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Complex Excitations in Advanced Functional Materials
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding the fundamental electronic properties of materials is a key step to develop innovations in many fields of technology. For example, this has allowed to design molecular based devices like organic field effect transistors, organic solar cells and molecular switches.

In this thesis, the properties of advanced functional materials, in particular metal-organic molecules and molecular building blocks of 2D materials, are investigated by means of Density Functional Theory (DFT), the GW approximation (GWA) and the Bethe-Salpeter equation (BSE), also in conjunction with experimental studies. The main focus is on calculations aiming to understand spectroscopic results.

In detail, the molecular architectures of lutetium-bis-phthalocyanine (LuPc2) on clean and hydrogenated vicinal Si(100)2×1, and of the biphenylene molecule on Cu(111) were analysed by means of X-ray Photoelectron spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy; DFT calculations were performed to obtain insights into the atomic and electronic structures. Furthermore, detailed information about the electronic states of the gas phase iron phthalocyanine (FePc) and of the gas phase biphenylene molecule were obtained through XPS and NEXAFS spectroscopy. I have studied by means of DFT, multiplet and GWA calculations the electronic correlation effects in these systems. Also the optical, electronic and excitonic properties of a hypothetical 2D material based on the biphenylene molecule were investigated by GWA and BSE calculations. Monolayers of metal-free phthalocyanine (H2Pc) on Au(111) and of FePc on Au(111) and Cu(100)c(2×2)-2N/Cu(111) with and without pyridine modifier were studied by XPS and final state calculations. A multiplet approach to compute L-edges employing the hybridizations function, known from dynamical mean field theory, was proposed and applied to transition metal oxides.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 90 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1365
Keyword [en]
X-ray Absorption Spectroscopy, Photoelectron Spectroscopy, Adsorption, Phthalocyanines, Biphenylene, Excitons, Functional Materials
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-282151ISBN: 978-91-554-9543-5 (print)OAI: oai:DiVA.org:uu-282151DiVA: diva2:916555
Public defence
2016-05-13, Å80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-04-22 Created: 2016-04-03 Last updated: 2016-04-29
List of papers
1. Photelectron spectroscopy studies of metal-free phthalocyanine on Au(111)
Open this publication in new window or tab >>Photelectron spectroscopy studies of metal-free phthalocyanine on Au(111)
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173389 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2016-04-29Bibliographically approved
2. Comparison of van der Waals corrected and sparse-matter density functionals for the metal-free phthalocyanine/gold interface
Open this publication in new window or tab >>Comparison of van der Waals corrected and sparse-matter density functionals for the metal-free phthalocyanine/gold interface
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2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 4, 045416- p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we report a systematic study on the effect of different van der Waals dispersion correction methods in conjunction with Density Functional Theory on the adsorption characteristics of a monolayer of metal-free phthalocyanine on Au(111). The chosen dispersion corrections were DFT-D2, the Tkatchenko-Scheffler method with and without self-consistent screening, and four sparse-matter density functionals. A comparison among different dispersion corrections was performed and the results are related to available experimental scanning tunnel microscopy and x-ray standing-wave measurements for similar molecules on Au(111). We found that the Tkatchenko-Scheffler method as well as a sparse-matter density functional which employs the exchange potential of optB86b and the nonlocal correlation of Dion describe the adsorbed system, e. g., electronic and geometric structure with an adsorption distance of 3.3 angstrom, reasonably well within moderate computational costs.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-221933 (URN)10.1103/PhysRevB.89.045416 (DOI)000332225400008 ()
Available from: 2014-04-07 Created: 2014-04-07 Last updated: 2017-12-05Bibliographically approved
3. Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine
Open this publication in new window or tab >>Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine
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2013 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 23, 234701- p.Article in journal (Refereed) Published
Abstract [en]

Using Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy, the thickness dependent formation of Lutetium Phthalocyanine (LuPc2) films on a stepped passivated Si(100)2x1 reconstructed surface was studied. Density functional theory (DFT) calculations were employed to gain detailed insights into the electronic structure. Photoelectron spectroscopy measurements have not revealed any noticeable interaction of LuPc2 with the H-passivated Si surface. The presented study can be considered to give a comprehensive description of the LuPc2 molecular electronic structure. The DFT calculations reveal the interaction of the two molecular rings with each other and with the metallic center forming new kinds of orbitals in between the phthalocyanine rings, which allows to better understand the experimentally obtained NEXAFS results. 

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-205011 (URN)10.1063/1.4809725 (DOI)000321012400026 ()
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2017-12-06Bibliographically approved
4. When the Grafting of Double Decker Phthalocyanines on Si(100)-2 × 1 Partly Affects the Molecular Electronic Structure
Open this publication in new window or tab >>When the Grafting of Double Decker Phthalocyanines on Si(100)-2 × 1 Partly Affects the Molecular Electronic Structure
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2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 26, 14270-14276 p.Article in journal (Refereed) Published
Abstract [en]

A combined X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) study has been performed to characterize the adsorbate interaction of lutetium biphthalocyanine (LuPc2) molecules on the Si(100)-2 × 1 surface. Large molecule–substrate adsorption energies are computed and are found to compete with the molecule–molecule interactions of the double decker molecules. A particularly good matching between STM images and computed ones confirms the deformation of the molecule upon the absorption process. The comparison between DFT calculations and XP spectra reveals that the electronic distribution in the two plateaus of the biphthalocyanine are not affected in the same manner upon the adsorption onto the silicon surface. This finding can be of particular importance in the implementation of organic molecules in hybrid devices.

