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  • 1.
    Alfredsson, Ylvi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Brena, Barbara
    Nilson, Katharina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Åhlund, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Kjeldgaard, Lisbeth
    Nyberg, Mats
    Luo, Yi
    Mårtensson, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Siegbahn, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Electronic structure of a vapor-deposited metal-free phthalocyanine thin film2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 21, p. 214723-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine(H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1sXAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.

  • 2.
    Arvanitis, D
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Dunn, JH
    Karis, O
    Hahlin, A
    Brena, Barbara
    Carr, R
    Martensson, N
    Magnetic X-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces2001In: JOURNAL OF SYNCHROTRON RADIATION, ISSN 0909-0495, Vol. 8, p. 120-124Article in journal (Refereed)
    Abstract [en]

    Epitaxic thin and ultrathin films on surfaces allow crystallographic phases that do not occur naturally in the bulk to be stabilized. They also offer new possibilities for an improved understanding of soft X-ray photoabsorption in magnetic systems. Data c

  • 3. Arvanitis, Dimitri
    et al.
    Hunter Dunn, Jonathan
    Hunter, Jonathan
    Hahlin, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Brena, Barbara
    Carr, Roger
    Mårtensson, Nils
    Magnetic x-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces2001In: Journal of Synchrotron Radiation, Vol. 8, p. 120-125Article in journal (Refereed)
  • 4.
    Balatsky, Alexander V.
    et al.
    NORDITA, Roslagstullsbacken 11, S-10691 Stockholm, Sweden.
    Brena, Barbara
    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.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Functional Dirac Materials: Status and Perspectives2018In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 12, no 11, article id 1870334Article in journal (Other academic)
  • 5.
    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.

  • 6.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Vienna Univ Technol, Inst Solid State Phys, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria..
    Schueler, Malte
    Univ Bremen, Inst Theoret Phys, Otto Hahn Allee 1, D-28359 Bremen, Germany.;Univ Bremen, Bremen Ctr Computat Mat Sci, Falturm 1, D-28359 Bremen, Germany..
    Thunstroem, Patrik
    Vienna Univ Technol, Inst Solid State Phys, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria..
    di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wehling, Tim
    Univ Bremen, Inst Theoret Phys, Otto Hahn Allee 1, D-28359 Bremen, Germany.;Univ Bremen, Bremen Ctr Computat Mat Sci, Falturm 1, D-28359 Bremen, Germany..
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Correlated electron behavior of metal-organic molecules: Insights from density functional theory combined with many-body effects using exact diagonalization2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 15, article id 155158Article in journal (Refereed)
    Abstract [en]

    A proper theoretical description of the electronic structure of the 3d orbitals in the metal centers of functional metalorganics is a challenging problem. We apply density functional theory and an exact diagonalization method in a many-body approach to study the ground-state electronic configuration of an iron porphyrin (FeP) molecule. Our study reveals that the consideration of multiple Slater determinants is important, and FeP is a potential candidate for realizing a spin crossover due to a subtle balance of crystal-field effects, on-site Coulomb repulsion, and hybridization between the Fe-d orbitals and ligand N-p states. The mechanism of switching between two close-lying electronic configurations of Fe-d orbitals is shown. We discuss the generality of the suggested approach and the possibility to properly describe the electronic structure and related low-energy physics of the whole class of correlated metal-centered organometallic molecules.

  • 7.
    Bhattacharjee, Satadeep
    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.
    Banerjee, Rudra
    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.
    Electronic structure of Co-phthalocyanine calculated by GGA plus U and hybrid functional methods2010In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 377, no 1-3, p. 96-99Article in journal (Refereed)
    Abstract [en]

    Electronic structure calculations have been performed for the Co-phthalocyanine molecule using density functional theory (DFT) within the framework of Generalized Gradient Approximation (GGA). The electronic correlation in Co 3d orbitals is treated in terms of the GGA+U method in the framework of the Hubbard model. We find that for U = 6 eV, the calculated structural parameters as well as the spectral features are in good agreement with the experimental findings. From our calculation both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are dominated by the pyrrole carbon, with a HOMO-LUMO gap of about 1.4 eV. The GGA+U results obtained with U = 6 eV compare reasonably well with the calculations performed using Gaussian basis set and hybrid functionals in terms of ground state geometry, spin state and spectral features. The calculated valence band photoemission spectrum is in quite good agreement with the recently published experimental results.

  • 8.
    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.

