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  • 1.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panchmatia, Pooja M.
    Brumboiu, Iulia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bernien, Matthias
    Weis, Claudia
    Krumme, Bernhard
    Etz, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kuch, Wolfgang
    Wende, Heiko
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Manipulation of spin state of iron porphyrin by chemisorption on magnetic substrates2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 2, p. 024401-Article in journal (Refereed)
    Abstract [en]

    One of the key factors behind the rapid evolution of molecular spintronics is the efficient realization of spin manipulation of organic molecules with a magnetic center. The spin state of such molecules may depend crucially on the interaction with the substrate on which they are adsorbed. In this paper we demonstrate, using ab initio density functional calculations, that the stabilization of a high spin state of an iron porphyrin (FeP) molecule can be achieved via chemisorption on magnetic substrates of different species and orientations, viz., Co(001), Ni(001), Ni(110), and Ni(111). The signature of chemisorption of FeP on magnetic substrates is evident from broad features in N K x-ray absorption (XA) and Fe L-2,L-3 x-ray magnetic circular dichroism (XMCD) measurements. Our theoretical calculations show that the strong covalent interaction with the substrate increases Fe-N bond lengths in FeP and hence a switching to a high spin state (S = 2) from an intermediate spin state (S = 1) is achieved. Due to chemisorption, ferromagnetic exchange interaction is established through a direct exchange between Fe and substrate magnetic atoms as well as through an indirect exchange via the N atoms in FeP. The mechanism of exchange interaction is further analyzed by considering structural models constructed from ab initio calculations. Also, it is found that the exchange interaction between Fe in FeP and a Ni substrate is almost 4 times smaller than with a Co substrate. Finally, we illustrate the possibility of detecting a change in the molecular spin state by XMCD, Raman spectroscopy, and spin-polarized scanning tunneling microscopy.

  • 2.
    Bidermane, Ieva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Brumboiu, Iulia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Totani, Roberta
    University of L'Aquila.
    Grazioli, Cesare
    University of Trieste.
    Shariati Nilsson, Masumeh Nina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Herper, Heike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ressel, B
    Univ Nova Gorica, Ajdovscina 5270, Slovenia.
    de Simone, Monica
    Lozzi, Luca
    University of L'Aquila.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Atomic Contributions to the Valence Band Photoelectron Spectra of Metal-free, Iron and Manganese Phthalocyanines2015In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 205, p. 92-97Article, review/survey (Other academic)
    Abstract [en]

    The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H2Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H2Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

  • 3.
    Brumboiu, Iulia E.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Anselmo, A. S.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dzwilewski, A.
    Svensson, K.
    Moons, E.
    Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM2013In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 568, p. 130-134Article in journal (Refereed)
    Abstract [en]

    The fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first pi*-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C-60-cage. 

  • 4.
    Brumboiu, Iulia Emilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Molecules and Light: A Journey into the World of Theoretical Spectroscopy2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two of the main technological challenges of the century are the production of clean energy, on the one hand, and the development of new materials for electronic and spintronic applications that could increase the speed and the storage capacity of regular electronic devices, on the other hand. Organic materials, including fullerenes, organic polymers and organic molecules with metal centres are promising candidates for low-cost, flexible and clean technologies that can address these challenges. A thorough description of the electronic properties of such materials is, therefore, crucial. The interaction of electromagnetic radiation with the molecule can provide the needed insight into the electronic and vibrational levels and on possible chemical interactions. In order to explain and interpret experimentally measured spectra, a good theoretical description of the particular spectroscopy is necessary. Within density functional theory (DFT), the current thesis discusses the theoretical tools used to describe the spectroscopic properties of molecules with emphasis on two classes of organic materials for photovoltaics, molecular electronics and spintronics. Specifically, the stability of the fullerene derivative PC60BM is investigated in connection with its use as an electron acceptor in organic solar cells and the valence band electronic structure of several transition metal phthalocyanines is studied for their possible application in electronics and spintronics. The spectroscopies discussed in the current work are: the photoelectron spectroscopy of the valence band, X-ray photoelectron spectroscopy of the core levels, near-edge X-ray absorption fine structure, Infrared and Raman vibrational spectroscopies

    List of papers
    1. Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
    Open this publication in new window or tab >>Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
    Show others...
    2013 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 568, p. 130-134Article in journal (Refereed) Published
    Abstract [en]

    The fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first pi*-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C-60-cage. 

