Abstract
Robust surface architectures are desirable for extended durability in many applications. Novel surface modification methods have recently emerged that permit the synthesis of complex interfaces of high thermal and chemical stability. In this thesis, these chemical modification methods were exploited in ultra-high vacuum (UHV) in two separate themes. Scanning tunnelling microscopy and low-energy electron diffraction were employed to examine the surface topography of the samples. Further characterisation was carried out using temperature programmed desorption, high-resolution electron energy loss spectroscopy and reflection-absorption infrared spectroscopy.In the first part, the challenges surrounding the direct synthesis of surface-confined covalent organic frameworks (sCOFs) on catalytically active metals are presented. A protocol based on AuPd metal alloys was developed to circumvent the reduced mobility of monomers on Pd(111) surfaces, which permits 2D polymerisation of 1,3,5-tris(4-bromophenyl)benzene
(TBPB) precursors and the formation of a porous sCOF. This protocol is transferable to the self-condensation of benzene-1,4-diboronic acid and 4-bromophenylboronic acid, however, the extend of polymerisation is compromised. Additionally, the quality of the resulting frameworks is inferior compared to the sCOF synthesised from TBPB precursors.
The second part of this thesis focuses on the fabrication of N-heterocyclic carbenes (NHC) films on Au(111) and Cu(111) surfaces, which offer superior stability over traditional organosulfur self-assembled monolayers. Vapour deposition of NHCs in UHV from the thermolysis of bicarbonate adducts is demonstrated. The substituent groups at the N, N position impact dramatically on the binding geometry and behaviour of the monolayer. The monolayer of a flat-lying NHC transforms into a surface-bound (NHC)₂Cu complex by incorporation of copper adatoms. In addition, the experimentally derived chemisorption energy of an upright-bound NHC onto Au(111) and Cu(111) is the same within error. Last, the results of exploratory experiments are presented where the role of NHC monolayers as passivators against copper oxidation and as oxide etchants is assessed. NHCs reduce a model copper oxide to metallic copper and some degree of passivation was qualitatively derived from thermal desorption spectroscopy. The substituents at the N, N-position have a tangible effect on the degree of passivation.
Date of Award | 27 Jun 2018 |
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Original language | English |
Awarding Institution |
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Supervisor | Christopher John Baddeley (Supervisor) |
Keywords
- Surface chemistry
- N-heterocyclic carbenes
- Surface-confined covalent organic frameworks
- Copper oxide
Access Status
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