Abstract
Porous silicon has been studied as an effective host, efficient emitter, sensor and
recently, a candidate for photonic crystals. Convenient surface modification chemistry
not only counteracts the drawbacks of surface instability that comes with nanostructured
morphology, it also adds useful functionalities such as specific target capture for
sensing utility. Structurally novel devices can also be realised through manipulating
porous silicon multilayers. This thesis extends on the effort to explore the optical
properties and applications of porous silicon through the construction of functional
porous silicon structures assisted by surface chemistry. In addition, extraordinary
optical properties resulting from peculiar behaviour of light in porous silicon
multilayers as photonic crystals are investigated and exploited to broaden the
understanding of structural novelty and practically, showing attractive prospects for
biosensing applications.
Quantum dot doped porous silicon one dimensional microcavity structures have been
fabricated by incorporating colloidal II-VI compound quantum dots into the microcavity
assembled from two separately anodised Bragg mirrors. The formation of microcavity
structures is facilitated by strong affinity between biomolecules. High quality
microcavity structures built on quantum dots at 565 nm, 625 nm and 780 nm with this
technique exhibit well defined stop bands and resonant modes with line-widths less than
3.5 nm. Enhancement of photoluminescence emission, spectral and spatial modification
by the microcavities is observed. Tunable emission from the microcavities also suggests
the potential applications in biosensing.
The outermost truncation of regular Bragg reflectors creates a new type of novel
structure sustaining Bloch surface waves with promising capability for biosensing. The
structure is passivated and functionalized using established surface chemistry.
Biosensing capability of the structures is demonstrated by protease-catalytic cleavage
reaction of grafted gelatin. A detection limit of 0.37 nM protease is obtained. The
possibility of kinetics study is explored.
Fabrication and characterisation of high quality protein spaced porous silicon
microcavities for sensing purposes are summarised. Gelatin is incorporated as the
central layer of the microcavity structure and, as the sensing element in biosensing
operation. Some constraints to the engendering protease sensing are identified and
possible solutions to these problems, proposed.