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-201237 (URN)10.1016/j.cplett.2013.03.031 (DOI)000318320300025 ()
    Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
    2. Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine
    Open this publication in new window or tab >>Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine
    Show others...
    2014 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 5, p. 927-932Article in journal (Refereed) Published
    Abstract [en]

    To shed light on the metal 3d electronic structure of manganese phthalocyanine, so far controversial, we performed photoelectron measurements both in the gas phase and as thin film. With the purpose of explaining the experimental results, three different electronic configurations close in energy to one another were studied by means of density functional theory. The comparison between the calculated valence band density of states and the measured spectra revealed that in the gas phase the molecules exhibit a mixed electronic configuration, while in the thin film, manganese phthalocyanine finds itself in the theoretically computed ground state, namely, the b2g1eg3a1g1b1g0 electronic configuration.

    Keywords
    MnPc, photoelectron spectroscopy, density functional theory
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-218224 (URN)10.1021/jp4100747 (DOI)000331153400015 ()
    Available from: 2014-02-10 Created: 2014-02-10 Last updated: 2017-12-06Bibliographically approved
    3. The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C-60 derivative PCBM
    Open this publication in new window or tab >>The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C-60 derivative PCBM
    Show others...
    2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 5, article id 054306Article in journal (Refereed) Published
    Abstract [en]

    Fullerenes have been a main focus of scientific research since their discovery due to the interesting possible applications in various fields like organic photovoltaics (OPVs). In particular, the derivative [6,6]-phenyl-C-60-butyric acid methyl ester (PCBM) is currently one of the most popular choices due to its higher solubility in organic solvents compared to unsubstituted C-60. One of the central issues in the field of OPVs is device stability, since modules undergo deterioration (losses in efficiency, open circuit voltage, and short circuit current) during operation. In the case of fullerenes, several possibilities have been proposed, including dimerization, oxidation, and impurity related deterioration. We have studied by means of density functional theory the possibility of oxygen adsorption on the C-60 molecular moiety of PCBM. The aim is to provide guidelines for near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) measurements which can probe the presence of atomic or molecular oxygen on the fullerene cage. By analysing several configurations of PCBM with one or more adsorbed oxygen atoms, we show that a joint core level XPS and O1s NEXAFS investigation could be effectively used not only to confirm oxygen adsorption but also to pinpoint the bonding configuration and the nature of the adsorbate.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-248192 (URN)10.1063/1.4907012 (DOI)000349614200019 ()25662644 (PubMedID)
    Available from: 2015-04-12 Created: 2015-03-30 Last updated: 2017-12-04Bibliographically approved
    4. Atomic Contributions to the Valence Band Photoelectron Spectra of Metal-free, Iron and Manganese Phthalocyanines
    Open this publication in new window or tab >>Atomic Contributions to the Valence Band Photoelectron Spectra of Metal-free, Iron and Manganese Phthalocyanines
    Show others...
    2015 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 205, p. 92-97Article, review/survey (Other academic) Published
    Abstract [en]

    The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H2Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H2Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

    Keywords
    Valence band; X-ray photoelectron spectroscopy; DFT; Phthalocyanines
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-217083 (URN)10.1016/j.elspec.2015.09.004 (DOI)000367282400011 ()
    Funder
    Swedish Research CouncilKnut and Alice Wallenberg FoundationCarl Tryggers foundation
    Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
    5. Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines
    Open this publication in new window or tab >>Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines
    Show others...
    2016 (English)In: Journal of Chemical Theory and Computation, Vol. 12, no 4, p. 1772-1785Article in journal (Refereed) Published
    Abstract [en]

    There exists an extensive literature on the electronic structure of transition-metal phthalocyanines (TMPcs), either as single molecules or adsorbed on surfaces, where explicit intra-atomic Coulomb interactions of the strongly correlated orbitals are included in the form of a Hubbard U term. The choice of U is, to a large extent, based solely on previous values reported in the literature for similar systems. Here, we provide a systematic analysis of the influence of electron correlation on the electronic structure and magnetism of several TMPcs (MnPc, FePc, CoPc, NiPc, and CuPc). By comparing calculated results to valence-band photoelectron spectroscopy measurements, and by determining the Hubbard term from linear response, we show that the choice of U is not as straightforward and can be different for each different TMPc. This, in turn, highlights the importance of individually estimating the value of U for each system before performing any further analysis and shows how this value can influence the final results.