  • 9.
    Bidermane, Ieva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahmadi, S.
    Materialfysik, KTH-Electrum.
    Grazioli, C.
    CNR-IOM, Laboratorio TASC.
    Bouvet, M.
    Institut de Chimie Moléculaire de l’Université de Bourgogne.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mårtensson, Niklas
    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.
    Witkowski, N.
    Institut des Nanosciences de Paris, UPMC.
    When the Grafting of Double Decker Phthalocyanines on Si(100)-2 × 1 Partly Affects the Molecular Electronic Structure2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 26, p. 14270-14276Article in journal (Refereed)
    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.

  • 10.
    Bidermane, Ieva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Boudet, S.
    Zhang, T.
    Ahmadi, S.
    Grazioli, C.
    Bouvet, M.
    Rusz, Jan
    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.
    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.
    Witkowski, N.
    Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 23, p. 234701-Article in journal (Refereed)
    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. 

  • 11.
    Bidermane, Ieva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Totani, Roberta
    University of L'Aquila.
    Grazioli, Cesare
    University of Trieste.
    de Simone, Monica
    Coreno, Marcello
    Kivimäki, Antti
    Åhlund, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Lozzi, Luca
    University of L'Aquila.
    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.
    Characterization of Gas Phase of Iron Phthalocyanine with X-ray Photoelectron and Absorption Spectroscopies2015In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1259-1265Article in journal (Refereed)
    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.

  • 12.
    Brena, Barbara
    et al.
    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.
    Influence of ligands on the electronic and magnetic properties of Fe porphyrin in gas phase and on Cu(001)2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 17, article id 17B318Article in journal (Refereed)
    Abstract [en]

    A study of the adsorption of different axial ligands on Fe porphyrin (FeP), both isolated and adsorbed on Cu(001), was performed by means of Density Functional Theory. The electronic and magnetic properties of the adsorbed FeP resulted to be strongly influenced by the axial ligands considered, Cl and O. Cl induces an enhancement of the overall molecular magnetic moment of 3.0 mu(B) while O or O-2 leave the spin state of the molecule unchanged. The influence of the Cl in the electronic states was moreover studied by means of theoretical NEXAFS N K-edge, where the spectra of isolated FeP and FeP with Cl ligand were calculated. The adsorption of the FeP molecules on Cu(001) leads in case of Cl to a further increase of the magnetic moment due to strong deformation of the Fe-N bond.

  • 13. Brena, Barbara
    et al.
    Luo, Yi
    Nyberg, M.
    Carniato, S.
    Nilson, K.
    Alfredsson, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Åhlund, J.
    Mårtensson, N.
    Siegbahn, Hans
    Puglia, C.
    Equivalent core-hole time-dependent density function theory calculations of carbon 1s shake-up states of phthalocyanine2004In: Phys. Rev. B, Vol. 70, no 19, p. 195214-Article in journal (Refereed)
  • 14. Brena, Barbara
    et al.
    Luo, Yi
    Nyberg, Mats
    Carniato, Stephane
    Nilson, Katharina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Alfredsson, Ylvi
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Åhlund, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Mårtensson, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Siegbahn, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Equivalent core-hole time-dependent density functional theory calculations of carbon 1s shake-up states of phthalocyanine2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 19, p. 195214-Article in journal (Refereed)
    Abstract [en]

    The shake-up transition energies of the carbon 1s photoelectron spectrum of metal-free phthalocyanine (H2Pc) have been calculated by means of time-dependent density functional theory, for which an equivalent core approximation is adopted. Model calculations for the C 1s shake-up states of benzene are in excellent agreement with the latest experimental results. The complex C 1s shake-up structures associated with the aromatic and pyrrole carbons in the phthalocyanine are computed, as well as their ionization potentials. They allow us to determine the origin of the anomalous intensity ratio between the pyrrole and benzene carbons in a high resolution C 1s photoelectron spectrum measured for a H2Pc film, as due to a benzene-related shake-up contribution, hidden under the pyrrole main intensity feature.

  • 15.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ojamae, Lars
    Surface effects and quantum confinement in nanosized GaN clusters: Theoretical predictions2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 35, p. 13516-13523Article in journal (Refereed)
    Abstract [en]

    The structure and the electronic properties of stoichiometric (GaN)(n) clusters (with 6 < ;= n < ;= 48) were investigated by means of quantum-chemical hybrid density functional theory (DFT) using the B3LYP functional. Particular emphasis was put on the investigation of the evolution of the physical properties of the clusters as a function of their size. Two types of model clusters were studied. Cage-type structures were found to be the most stable for smaller cluster sizes, whereas for larger sizes conformations cut out from the GaN wurtzite crystal were favorable. The study of the electronic structure shows that the energy gap of the clusters tends to become larger as the dimensions of the clusters increase. The vertical electronic absorption energies were calculated by means of time-dependent (TD) DFT. For such small clusters, probably due to the predominant amount of surface atoms, well-defined quantum confinement effects, as commonly observed in crystalline quantum dots, are not apparent.