Keyword
lutetium bi-phthalocyanine, XPS, STM, XAS, DFT, Si(100)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-281565 (URN)10.1021/acs.jpcc.6b05552 (DOI)000379457000044 ()
Funder
EU, FP7, Seventh Framework Programme, 321319Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish Research Council, 2014-3776
Available from: 2016-03-24 Created: 2016-03-24 Last updated: 2017-11-30Bibliographically approved
5. Characterization of Gas Phase of Iron Phthalocyanine with X-ray Photoelectron and Absorption Spectroscopies
Open this publication in new window or tab >>Characterization of Gas Phase of Iron Phthalocyanine with X-ray Photoelectron and Absorption Spectroscopies
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2015 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, 1259-1265 p.Article in journal (Refereed) Published
Abstract [en]

Despite the numerous studies dedicated to phthalocyanine molecules adsorbed on surfaces, in monolayer or thin film, very few works have been focused on the characterization of vapors of these molecules. In this article we present the C 1s, N 1s and Fe 2p photoemission results as well as N K-edge X-ray absorption data of iron phthalocyanine (FePc) in gas phase. Presented comparison of X-ray photoelectron spectroscopy and X-ray absorption spectroscopy spectra of FePc films show a great similarity with the gas phase results, confirming the molecular character of thick films. The Fe2p photoemission spectrum of the gas phase FePc, shown for the first time, can be considered as a fingerprint of the Fe(II) ionic state of the central metal of the iron phthalocyanine. The performed multiplet calculations for describing the Fe 2p XP spectrum indicate 3Eg (a1g2eg32g1) state as the most probable ground state for thick film of iron phthalocyanine.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-217080 (URN)10.1002/pssb.201451147 (DOI)000355756200010 ()
Funder
Swedish Research CouncilCarl Tryggers foundation
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
6. Nature of the bias-dependent symmetry reduction of iron phthalocyanine on Cu(111)
Open this publication in new window or tab >>Nature of the bias-dependent symmetry reduction of iron phthalocyanine on Cu(111)
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 7, 075428Article in journal (Refereed) Published
Abstract [en]

Subtle changes in the geometric and electronic properties of supported molecules, with a potential impact on the functioning of molecular devices, can typically be imaged by scanning probe microscopy, but their exact origin and nature often remain unclear. Here we show explicitly that the symmetry reduction of iron phthalocyanine upon adsorption on Cu(111) can be observed not only in scanning tunneling microscopy, but also in core-level spectroscopy, and that it is related to nonisotropic charge transfer into the two principal molecular axes, but in combination with topographic influences.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-262426 (URN)10.1103/PhysRevB.92.075428 (DOI)000359859600005 ()
Funder
Swedish Research Council, 2010-5080 2014-3776EU, European Research Council, 247299
Available from: 2015-09-17 Created: 2015-09-15 Last updated: 2017-12-04Bibliographically approved
7. Iron phthalocyanine on copper nitride: geometry, spin state, and modification by pyridine adsorption
Open this publication in new window or tab >>Iron phthalocyanine on copper nitride: geometry, spin state, and modification by pyridine adsorption
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Using a monolayer of iron phthalocyanine adsorbed on the Au(111) surface and on a Cu(111)-supported two-dimensional copper nitride layer, we show how the modification of the support can influence the electronic and magnetic properties of an adsorbed transition metal complex. The two systems have been studied by a combination of electron spectroscopy and first principles theoretical calculations, which included modelling of the van der Waals interactions. For adsorption of iron phthalocyanine on the Cu(100)c(2x2)-2N/Cu(111) surface we find several different adsorbate structures at different surface sites, which all have very similar energies. Depending on the adsorption site - above a support nitrogen or a support copper atom - the spin magnetic moment of the molecular iron ion assumes different values. Although pyridine adsorption on the iron phthalocyanine monolayer reduces the spin magnetic moments for all phthalocyanine adsorption sites, the difference between the different sites persists: only for the iron phthalocyanine adsorbates with the central iron ion above a support nitrogen atom the spin is quenched completely, while a residual spin magnetic moment is found for the adsorption structures with the iron ion above a copper atom. The results illustrate clearly the relevance of the support as a ligand to the central ion.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-281585 (URN)
Available from: 2016-03-24 Created: 2016-03-24 Last updated: 2016-04-29
8. Many-body effects and excitonic features in 2D biphenylene carbon
Open this publication in new window or tab >>Many-body effects and excitonic features in 2D biphenylene carbon
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2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 2, 024702Article in journal (Refereed) Published
Abstract [en]

