Chemistry Reference
In-Depth Information
nanoparticles
ca.
4
5 nm in diameter with emission tuneable between
ca.
400 nm and 600 nm depending on the temperature of the reaction.
130,131
A
cadmium : phosphorus ratio of 1.6 : 1 was obtained at lower temperature; at
higher temperatures, the ratio was as high as 7 : 1. Reactions with a related
diorganophosphide, [MeCd(
m
-PPh
2
)]
3
(HPPh
2
)
2
, with no
b
-hydrogen atoms,
resulted in predominantly elemental cadmium being formed, highlighting
the importance of the organic groups to the decomposition mechanism. Of
note is the lack of XRD data, as the material gave no useable re
-
d
n
1
y
4
n
g
|
4
ections,
unlike the analogous III
V QDs. It is worth noting that cadmium phosphide
has been investigated by a number of groups; Weller has described an
essentially colloidal route to Cd
3
P
2
using a variety of metal salts and phos-
phine gas in triethylamine and methyl methacrylate, followed by room-
temperature vacuum polymerisation in a sealed quartz cuvette.
132
The
resultant QDs were characterised primarily by measurements of lattice
fringes with no XRD data reported. Buhro has developed organometallic
routes to nanoparticulate Cd
3
P
2
using a variety of routes, although the
material was not reported in depth.
133
One notable route involves the
methanolysis of a silylated single-source precursor, Cd[P(SiPh
3
)
2
]
2
.
134
The resulting nanocrystals were capped by Ph
3
Si at the phosphide sites and
by OMe at the metal sites. Replacement of the phenyl groups on the
precursors for methyl groups resulted in bulk material being formed.
The use of diorganophosphides was extended to the preparation of InP and
GaP.
135
In(P
t
Bu
2
)
3
was thermolysed in 4-ethylpyridine which gave capped
nanoparticles
ca.
7 nm in diameter with a blue-shi
-
ed band edge at
ca.
2.7 eV
(
ca.
460 nm) and broad, near band edge luminescence.
136
GaP nanoparticles
ca.
7 nm in diameter could be also be prepared using Ga(P
t
Bu
2
)
3
in 4-ethyl-
pyridine, the resulting nanoparticles showing similar optical characteristics
to the analogous InP particles. Similar experiments where the precursors
were thermolysed in TOPO were unsuccessful. The particles had a large
amount of metal-based impurities, either elemental metal or the metal oxide,
which was found on prolonged heating. MS investigations into the decom-
position products suggested reductive elimination,
b
-hydrogen elimination
and strain-induced bond rupture as the relevant decomposition mecha-
nisms. This supported the use of organic side chains such as tertiary butyl
groups, in which all hydrogen atoms are in the
b
position. Despite this,
unpublished work has demonstrated the preparation of InP particles by
thermolysis of In(PPh
2
)
3
.
137
Di
.
erent-shaped nanoparticles of GaP could also
be formed when Ga(P
t
Bu
2
)
3
was thermolysed in a mixture of TOA and HDA.
When the ratio of TOA : HDA was 1 : 1, a mixture of rods (
ca.
42
8 nm) and
dots were obtained. Increasing the ratio to 1 : 1.25, wurtzite-structured rods
(45
8 nm) were uniquely formed. By using just TOA alone as a capping
agent, spherical particles of
ca.
8 nm diameter GaP with a zinc blende
structure were obtained. The di
erence in structures was attributed to the
steric properties of the capping agents,
i.e.
the sterically bulky TOA drove the
particle growth towards the staggered zinc blende GaP con
rmation, whereas
the less sterically demanding HDA reduced rotational barriers to wurtzite
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