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forming a CuIn(SR)
x
intermediate, and le
xed time, turning a deep
red in colour consistent with the formation of CuInS
2
. The tetragonal phase
of the ternary compound was con
for a
rmed by XRD and the particles found to be
2.6 nm in diameter, which grew to 3 nm a
er several hours growth, with the
presence of some anisotropic particles. The particles exhibited tuneable
absorption edges between 550 nm and 760 nm, with near band edge emis-
sion also observed between 600 nm and 750 nm and quantum yields of up to
5%. Dodecanethiol has also been used as a sulfur precursor and capping
agent in the preparation of CuInS
2
/ZnS core/shell particles with a tetragonal
crystalline core, which displayed emission quantum yields of up to 60% in
the red region of the visible spectrum, and used in cellular imaging.
12
Polytypic CuInS
2
could also be prepared using metal chlorides as precur-
sors and thiourea as the sulfur source in OAm.
13
The resulting disc-shaped
particles were relatively monodispersed and exhibited the wurtzite meta-
stable phase when examined by X-ray powder di
d
n
1
y
4
n
g
|
2
raction; chalcopyrite
regions were also observed when the particles were examined by electron
microscopy. Other investigations have also uncovered the sensitivity of the
crystalline phase to the reaction solvent and, unusually, reagent storage time.
Typical metal salts and elemental sulfur were used as precursors with ODE as
a solvent, to which were added various surfactants. The reagents were
prepared and mixed together, and le
to stand for either 3 minutes or
3 hours, prior to heating in an oil bath for up to 5 minutes. Generally, the use
of precursor solutions stored for only 3 minutes gave either zinc blende or
chalcopyrite structures, the di
er-
entiate, whereas the use of precursors stored for longer ultimately gave
wurtzite-structured particles.
14
The use of other sulfur sources as also been reported, with (SC(CH
3
)
3
)
2
being successfully used to prepare wurtzite-structured CuInS
2
, with
In(CH
3
C(O)CH
2
C(O)CH
3
)
3
and CuCl as precursors, dodecanethiol and OAm
as solvents, an injection temperature of 95
C and a growth temperature
of 180
C over 33 minutes.
15
The particles were extremely monodispersed,
ca.
7 nm in diameter with a gradual onset of absorption at around 1000 nm.
The presence of dodecanethiol was essential for the production of mono-
dispersed samples, as without it large hexagonal platelets up to 130 nm
resulted. The growth kinetics of this reaction were studied and revealed size-
focusing and Ostwald ripening.
Quaternary semiconductors of related materials have also been made in
QD form using very similar chemistry, reported in several paper published at
around the same time; crystalline particles of Cu
2
ZnSnS
4
(CZTS) with
a tetragonal kesterite phase,
ca.
10 nm in diameter with an irregular faceted
shape were prepared by the thermolysis of Cu(CH
3
C(O)CH
2
C(O)CH
3
)
2
,
Zn(O
2
CCH
3
)
2
, SnCl
2
and elemental sulfur in OAm at 280
C for 1 hour.
16
The
particles were tin-rich and slightly sulfur-de
raction patterns being too similar to di
.
cient (Cu
2.08
Zn
1.01
Sn
1.2
S
3.7
) and
used in photovoltaic devices with a power conversion e
ciency of up to
0.23%. In another report, Cu(CH
3
C(O)CH
2
C(O)CH
3
)
2
, Zn(CH
3
C(O)CH
2
C(O)
CH
3
)
2
, SnBr
2
(CH
3
C(O)CH
2
C(O)CH
3
)
2
and elemental sulfur were used as
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