwald then used the developed chemistry to prepare discrete CdSe
nanoparticles in inverse micelles, which can be thought of as the
rst pseudo-organometallic route to nanomaterials.
14
A dioctyl sodium
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