  • 16.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Palmgren, P
    Nilson, K
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Yu, Shun
    Hennies, F
    Agnarsson, B
    Onsten, A
    Månsson, M
    Göthelid, M
    InSb-TiOPc interfaces: Band alignment, ordering and structure dependent HOMO splitting2009In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, no 20, p. 3160-3169Article in journal (Refereed)
    Abstract [en]

    Thin films of titanyl phthalocyanine (TiOPc) have been adsorbed on InSb(1 1 1) (3 x 3) and InSb(1 0 0) c(8 x 2) surfaces and studied with respect to their electronic structure using photoemission (PES), density functional theory (DFT) and scanning tunneling microscopy (STM). The interface chemical interaction is weak in both cases; no adsorbate induced surface band bending is observed and the energy level alignment across the interface is determined by the original position of the substrate Fermi level and the charge neutrality level of the molecule. Room temperature adsorption results in disordered films on both surfaces. The behaviors after annealing are different; on InSb(1 0 0) well-ordered molecular chains form along and on top of the In-rows, whereas on (1 1 1) no long range order is observed. The disorder leads to intermolecular interactions between the titanyl group and neighboring benzene rings leading to a split of TiOPc HOMO (highest occupied molecular orbital) by as much as 0.8 eV. (C) 2009 Elsevier B.V. All rights reserved.

  • 17.
    Brena, Barbara
    et al.
    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, Surface and Interface Science.
    de Simone, Monica
    Coreno, Marcello
    Tarafder, Kartick
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Feyer, Vitaly
    Banerjee, Rudra
    Gothelid, Emmanuelle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    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.
    Valence-band electronic structure of iron phthalocyanine: An experimental and theoretical photoelectron spectroscopy study2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 7, p. 074312-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of iron phthalocyanine (FePc) in the valence region was examined within a joint theoretical-experimental collaboration. Particular emphasis was placed on the determination of the energy position of the Fe 3d levels in proximity of the highest occupied molecular orbital (HOMO). Photoelectron spectroscopy (PES) measurements were performed on FePc in gas phase at several photon energies in the interval between 21 and 150 eV. Significant variations of the relative intensities were observed, indicating a different elemental and atomic orbital composition of the highest lying spectral features. The electronic structure of a single FePc molecule was first computed by quantum chemical calculations by means of density functional theory (DFT). The hybrid Becke 3-parameter, Lee, Yang and Parr (B3LYP) functional and the semilocal 1996 functional of Perdew, Burke and Ernzerhof (PBE) of the generalized gradient approximation (GGA-) type, exchange-correlation functionals were used. The DFT/B3LYP calculations find that the HOMO is a doubly occupied pi-type orbital formed by the carbon 2p electrons, and the HOMO-1 is a mixing of carbon 2p and iron 3d electrons. In contrast, the DFT/PBE calculations find an iron 3d contribution in the HOMO. The experimental photoelectron spectra of the valence band taken at different energies were simulated by means of the Gelius model, taking into account the atomic subshell photoionization cross sections. Moreover, calculations of the electronic structure of FePc using the GGA+U method were performed, where the strong correlations of the Fe 3d electronic states were incorporated through the Hubbard model. Through a comparison with our quantum chemical calculations we find that the best agreement with the experimental results is obtained for a U-eff value of 5 eV.

  • 18.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Siegbahn, P. E. M.
    Ågren, H.
    Modeling near-edge fine structure x-ray spectra of the manganese catalytic site for water oxidation in photosystem II2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 41, p. 17157-17167Article in journal (Refereed)
    Abstract [en]

    The Mn 1s near-edge absorption fine structure (NEXAFS) has been computed by means of transition-state gradient-corrected density functional theory (DFT) on four Mn 4Ca clusters modeling the successive S 0 to S 3 steps of the oxygen-evolving complex (OEC) in photosystem II (PSII). The model clusters were obtained from a previous theoretical study where they were determined by energy minimization. They are composed of Mn(III) and Mn(IV) atoms, progressing from Mn(III) 3Mn(IV) for S 0 to Mn(III) 2Mn(IV) 2 for S 1 to Mn(III)Mn(IV) 3 for S 2 to Mn(IV) 4 for S 3, implying an Mn-centered oxidation during each step of the photosynthetic oxygen evolution. The DFT simulations of the Mn 1s absorption edge reproduce the experimentally measured curves quite well. By the half-height method, the theoretical IPEs are shifted by 0.93 eV for the S 0 → S 1 transition, by 1.43 eV for the S 1 → S 2 transition, and by 0.63 eV for the S 2 → S 3 transition. The inflection point energy (IPE) shifts depend strongly on the method used to determine them, and the most interesting result is that the present clusters reproduce the shift in the S 2 → S 3 transition obtained by both the half-height and second-derivative methods, thus giving strong support to the previously suggested structures and assignments.

