Chemistry Reference
In-Depth Information
amine to give elemental bismuth.
52
Addition of elemental sulfur in OAm at
130
C resulted in either monodispersed Bi
2
S
3
dots or rods depending on the
precursor ratio. Expanding this reaction to use bismuth citrate as
a precursor resulted in the formation of ultrathin Bi
2
S
3
necklace nanowires,
1.6 nm in diameter, formed of individual nanoparticles separated by
amorphous sections or grain boundaries.
53
The crystal structure was found
to be similar to the bulk, with 75% of the bismuth atoms found on the
surface, available to coordinate to surface ligands.
54
Elemental sulfur was
not the only precursor to be used in the synthesis of the sul
d
n
1
y
4
n
g
|
2
des: S(SiMe
3
)
2
has also been used, along with Bi(CH
3
CO
2
)
3
in oleic acid (forming the oleate)
at 170
C, yielding Bi
2
S
3
rods
ca.
22 nm in length and
ca.
7 nm wide.
55
In this
case, the absorption spectrum was also measured, giving a bandgap close to
the bulk value due to the small exciton. Particles with a branched
morphology have also been prepared by the reaction of Bi(OCOC
17
H
33
)
3
with
sulfur in ODE and oleic acid at either 150
Cor180
C, showing evidence of
crystal splitting. The structures adopting a multiple sheaf-like morphology,
with individual
laments having a diameter of
ca.
9 nm and an average
length of
ca.
570 nm.
56
Hexagonal nanoplates of Bi
2
Te
3
, with edges 200
300 nm long and 15 nm
thick, were prepared by the injection of TOPTe into a hot solution of
diphenylether, with oleic acid as a capping agent and Bi(OCOC(C
2
H
5
)(C
4
H
9
))
3
as the bismuth precursor at 150
C, followed by 30 minutes growth at the
same temperature.
57
The shape and thickness was controlled by reaction
temperature, with the relatively high temperature necessary for the hexag-
onal shape. Interestingly, including 5% TOPSe in the reaction in an attempt
to dope the material resulted in strings of tellurium with individual Bi
2
Te
3
plates incorporated into the rod perpendicularly.
Spherical particle of Bi
2
Te
3
with diameters below 10 nm could, however, be
obtained by again using a two-step reaction;
-
.
rst preparing bismuth nano-
particles by reducing Bi(CO
2
CH
3
)
3
using OAm (or TOP) in the presence of
dodecanethiol, a capping agent. To the metal particles was added TOPTe and
a phosphonic acid at 60
C, followed by stirring for 2
3 days, resulting in the
formation of a Bi/Te alloy. The alloy converted to Bi
2
Te
3
particles upon
heating at 110
C for 18 hours.
58
The resulting particles exhibited a reduced
thermal conductivity and similar electrical conductivity to bulk n-type Bi
2
Te
3
.
By including Sb(CO
2
CH
3
)
3
in the reaction, Sb
(2
x
)
Bi
x
Te
3
was formed which
exhibited an obvious change in particle morphology, with either nano
-
akes
or agglomerations of nano
akes (termed nanosheets) resulting, depending
on reaction temperature.
59
A
er ligand removal using a methanolic solution
of NH
3
, and further processing by plasma sintering, the material showed
a 15% increase in the
gure of merit.
A very similar method to Bi
2
Te
3
and antimony-doped nanomaterials was
reported by Zhao and Burda, who used a one-step reaction, where a phenyl
ether solution of dodecanethiol and Bi(CO
2
CH
3
)
3
was heated to 100
120
C,
followed by injection of TOPTe and growth for up to 60 minutes.
60
In this
case, the resulting Bi
2
Te
3
particles were
ca.
50 nm in diameter and clearly
-
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