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nanoparticles isolated. Absorption and emission spectroscopies showed
a shi
from the usual absorption edge (1.55 eV to
ca.
2.0 eV, 800 nm to 620
nm) with a maximum quantum yield of 4.4%, and XRD of the particles
showed agreement with the patterns from the bulk material. This is an
excellent example of where single-source precursors can greatly simplify the
preparation of solid-state materials (one might argue that preparing the
precursor is itself relatively di
d
n
1
y
4
n
g
|
4
cult and overly time consuming, but once it is
prepared further steps are greatly simpli
ed). The same compound,
combined with another related single-source precursor, (PPh
3
)
2
CuGa(SEt)
4
,
when heated by microwave in benzylacetate with 1,2-ethanediol yielded
CuIn
x
Ga
1
x
S
2
.
117
The ratio between indium and gallium was found to be
controllable by varying the ratio of precursors, and the presence of the diol
was found to be essential, suggested to link the two precursors together. The
optical band edge was controlled by varying the metal content, with band
edges between
ca.
550 nm (CuGaS
2
) and
ca.
800 nm (CuInS
2
) obtained.
Similarly, [(Ph
3
)CuIn(SC{O}Ph)
4
] was used as a single-source precursor for
CuInS
2
, but this time TOPO and TOP were used as surfactants alongside
dodecanethiol. The ratio of surfactants was altered to control the crystallinity
of the material, with the di
raction patterns displaying the dominant wurt-
zite phase along with evidence of zinc blende particles in some reactions. It
was also shown that CuInS
2
could be prepared from the reaction of two
separate single-source precursors, [Cu(SC{O}Ph)] and [In(bipy)(SC{O}Ph
3
]
(where bipy
2,2
0
-bipyridine) under similar experimental conditions.
118
A similar precursor, [(PPh
3
)
2
Cu(
m
-SePh)
2
In(SePh)
2
], has been used in the
catalytic SLS growth preparation of high-quality stoichiometric CuInSe
2
wires, 33 nm in diameter and several micrometres long.
119
In this reaction,
the precursor was dissolved in TOP, then injected in a mixture of OA and TOP
at 300
C immediately a
¼
.
er the injection of Au/Bi core/shell catalysts parti-
cles. A
er under 5 minutes growth, the wires were isolated by rapid cooling
and the addition of a non-solvent. The wires, clearly the ternary phase as
determined by X-ray powder di
raction, had an absorption edge in the
infrared region. Another related ternary compound, CuInS
2
, has been
prepared by the thermolysis of two single-source precursors, Cu(S
2
CNEt
2
)
2
and In(S
2
CNEt
2
)
3
, in various capping agents which dictated the crystalline
phase of the nanoparticles.
120
Bandgap-sensitive elements, gallium and
tellurium, have also been introduced into the CuInS
2
system by preparing
a range of quaternary materials by single-source precursor.
121
Cu
1.0
Ga
x
In
2
x
S
3.5
was prepared by the thermolysis of dieth-
yldithiocarbamates of copper, indium and gallium in toluene with OA and
OAm, for 90 minutes at 180
C in an autoclave. Likewise, Cu
1.0
In
x
Tl
2
x
S
3.5
was prepared using single-source precursors in OA and ODE, followed by the
addition of OAm at 200
C for 1 minute, although no autoclave was necessary.
OAm was found to be essential, and no reactions occurred without it. The
inclusion of gallium and tellurium did not a
ect the cubic crystalline
structure. Electron microscopy of Cu
1.0
Ga
1.0
In
1.0
S
3.5
revealed approximately
spherical particles
ca.
6 nm in diameter, whereas particles of
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