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Title: Highly-reactive dissociative adsorption : molecular dynamics of ozone on silicon and diamond surfaces
Author: Fink, C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2009
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The dissertation consists of two parts. The first part investigates the oxidation of silicon by O3. To elucidate the initial oxidation stage, first-principles molecular dynamics simulations are carried out to study the adsorption of O3 on clean Si{001}, partially-oxidised Si{001} and the most relevant hydrogen-passivated silicon surfaces. On clean Si{001} it is found that O3 favours a barrierless dissociation with two surface reaction centres, leading to a partial or complete dissociative adsorption. The underlying electronic structure is analysed to explain this reaction. On partially-oxidised Si{001} the sticking probability of O3 decreases with increasing oxygen coverage, but O3 is found to react even with the partially-oxidised Si atoms. An interesting diffusion mechanism is observed, which leads to the oxidation of a Si-Si subsurface bond and the formation of a fully-oxidised Si species. On hydrogen-passivated silicon, the surface hydrogens are found to have a strong repelling effect on O3. Yet, the simulations reveal an intriguing radical-mediated adsorption mechanism, which enables O3 to oxidise the Si-H bond and form a surface hydroxyl (Si-OH). A mapping of the potential energy surface reveals several narrow adsorption channels, where O3 oxidises the Si-Si dimer, backbond, and subsurface bond. The second part focuses on the oxidation of diamond by O2 and O3. In the interaction between O2 and C{001} two new adsorption structures are identified. The most likely reaction pathways are suggested from transition state search calculations, which show how gas-phase O2 adsorbs onto the surface, and eventually dissociates. In addition, the reaction pathways for the dissociative adsorption of O3 on C{001}are revealed, which suggest that O3 allows a low temperature oxidation of diamond.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available