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Exploring the electronic structure of CoPc by photoemission and absorption spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
University of Trieste.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Photoelectron spectroscopy  and X-ray absorption spectroscopy were used to investigate the occupied and empty density of states of cobalt phthalocyanine (CoPc) in the gas phase and in thin films of different thicknesses, deposited onto a Au (111) single crystal. The comparison between experimental gas phase results and density functional theory single molecule simulations confirmed that the CoPc ground state is correctly described by the 2A1g electronic configuration. Moreover, the atomic character of the highest occupied molecular orbital of CoPc was addressed by performing photon energy dependent valence photoemission spectroscopy experiments on both CoPc gas phase and film samples. Our results clearly show that the highest occupied molecular orbital is derived only from the organic ligand, with mainly contribution from the carbon atoms. Multiplet ligand field theory was employed to simulate the Co L edge X-ray absorption spectroscopy results.

National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-307777OAI: oai:DiVA.org:uu-307777DiVA: diva2:1048379
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-12-07
In thesis
1. Synchrotron radiation study of free and adsorbed organic molecules
Open this publication in new window or tab >>Synchrotron radiation study of free and adsorbed organic molecules
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this licentiate thesis, organic molecules, namely Cobalt Phthalocyanine (CoPc) and Biphenylene, have been studied by means of synchrotron radiation-based spectroscopic methods (Photoemission Spectroscopy (PES) and X-ray Absorption Spectroscopy (XAS) in combination with Density Functional Theory (DFT) calculations.

Paper I is a combined experimental and theoretical investigation of electronic structure of CoPc. addressing the atomic character of the Highest Occupied Molecular Orbital (HOMO) and the electronic configuration of the molecular ground state. Both these aspects are still under discussion since different experimental and theoretical studies have given controversial results. Previous works have indicated the CoPc ground state to either be described by the 2A1g or 2Eg, or by a mix of the two electronic configurations. Regrading the debated the atomic character of the HOMO of CoPc, it has been suggested to be either metal 3d-like and localized on the central Co atom or originating in the organic ligand of the molecule. In this thesis the valence photoemission results for CoPc in gas phase and as adsorbed films on Au(111) together with the DFT simulations, consistently indicate that the HOMO is derived only by the organic ligand, with mainly contribution from the carbon atoms with no metal character. Moreover, the good agreement between the experimental and theoretical results, confirms that the ground state of CoPc is correctly described by the 2A1g configuration.

In Paper II, PES and XAS have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, XAS measurements allowed the characterizion of the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 41 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214
Keyword
Synchrotron radiation, Phthalocyanine, Cobalt phthalocyanine, Biphenylene, Functional materials, CoPc, Photoemission spectroscopy, Absorption spectroscopy, PES, XAS, Electronic structure, Gas phase, film, Organic molecule
National Category
Natural Sciences Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-307787 (URN)
Presentation
2016-12-12, Å2001, Ångstrom Laboratory, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2016-12-07 Created: 2016-11-21 Last updated: 2016-12-28Bibliographically approved

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