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Modelling of adsorption of atomic and molecular species on defective surfaces

Gaberle, Julian; (2019) Modelling of adsorption of atomic and molecular species on defective surfaces. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis focuses on the study of adsorption phenomena on pristine and defective surfaces with respect to surface reactions, functionalisation and thermodynamic sta- bility. For that purpose the thesis is split into three parts: Part I discusses entropic effects to molecular adsorption. Free energy profiles were calculated using classical potentials and molecular dynamics simulations for two large organic molecules and the entropic contribution to adsorption was de- rived, which was used to explain dewetting behaviour at higher temperatures. Fur- thermore, the entropic contributions to step adhesion and dimer formation were calculated for one of the molecules. It is shown that entropic effects counteract step adhesion enthalpies and lead to desorption above room temperature, whereas dimers retain some rotational and translational entropy and are thus stable even at higher temperatures. These results are important for self-assembled films, where entropic contributions dictate film stability at room temperature. Part II investigates the rutile TiO2 (110) surface and how surface reduction impacts Ti interstitial defect formation and diffusion from the surface to the bulk. Point defects were calculated in the bulk as well as at a surface of TiO2. The barrier for Ti interstitial formation is significantly lowered for reduced (110) surfaces and their diffusion barrier rapidly recovers bulk diffusion due to effective screening of the Ti vacancy and the interstitial. In Part III point defects in black phosphorus, a novel 2D material, are studied as well as how their presence influences adsorption of O2, H2O, H2 and H atoms in the context of surface degradation. Comparing first principles calculations to ex- perimental data, observed defects could be attributed to SnP defects. Furthermore, the degradation mechanism under ambient conditions was found to be exothermic, leading to rapid oxidation of the surface and subsequent decomposition into phosphoric acid. These results are relevant for future applications of black phosphorus, since its instability hinders its integration into novel technologies.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Modelling of adsorption of atomic and molecular species on defective surfaces
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10067417
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