Chemistry Reference
In-Depth Information
feature, attributed to a wider size distribution due to a lack of indium sites
for the TOPO to coordinate to. Talapin
et al.
extended the study to report that
the etching process was predominately photochemical in nature, and
required illumination from a xenon lamp to generate reliable and repro-
ducible materials.
36,40
Combining the etching process with size-selective
precipitation allowed a wide range of luminescent particles to be isolated in
the size range
ca.
1.7
d
n
1
y
4
n
g
|
3
6.5 nm, giving materials emitting from the green part of
the visible spectrum through to the near infrared, with quantum yields of
20
-
40%. An elegant extension is the
in situ
etching of InP QDs during particle
growth.
41
In this reaction, indium palmitate and P(SiMe
3
)
3
were dissolved in
decane and injected into a microwave reactor containing a microwave-
absorbing
-
uorine-based ionic liquid which generated F
ions during the
reaction. By varying the ionic liquid and reaction conditions, zinc blende InP
QDs
ca.
3 nm in diameter were obtained with emission quantum yields of up
to 47% without the need of further processing. Interestingly, the ionic liquid
is suggested to be a spectator solvent and takes no place in the reaction other
than generating the etchant. Another method of blocking dangling bonds on
the surface of InP is the inclusion of Zn(COOC
10
H
19
)
2
in the reaction, which
blocks surface trapping sites, resulting in impressive emission quantum
yields of up to 30% without further processing.
42
Interestingly, extremely small (1.5
2.3 nm diameter) particles of InP have
also been reported using essentially the same chemistry, but with a much
shorter synthesis time, lower temperature and di
-
erent capping group such
as trioctylamine (TOA).
43
The particles of InP 1.5 nm in diameter were
reported to have a very clear excitonic peak at
ca.
420 nm and a broad band
edge emission spectrum with a quantum yield of 20% without any etching,
shelling or processing. Interestingly, the high quantum yields cannot be
explained by the formation of an In
2
O
3
shell as the tertiary amine capping
agent would not undergo the relevant condensation reaction. The role of
amines in InP formation is still unresolved. The majority of papers
43,44
suggest amines (and protic reagents such as alcohols) activate the reaction,
leading to faster nucleation and improved particle quality. This role has been
disputed and will be discussed later.
.
2.2.2 The Growth of Anisotropic Particles
Most of the work on III
V nanomaterials has resulted in small spherical
particles, possibly because of the di
-
culty of controlling the nucleation and
growth steps. Anisotropic particles have, however, been prepared by control-
ling the surfactant chemistry. The thermolysis of a single-source precursor,
Ga(P
t
Bu
2
)
3
, in a mixture of HDA and TOA resulted in wurtzite-structured GaP
nanorods, 8 nm
45 nm in size.
45
The crystallinity of the rods could be
controlled by altering the surfactant ratio, with HDA directing anisotropic
particle growth and the formation of the hexagonal phase, whereas the use of
just TOA resulted in zinc blende spherical particles. The optical characteristics
were similar, with rods emitting at
ca.
3.46 eV and spheres at 3.48 eV.
Search WWH ::
Custom Search