  • 19.
    Brena, Barbara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Zhuang, G V
    Augustsson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Liu, G
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Guo, Jinghua
    Ross, P N
    Luo, Yi
    Conformation dependence of electronic structures of poly(ethylene oxide)2005In: Journal of Physical Chemistry B, Vol. 109, no 16, p. 7907-7914Article in journal (Refereed)
  • 20.
    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. 

  • 21.
    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.

  • 22.
    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.

  • 23.
    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.

  • 24.
    Brumboiu, Iulia Emilia
    et al.
    Royal Inst Technol, Sch Biotechnol, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Prokopiou, Georgia
    Weizmann Inst Sci, Dept Mat & Interfaces, IL-76100 Rehovot, Israel..
    Kronik, Leeor
    Weizmann Inst Sci, Dept Mat & Interfaces, IL-76100 Rehovot, Israel..
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Valence electronic structure of cobalt phthalocyanine from an optimally tuned range-separated hybrid functional2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 4, article id 044301Article in journal (Refereed)
    Abstract [en]

    We analyse the valence electronic structure of cobalt phthalocyanine (CoPc) by means of optimally tuning a range-separated hybrid functional. The tuning is performed by modifying both the amount of short-range exact exchange (alpha) included in the hybrid functional and the range-separation parameter (gamma), with two strategies employed for finding the optimal gamma for each alpha. The influence of these two parameters on the structural, electronic, and magnetic properties of CoPc is thoroughly investigated. The electronic structure is found to be very sensitive to the amount and range in which the exact exchange is included. The electronic structure obtained using the optimal parameters is compared to gas-phase photo-electron data and GWcalculations, with the unoccupied states additionally compared with inverse photo-electron spectroscopy measurements. The calculated spectrum with tuned gamma, determined for the optimal value of alpha = 0.1, yields a very good agreement with both experimental results and with GW calculations that well-reproduce the experimental data.

  • 25.
    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.

  • 26. Chaudhary, Shilpi
    et al.
    Head, Ashley R.
    Sanchez-de-Armas, Rocio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tissot, Heloise
    Olivieri, Giorgia
    Bournel, Fabrice
    Montelius, Lars
    Ye, Lei
    Rochet, Francois
    Gallet, Jean-Jacques
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schnadt, Joachim
    Real-Time Study of CVD Growth of Silicon Oxide on Rutile TiO2(110) Using Tetraethyl Orthosilicate2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 33, p. 19149-19161Article in journal (Refereed)
    Abstract [en]

    The interaction of the ruffle TiO2(110) surface with tetraethyl orthosilicate (TEOS) in the pressure range from UHV to 1 mbar as well as the TEOS-based chemical vapor deposition of SiO2 on the TiO2(110) surface were monitored in real time using near-ambient pressure X-ray photoelectron spectroscopy. The experimental data and density functional theory calculations confirm the dissociative adsorption of TEOS on the surface already at room temperature. At elevated pressure, the ethoxy species formed in the adsorption process undergoes further surface reactions toward a carboxyl species not observed in the absence of a TEOS gas phase reservoir. Annealing of the adsorption layer leads to the formation of SiO2, and an intermediate oxygen species assigned to a mixed titanium/silicon oxide is identified. Atomic force microscopy confirms the morphological changes after silicon oxide formation.

  • 27.
    Farronato, M.
    et al.
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Bidermane, Ieva
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Helmholtz Zentrum Berlin Bessy II, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Natl Univ Singapore, Dept Mech Engn, Block EA 07-08,9 Engn Dr 1, Singapore 117576, Singapore.
    Bouvet, M.
    Univ Bourgogne, CNRS, ICMUB, UMR 6302, F-21078 Dijon, France.
    Vlad, A.
    Synchrotron SOLEIL, F-91192 Gif Sur Yvette, France.
    Jones, A.
    Graz Univ Technol, Inst Solid State Phys, A-8010 Graz, Austria.
    Simbrunner, J.
    Graz Univ Technol, Inst Solid State Phys, A-8010 Graz, Austria.
    Resel, R.
    Graz Univ Technol, Inst Solid State Phys, A-8010 Graz, Austria.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Prevot, G.
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Witkowski, N.
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    New Quadratic Self-Assembly of Double-Decker Phthalocyanine on Gold(111) Surface: From Macroscopic to Microscopic Scale2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 46, p. 26480-26488Article in journal (Refereed)
    Abstract [en]

