CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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In the above equation Pr () is the spatial distribution of trapped electrons and r 0
is the
adsorbate distance from semiconductor surface. krt (,) is the ET rate for trapped electrons at
that distance. It is clear from the equation that ET rates are highly non-exponential.
According to Marcus theory as described earlier, in normal region
0
G
therefore
BET rate constant increases with increasing driving force. For
0
G
or inverted regime
BET rate constant decreases with increasing driving force. The existence of inverted region
has been verified in several systems.
1. 8. Synthesis of Semiconductor Quantum Dots
Synthesis methodology of semiconductors may be classified into basically two methods (i)
Top down approach and (ii) Bottom Up approach. In the top down approach we start with a
bulk nanocrstal and reduced the size and create nanoparticles. Familiar top down approaches
are focused ion beam etching and ball milling [1.48, 1.49]. In bottom up approach we start
with precursor molecules and coax them by synthesis control to form crystals. All chemical
synthesis based approach falls under this category for e.g. colloidal methods, sol gel
approach, MOCVD, MBE, ALD etc [1.50]. In this approach we can have significant
reproducibility for given reaction conditions. In our synthesis for all of present study we use
colloidal methods for synthesis of quantum dots. To study charge carrier dynamics for
different sizes it can be clearly seen that we need a sharp distribution of size. Therefore a
proper size control is of utmost imperative for studying size dependent properties. It is
known previously that in colloidal synthesis, precipitation or nucleation and growth can
happen at the same time. Therefore under this condition it is difficult to achieve good size