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Mikulec reported essentially the same procedure as described above, but
replaced TOP with hexapropylphosphorous triamide, P(N(C
3
H
7
)
2
)
3
, which
exhibited an improved tellurium a
nity, attributed to the lone pair donation
from the phosphorus-bound nitrogen atoms.
26
The hexapropylphosphorous
triamide telluride complex was then diluted in TOP, and injected into hot
TOPO with Me
2
Cd at 350
C under an inert atmosphere, upon which the
temperature dropped to 270
C. Initial sampling a
d
n
1
y
4
n
g
|
1
er injection revealed
a wide size distribution, which tightened a
er further particle growth at
290
C. In this case, methanol was found to be an unsuitable non-solvent and
acetonitrile was used instead, with the particle being soluble in
n
-butanol
and tetrahydrofuran. Particles, once isolated in solution, had a drop of TOP
to maintain the high quantum yields, presumably capping surface sites that
were stripped of surfactant during isolation. Mikulec also reported the
importance of precursor purity, with improvements in reaction reproduc-
ibility observed when using Me
2
Cd which had been vacuum transferred
through a 0.2
d
n
4
.
lter and phosphine which had been distilled. Increasing
the cadmium : tellurium ratio to 2 : 1 appeared to provide optimum
materials.
Materials prepared by the Mikulec method could be tuned to display band
edge emission between 590 and 760 nm with consistently high quantum
yields (average of 60%, a highest recorded value of 70%), and had a zinc
blende (cubic) crystal structure. The emission quantum yield was found to
increase with reaction time, attributed to annealing e
m
m
ects. The material,
which could be grown between 4.4 and 13 nm in diameter, was found to be
extremely air sensitive with quantum yields dropping to practically zero a
er
2.5 hours exposure to air.
Talapin
et al.
also reported an organometallic route to CdTe nanoparticles
between 2.5 and 7 nm in diameter, based on the TOPO route.
37
In this route,
two synthetic procedures were reported; the
rst involved mixing TOP and
dodecylamine (DDA) under an inert atmosphere, followed by room-
temperature addition of tellurium powder and Me
2
Cd (molar ratio 1 : 1.47).
The materials were slowly heated to 180
C for 30 minutes, followed by
further heating at 200
C for a further 20 hours, allowing the tellurium to
slowly dissolve in the reagents, promoting a slow growth of the particles.
Nanoparticles prepared by this method were between 4 and 6 nm in diameter
and exhibited quantum yields of up to 65%. This method is notable for the
small size distribution range without employing a hot injection delivery of
the precursors.
The second method involved heating tellurium powder with TOP at 220
C
to a
ect dissolution, followed by cooling and the addition of Me
2
Cd and
more TOP. Notably, in this case the molar ratio of Cd : Te was
ca.
1 : 3.5. The
reagents were then injected into DDA at 150
C. Prior to injection, the
ask
was removed from the heat source which allowed nucleation with little
growth. Heat was reapplied a
er
ca.
15 minutes, allowing the particles to
grow slowly. The temperature and growth time determined particle size, with
particles averaging 3 nm in diameter when grown for a few hours at between
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