Reactive nano silicon: mediated processes

Abstract

In this thesis basic methods for the fabrication and characterisation of several nano-silicon containing systems are presented. Due to their morphology, these systems are highly reactive. Silicon wafers were used to prepare layers of porous silicon via electrochemically etching and micro– and nano– sized silicon powders were chemically etched in order to yield silicon nanoparticles. Dependent on the fabrication, particle size of the nanocrystals and porosity of the assemblies can be tailored over a wide range: mean particle sizes can be between 3 to 20 nm and porosities can be varied from 10 to 90 %. A huge surface area of up to 500m2/g which is in addition, due to the fabrication process, hydrogen terminated, entail the outstanding chemical and photo-chemical properties of nanocrystalline silicon. Both, chemical and photo-chemical properties of silicon nanocrystal structures are investigated. The emphasis lies on optical spectroscopy. The indirect band gap structure of silicon in combination with quantum confinement effects are the origin of the interesting luminescence properties of nano-silicon. The energy transfer process from photo-excited excitons confined in silicon nanocrystals to molecules present in the surrounding ambient, like oxygen or a variety of organic substances, has been studied. Measurements demonstrated that long-living excitons very efficiently transfer their energy to surrounding molecules. The low probability of creating excitons which can persist for a long time, from μs to ms, by a photon and structural properties of porous silicon, or rather its reactive surface, however, seem to be the reason for a low total quantum yield of sensitised excited singlet state oxygen.

Date of Award	1 Aug 2009
Original language	English
Awarding Institution	University of Bath
Supervisor	Dmitry Kovalev (Supervisor)