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n
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y
4
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Figure 2.5
Mechanism of InP formation. Reprinted with permission from P. M.
Allen, B. J. Walker and M. G. Bawendi,
Angew. Chem., Int. Ed.
, 2010,
49, 760. Copyright Wiley-VCH Verlag GmbH & Co. KGaA.
separate growth stage at a slightly lower temperature for up to 2 hours. In this
case, the growth of the nanoparticles did not signi
the absorp-
tion edge from the initial position, although by varying reaction tempera-
tures, time and carboxylate chain length, the absorption excitonic shoulder
could be altered from 476 nm to 574 nm, with associated near band edge
emission tuneable from 545 nm to 661 nm and quantum yields of up to 2%.
One method of obtaining controlled nucleation is the use of weakly
coordinating solvents such as high-boiling esters, as described by Xu
et al.
87
Compounds such as methyl myristate and dibutylsebacate were combined
with long-chain carboxylic acids (myristic acid was found to be the most
favourable) and amines and heated to 260
C, followed by the injection of
a mixture of (CH
3
)
3
In and P(SiMe
3
)
3
in an ester. The reaction was then cooled
to 200
C for growth, a
cantly shi
.
er which the InP particles could be isolated by
precipitation using acetone/methanol and redispersed in chloroform.
Comparison of the optical properties of InP grown in esters to InP grown in
ODE suggested that the nucleation of ester-grown materials was slower than
those grown in the truly non-coordinating solvent, although faster than those
grown in TOPO. The use of the metal alkyl rather than the metal carboxylate
gave InP of a higher quality with higher emission quantum yields. Although
these values were not reported, the emission was shown to be predominantly
band edge in origin. The use of protic amines, again suggested to accelerate
the nucleation, was found to improve the optical properties of the particles.
Although most of the work on the synthesis of III
V materials in non-
coordinating solvents has focused on InP, high-quality InAs can also be made
by a di
-
erent precursor. An interesting report
88
describes the generation of
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