    Unveiling the self-organization mechanism of semiconducting organic molecules onto metallic surfaces is the first step to design hybrid devices in which the self-assembling is exploited to tailor magnetic properties. In this study, double-decker rare-earth phthalocyanines, namely, lutetium phthalocyanine (LuPc2), are deposited on Au(111) gold surface forming large-scale self-assemblies. Global and local experimental techniques, namely, grazing incidence X-ray diffraction and scanning tunneling microscopy, supplemented by density functional theory calculations with van der Waals corrections, give insight into the molecular structural arrangement of the thin film and the self organization at the surface. Our results show unambiguously that the two plateaus of the double-decker phthalocyanine present a different rotation than the isolated molecule. This is evidenced by density functional theory simulations of optimized LuPc2 monolayer showing a perfect agreement with experimental findings. Moreover, the stabilized structure of double layers reveals an eclipsed configuration of the molecules in the stacking, having the ligand plateaus parallel to the gold surface. The high crystallinity of the molecular assembly and its weak electronic coupling with the metallic substrate is expected to open new perspective in magnetic devices.

  • 28.
    Farronato, Mattia
    et al.
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, F-75005 Paris, France.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Natl Sun Yat Sen Univ, Dept Mat & Optoelect Sci, Kaohsiung 804, Taiwan.
    Longo, Danilo
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, F-75005 Paris, France.
    Cruguel, Herve
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, F-75005 Paris, France.
    Bouvet, Marcel
    Univ Bourgogne Franche Comte, Univ Bourgogne, Inst Chim Mol, CNRS,UMR 6302, F-21000 Dijon, France.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Witkowski, Nadine
    Sorbonne Univ, CNRS, Inst Nanosci Paris, UMR 7588, F-75005 Paris, France.
    High Tolerance of Double-Decker Phthalocyanine toward Molecular Oxygen2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 35, p. 20244-20251Article in journal (Refereed)
    Abstract [en]

    Because organic electronics suffer from degradation-inducing oxidation processes, oxygen-tolerant organic molecules could solve this issue and be integrated to improve the stability of devices during operation. In this work, we investigate how lutetium double-decker phthalocyanine (LuPc2) reacts toward molecular oxygen and we report microscopic details of its interaction with LuPc2 film by combining X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and density functional theory. Surprisingly, LuPc2 molecules are found to weakly physisorb below 120 K and appear rather inert to molecular oxygen at more elevated temperatures. We are able to draw a microscopic picture at low temperature, in which oxygen molecules stick on top of the pyrrolic carbon of LuPc2. Our work sheds light on a class of semiconducting molecules, namely, double-decker phthalocyanines, which present a high tolerance toward molecular oxygen, opening promising perspectives for the design of stable materials to be applied in the next generation of organic-based electronic devices operating under ambient conditions.

  • 29.
    Forsberg, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Duda, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Angular anisotropy in resonant inelastic soft X-ray scattering of liquid water2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 13, p. 132203-Article in journal (Refereed)
    Abstract [en]

    Resonantly excited soft x-ray emission spectra of liquid water have been measured at two different angles relative to the polarization direction of the exciting radiation. The results demonstrate that the emission is much more isotropic than expected for the free water   molecule but that the trends in the remaining anisotropy qualitatively agree. It is found that the two sharp oxygen peaks at high emission energy correspond to states of different symmetry.

     

  • 30.
    Gråsjö, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Andersson, Egil
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Forsberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Aziz, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Johansson, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Duda, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Hansson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Oxygen K-edge studies of water poor surfactant gel systems2008Conference paper (Other (popular science, discussion, etc.))
  • 31.
    Gråsjö, Johan
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Andersson, Egil
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Forsberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Aziz, Emad F.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Johansson, Christian
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Duda, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Hennies, Franz
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Hansson, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Electronic structure of water molecules confined in a micelle lattice2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 24, p. 8201-8205Article in journal (Refereed)
    Abstract [en]

    Oxygen K absorption and emission spectra of water molecules confined in dodecyltrimethyl ammonium chloride micelle structures are presented. The local electronic structure of the water molecules is found to be dramatically different from the electronic structure of water molecules in the gas-phase as well as in liquid water. Hybridization with states of the ions in the surrounding ions is directly observed, and evidence for stabilization of the water molecules relative to molecules in bulk water is found.