    National Category
    Physical Sciences Materials Chemistry Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-281097 (URN)10.1021/acs.jctc.6b00091 (DOI)000374196400034 ()26925803 (PubMedID)
    Funder
    Swedish Research CouncilKnut and Alice Wallenberg Foundation
    Available from: 2016-03-17 Created: 2016-03-17 Last updated: 2017-01-25Bibliographically approved
    6. Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines
    Open this publication in new window or tab >>Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines
    Show others...
    2019 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 123, no 14, p. 3214-3222Article in journal (Refereed) Published
    Abstract [en]

    It is established that density functional theory (DFT) + U is a better choice compared to DFT for describing the correlated electron metal center in organometallics. The value of the Hubbard U parameter may be determined from linear response, either by considering the response of the metal site alone or by additionally considering the response of other sites in the compound. We analyze here in detail the influence of ligand shells of increasing size on the U parameter calculated from the linear response for five transition metal phthalocyanines. We show that the calculated multiple-site U is larger than the single-site U by as much as 1 eV and the ligand atoms that are mainly responsible for this difference are the isoindole nitrogen atoms directly bonded to the central metal atom. This suggests that a different U value may be required for computations of chemisorbed molecules compared to physisorbed and gas-phase cases.

    National Category
    Theoretical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-300117 (URN)10.1021/acs.jpca.8b11940 (DOI)000464768100011 ()30892039 (PubMedID)
    Funder
    Swedish Research Council, 2014-3776Swedish Research Council, 2016-05366Swedish Research Council, 2017-05447Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish National Infrastructure for Computing (SNIC)
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2019-05-15Bibliographically approved
    7. The valence band electronic structure of cobalt phthalocyanine from optimally tuned range-separated hybrid functionals
    Open this publication in new window or tab >>The valence band electronic structure of cobalt phthalocyanine from optimally tuned range-separated hybrid functionals
    (English)Manuscript (preprint) (Other academic)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-300118 (URN)
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
    8. Photon and binding energy dependent valence band photoelectron spectroscopy of organic molecules
    Open this publication in new window or tab >>Photon and binding energy dependent valence band photoelectron spectroscopy of organic molecules
    (English)Manuscript (preprint) (Other academic)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-300119 (URN)
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
    9. C1s NEXAFS investigations of PC60BM exposed to oxygen: a novel approach for the comparison of computed and experimental spectra
    Open this publication in new window or tab >>C1s NEXAFS investigations of PC60BM exposed to oxygen: a novel approach for the comparison of computed and experimental spectra
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-300121 (URN)
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
    10. Spectroscopy of photo-oxidized PC60BM
    Open this publication in new window or tab >>Spectroscopy of photo-oxidized PC60BM
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-300122 (URN)
    Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
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  • 5.
    Brumboiu, Iulia Emilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    The Electronic Structure of Organic Molecular Materials: Theoretical and Spectroscopic Investigations2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively.

    The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure is the first step in elucidating the photodegradation process. The electronic excitations from core levels to unoccupied molecular orbitals reveal not only the empty level structure of the molecule, but provide additional information related to the chemical bonds involving a specific atom type. In this way, they represent a means of determining the chemical changes that the molecule might withstand. The electronic transitions from carbon 1s core levels to unoccupied states are explained for the unmodified PCBM by a joint theoretical (DFT) and experimental study using the near edge x-ray absorption fine structure (NEXAFS) spectroscopy.

    The second investigated system is the transition metal phthalocyanine with a manganese atom as the metal center. Manganese phthalocyanine (MnPc) is a single molecular magnet in which the spin switch process can be triggered by various methods. It has been shown, for instance, that the adsorption of hydrogen to the Mn center changes the spin state of the molecule from 3/2 to 1. More interestingly, the process is reversible and can be controlled, opening up the possibility of using MnPc as a quantum bit in magnetic memory devices. Up to this date, the d orbital occupation in MnPc has been under a long debate, both theoretical and experimental studies revealing different configurations. In this thesis the electronic structure of the phthalocyanine is thoroughly analysed by means of DFT and the calculated results are compared to photoelectron spectroscopy measurements. The combination of theoretical and experimental tools reveals that in gas phase at high temepratures the molecule exhibits a mixed electronic configuration. In this light, the possible control of the specific electronic state of the central metal represents an interesting prospect for molecular spintronics.

    List of papers
    1. Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
    Open this publication in new window or tab >>Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
    Show others...
    2013 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 568, p. 130-134Article in journal (Refereed) Published
    Abstract [en]

    The fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first pi*-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C-60-cage. 

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-201237 (URN)10.1016/j.cplett.2013.03.031 (DOI)000318320300025 ()
    Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
    2. Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine
    Open this publication in new window or tab >>Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine
    Show others...
    2014 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 5, p. 927-932Article in journal (Refereed) Published
    Abstract [en]

    To shed light on the metal 3d electronic structure of manganese phthalocyanine, so far controversial, we performed photoelectron measurements both in the gas phase and as thin film. With the purpose of explaining the experimental results, three different electronic configurations close in energy to one another were studied by means of density functional theory. The comparison between the calculated valence band density of states and the measured spectra revealed that in the gas phase the molecules exhibit a mixed electronic configuration, while in the thin film, manganese phthalocyanine finds itself in the theoretically computed ground state, namely, the b2g1eg3a1g1b1g0 electronic configuration.

