Chemistry Reference
In-Depth Information
atom-like electronic states
70,71
and the preparation of InAs-based near
infrared light-emitting devices.
72
InAs QDs capped with TOP were prepared in an analogous manner to the
InP particles mentioned above.
73,74
The zinc blende particles, 2.5
6nmin
diameter were prepared using InCl
3
and As(SiMe
3
)
3
(As : In molar ratio
1.15
-
1.2) which were mixed together in TOP forming a stock solution,
a portion of which was then injected into TOP at a temperature of 240
-
d
n
1
y
4
n
g
|
3
265
C.
The particles showed near band edge emission at
ca.
1.5 eV (
ca.
830 nm) for
3.4 nm diameter particles, to
ca.
1.0 eV (
ca.
1240 nm) for 6 nm diameter
particles, with quantum yields of 0.5
-
2.5%. Interestingly, the particles were
insensitive to oxidation, unlike the InP particles described above.
Zinc blende InAs nanorods could also be prepared using gold nano-
particles as catalysts for anisotropic growth in an SLS-inspired reaction, as
described above.
75
In these examples, the nanorods were prepared by a rapid
injection of a precursor stock solution containing dodecanethiol-stabilised
gold particles into TOPO at 360
C, followed by almost immediate reaction
quenching. The reaction solution was then repeatedly puri
-
ed using solvent/
non-solvent interactions, initially removing nanowires (20 nm width up to
1
m in length) from the reaction solution, followed successively by quantum
rods of progressively smaller lengths, until spherical InAs dots remained.
The rods varied from 22.7 nm
m
4.4 nm to a length of 9.4 nm while keeping
the same diameter. In some cases, the gold particle was visible. The rods
exhibited a signi
in bandgap with increasing length, unlike the
CdSe rods described in Chapter 1 which displayed minimal change in the
optical spectra. The red shi
cant red shi
.
in bandgap was also accompanied by a reduc-
tion in emission intensity, although no quantum yields were given. Similarly,
InAs rods with similar optical properties could be grown using either indium
or silver particles or gold clusters as catalysts.
76
The use of indium catalysts
resulted in slightly narrower rods (
ca.
3
-
4 nm), whereas gold clusters gave
signi
cantly narrower rods (
ca.
2 nm), and the use of 3 nm diameter silver
particles gave rods of relatively poor quality. The use of 4 nm silver particles
resulted in the formation of spherical particles. Interestingly, simple GaAs
spherical particles could not be grown using the dehalosilylation reaction;
this was attributed to the ligand binding too strongly to the gallium
precursor. However, using gold nanoparticles as catalysts, slightly aniso-
tropic GaAs particles were observed, although the yield was reportedly low.
This same methodology has also been applied to the synthesis of GaAs wires
using bismuth particles as catalysts, where (
t
Bu)
3
Ga and As(SiMe
3
)
3
were
added to an ODE solution containing TOPO/TOP, followed by rapid but brief
heating and the injection of the catalyst particles.
77
A
er a further short
period of growth, the rods could be isolated by centrifugation. The use of just
TOPO as a surfactant did not result in wire growth, but the use of ODE
resulted in zinc blende GaAs wires 500
1000 nm in length. InAs rods were
reported by the same group, who used essentially the same reaction, with
In(COO(CH
2
)
12
CH
3
), TOP, HDA and polydecene in the reaction
-
ask, to
330
C.
78
which was added As(SiMe
3
)
3
and bismuth simultaneously at 240
-
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