  • 32.
    Hahlin, A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Karis, O
    Brena, Barbara
    Dunn, JH
    Arvanitis, D
    Quantitative analysis of L-edge white line intensities: the influence of saturation and transverse coherence2001In: JOURNAL OF SYNCHROTRON RADIATION, ISSN 0909-0495, Vol. 8, p. 437-439Article in journal (Refereed)
  • 33.
    Hahlin, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Karis, Olof
    Brena, Barbara
    Hunter Dunn, Jonathan
    Arvanitis, Dimitri
    Quantitative analysis of L-edge white line intensities: the influence of saturation and transverse coherence2001In: Journal of Synchrotron Radiation, Vol. 8, p. 437-439Article in journal (Refereed)
  • 34.
    Herper, Heike C.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bhandary, Sumanta
    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.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fe phthalocyanine on Co(001): Influence of surface oxidation on structural and electronic properties2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 8, p. 085411-Article in journal (Refereed)
    Abstract [en]

    The adsorption of FePc on Co(001) and c(2 x 2)O/Co(001) was studied by means of density functional theory calculations, taking into account the long range van der Waals dispersion forces. Several high symmetry adsorption sites were analyzed, together with two possible orientations of the molecules. For the adsorption of FePc on the bare surface the on-top-of Co position, rotated by 45 degrees relative to the substrate orientation, is most stable, whereas on the surface covered by an O adlayer the on-top-of O position is preferred. This has strong impact on the magnetic coupling but leaves the spin state of S = 1 unaltered. The total energies of the studied adsorption sites on the bare metal differ by at least 0.75 eV and are characterized by a strong hybridization of the carbon atoms in the peripheral benzenic rings with the Co atoms beneath. In the presence of the O adlayer the various sites are closer in energy, which turns out to be related to the screening of the ferromagnetic film by the oxygen atoms.

  • 35. Klar, D.
    et al.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Herper, Heike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bhandary, Sumanta
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Weis, C.
    Krumme, B.
    Schmitz-Antoniak, C.
    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.
    Wende, H.
    Oxygen-tuned magnetic coupling of Fe-phthalocyanine molecules to ferromagnetic Co films2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 22, p. 224424-Article in journal (Refereed)
    Abstract [en]

    The coupling of submonolayer coverages of Fe-phthalocyanine molecules on bare and oxygen-covered ferromagnetic Co(001) films was studied by x-ray-absorption spectroscopy, especially the x-ray magnetic circular dichroism, in combination with density functional theory. We observe that the magnetic moments of the paramagnetic molecules are aligned even at room temperature, resulting from a magnetic coupling to the substrate. While the magnetization of the Fe ions directly adsorbed on the Co surface is parallel to the magnetization of the Co film, the introduction of an oxygen interlayer leads to an antiparallel alignment. As confirmed by theory, the coupling strength is larger for the system FePc/Co than for FePc/O/Co, causing a stronger temperature dependence of the Fe magnetization for the latter system. Furthermore, the calculations reveal that the coupling mechanism changes due to the O layer from mostly direct exchange to Co of the bare surface to a 180 degrees antiferromagnetic superexchange via the O atoms. Finally, by comparing the experimental x-ray-absorption spectra at the N K edge with the corresponding calculations, the contribution of the individual orbitals has been determined and the two inequivalent N atoms of the molecules could be distinguished.

  • 36.
    Lanzilotto, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhang, Teng
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Stredansky, Matus
    Univ Trieste, Dept Phys, Via A Valerio 2, I-34127 Trieste, Italy;CNR, IOM, Lab TASC, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Grazioli, Cesare
    CNR, ISM, Unit LD2, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Simonov, Konstantin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    De Simone, Monica
    CNR, IOM, Lab TASC, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Coreno, Marcello
    CNR, ISM, Unit LD2, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Araujo, Carlos Moyses
    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.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Spectroscopic Fingerprints of Intermolecular H-Bonding Interactions in Carbon Nitride Model Compounds2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 53, p. 14198-14206Article in journal (Refereed)
    Abstract [en]

    The effect of intermolecular H-bonding interactions on the local electronic structure of N-containing functional groups (amino group and pyridine-like N) that are characteristic of polymeric carbon nitride materials p-CN(H), a new class of metal-free organophotocatalysts, was investigated. Specifically, the melamine molecule, a building block of p-CN(H), was characterized by X-ray photoelectron (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule was studied as a noninteracting system in the gas phase and in the solid state within a H-bonded network. With the support of DFT simulations of the spectra, it was found that the H-bonds mainly affect the N1s level of the amino group, leaving the N1s level of the pyridine-like N mostly unperturbed. This is responsible for a reduction of the chemical shift between the two XPS N1s levels relative to free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N1s level also shift to lower photon energies. Moreover, the solid-state absorption spectra showed significant modification/quenching of resonances related to transitions from the amino N1s level to sigma* orbitals involving the NH2 termini.