    Keywords
    MnPc, photoelectron spectroscopy, density functional theory
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-218224 (URN)10.1021/jp4100747 (DOI)000331153400015 ()
    Available from: 2014-02-10 Created: 2014-02-10 Last updated: 2017-12-06Bibliographically approved
    Download full text (pdf)
    fulltext
  • 6.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Photon and binding energy dependent valence band photoelectron spectroscopy of organic moleculesManuscript (preprint) (Other academic)
  • 7.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    The valence band electronic structure of cobalt phthalocyanine from optimally tuned range-separated hybrid functionalsManuscript (preprint) (Other academic)
  • 8.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ericsson, Leif
    Blazinic, Vanja
    Hansson, Rickard
    Moons, Ellen
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    C1s NEXAFS investigations of PC60BM exposed to oxygen: a novel approach for the comparison of computed and experimental spectraManuscript (preprint) (Other academic)
  • 9.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ericsson, Leif
    Hansson, Rickard
    Moons, Ellen
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C-60 derivative PCBM2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 5, article id 054306Article in journal (Refereed)
    Abstract [en]

    Fullerenes have been a main focus of scientific research since their discovery due to the interesting possible applications in various fields like organic photovoltaics (OPVs). In particular, the derivative [6,6]-phenyl-C-60-butyric acid methyl ester (PCBM) is currently one of the most popular choices due to its higher solubility in organic solvents compared to unsubstituted C-60. One of the central issues in the field of OPVs is device stability, since modules undergo deterioration (losses in efficiency, open circuit voltage, and short circuit current) during operation. In the case of fullerenes, several possibilities have been proposed, including dimerization, oxidation, and impurity related deterioration. We have studied by means of density functional theory the possibility of oxygen adsorption on the C-60 molecular moiety of PCBM. The aim is to provide guidelines for near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) measurements which can probe the presence of atomic or molecular oxygen on the fullerene cage. By analysing several configurations of PCBM with one or more adsorbed oxygen atoms, we show that a joint core level XPS and O1s NEXAFS investigation could be effectively used not only to confirm oxygen adsorption but also to pinpoint the bonding configuration and the nature of the adsorbate.

  • 10.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. KTH Royal Inst Technol, Dept Theoret Chem & Biol, SE-10691 Stockholm, Sweden.;Nicolaus Copernicus Univ, Fac Phys Astron & Informat, PL-87100 Torun, Poland..
    Ericsson, Leif K. E.
    Karlstad Univ, Dept Engn & Phys, SE-65188 Karlstad, Sweden..
    Blazinic, Vanja
    Karlstad Univ, Dept Engn & Phys, SE-65188 Karlstad, Sweden..
    Hansson, Rickard
    Karlstad Univ, Dept Engn & Phys, SE-65188 Karlstad, Sweden..
    Opitz, Andreas
    Humboldt Univ, Inst Phys, D-12489 Berlin, Germany..
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Moons, Ellen
    Karlstad Univ, Dept Engn & Phys, SE-65188 Karlstad, Sweden..
    Photooxidation of PC60BM: new insights from spectroscopy2022In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 42, p. 25753-25766Article in journal (Refereed)
    Abstract [en]

    This joint experimental-theoretical spectroscopy study of the fullerene derivative PC60BM ([6,6]-phenyl-C-60-butyric acid methyl ester) aims to improve the understanding of the effect of photooxidation on its electronic structure. We have studied spin-coated thin films of PC60BM by X-ray Photoelectron Spectroscopy (XPS), Near-edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, and Fourier Transform Infrared Spectroscopy (FTIR), before and after intentional exposure to simulated sunlight in air for different lengths of time. The pi* resonance in the C1s NEXAFS spectrum was found to be a very sensitive probe for the early changes to the fullerene cage, while FTIR spectra, in combination with O1s NEXAFS spectra, enabled the identification of the oxidation products. The changes observed in the spectra obtained by these complementary methods were compared with the corresponding Density Functional Theory (DFT) calculated single-molecule spectra of a large set of in silico generated oxidation products of PC60BM where oxygen atoms were attached to the C-60 cage. This comparison confirms that photooxidation of PC60BM disrupts the conjugation of the fullerene cage by a transition from sp(2) to sp(3)-hybridized carbon and causes the formation of several oxidation products, earlier proposed for C-60. The agreement between experimental and calculated IR spectra suggests moreover the presence of dicarbonyl and anhydride structures on the fullerene cage, in combination with cage opening at the adsorption site. By including PC60BM with physisorbed O-2 molecules on the cage in our theoretical description in order to model oxygen diffused through the film, the experimental O1s XPS and O1s NEXAFS spectra could be reproduced.

