Chemistry Reference
In-Depth Information
The SLS growth of InP wires, with diameters of 4.3
-
19 nm and lengths
50
m for the thicker wires, has been
achieved
51
using essentially the same method but including 1-octylphosphonic
acid with HDA; the phosphonic acid is essential for high-quality wires and the
inclusion of TOPO and TOP altered the wire
-
500 nm for thin wires and up to 10
m
s width. All four surfactants were
found to be necessary for the growth of high-quality wires longer than 10 nm.
The absorption spectra displayed band edges from
ca.
700 to 850 nm with few
discernible excitonic features. Attempts to obtain emission from the sample by
photochemical etching using HF resulted in the thinning of the wires, and
intense irradiation resulted in the oxidation of the wires, giving InPO
4
with
luminescent InP domains.
Another SLS method of preparing InP rods involved the use of indium
nanoparticles, which acted as an indium source rather than a catalyst.
44
The
monodispersed indium particles, prepared by the thermolysis of indium
alkyls in TOP and had, were reacted with phosphine ions generated from the
hydrolysis of P(SiMe
3
)
3
. This route was notable as the resulting rods were
composed entirely of InP, as the seed reacted with the phosphorous
precursor giving materials with no catalyst contamination. Similar work has
been reported where InP and GaP nanowires have been produced, using
metal alkyls and P(SiMe
3
)
3
in octadecene (ODE) at 305
C with myristic acid
as a capping agent, where the metal alkyls form the metal seed catalysts.
52
'
d
n
1
y
4
n
g
|
3
2.2.3 Other Phosphorus Precursors
Few suitable solution-based precursors exist for phosphide-based nano-
materials, with P(SiMe
3
)
3
clearly the most suitable starting material. Despite
the e
.
ectiveness of silylated precursors, they still have limitations. They are
di
cult to prepare, expensive (where commercially available) and extremely
air sensitive. Although silylated phosphines are the solution functional
equivalent of phosphine gas (PH
3
), it is still possible to produce InP QDs by
generating PH
3
in situ
by adding HCl to Ca
3
P
2
under an argon atmosphere,
then bubbling the nascent gas through a reaction
ask containing ODE,
InCl
3
and myristic acid at 250
C.
53
Notably, the phosphine delivery was
strongest in the
rst few minutes, but was maintained throughout the
reaction, although at a lower output, allowing size-focusing of the particle
size and yielding particles with excellent optical properties and narrow size
distributions of
ca.
10%. This continuous delivery also overcame the phos-
phorus depletion problem associated with P(SiMe
3
)
3
. The particles, 3
6nm
in diameter, exhibited a zinc blende core, with no evidence of oxide side
products. The resulting nanoparticles exhibited a clear excitonic peak which
could be tuned between 650 and 700 nm, with emission between 675 and
720 nm by varying precursor ratios. The emission quantum yield was low, less
than 1%, but could be improved using a shelling technique to give InP/ZnS
QDs. An interesting alternative is the use of solid hydrogen phosphide (PH)
x
,
generated by the reaction between PBr
3
and LiAlH
4
.
54
The solid, which can be
handled in air, was prepared
in situ
during the formation of InP wires using
-
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