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X-ray Spectroscopy Investigations of TPA/Au(111): Charge Redistribution via Core Exitation?
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.ORCID iD: 0000-0001-8739-7773
Royal Institute of Technology (KTH), Department of Theoretical Chemistry and Biology.ORCID iD: 0000-0003-1671-8298
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
ISM-CNR, Trieste LD2 Unit, Italy.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Triphenylamine (TPA) is a well-known electron donor molecule largely used in photovoltaics. In this article we analyze the electronic structure modifications due to the adsorption of the molecules at a monolayer coverage on a Au(111) surface. Only a weak interaction was observed between the TPA and the gold during the adsorption process, being impossible to get more than 1ML coverage at room temperature. The characterizations have been performed by core and valence Photoelectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The results were compared with our previous investigations on free TPA, and theoretical models were used to explain the changes of the electronic structure due to the adsorption on the metallic gold surface. The calculation confirms the weak interaction between the adsorbed TPA and the Au(111), with only a slight change of the twisting angle of the TPA phenyl rings. The resulting adsorption geometry can be used to explain the broadening of the C 1s PES line with respect to the gas-phase results and the expected absence of angle dependence in the C K-edge NEXAFS. However, a significant modification was observed in the N K-edge NEXAFS spectra of TPA/Au(111), showing a new pre-edge feature due to transitions involving out-of-plane orbitals. This pre-edge feature is ascribed to the interaction between the molecules and the surface, having a different character and energy position than the pre-edge observed for free TPA. A model, considering a TPA+ cation formed by a charge redistribution process between the adsorbate and the surface valence states seems to give a qualitative explanation of this pre-edge intensity. Since our calculations predict only a weak interaction between the TPA molecules and the gold surface, we propose that such a charge redistribution happens in the core-excited state created by photon absorption.

National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-355120OAI: oai:DiVA.org:uu-355120DiVA, id: diva2:1228913
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-06-29
In thesis
1. Synchrotron Radiation Studies of Molecular Building Blocks for Functional Materials
Open this publication in new window or tab >>Synchrotron Radiation Studies of Molecular Building Blocks for Functional Materials
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The research on new materials is a primary driving force for progress in human society. One of the most significant research topic nowadays is the development of new functional materials for technological applications, like perovskite implemented in solar cells, and graphene as a representative for the new 2D materials family. It is then crucial to fully understand the functionality of such materials from a fundamental point of view, as a complementary and useful guide to develop/design new devices of improved performance and energy efficiency.

In the thesis, comprehensive characterizations of molecular building blocks used in i) novel energy conversion devices (CoPc, TPA, DPTA and m-MTDATA), and ii) in 2D materials (biphenylene and melamine) have been performed by PhotoElectron Spectroscopy (PES), and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy carried out at synchrotron radiation facilities, representing effective, powerful light source dedicated to the front-line materials research of great value in both science and industry. PES and NEXAFS spectroscopy, in combination with Density Functional Theory (DFT) calculations have provided a deep understanding of the electronic structure of the investigated systems in relation to their functionality. The investigations always included the combination and comparison between experimental and theoretical results. The studied molecules were characterized as free and adsorbed on surfaces, from the simple building blocks to more complex molecular systems. The characterizations allowed us to identify the electronic structure modifications due to substitutions (Paper III), increasing complexity of the molecules (Paper V), molecule-substrate interactions (Paper I, II, IV, V) and intra-molecular H-bonding interactions (Paper VI).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 97
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1693
Keywords
Synchrotron radiation study, Functional materials, Molecular building blocks, Electron donor, 2D material, Gas-phase, Organic thin film, Electronic structure, Molecule-molecule interaction, Molecule-substrate interaction, Photoelectron spectroscopy, PES, XPS, Near edge X-ray absorption fine structure, NEXAFS, X-ray Absorption Spectroscopy, XAS, Au(111), Cu(111), Surface, Interface, Electronic structure, H-bonding, Cobalt phthalocyanine, CoPc, Triphenylamine, TPA, DPTA, m-MTDATA, Melamine, Biphenylene, Carbon nitride, Graphenylene, Density functional theory, DFT
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-354766 (URN)978-91-513-0383-3 (ISBN)
Public defence
2018-09-07, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Supervisors
Available from: 2018-08-14 Created: 2018-06-29 Last updated: 2018-08-28

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Zhang, TengBrumboiu, Iulia E.Lanzilotto, ValeriaJohansson, FredrikBrena, BarbaraPuglia, Carla

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