Chemistry Reference
In-Depth Information
through hydrogen abstraction. InN was, however, reportedly prepared using
TOPO. A stabilised azide, In(CH
2
)
3
N(CH
3
)
2
N
3
was thermolysed in TOPO at
230
C for several hours, yielding InN, as determined by electron microscopy
and XPS.
98
The origin of the optical characteristics was unclear, with bright
blue emission being observed and assigned as emission from TOPO, with
absorption from the nanoparticles measured at 570 nm and weak emission
at 690 nm, consistent with InN particles
ca.
4.5 nm in diameter.
The same surfactant was again successfully used in the production of
relatively monodispersed sample of GaN,
ca.
5 nm in diameter, using GaCl
3
and Li
3
N as precursors in dibenzofuran containing TOPO at 280
C.
99
The
particle size could be tuned by altering the dibenzofuran : precursor ratio.
The particles were analysed by XRD; however, a crystalline phase was not
assigned despite the presence of clear re
d
n
1
y
4
n
g
|
3
ections. Few optical properties were
discussed, although a broad emission spectrum was reported which sug-
gested, when referring to the known di
erence in conduction band between
zinc blende and wurtzite-structured materials, that a mix of crystalline
materials might have been present.
In contrast to earlier reports by Wells,
94
a similar method using InBr
3
and
NaNH
2
has been reported, where the two precursors were reacted at 250
C
under ammonia, and the resulting powder (InN) isolated by centrifuga-
tion.
100
The black powder was then washed to remove excess indium
precursor. At this point, the product consisted of aggregated materials,
which, when sonicated with nitric acid, released the nitride nanoparticles
and removed indium metal contaminants. These particles could then
be sonicated with OAm, forming a stable colloidal solution of InN. The
particle shape was polydispersed and irregular, with an average particle size
of 6.2
.
2.0 nm and an optical room-temperature band edge of 1.29 eV
(
ca.
960 nm), although no emission was observed and the actual band edge
was estimated to be approximately 0.8 eV (
ca.
1550 nm), a result of the
Moss
. This method is notable as the nanoparticles could be
obtained from the large aggregates obtained initially a
-
Burstein shi
er the reaction by
simple processing, and the capping agent was added a
er the reaction and
processing was
nished.
In conclusion, it might be assumed that III
-
V QDs are poor relations to the
more popular II
V materials
are harder to prepare, recent advances such as the use of non-coordinating
solvents have resulted in high-quality monodispersed samples that are
structurally the equal of, for example, CdSe. The optical properties are also of
high quality, with the exception of quantum yield, although simple proce-
dures such as
-
VI materials. This is not the case; although III
-
uoride etching produce materials that are actually more
emissive. It is also simple to prepare brightly emitting high-quality core/shell
materials, of, for example InP/ZnS in a single-pot reaction which will be
described in Chapter 5. These materials can be tuned to emit across the
entire visible region, with the added bene
t of avoiding cadmium, which is
important in applications where the particles may come into contact with the
environment or biological materials.
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