  • 37.
    Lanzilotto, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhang, Teng
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Stredansky, Matuš
    Department of Physics University of Trieste.
    Grazioli, Cesare
    CNR-ISM, Istituto di Struttura della Materia (LD2 Unit).
    Simonov, Konstantin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Giangrisostomi, Erika
    Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin GmbH.
    Ovsyannikov, Ruslan
    Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin GmbH.
    de Simone, Monica
    CNR-IOM, Istituto Officina dei Materiali (Laboratorio TASC).
    Coreno, Marcello
    CNR-ISM, Istituto di Struttura della Materia (LD2 Unit).
    Araujo, Carlos Moyses
    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. 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.
    Spectroscopic Fingerprints of Carbon Nitride Functional Groups Locked-up in Intermolecular H-bonding InteractionsIn: Chemistry: A European Journal, ISSN 0947-6539Article in journal (Refereed)
    Abstract [en]

    We have investigated the effect of intermolecular H- bonding interactions on the local electronic structure of N- functionalities, amino group and pyridine-like N, which are characteristic of a new class of metal-free polymeric photo-catalysts named graphitic carbon nitrides, g-C3N4. Specifically, we have performed a characterization of the melamine molecule, a building block of g-C3N4, combining X-ray photoemission (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule has been studied in the gas phase, as non-interacting system, and in the solid state within a hydrogen bonded network. With the support of density functional theory (DFT) simulations of the spectra, we have found that the H-bonds mainly affect the N 1s level of the amino group, leaving the N 1s level of the pyridine-like N mostly unperturbed. This fact is responsible for a reduction of the chemical shift between the two XPS N 1s levels, compared to the free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N 1s level also shift to lower photon energies. Moreover, the solid state absorption spectra have shown strong modification/quenching of resonances related with transitions from the amino N 1s level towards σ*orbitals involving the -NH2 terminations. 

  • 38.
    Luder, Johann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    de Simone, Monica
    Totani, Roberta
    Coreno, Marcello
    Grazioli, Cesare
    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.
    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.
    The electronic characterization of biphenylene-Experimental and theoretical insights from core and valence level spectroscopy2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 7, article id 074305Article in journal (Refereed)
    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.

  • 39.
    Luder, Johann
    et al.
    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.
    Comparison of van der Waals corrected and sparse-matter density functionals for the metal-free phthalocyanine/gold interface2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 4, p. 045416-Article in journal (Refereed)
    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.

  • 40.
    Lüder, Johann
    et al.
    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.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 12, p. 124711-Article in journal (Refereed)
    Abstract [en]

    We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 mu(B) distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of - 1.45 and 1.45 eV.

  • 41.
    Lüder, Johann
    et al.
    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.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    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.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Many-body effects and excitonic features in 2D biphenylene carbon2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 2, article id 024702Article in journal (Refereed)
    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.

  • 42.
    Lüder, Johann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. National University of Singapore, Department of Mechanical Engineering.
    Schött, Johan
    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.
    Haverkort, Maurits W.
    Heidelberg University, Institute for Theoretical Physics.
    Thunström, Patrik
    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. Örebro University, School of Science and Technology.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theory of L-edge spectroscopy of strongly correlated systems2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245131Article in journal (Refereed)
    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 modeling of the 2p→3d excitation processes remains to be challenging for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work, we present a realization of the method combining the density-functional theory with multiplet ligand field theory, proposed in Haverkort et al. [Phys. Rev. B 85, 165113 (2012)]. In this approach, a single-impurity Anderson model (SIAM) is constructed, with almost all parameters obtained from first principles, and then solved to obtain the spectra. In our implementation, we adopt the language of the dynamical mean-field theory and utilize the local density of states and the hybridization function, projected onto TM 3d states, in order to construct the SIAM. The developed computational scheme is applied to calculate the L-edge spectra for several TM monoxides. A very good agreement between the theory and experiment is found for all studied systems. The effect of core-hole relaxation, hybridization discretization, possible extensions of the method as well as its limitations are discussed.