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  • 11.
    Brumboiu, Iulia Emilia
    et al.
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden;Korea Adv Inst Sci & Technol, Dept Chem, Daejeon 34141, South Korea.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Technol, S-70182 Orebro, Sweden.
    Norman, Patrick
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden.
    Photoelectron Spectroscopy of Molecules Beyond the Electric Dipole Approximation2019In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 15, no 10, p. 5483-5494Article in journal (Refereed)
    Abstract [en]

    A methodology implemented to compute photoionization cross sections beyond the electric dipole approximation using Gaussian type orbitals for the initial state and plane waves for the final state is applied to molecules of various sizes. The molecular photoionization cross sections computed for valence molecular orbitals as a function of photon energy present oscillations due to the wave-like nature of both the outgoing photoelectron and of the incoming photon. These oscillations are damped by rotational and vibrational averaging or by performing a k-point summation for the solid state case. For core orbitals, the corrections introduced by going beyond the electric dipole approximation are comparable to the atomic case. For valence orbitals, nondipole corrections to the total photoinization cross sections can reach up to 20% at photon energies above 1 keV. The corrections to the differential cross sections calculated at the magic angle are larger, reaching values between 30% and 50% for all molecules included. Our findings demonstrate that photoelectron spectroscopy, especially angle-resolved, on, e.g., molecules and clusters on surfaces, using high photon energies, must be accompanied by theories that go beyond the electric dipole approximation.

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  • 12.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Haldar, Soumyajyoti
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines2016In: Journal of Chemical Theory and Computation, Vol. 12, no 4, p. 1772-1785Article in journal (Refereed)
    Abstract [en]

    There exists an extensive literature on the electronic structure of transition-metal phthalocyanines (TMPcs), either as single molecules or adsorbed on surfaces, where explicit intra-atomic Coulomb interactions of the strongly correlated orbitals are included in the form of a Hubbard U term. The choice of U is, to a large extent, based solely on previous values reported in the literature for similar systems. Here, we provide a systematic analysis of the influence of electron correlation on the electronic structure and magnetism of several TMPcs (MnPc, FePc, CoPc, NiPc, and CuPc). By comparing calculated results to valence-band photoelectron spectroscopy measurements, and by determining the Hubbard term from linear response, we show that the choice of U is not as straightforward and can be different for each different TMPc. This, in turn, highlights the importance of individually estimating the value of U for each system before performing any further analysis and shows how this value can influence the final results.

  • 13.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden; Korea Adv Inst Sci & Technol, Dept Chem, Daejeon 34141, South Korea.
    Haldar, Soumyajyoti
    Lüder, Johann
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines2019In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 123, no 14, p. 3214-3222Article in journal (Refereed)
    Abstract [en]

    It is established that density functional theory (DFT) + U is a better choice compared to DFT for describing the correlated electron metal center in organometallics. The value of the Hubbard U parameter may be determined from linear response, either by considering the response of the metal site alone or by additionally considering the response of other sites in the compound. We analyze here in detail the influence of ligand shells of increasing size on the U parameter calculated from the linear response for five transition metal phthalocyanines. We show that the calculated multiple-site U is larger than the single-site U by as much as 1 eV and the ligand atoms that are mainly responsible for this difference are the isoindole nitrogen atoms directly bonded to the central metal atom. This suggests that a different U value may be required for computations of chemisorbed molecules compared to physisorbed and gas-phase cases.

  • 14.
    Brumboiu, Iulia Emilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Totani, Roberta
    de Simone, Monica
    Coreno, Marcello
    Grazioli, Cesare
    Lozzi, Luca
    Herper, Heike C
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine2014In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 5, p. 927-932Article in journal (Refereed)
    Abstract [en]

    To shed light on the metal 3d electronic structure of manganese phthalocyanine, so far controversial, we performed photoelectron measurements both in the gas phase and as thin film. With the purpose of explaining the experimental results, three different electronic configurations close in energy to one another were studied by means of density functional theory. The comparison between the calculated valence band density of states and the measured spectra revealed that in the gas phase the molecules exhibit a mixed electronic configuration, while in the thin film, manganese phthalocyanine finds itself in the theoretically computed ground state, namely, the b2g1eg3a1g1b1g0 electronic configuration.

