Chemistry Reference
In-Depth Information
observation of atom-like states in III
V QDs,
9
and the production of hydrogen
by a nanophotocathode containing InP.
10
The III
-
V family of materials are of
immense interest because of the large excitonic diameters,
2
which should
allow size quantisation e
-
ects to manifest at much larger particle sizes than
in the analogous II
VI materials, allowing size-dependent properties to be
explored in more detail. The chemistry is somewhat more di
-
cult with this
d
n
1
y
4
n
g
|
3
group of materials; problems with the synthesis of III
V QDs have been
highlighted by Heath and Shiang,
11
notably the separation of the nucleation
and growth steps, attributable to both the strongly complexed precursors
used and the relatively covalent nature of the resulting materials when
compared to II
-
-
VI materials.
Reports describing the synthesis of capped III
-
V materials emerged shortly
a
rst papers on TOPO-capped CdSe, and the use of QDs in biology
has ensured the continued development of such materials, providing alter-
natives to cadmium-containing biolabels. Whereas simple precursors are
available for II
er the
VI materials, notably the anionic components which can be
provided by the simple elemental species, there are few suitable group V
precursors; elemental precursors have not been successfully utilised in the
same manner. The origins of III
-
V nanomaterials might be traced back to
researchers examining novel organometallic compounds,
12
with the
emphasis not on the end products but on new precursors, which were usually
thin
-
lms prepared by chemical vapour deposition (CVD); such precursors
could also be used in the solution synthesis of simple nanomaterials.
13
The key reaction for the synthesis of III
V QDs was described in 1989 by
both the Wells
14
and the Barron
15
groups, for the synthesis of GaAs, InAs and
InP respectively. The reaction, termed dehalosilylation, was based on
previous work by Wells using silylated compounds to form Ga
-
.
As bonds
16
and was initially envisaged as a possible alternative to the use of gaseous
group V precursors. The work described a simple solution route to III
-
Vbulk
materials using a group III salt, such as GaCl
3
or InCl
3
, with a silylated
pnictogen such as As(SiMe
3
)
3
or P(SiMe
3
)
3
in solution at low temperatures.
Although the reaction between InCl
3
and P(SiMe
3
)
3
yielded [Cl
2
InP(SiMe
3
)
2
]
x
,
heating the intermediate at 650
C under vacuum yielded bulk InP of high
purity. The analogous reaction with GaCl
3
or InCl
3
and As(SiMe
3
)
3
proceeded
via
an unidenti
-
ed intermediate stage, yielding the bulk material of at least
84% purity upon thermolysis. These reactions are extremely important as they
provide the
V materials using
precursors that are readily available and easy to handle. It is worth noting at
this point that a similar reaction was reported a couple of years later,
describing the use of an indium metal alkyl and P(SiMe
3
)
3
yielding InP,
17
although this has proved less popular, possibly due to the air sensitivity and
the di
rst simple solution routes to high-quality III
-
culties associated with handling metal alkyls.
This was the starting point for numerous explorations into III
V chemistry,
by variations on the dehalosilylation reaction. Reports included the alco-
holysis of single-source precursors such as [R(Cl)In(
-
-P(SiMe
3
)
2
)]
2
(prepared
from R
2
InCl and P(SiMe
3
)
3
), giving a mixture of InP and In
2
O
3
, although
m
Search WWH ::
Custom Search