Milton, Katherine;
(2025)
Structure and properties of interfaces between monolayer WS2 and dielectric substrates.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This thesis utilises density functional theory and ab initio molecular dynamics methods to model a realistic interface between the transition metal dichalcogenide WS2 and SiO2, with confined water between the two materials. The electronic structure of the bulk α-cristobalite phase of SiO2 was first investigated, focusing on the characteristics of oxygen vacancies in various charge states. It was found that the oxygen vacancy configuration with a stabilising Si-Si bond (i.e. dimer configuration) for the positively charged oxygen vacancy is the most stable in α-cristobalite, in contrast to the α-quartz phase of SiO2. Subsequently, the impact of confined water at the WS2/SiO2 interface was examined. The structure and dynamics of the water at this interface demonstrated that it is strongly influenced by hydrogen bonding to silanol groups on the SiO2 surface, resulting in a hydrogen bonding network in one layer with very few water-water hydrogen bonds. Investigation of the electronic properties at this interface revealed that, on average, the band alignment is not significantly affected by the presence of confined water. However, at shorter timescales, in-gap states are formed between confined water and WS2. The oxidation of WS2 was also studied, showing that water dissociates spontaneously only when both tungsten and sulphur atoms with dangling bonds are exposed at defect sites and edges. Further efforts were made to employ machine learning to generate density functional tight binding repulsive potentials and confinement parameters for the SiO2/H2O/WS2 interface, allowing for exploration over longer timescales.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Structure and properties of interfaces between monolayer WS2 and dielectric substrates |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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 UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10208346 |
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