Chemistry Reference
In-Depth Information
faceted, and surface studies uncovered oxidation of the surface tellurium
sites. The surface bismuth sites appeared protected, presumably by the
surfactant. This method was also used to prepare Bi
0.5
Sb
1.5
Te
3
particles of
ca.
50 nm, by again including Sb(CO
2
CH
3
)
3
in the reaction. These doped mate-
rials also exhibited a threefold increase in the power factor.
61
Sb(CO
2
CH
3
)
3
has also been used to prepare antimony chalcogenides, by dissolving the
precursor in a long-chain amine followed by mixing with an amine solution/
dispersion of the elemental chalcogen, and heating. The resulting particles
displayed a variety of structures.
62
Transition metal-based particles, which o
d
n
1
y
4
n
g
|
2
en display a layered
morphology, include MoS, prepared by the thermolysis of Mn(CO)
6
and
sulfur in ODE between 270
C and 330
C, using TOPO as a capping agent.
The resulting particles were less than 5 nm in diameter with a size distri-
bution of up to 15%.
63
Nanoplates of NbSe
2
have also been grown from NbCl
5
and Se in OAm or dodecylamine (DDA) at 280
C, although di
erent
morphologies were obtained by di
erent synthesis temperatures, giving
either lamellar-structured plates or wires.
64
Possibly the most successful transition metal chalcogenide nanoparticles
prepared by the organometallic route are the silver-based materials, such as
Ag
2
S, which are usually prepared by single-source precursor as described in
Chapter 7. An interesting method of preparing Ag
2
S has been described by
Huxter
et al.
, where AgNO
3
and NH
2
CSCSNH
2
were mixed with HDA and
compressed into a pellet in speci
c layers. The pellet was then purged with
nitrogen gas, and heated in an air oven to just above the melting point of
HDA for 20 minutes. The resulting black material was then dispersed in
acetone, centrifuged, washed, and dispersed in toluene. This solventless
process yielded monodispersed particles,
ca.
10 nm in diameter with a near
infrared band edge at
ca.
1170 nm, consistent with the bulk bandgap of
Ag
2
S.
65
Other materials which are not accessible by single-source precursor,
such as Ag
2
Te, have been prepared using AgCl dissolved in TOP, with TOPTe,
both of which were injected into OAm at 140
C, followed by overnight
growth and ageing.
66
Similarly, AgNO
3
has also been mixed with dodeca-
nethiol in water, then transferred to toluene, followed by injection of TOPTe
at 85
C yielding Ag
2
Te particles. Prolonged heating of up to 1 day resulted in
large anisotropic nanoparticles up to 15 nm in size, along with smaller
particles
ca.
5 nm in diameter. Further heating resulted in the larger parti-
cles stacking together, while the smaller particles formed islands of parti-
cles. In all cases, the particles displayed an excitonic peak at
ca.
1150 nm,
signi
.
ed from the bulk bandgap of 0.064 eV (
ca.
19 300 nm).
67
Ternary Ag-based nanorods can also be prepared by similar methods to
those described above for copper-based ternary materials. AgNO
3
,In(NO
3
)
3
and elemental sulfur were dispersed in ODA at 120
C, where they were le
cantly shi
to decompose giving anisotropic AgInS
2
particles with an orthorhombic
crystalline core.
68
Using less sulfur resulted in spherical nanoparticle
formation, whereas increasing the synthesis temperature to 200
C resulted
in worm-like wires.
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