Chemistry Reference
In-Depth Information
The chemistry described above has also been applied to other metal
chalcogenide (S, Se, Te) systems by simply altering the precursors. Nickel
sul
de particles, Ni
3
S
4
, have been prepared by the thermolysis of NiCl
2
and
elemental sulfur in OAm and TOP at 220
C for 1 hour. The particles,
produced by a two-step reduction and sul
dation mechanism, exhibited
irregular shapes with elemental nickel as a by-product.
28
Nickel selenide
particles, NiSe, have so far only been made by single-source precursor.
43
One of the earliest applications of organometallic-based chemistry to the
synthesis of metal chalcogenide (that was not based on group II materials),
was the synthesis of
a
-MnS, a potentially useful magnetic material, where
MnCl
2
and S(SiMe
3
)
2
were thermolysed in TOPO. The particle size varied
between 20 and 80 nm depending on precursor concentration.
44
Non-
coordinating solvents have also been used;
45
manganese carboxylates and
elemental sulfur (molar ratio 1 : 2) were dissolved in ODE, followed by
heating at 300
Cfor30minutes,yielding
a
-MnS. Isolation by addition of
non-solvent resulted in octahedral particles
ca.
30 nm in diameter.
Anisotropic particles (rods and T-shaped) could be obtained when
manganesestearatewasusedasaprecursor.Theabsenceofsulfur(or
a lower concentration, S : Mn
d
n
1
y
4
n
g
|
2
0.6) resulted in MnO particles. Similarly,
bullet, hexagonal or rod-shaped MnS, with a wurtzite structure (
g
-MnS)
were obtained when MnCl
2
and elemental sulfur were used as precursors
in OAm at 280
C.
46
Large particles of MnSe (several hundred of nano-
metres) have also been prepared using the metal salt and elemental sele-
nium in octadecylamine (ODA), although few details were provided.
47
Similar experiments resulted in wurtzite-structured MnSe, prepared
using MnCl
2
, oleic acid and selenium in tetraethylene glycol at 235
Cfor
1hour.
48
Bismuth chalcogenides, notably Bi
2
Te
3
, are known as excellent thermo-
electric materials and these compounds have also been developed due to the
theoretical high
#
.
gures of merit when prepared on the nano scale,
49
although the synthesis of monodispersed sub-10 nm particles is problem-
atic because of the high reactivity of chalcogens with bismuth precursors.
Nanowires of Bi
2
Te
3
were
rst prepared by utilising tellurium nanowires
(prepared from TeCl
4
and TOPO) and Bi[N(SiMe
3
)
2
]
3
or Bi(C
6
H
5
)
3
as
precursors. Thermolysis of the precursors in solvents such a polydecene and
1,3-diisopropylbenzene at either 160 or 200
C for between 2 and 12 hours
yielded micrometre-long wires, with amorphous sheaths of either Bi
2
Te
3
or
an oxide of tellurium.
50
In a simpler fashion, nanowafers of Bi
2
Te
3
could be
prepared by the reaction between Bi(CH
3
CO
2
)
3
and elemental tellurium in
octylamine (OA), which required prolonged re
uxing (>24 hours), whereas
the analogous reactions with selenium or sulfur required only 2 hours of
re
uxing, yielding either Bi
2
Se
3
nanowafers or Bi
2
S
3
nanorods respectively.
51
Interestingly, the bismuth precursor reacted prior to nanoparticle formation
to give bismuth oxo-acetate as an intermediate. A similar reaction reported
by Malakooti
et al.
described the use of BiCl
3
as a precursor, where the
intentional inclusion of oxygen yielded BiOCl which was then reduced by the
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