| Summary: | Nanotechnology is at the forefront of current scienti c research and nanocrystals
are being hailed as the `arti cial' atoms of the 21st century. Semiconducting silicon
nanocrystals (SiNCs) are prime candidates for potential commercial applications
because of silicon's already ubiquitous presence in the semiconductor industry,
nontoxicity and abundance in nature. For realization of these potential applications,
the properties and behavior of SiNCs need to be understood and enhanced.
In this report, some of the main SiNC synthesis schemes are discussed, including
those we are currently experimenting with to create our own SiNCs and the one
utilized to create the SiNCs used in this study. The underlying physics that governs
the unique behavior of SiNCs is then presented. The properties of the as-produced
SiNCs are determined to depend strongly on surface passivation and environment.
Size puri cation, an important aspect of nanomaterial utilization, was successfully
performed on our SiNCs though density gradient ultracentrifugation. We demonstrate
that the size-puri ed fractions exhibit an enhanced ability for colloidal self-assembly,
with better aligned nanocrystal energy levels which promotes greater photostability
in close-packed lms and produces a slight increase in photoluminescence (PL)
quantum yield. The qualities displayed by the fractions are exploited to form
SiNC clusters that exhibit photostable PL. An analysis of SiNC cluster (from
individual nanocrystals to collections of more than one thousand) blinking and
PL shows an improvement in their PL emitting `on' times. Pure SiNC lms
and SiNC-polymer nanocomposites are created and the dependence of their PL
on temperature is measured. For such nanocomposites, the coupling between the
`co ee-ring' e ect and liquid-liquid phase separation is also examined for ternary
mixtures of solvent, polymer and semiconducting nanocrystal. We discover that
with the right SiNC-polymer concentration and polymer molecular weight, phase separation can be supressed; we use this to build a prototype nanocomposite printing
device. Finally, the nanocrystals are PEGylated and introduced into an aqueous
biological environment to demonstrate their potential for use in biological labelling
and sensing devices. The development of superlattice structures from monodisperse
SiNC fractions and their use in solid-state lighting and solar cell applications are also
explored.
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