Chemistry Reference
In-Depth Information
Interestingly, emission spectra were recorded as far into the red region of the
electromagnetic spectrum as 2500 nm.
Again, the chemistry of arsenide-containing particles has changed rela-
tively little, with few advances being made, possibly due to the lack of simple
alternative precursors. Other precursors and solvent systems have been
explored, such as the use of As(NMe
2
)
3
in the synthesis of InAs nanoparticles
using 4-ethylpyridine as solvent and capping agent.
79
In this case, the
InCl
3
was found to form an air-stable complex with the solvent, yielding
mer
-
[In(4-ethylpyridine)
3
Cl
3
], which gave small (2 nm) poorly crystalline InAs
particles when slowly heated to re
d
n
1
y
4
n
g
|
3
ux with As(NMe
2
)
3
. The particles could be
isolated using petroleum spirits as a non-solvent, although size-selective
precipitation could not be achieved because of the formation of a surface
oxide, as described above for InP. The particles exhibited substantial shi
sin
the bandgap to between 2.63 and 2.96 eV a
er several days of growth, with
emission pro
les between
ca.
475 and 550 nm, although no quantum yield
was reported. Further growth could be e
ected by the introduction of addi-
tional precursors, which resulted in particle growth and a red shi
in the
optical spectra, with the emergence of an excitonic feature in the absorption
spectra along with a narrowing of the emission pro
le, consistent with
growth focusing as described in Chapter 1. Nanoparticles of GaAs
ca.
4nmin
diameter have also been prepared using the same precursor and GaCl
3
.
80
Although slightly larger, the particles were still poorly crystalline as deter-
mined by X-ray powder di
raction (XRD), and the presence of Ga
2
O
3
and
As
2
O
3
was also observed. When annealed in air the di
raction pattern for
GaAsO
4
was obtained. The absorption spectra exhibited an excitonic
shoulder at
ca.
475 nm, with emission varying at
ca.
450 nm. Interestingly,
the capping agent was found to emit in the same spectral region, although
GaAs was thought to be the predominant emitting species.
.
2.3.1 Non-Coordinating Solvent Route
In all the cases described so far, prolonged synthesis is required to obtain
materials that are ultimately of a lower quality than the II
-
VI analogues as the
nucleation and growth steps are hard to separate. The materials are poorly
crystalline, polydispersed with, more o
en than not, poor optical properties.
An important advance has been reported by Battaglia and Peng,
81
where non-
coordinating solvents have been used to prepare monodispersed, high-
quality crystalline samples of zinc blende InP and InAs in a similar manner to
the green route used by the same research group, as described in Chapter 1.
In this route, rather than using the capping agent as the solvent, a high-
boiling point solvent, ODE, was used into which could be added precise
amounts of the required capping agent. The use of non-coordinating solvents
allowed controllable nucleation and hence improved the growth process. In
contrast to the work described above, common passivating agents such as
phosphines, phosphine oxides and amines were initially suggested to be
ine
ective, but fatty acids of an intermediate chain length were found to be
Search WWH ::
Custom Search