The Preparation of Other Chalcogenides and Pnictide Nanomaterials - Semiconductor Quantum Dots: Organometallic and Inorganic Synthesis - page 98

and OAm at 175 C, followed by 10 minutes growth. 32 The resulting Cu 2 x Se
disc-like nanoparticles were isolated by solvent/non-solvent interactions,
and found to have broad absorption spectra covering the majority of the
visible region with an excitonic shoulder at 400 nm. It was suggested the
resulting heterocyclic carbene was involved with the growth process and also
coordinated to the particle surface. In this example, substituting 1,3-
dimethylimidazoline-2-selenone with TOPSe resulted in small nanomaterials
that could not be observed by electron microscopy. The copper-de

d n 1 y 4 n g | 2

cient
Cu 2 x Se could be prepared without the use of phosphines, using CuCl and
ODE/Se at 300 C, with ODE as solvent and oleylamine



found to be essential
as both capping species and reducing agent for the selenium, yielding Se 2 . 33
The resulting material included a small amount of large (>100 nm) CuSe
hexagonal plates, but the majority product was monodispersed cuboocta-
hedral Cu 2 x Se of ca. 16 nm diameter. The optical spectra displayed an
absorption shoulder at 480 nm, and a broad feature at 1150 nm, assigned as
an indirect transition, although later described as a surface plasmon 34 which
could be reversibly tuned by varying the copper stoichiometry (oxidation and
reduction of the particles). 35

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4.2 Other Chalcogenide-Containing Materials
Investigations into CuInSe 2 and related materials lead to the development of
simple group III chalcogenides. Materials such as InSe, a simple layered

semiconductor with a hexagonal structure and bulk bandgap of 1.24 eV, were
initially prepared by single-source precursors as described in Chapter 7. 36
The preparation of diselenocarbamates precludes the routine preparation of
InSe, however, therefore simple routes are desirable. The injection of
a solution of (CH 3 ) 3 In in TOP into a solution of TOPO, TOP and Se at 250 C
resulted in InSe QDs ca. 3 nm in diameter with a disc-like geometry. The
inclusion of a phosphonic acid in the synthesis resulted in few particles
nucleating, yielding fewer but larger particles. Using this method, particles as
large as 80 nm were obtainable, although these were much larger than the
InSe excitonic diameter of 5 nm and only the smaller particles exhibited
notable emission. The polarised emission of the smaller (2.9 nm) particles
was found to be tuneable, with excitation wavelength between 350 and 450 nm.
This emission anisotropy was attributed to the morphology and associated
electronic structure, with quantum yields of up to 25% observed in the
smaller particles. 37 Park et al. explored a one-pot reaction to InSe nanowires,
where the reactants, InCl 3 and selenium, were heated with OAm to 215 C
and stirred for 5 hours. 38 The method utilised the insolubility of selenium
in the long-chain amine below 205 C, above which the precursor dissolved,
becoming a suitable starting material. The nanowires, ca. 8 nm thick and 5
m m long, were extremely monodispersed, and were found by XRD to be
cubic rather than the inherent hexagonal phase. By altering the amount of
selenium, the wires could be made thinner and longer, or thicker and
shorter. Rods of

-

.

In 2 S 3 could also be prepared by the injection of