Chemistry Reference
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excellent capping agents although the concentration of the ligand was crucial
to the quality of the particles produced. The unsuitability of amines is
surprising because of their previous successful use in InP synthesis, espe-
cially as they have previously been noted as activating the phosphorus
precursor.
43,44
The reaction utilised the same precursors as those described
above;
In(COOCH
3
)
3
and E(SiMe
3
)
3
,(E
¼
As, P) as
—
unlike the non-
d
n
1
y
4
n
g
|
3
coordinating solvent route to II
metal oxides or elemental
phosphorus were found to be insoluble and unreactive respectively. The
indium precursor was mixed in ODE with the capping agent and heated to
120
Ctoa
-
VI materials
—
ect dissolution, which was followed by 2 hours of evacuation and
back-
ushing three times with an inert gas. This was followed by injection of
an ODE solution of E(SiMe
3
)
3
(E
As, P) at 300
C, and growth at 270
C.
Successive precursor additions could be performed, dropwise, at 250
C,
where the precursors were added separately to maintain the indium-rich
reaction and the tight size distribution. For the best-quality results, the
indium : pnictide ratio was found to be 2 : 1 for InP, and 8 : 1 for InAs. The
solvent also had to be rigorously dried before use, unlike the synthesis of
II
¼
VI, some of which could even be prepared in air. The absorption spectra of
both InP and InAs displayed clear excitonic shoulders at 500
-
-
600 nm for InP
and 600
900 nm for InAs, which suggested a limited size range of materials
with an excellent low size distribution. Unfortunately, the emission quantum
yield of InP was described as low and the emission of InAs was not reported.
The synthesis of InAs was reported in more depth elsewhere,
82
which
described the synthesis of extremely small (
ca.
2 nm) InAs QDs with TOP in
ODE at 150
C; their small size was due to the high reactivity of As(SiMe
3
)
3
.
The particles exhibited absorption spectra with features in the blue region
consistent with magic cluster formation, and the particles grew through self-
focusing by interparticle di
-
.
ing the absorption spectra well into
the red with a maximum excitonic shoulder at
ca.
850 nm.
The use of ODE is not without problems. It was suggested that the high
temperatures used with long-chain carboxylate precursors resulted in
hydrolysis leading to In
2
O
3
particle formation unless thorough degassing
was employed.
83
This oxidation could reportedly be avoided and the need for
a degassing step removed completely by using low temperatures (<200
C)
and long-chain amines to activate the reaction, even though previously these
ligands were found to be unsuitable. Using this reaction, where a mixture of
P(SiMe
3
)
3
and octylamine (OA) were injected into a hot solution (178
C) of
indium acetate and myristic acid in ODE, InP particles that emitted across
the entire visible region of the electromagnetic spectrum could be obtained
by varying reaction conditions, notably the concentration of myristic acid.
Clear excitonic peaks could be obtained in the absorption spectra from 500 to
700 nm, suggesting that the particles were monodispersed, which was
con
usion, shi
rmed by electron microscopy. The particles were shown to oxidise
rapidly in air, with the absorption spectra changing over 12 hours. The
emission quantum yields were typically low (<1%) but were markedly
improved to a maximum of 40% by simple passivation with a ZnS shell.
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