  • 15. Ericsson, Leif
    et al.
    Brumboiu, Iulia Emilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Blazinic, Vanja
    Hansson, Rickard
    Lindqvist, Camilla
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Moons, Ellen
    Spectroscopy of photo-oxidized PC60BMManuscript (preprint) (Other academic)
  • 16.
    Savchenko, Viktoriia
    et al.
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden; Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia; Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Krasnoyarsk 660036, Russia.
    Brumboiu, Iulia Emilia
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden; Korea Adv Inst Sci & Technol, Dept Chem, Daejeon 34141, South Korea.
    Kimberg, Victor
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden; Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia; Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Krasnoyarsk 660036, Russia.
    Odelius, Michael
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden.
    Krasnov, Pavel
    Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia; Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Krasnoyarsk 660036, Russia.
    Liu, Ji-Cai
    North China Elect Power Univ, Dept Math & Phys, Beijing 102206, Peoples R China.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Såthe, Conny
    Lund Univ, MAX Lab 4, Box 118, S-22100 Lund, Sweden.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry.
    Dong, Minjie
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Pietzsch, Annette
    Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Föhlisch, Alexander
    Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany; Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany.
    Schmitt, Thorsten
    Paul Scherrer Inst, Photon Sci Div, Swiss Light Source, CH-5232 Villigen, Switzerland.
    McNally, Daniel
    Paul Scherrer Inst, Photon Sci Div, Swiss Light Source, CH-5232 Villigen, Switzerland.
    Lu, Xingye
    Paul Scherrer Inst, Photon Sci Div, Swiss Light Source, CH-5232 Villigen, Switzerland.
    Polyutov, Sergey P.
    Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia; Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Krasnoyarsk 660036, Russia.
    Norman, Patrick
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden.
    Iannuzzi, Marcella
    Univ Zurich, Phys Chem Inst, CH-8057 Zurich, Switzerland.
    Gel'mukhanov, Faris
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden; Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia; Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Krasnoyarsk 660036, Russia.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Lund Univ, MAX Lab 4, Box 118, S-22100 Lund, Sweden.
    Vibrational resonant inelastic X-ray scattering in liquid acetic acid: a ruler for molecular chain lengths2021In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, no 1, article id 4098Article in journal (Refereed)
    Abstract [en]

    Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O-H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.

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  • 17.
    Savchenko, Viktoriia
    et al.
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, SE-10691 Stockholm, Sweden.;Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia.;RAS, Kirensky Inst Phys, SB, Fed Res Ctr KSC, Krasnoyarsk 660036, Russia..
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Lund Univ, MAX Lab 4, POB 118, SE-22100 Lund, Sweden..
    Brumboiu, Iulia Emilia
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, SE-10691 Stockholm, Sweden.;Pohang Univ Sci & Technol POSTECH, Dept Chem, Pohang 37673, South Korea..
    Norman, Patrick
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, SE-10691 Stockholm, Sweden..
    Pietzsch, Annette
    Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Foehlisch, Alexander
    Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.;Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany..
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Sathe, Conny
    Lund Univ, MAX Lab 4, POB 118, SE-22100 Lund, Sweden..
    Dong, Minjie
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Schmitt, Thorsten
    Paul Scherrer Inst, Swiss Light Source, Photon Sci Div, CH-5232 Villigen, Switzerland..
    McNally, Daniel
    Paul Scherrer Inst, Swiss Light Source, Photon Sci Div, CH-5232 Villigen, Switzerland..
    Lu, Xingye
    Paul Scherrer Inst, Swiss Light Source, Photon Sci Div, CH-5232 Villigen, Switzerland..
    Krasnov, Pavel
    Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia.;RAS, Kirensky Inst Phys, SB, Fed Res Ctr KSC, Krasnoyarsk 660036, Russia..
    Polyutov, Sergey P.
    Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia.;RAS, Kirensky Inst Phys, SB, Fed Res Ctr KSC, Krasnoyarsk 660036, Russia..
    Gel'mukhanov, Faris
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, SE-10691 Stockholm, Sweden.;Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia.;RAS, Kirensky Inst Phys, SB, Fed Res Ctr KSC, Krasnoyarsk 660036, Russia..
    Odelius, Michael
    Stockholm Univ, Dept Phys, AlbaNova Univ Ctr, S-10691 Stockholm, Sweden..
    Kimberg, Victor
    KTH Royal Inst Technol, Dept Theoret Chem & Biol, SE-10691 Stockholm, Sweden.;Siberian Fed Univ, Int Res Ctr Spect & Quantum Chem IRC SQC, Krasnoyarsk 660041, Russia.;RAS, Kirensky Inst Phys, SB, Fed Res Ctr KSC, Krasnoyarsk 660036, Russia..
    Hydrogen bond effects in multimode nuclear dynamics of acetic acid observed via resonant x-ray scattering2021In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 154, no 21, article id 214304Article in journal (Refereed)
    Abstract [en]

