Title:
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A First Principles Study of Oxidation Processes for Silicon Quantum Dots
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Silicon quantum dots have a multitude of potential uses within the biomedical
and optoelectronic industries due to the outstanding optical properties
they exhibit. However, they are susceptible to oxidation, which may have
a significant impact on the yield and emission wavelength. These effects may
be traced to the growth of a Si02 capping layer, or the inclusion of surface
defects that yield optically active mid-gap states.
Therefore the results of density functional calculations examining important
oxidation processes for silicon quantum dots are presented within this
thesis. The results have been obtained using the AIMPRO (Ab Initio Modelling
PROgram) DFT code.
First, a discussion is included concerning the thermodynamic and kinetic
preferences for oxygen migration at the surface of a quantum dot, a key
process in the growth of a Si02 layer, in particular examining the effects of
local surface bonding and charging.
Following on from this analysis, the progressive oxidation of a quantum
dot through the formation of Si-O-Si bonds or the oxidation of surface SiH
bonds has been examined to determine the most energetically favourable
route for oxidation and the effect on the optical response of the system.
Finally, the silanone surface defect (Si=O) has often been cited in the
literature as a potential source of optical shifts upon exposure to an oxidising
source. However the stability of this structure has only been analysed in a
few idealised circumstances, and a more general and significantly extended
study is included.
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