Biomedical Engineering Reference
In-Depth Information
Figure 1.1 shows the TEM figure of the CdTe using EC-ALE with
200 cycles [13]. The regular layered structure, parallel with the
substrate gold (Au) lattice planes, suggests the epitaxial nature of the
deposit. There are a number of ways to introduce dopants into an EC-
ALE deposit and they can be introduced homogeneously throughout
the deposit. Such doping studies of ZnS were initially run with the idea
of forming phosphor screens for flat panel display applications [14].
Control of growth at the nanoscale is a major frontier of materials
science. The manipulation of a compound's dimensions and unit
cell, at the nanoscale, can result in materials with unique properties.
By forming nanocrystalline materials or constructing superlattices,
nanowires, and nanoclusters, the electronic structure (bandgap) of a
semiconductor can be engineered. EC-ALE has been developed as an
electrochemical methodology to grow semiconducting compounds
with atomic layer control.
1.2 ELECTROCHEMICAL SYNTHESIS OF
QUANTUM DOTS AND SEMICONDUCTING
NANOCOMPOUNDS
Electrodeposition normally leads to small particle size, largely
because it is a low-temperature technique, thereby minimizing grain
growth. However, it possesses the additional feature of a very high
degree of control over the amount of deposited material through
Faraday's law, which relates the amount of material deposited to
the deposition charge. This feature is particularly desirable when
isolated nanocrystals are to be deposited on a substrate.
Quantum dots are semiconductor particles having diameters
that are smaller than about 10 nm. Such semiconductor nanoparticles
exhibit a bandgap that depends on the particle diameter: the
smaller the nanoparticle, the larger the bandgap. Because quantum
dots possess a “size-tunable” bandgap, these diminutive particles
have potential applications in detectors, light-emitting diodes,
electroluminescent devices, and lasers. Electrochemical methods
can synthesize size-monodisperse quantum dots on graphite
surfaces, which provide an electrical connection to the graphite
in situ
. The essential features of these methods can be depicted
as in Fig. 1.2.
 
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