    A theoretical and experimental study of the gas phase and liquid acetic acid based on resonant inelastic x-ray scattering (RIXS) spectroscopy is presented. We combine and compare different levels of theory for an isolated molecule for a comprehensive analysis, including electronic and vibrational degrees of freedom. The excitation energy scan over the oxygen K-edge absorption reveals nuclear dynamic effects in the core-excited and final electronic states. The theoretical simulations for the monomer and two different forms of the dimer are compared against high-resolution experimental data for pure liquid acetic acid. We show that the theoretical model based on a dimer describes the hydrogen bond formation in the liquid phase well and that this bond formation sufficiently alters the RIXS spectra, allowing us to trace these effects directly from the experiment. Multimode vibrational dynamics is accounted for in our simulations by using a hybrid time-dependent stationary approach for the quantum nuclear wave packet simulations, showing the important role it plays in RIXS.

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  • 18.
    Zhang, Teng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Brumboiu, Iulia E.
    KTH Royal Institute of Technology, Department of Theoretical Chemistry and Biology & Korea Advanced Institute of Science and Technology (KAIST), Department of Chemistry.
    Grazioli, Cesare
    ISM-CNR, Trieste LD2 Unit, Italy.
    Guarnaccio, Ambra
    ISM-CNR, Tito Scalo (Pz), Italy.
    Coreno, Marcello
    ISM-CNR, Trieste LD2 Unit, Italy.
    de Simone, Monica
    IOM-CNR, Laboratorio TASC, Sincrotrone Trieste, Basovizza, Trieste, Italy.
    Santagata, Antonio
    ISM-CNR, Tito Scalo (Pz), Italy.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lanzilotto, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Lone-Pair Delocalization Effects within Electron Donor Molecules: The Case of Triphenylamine and Its Thiophene-Analog2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 31, p. 17706-17717Article in journal (Refereed)
    Abstract [en]

    Triphenylamine (TPA) and its thiophene-analog, N,N-diphenyl-2-thiophenamine (DPTA), are both well-known as electron-donating molecules implemented in optoelectronic devices such as organic solar cells and LEDs. Comprehensive valence and core level photoelectron spectroscopy, as well as near edge X-ray absorption spectroscopy (NEXAFS), measurements have been performed on gas phase TPA and DPTA. The experimental results have been compared to density functional theory calculations, providing a detailed description of the molecular electronic structure. Specifically, the C 1s photoelectron lines of both TPA and DPTA were resolved in the different C atom contributions and their binding energies explained as the result of two counter-acting effects: (1) the electronegativity of the nitrogen atom (and sulfur atom in DPTA) and (2) the the N (and S in DPTA) lone-pair electrons. In addition, the C K-edge NEXAFS spectrum of DPTA reveals that the lowest unoccupied molecular orbital (LUMO) energy position is affected differently if the core hole site is on the phenyl compared to the thiophene ring. The electron-donating properties of these two molecules are largely explained by the significant contribution of the N lone-pair electrons (p(z)) to the highest occupied molecular orbital. The contribution to the LUMO and to the empty density of states of the sulfur of the thiophene ring in DPTA explains the better performance of donor-pi-acceptor molecules containing this moiety and implemented in photoenergy conversion devices.

  • 19.
    Zhang, Teng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Brumboiu, Iulia E.
    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, Theoretical Physics.
    Lanzilotto, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Grazioli, Cesare
    ISM-CNR, Trieste LD2 Unit, Italy.
    Guarnaccio, Ambra
    ISM-CNR, Tito Scalo (Pz), Italy.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ševčíková, Klára
    Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic.
    Coreno, Marcello
    ISM-CNR, Trieste LD2 Unit, Italy.
    de Simone, Monica
    IOM-CNR, Laboratorio TASC, Sincrotrone Trieste, Basovizza, Trieste, Italy.
    Santagata, Antonio
    ISM-CNR, Tito Scalo (Pz), Italy.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Electronic Structure Study of Free and Adsorbed m-MTDATAManuscript (preprint) (Other academic)
    Abstract [en]

