Use this URL to cite or link to this record in EThOS:
Title: Porphyrin on metal surfaces : a density functional study
Author: Poli, Paolo
ISNI:       0000 0004 7657 0325
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
Availability of Full Text:
Access from EThOS:
Access from Institution:
In this thesis various aspects of porphyrin adsorption on metal surfaces were studied using Density Functional Theory (DFT) calculations. The studies were motivated by recent experiments and include self-assembly of adsorbed porphyrins, CO bonding to the metal centres of the porphyrins and the associated anharmonicity of the internal stretch mode and on-surface porphine dimerisation. This reaction is a precursor for the oligomerisation of Porphines into various nano structures such as nano wires and tapes with a potential interest for the development of nanotechnologies and molecular devices. Chapter 1 gives a brief introduction to porphyrin and surface science. The experimental methods such as reflection absorption infrared spectroscopy, Sum Frequency Generation (SFG) and Scanning Tunnelling Microscopy (STM), which are central to the thesis, are discussed shortly in Chapter 2. Chapter 3 gives a brief background of the theory behind the DFT calculations with results presented in Chapters 4-6. Finally, concluding remarks and a future outlook are presented in Chapter 7. Chapter 4 presents results for the adsorption energies and structures of isolated and adsorbed Tetra Phenyl Porphyrin (TPP) with three different metal centres, Ru, Co and Zn, on a Cu(110) surface. These results include also a study of the bonding of CO to these isolated and adsorbed complexes. Their electronic structures are analysed using calculated projected and partial density of states. The calculated STM images compared favourably with the observed images. The adsorption on the Cu(110) surface is found to have a significant effect on their geometric structures but also on the CO bonding. The analysis of the CO bonding to the porphyrins continues in Chapter 5 with a study of the anharmonicity of the internal stretch mode based of DFT calculations of potential energy curves for the internal stretch of CO in various bonding situations. This study was motivated by the relatively large value of this anharmonicity observed by SFG for CO bonded to Ru-TPP adsorbed on a Cu(110) surface. Furthermore, some attention was paid concerning the possibility to use the anharmonicity to estimate important quantities such as the dissociation energy. Chapter 6 presents the results of reaction thermodynamics calculations of dimer formation of physisorbed porphine monomers on the Au(111) surface through C-C coupling. This study is motivated by recent observations by STM of this reaction under ultra high vacuum conditions carried out at University of Liverpool and University of Graz. In particular, a puzzling observation is the different occurrences of various bonding motifs at different surface temperatures. These calculations include also free energy contributions from translational and rotational motions of the reactants and products. The large entropy of the hydrogen gas under ultra high vacuum conditions is found to be a strong thermodynamic driving force for the dimerisation reaction. The calculated STM images helped the assignment of the observed STM images to different bonding motifs. The reaction free energy calculations were able to rationalise the different occurrences of the most observed dimer bonding motifs.
Supervisor: Persson, Mats Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral