Chemistry Reference
In-Depth Information
CHAPTER 1
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The Preparation of II
-
VI
Semiconductor Nanomaterials
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1.1 Origins of Organometallic Precursors
Although nanoparticles (notably metals) can be traced to antiquity, the
origins of modern semiconductor quantum dots (QDs) is a much later
development. Speci
ned semiconductor parti-
cles can be traced to Gratzel,
1
who reported the synthesis of colloidal CdS to
examine photo-corrosion, and Brus
2
who notably reported the band edge
luminescence of the same material. At approximately the same time, Ekimov
reported quantum con
c advances in quantum-con
nement in CuCl prepared in a silica glass,
3,4
while
Henglein, an early pioneer of colloidal semiconductors, reported the
synthesis of CdS on colloidal SiO
2
.
5
Fendler then reported the use of a reverse
micelle to prepare CdS nanoparticles,
6
which was importantly improved on
by Henglein, who used polyphosphates as a well-de
ned passivating agent,
allowing nanoparticles to be processed and redispersed.
7
The work described above utilised mainly inorganic salts as precursors in
aqueous-based reactions. Consequently, the low temperatures used and the
presence of air and water o
en resulted in polydispersed materials with
relatively poor optical and crystalline properties. The small number of
available suitable precursors also reduced the number of systems that could
be explored. The need to improve these reactions by removing air and water
dictated the use of organic-based starting materials; however, inorganic
reagents such as Na
2
Se could not easily be used in organic solvents so
alternatives were required.
Independently, Steigerwald pioneered many of the early chemical routes to
bulk solid-state materials,
8
inspired by the early work on the deposition of
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