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Title: Electron harvesting and dynamics at a metal-semiconductor interface
Author: Doiron, Brock
ISNI:       0000 0004 8504 8336
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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In this thesis, optical measurements are combined with theoretical modelling to evaluate the viability of metal-semiconductor interfaces for use in plasmonic applications. Firstly, the optical response of metals and metallic nanoparticles is presented with emphasis placed on relating the observable optical properties to the underlying electronic processes. This is then extended to describe metal-semiconductor heterojunctions in the context of light-induced electron transfer between the metal and the semiconductor. An overview of the experimental methods used in this work is given along with how the relevant optical properties of a given sample are extracted from the collected data. The key material system of this work, titanium oxynitride, is introduced in the context of the developed models. Ultrafast pump-probe spectroscopy is then performed on various titanium oxynitride thin films. Unlike the femtosecond decay expected from density function theory calculations, the transient signal of the titanium oxynitride film persists on the scale of nanoseconds. This is shown to be a result of energetic electrons excited in the metal transferring into the surface oxide and remaining at the surface. The knowledge gained from this is then applied to titanium oxynitride nanostructures where the role of plasmon-enhanced electron harvesting is explored using pump-probe spectroscopy. Interestingly, the electron harvesting efficiencies into the titania surface oxide layer is shown to exceed what is expected by plasmon-enhanced absorption alone as a result of additional damping due to the encapsulating oxide layer. Finally, the thermal resistance of titanium oxynitride is explored at high laser powers, which is a proposed advantage of titanium oxynitride over gold. As a result of the unique thermal, optical and electronic properties provided by the spontaneously occurring titanium oxynitride-titanium dioxide interface, it is likely to play a critical role in the future development of electron harvesting and photocatalytic applications.
Supervisor: Oulton, Rupert ; Maier, Stefan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral