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Title: Interaction of a copper surface with light : plasmons, electrons and molecular vibrations
Author: García Rey, Natalia
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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The interaction of light with a copper surface has been explored in this thesis in order to understand and enhance a photochemical process. The thesis is split into three main results sections: Surface photochemistry: from NO/Cu(110) photochemistry (chapter 3), towards the analysis of the nonlinear response of Cu(110) (chapter 4). Vibrational dynamics at surfaces, pyridine analyzed by SFG in combination with work function measurements (chapter 5) and, the ultrafast dynamics of pyridine/Cu(110) (chapter 6). Surface enhanced photochemistry, where we present our conclusions on plasmon-enhanced photochemistry combined with field enhancement modeling on copper surfaces (chapter 7). In chapter 3 we investigate the photochemistry of NO dimers on a Cu(110) surface. Green light irradiation splits the dimer to generate a monomer on a thermally inaccessible atop site. The dimer dissociation is reversible. Wavelength-dependent measurements indicate that long-lived hot holes at the top of the copper d-band are responsible for the observed photochemistry. In chapter 4 we investigate the electronic structure of clean and oxygen or pyridine covered Cu(110) using electronic sum frequency generation. We discover dynamically enhanced sum frequency related to long decoherence times of hot holes in the d-band. Chapter 5 investigates the adsorption of pyridine on copper using vibrational sum frequency gener- ation and work function measurements. A monolayer of pyridine/Cu(110) is revealed as an ultra-low work function surface (1.46 eV). The connection between the nonresonant sum frequency response and the surface work function is investigated for pyridine and some substituted pyridines. Chapter 6 looks at the charge transfer between the Cu(110) surface and adsorbed pyridine in real time using femtosecond pump - broadband vibrational SFG probe spectroscopy. We investigate the ultrafast charge transfer for a range of coverages, pump wavelengths and pump polarisation and ftuence. We detect a long-lived (400 fs) excited state of pyridine which is tentatively identified as an anion or a dipole-bound electron. Upon deexcitation this causes disorder in the highly ordered pyridine layer which relaxes on a 40 picosecond timescale. Chapter 7 finally looks into the question how efficiently photochemical processes can be enhanced by plasmon excitation on copper. We use finite element modeling to calculate electric field enhancement and and look at how this is related to the absorption cross section. We summarise our calculations in a guide of how to successfully use plasmons to enhance photochemical reaction rates.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available