Chemistry Reference
In-Depth Information
PbSe particles with an alloyed PbSe/PbSe
x
S
1
x
shell. In this case, the shi
became more pronounced with increasing sulfur content, becoming
extremely predominant at PbSe/PbSe
0.5
S
0.5
. The origin of this anti-Stokes
emission is unknown, although it has been attributed to the smaller particles
to the blue side of the excitonic peak having a larger oscillator strength.
Further explorations into PbSe/PbS structures suggested that the addition
of the PbS shell did not in fact improve stability, unlike the II
d
n
1
y
4
n
g
|
3
VI analogue
heterostructures.
169
The core particles were prepared using a standard route
to oleic acid-capped PbSe, a
-
er which the particles were isolated and puri-
ed. The particles were then redissolved in ODE with a small amount of oleic
acid. The lead precursor was then added, the solution heated to 130
C,
which was followed by the addition of S(SiMe
3
)
2
in TOP. Emission pro
les of
the resulting particles displayed two emission peaks, consistent with the
presence of separate PbS particles, due to the highly reactive S(SiMe
3
)
2
, and
a red-shi
ed emission peak due to the PbSe/PbS. The use of TOPS as a sulfur
precursor avoided this side reaction. Unfortunately, the PbSe/PbS particles
did not show enhanced emission, unlike CdSe/ZnS for example, and readily
blue-shi
ed upon storage in ambient conditions, like the core materials,
attributed to incomplete shell formation.
Talapin
et al.
also explored the synthesis of PbSe/PbS nanostructures.
170
Using methods similar to those described above, it was reported that the
sulfur precursor made a notable di
erence when growing a PbS shell on
quasi-spherical PbSe particles. The use of TOPS as a sulfur precursor resulted
in even shell growth, yielding approximately spherical particles of PbSe/PbS.
The use of the more reactive sulfur in ODE at lower temperatures, however,
resulted in cubic particles. The growth of PbS shell on PbSe wires was also
reported, with an interesting di
.
erence in the growth mode. The growth of
PbS shells on PbSe occurred
via
layer-by-layer deposition, but the growth of
PbS on PbSe wires occurred by a Stranski
Krastanov mechanism, yielding
strain-grown pyramids along the wire. Notably, pre-synthesised particles of
PbS also attached to preformed PbSe wires
via
oriented attachment at 120
C.
Similarly, gentle heating of HAuCl
4
in a solution of preformed PbSe nano-
wires with a surfactant resulted in the growth of gold islands at relatively
regular intervals along the wire. The growth of gold on PbS has also been
observed previously by others.
171
The growth of a PbTe shell on PbSe wires
has also been achieved using a similar method and utilising TOPTe as
a precursor.
172
The growth of a PbTe shell required a slightly higher growth
temperature of 190
C
-
unsurprising, as TOPTe has previously been noted to
be relatively unreactive.
173
The capping of PbSe with II
—
VI materials has also been undertaken.
Materials such as CdSe are excellent candidates for capping due to the low
lattice mismatch (
ca.
1%), relatively better stability to ambient conditions,
and the much wider bandgap which theoretically should lead to better charge
carrier con
-
VI shell by the slow
introduction of precursors was found to be unsuccessful, so a di
nement. The usual method of depositing a II
-
erent
approach was taken,
174
similar to the ion exchange method of preparing new
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