Chemistry Reference
In-Depth Information
also resulted in CoP. The di
ering reaction products were attributed to the
presence of TOP, which might therefore be classed as a reagent as well as
a capping agent. The related compound [
t
Bu
2
PS
2
]
2
Co was found to give
Co
9
S
8
when reacted under similar conditions.
78
This reaction has been
extended to the preparation of NiSe or Ni
2
PorNi
12
P
5
using [Ni(Se
2
PR
2
)
2
],
(R
i
Pr,
t
Bu, Ph).
79
These precursors are interesting due to the ability to
prepare di
¼
d
n
1
y
4
n
g
|
4
ering reaction conditions. The cobalt
precursors and the nickel variants of this speci
ering materials using di
c family of precursors have
also exhibited mixed chalcogen/phosphide products when used as CVD
precursors, again dictated by reaction conditions. In this case, TOP was
absent so the same mechanism cannot be responsible for the phosphide
phase.
80
-
82
Related to these precursors are dimorpholinodithioacetylaceto-
nate compounds, which form a similar system and have been used as
precursors for CdS nanorods.
83
A useful and convenient family of single-source precursors has been
described by Cumberland
et
al.
84
The
cluster-based precursors,
Li
+
, (CH
3
)
3
NH
+
;M
(X)
4
[M
10
Se
4
(SPh)
16
](X
Cd, Zn) are simply prepared by
an established route
85
and utilised elemental selenium during synthesis.
Similar materials have been investigated as precursors to the larger cluster
Cd
32
S
14
(SPh)
36
,a15A diameter crystal which is midway between a cluster
and a small QD.
86
Once prepared, the cadmium selenide precursor
(Li)
4
[Cd
10
Se
4
(SPh)
16
] was mixed with HDA and heated to 240
C, inducing
precursor decomposition and passivation of the resulting particles with the
amine. Once the desired size of particle was obtained (as determined by
absorption spectroscopy), the CdSe nanoparticles were cooled to 20
C and
le
¼
¼
.
occulated by
addition of methanol. A shell of ZnS could be deposited using Me
2
Zn and
S(SiMe
3
)
2
as described in Chapter 5.
Interestingly, blue-emitting CdSe nanorods up to 12 nm in length with
a diameter of 2.5 nm which self-assembled have been prepared using the
same method. Typically, the concentration of the precursor solution may
o
overnight to anneal and reduce the size distribution, then
en be the driving force behind anisotropic growth, but in this case the
surfactant system and more importantly the reaction temperature was the
de
ning factor inducing anisotropic growth. The authors also stated
a slightly di
(Li)
2
[Cd
10
Se
4
(SPh)
16
].
87
The same precursors,
when used in dimethylsulfoxide (DMSO), have shown larger clusters (Cd
32
and Cd
54
) in the stepwise growth of CdS.
88
A similar method was used to prepare ZnSe nanoparticles using the
precursor ((CH
3
)
3
NH)
4
[Zn
10
Se
4
(SPh)
16
] in HDA at 220
erent precursor
—
C. The ZnSe
-
280
particles were 2
5 nm in diameter, again exhibited band edge emission and
displayed a cubic lattice. This route is notable for the ease of preparation of
the precursors and particles. A detailed discussion regarding the growth
mechanism was reported, and a mechanism incorporating fragmentation of
the cluster was proposed, as opposed to the intact clusters acting as the
nuclei, as previously suggested for the growth of GaS by MOCVD using single-
source precursors.
89,90
-
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