The remarkable excitonic effects in low dimensional materials in connection to large binding energies of excitons are of great importance for research and technological applications such as in solar energy and quantum information processing as well as for fundamental investigations. In this study, the unique electronic and excitonic properties of the two dimensional carbon network biphenylene carbon were investigated with GW approach and the Bethe-Salpeter equation accounting for electron correlation effects and electron-hole interactions, respectively. Biphenylene carbon exhibits characteristic features including bright and dark excitons populating the optical gap of 0.52 eV and exciton binding energies of 530 meV as well as a technologically relevant intrinsic band gap of 1.05 eV. Biphenylene carbon's excitonic features, possibly tuned, suggest possible applications in the field of solar energy and quantum information technology in the future.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-278016 (URN)10.1063/1.4939273 (DOI)000368618400036 ()26772582 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation
Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2017-11-30Bibliographically approved
9. The electronic characterization of biphenylene-Experimental and theoretical insights from core and valence level spectroscopy
Open this publication in new window or tab >>The electronic characterization of biphenylene-Experimental and theoretical insights from core and valence level spectroscopy
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2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 7, 074305Article in journal (Refereed) Published
Abstract [en]

In this paper, we provide detailed insights into the electronic structure of the gas phase biphenylene molecule through core and valence spectroscopy. By comparing results of X-ray Photoelectron Spectroscopy (XPS) measurements with Delta SCF core-hole calculations in the framework of Density Functional Theory (DFT), we could decompose the characteristic contributions to the total spectra and assign them to non-equivalent carbon atoms. As a difference with similar molecules like biphenyl and naphthalene, an influence of the localized orbitals on the relative XPS shifts was found. The valence spectrum probed by photoelectron spectroscopy at a photon energy of 50 eV in conjunction with hybrid DFT calculations revealed the effects of the localization on the electronic states. Using the transition potential approach to simulate the X-ray absorption spectroscopy measurements, similar contributions from the non-equivalent carbon atoms were determined from the total spectrum, for which the slightly shifted individual components can explain the observed asymmetric features.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-251526 (URN)10.1063/1.4907723 (DOI)000350547500018 ()25702013 (PubMedID)
Available from: 2015-04-22 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
10. Electronic correlations revealed by hybrid functional and GW calculations in the anti-aromatic biphenylene molecule
Open this publication in new window or tab >>Electronic correlations revealed by hybrid functional and GW calculations in the anti-aromatic biphenylene molecule
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The biphenylene molecule is an interesting new candidate as a building block for advanced 2D materials. In this study, the molecular properties of biphenylene, like ionization potential and electron affinity, as well as the HOMO-LUMO gap were computed with the GW approach and with hybrid functional Density Functional Theory. B3LYP, HSE and HSE06 were compared as well as with the OT-RSH approach. The electronic structure of the valence states obtained by GW calculations and hybrid functionals was compared to experimental valence photoelectron spectroscopy data.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-281568 (URN)
Available from: 2016-03-24 Created: 2016-03-24 Last updated: 2016-04-29
11. Core levels, valence band structures and unoccupied states of biphenylene films
Open this publication in new window or tab >>Core levels, valence band structures and unoccupied states of biphenylene films
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Biphenylene is a cyclic hydrocarbon made of two benzene rings connected by a cyclobutadiene ring. We performed a photoemission and near-edge absorption (PES and NEXAFS) spectroscopy investigation on biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. By PES we studied the occupied core and valence levels, while NEXAFS gave us information on the unoccupied states. The obtained results have been compared to previous gas phase spectra and density functional theory (DFT) calculations on single biphenylene molecule to get insights in the film electronic structure and possible modification induces by the adsorption. Furthermore, NEXAFS results of biphenylene films of different thicknesses allowed the characterization of the molecular arrangement in the overlayer on the Cu surface and helped to clarify the substrate-molecule interactions.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-281566 (URN)
Available from: 2016-03-24 Created: 2016-03-24 Last updated: 2016-04-29
12. Theory of X-ray spectroscopy of strongly correlated systems
Open this publication in new window or tab >>Theory of X-ray spectroscopy of strongly correlated systems
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

X-ray absorption spectroscopy measured at the L-edge of transition metals (TMs) is a powerful element-selective tool providing direct information about the correlation effects in the 3d states. The theoretical modelling of the 2p to 3d excitation processes remains a challenge for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work we present a realisation of the method combining the density functional theory with multiplet ligand field theory, proposed in Phys. Rev. B 85, 165113 (2012). The core of this approach is the solution of the single-impurity Anderson model (SIAM), parameterised from first principles.In our implementation, we adopt  the dynamical mean-field theory and utilize the local Hamiltonian and the hybridisation function, projected onto TM 3d states, in order to construct the SIAM. We show that the current method can be used as an alternative to the construction of the Wannier functions. The developed computational scheme is applied to calculate the L-edge spectra for several TM monoxides. An excellent agreement between the theory and experiment is found for all studied systems. The possible extensions of the method as well as its limitations are discussed.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-281570 (URN)
Available from: 2016-03-24 Created: 2016-03-24 Last updated: 2016-04-29

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