Chemistry Reference
In-Depth Information
86 : 14 due to the di
erence in reactivity of the precursors. Increasing the
antimony content resulted in a red shi
in the optical properties due to the
small bandgap on InSb relative to InAs, with emission tuneable between 770
nm and 880 nm. Attempts to prepare InP
x
Sb
1
x
were less successful because
of the large size di
erence between phosphorus and antimony atoms.
d
n
1
y
4
n
g
|
3
2.5 Group III
Nitrides
-
Group III
nitrides are a class of wide-bandgap semiconductors with
numerous applications in optoelectronics. Although several chemical
precursor routes exist to nitrogen-containing nanoparticles,
2
these have not
expanded into organometallic solution routes as easily as other III
-
-
V mate-
rials. Unlike most other III
V QDs, which are easily accessible using the
dehalosilylation reaction, nitride-containing QDs are hard to prepare
because there are few obvious, simple or available precursors. The use of
silylated precursors is not possible because of the relatively strong N
-
-
Si bond
(when compared to the P
Si bond) although the successful use of HN(SiMe
3
)
2
to prepare GaN in an autoclave has been reported; however, no optical
properties were discussed.
92
The use of simple compounds, such as InBr
3
,
has been found to be unsuitable for the synthesis of InN, for example, when
using Li
3
N.
93
Interestingly, indium metal formation has been reported as an
unwanted side product in similar reactions.
94
In some of the earliest work towards solution synthesis of nitride-based
QDs, zinc blende-structured GaN QDs, 3.0
-
1.2 nm in diameter were
prepared by the thermolysis of the poly(imidogallane){Ga(NH)
3/2
}
n
in TOA at
360
C over 24 hours, under an ambient
.
ow of ammonia, followed by
cooling to 220
C and the addition of a further surface capping agent (HDA).
95
GaN reportedly has an excitonic diameter of just 5 nm, so the materials
prepared can be described as weakly con
ned, exhibiting an excitonic feature
at
ca.
330 nm, shi
ed from the bulk band edge at 390 nm with weak broad
emission centred at
ca.
380 nm. This route was improved by using a dimeric
version of the poly(imidogallane), Ga
2
[N(Me)]
6
, avoiding the need for
ammonia, which was thermolysed in TOA and HDA for up to 3 days.
96
The
resulting GaN, 2
-
4 nm in diameter, with an average size of 2.4 nm, had a clear
zinc blende structure as determined by XRD and an optical band edge at
ca.
290 nm a
er 60 hours. Impressively,
the 60 hour sample appeared to have a slight excitonic shoulder. Emission
was dominated by broad deep trap emission between 400 and 600 nm,
although importantly, band edge emission was observed at 305 nm. Inter-
estingly, the use of HDA was found to be essential for the formation of GaN.
This amendment to the earlier route by Micic produced a larger yield of
materials, although solubility in the desired solvent was still an issue.
The use of TOA has been explored in the synthesis of InN materials using
InBr
3
and NaN
3
as precursors,
97
although it was suggested that the ligand was
not entirely suitable as it induced the reduction of the indium precursor to its
elemental form and promoted the transformation of the azide to ammonia
er 1 day of heating, and
ca.
300 nm a
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