    The starburst p-conjugated molecule based on triphenylamine (TPA) building block, 4,4',4" -Tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA), is widely used in optoelectronic devices due to its electron-donating properties. The electronic structure of m-MTDATA was investigated in the gas-phase and when deposited in thin films on a Au(111) surface by means of PhotoElectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. Density Functional Theory (DFT) calculations were compared to the experimental gas-phase results, providing a comprehensive description of the molecular electronic structure. Moreover, the results were compared with previous TPA measurements, shedding light on the electronic structure modification due to the increased molecular complexity.  Similar to TPA, but more complex, the binding energy of the C 1s photoelectron line of m-MTDATA results from the balance of two counter-acting effects: (1) the electronegativity of the N atoms and (2) the delocalization of lone-pair electrons of the nitrogen. Compared to TPA, the outermost valence PE spectrum of m-MTDATA shows a 3-peak feature with N 2pz character and a lowering of the binding energy of the HOMO. When adsorbed on Au(111),  the changes observed in PES and NEXAFS spectra with respect to the free molecules,  can be explained by a significant modification of m-MTDATA molecular and electronic structure, due to the molecule-substrate interaction.

  • 20.
    Zhang, Teng
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Brumboiu, Iulia E.
    Royal Institute of Technology (KTH), Department of Theoretical Chemistry and Biology.
    Lanzilotto, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Grazioli, Cesare
    ISM-CNR, Trieste LD2 Unit, Italy.
    Guarnaccio, Ambra
    ISM-CNR, Tito Scalo (Pz), Italy.
    Johansson, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ševčíková, Klára
    Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic.
    Coreno, Marcello
    ISM-CNR, Trieste LD2 Unit, Italy.
    de Simone, Monica
    IOM-CNR, Laboratorio TASC, Sincrotrone Trieste, Basovizza, Trieste, Italy.
    Santagata, Antonio
    ISM-CNR, Tito Scalo (Pz), Italy.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    X-ray Spectroscopy Investigations of TPA/Au(111): Charge Redistribution via Core Exitation?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.

  • 21.
    Zhang, Teng
    et al.
    Beijing Inst Technol, Sch Integrated Circuits & Elect, MIIT Key Lab Low Dimens Quantum Struct & Devices, Beijing 100081, Peoples R China..
    Svensson, Pamela
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Chemical and Bio-Molecular Physics.
    Brumboiu, Iulia Emilia
    Pohang Univ Sci & Technol POSTECH, Dept Chem, Pohang 37673, South Korea..
    Lanzilotto, Valeria
    Sapienza Univ Roma, Dept Chem, I-00185 Rome, Italy..
    Grazioli, Cesare
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Italy..
    Guarnaccio, Ambra
    ISM CNR, Ist Struttura Mat, I-85050 Tito, Pz, Italy..
    Johansson, Fredrik O.L.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials. KTH Royal Inst Technol, Dept Chem, Div Appl Phys Chem, S-10044 Stockholm, Sweden.;Sorbonne Univ, Inst Nanosci Paris, UMR CNRS 7588, F-75005 Paris, France..
    Beranova, Klara
    Elettra Sincrotrone Trieste SCpA, I-34149 Trieste, Italy.;Czech Acad Sci, FZU Inst Phys, Prague 18221, Czech Republic..
    Coreno, Marcello
    ISM CNR, Ist Struttura Mat, I-85050 Tito, Pz, Italy..
    de Simone, Monica
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Italy..
    Floreano, Luca
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Italy..
    Cossaro, Albano
    IOM CNR, Lab TASC, Sincrotrone Trieste, I-34149 Trieste, Italy.;Univ Trieste, Dept Chem & Pharmaceut Sci, I-34127 Trieste, Italy..
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
    Clarifying the Adsorption of Triphenylamine on Au(111): Filling the HOMO-LUMO Gap2022In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 3, p. 1635-1643Article in journal (Refereed)
    Abstract [en]

    In this article, we analyze the electronic structure modifications of triphenylamine (TPA), a well-known electron donor molecule widely used in photovoltaics and optoelectronics, upon deposition on Au(111) at a monolayer coverage. A detailed study was carried out by synchrotron radiation-based photoelectron spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, scanning tunneling microscopy (STM), and ab initio calculations. We detect a new feature in the pre-edge energy region of the N K-edge NEXAFS spectrum that extends over 3 eV, which we assign to transitions involving new electronic states. According to our calculations, upon adsorption, a number of new unoccupied electronic states fill the energy region between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the free TPA molecule and give rise to the new feature the pre-edge region of the NEXAFS spectrum. This finding highlights the occurrence of a considerable modification of the electronic structure of TPA. The appearance of new states in the HOMO-LUMO gap of TPA when adsorbed on Au(111) has crucial implications for the design of molecular nanoelectronic devices based on similar donor systems.

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