  • 43.
    Nilson, Katharina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Åhlund, John
    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.
    Göthelid, Emmanuelle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Schiessling, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Mårtensson, Nils
    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.
    Scanning tunneling microscopy study of metal-free phthalocyanine monolayer structures on graphite2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 11, p. 114702-Article in journal (Refereed)
    Abstract [en]

    Low temperature scanning tunneling microscopy (STM) studies of metal-free phthalocyanine (H2Pc) adsorbed on highly oriented pyrolytic graphite (HOPG) have shown ordered arrangement of molecules for low coverages up to 1 ML. Evaporation of H2Pc onto HOPG and annealing of the sample to 670 K result in a densely packed structure of the molecules. Arrangements of submonolayer, monolayer, and monolayer with additional adsorbed molecules have been investigated. The high resolution of our investigations has permitted us to image single molecule orientation. The molecular plane is found to be oriented parallel to the substrate surface and a square adsorption unit cell of the molecules is reported. In addition, depending on the bias voltage, different electronic states of the molecules have been probed. The characterized molecular states are in excellent agreement with density functional theory ground state simulations of a single molecule. Additional molecules adsorbed on the monolayer structures have been observed, and it is found that the second layer molecules adsorb flat and on top of the molecules in the first layer. All STM measurements presented here have been performed at a sample temperature of 70 K.

  • 44.
    Nilson, Katharina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Åhlund, John
    Schiessling, Joachim
    Palmgren, Pål
    Brena, Barbara
    Göthelid, Emmanuelle
    Hennies, Franz
    Rudolf, Petra
    Göthelid, Mats
    Mårtensson, Nils
    Potassium doped H2Pc films: alkali induced electronic and geometrical modificationsManuscript (Other academic)
  • 45.
    Nilson, Katharina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Åhlund, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Shariati, Masumeh-Nina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Schiessling, Joachim
    Palmgren, Pål
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Göthelid, Emmanuelle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Hennies, Franz
    Huismans, Y
    Evangelista, F
    Rudolf, Petra
    Göthelid, Mats
    Mårtensson, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Potassium-intercalated H2Pc films: Alkali-induced electronic and geometrical modifications2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 4, p. 044708-Article in journal (Refereed)
    Abstract [en]

    X-ray spectroscopy studies of potassium intercalated metal-free phthalocyanine multilayers adsorbed on Al(110) have been undertaken. Photoelectron spectroscopy measurements show the presence of several charge states of the molecules upon K intercalation, due to a charge transfer from the alkali. In addition, the comparison of valence band photoemission spectra with the density functional theory calculations of the density of states of the H2Pc anion indicates a filling of the formerly lowest unoccupied molecular orbital by charge transfer from the alkali. This is further confirmed by x-ray absorption spectroscopy (XAS) studies, which show a decreased density of unoccupied states. XAS measurements in different experimental geometries reveal that the molecules in the pristine film are standing upright on the surface or are only slightly tilted away from the surface normal but upon K intercalation, the molecular orientation is changed in that the tilt angle of the molecules increases.

  • 46. O'Shea, J. N.
    et al.
    Schnadt, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Andersson, S.
    Patthey, L.
    Rost, S.
    Giertz, A.
    Brena, Barbara
    Forsell, J.-O.
    Sandell, A.
    Björneholm, O.
    Brühwiler, P. A.
    Mårtensson, N.
    X-ray photoelectron spectroscopy of low surface concentration mass-selected Ag clusters2000In: J. Chem. Pys., Vol. 113, p. 9233-9238Article in journal (Refereed)
  • 47. O´Shea, J. N.
    et al.
    Swarbrick, J. C.
    Nilson, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V.
    Brena, Barbara
    Luo, Yi
    Dhanak, V. R.
    Molecular ordering in isonicotinic acid on rutile TiO2 (110) investigated with valence band photoemission2004In: The Journal of Chemical Physics, Vol. 121, p. 10203-Article in journal (Refereed)
  • 48.
    O'Shea, JN
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Schnadt, J
    Andersson, S
    Patthey, L
    Rost, S
    Giertz, A
    Brena, Barbara
    Forsell, JO
    Sandell, A
    Bjorneholm, O
    Bruhwiler, PA
    Martensson, N
    X-ray photoelectron spectroscopy of low surface concentration mass-selected Ag clusters2000In: JOURNAL OF CHEMICAL PHYSICS, ISSN 0021-9606, Vol. 113, no 20, p. 9233-9238Article in journal (Refereed)
    Abstract [en]

    We have developed an experimental setup for the study of small mass-selected clusters delivered by soft landing to a model oxide support. An automated deposition system to achieve accurately quantified homogeneous surfaces is described which also overcome

  • 49.
    Roberta, Totani
    et al.
    Department of physical and chemical sciences, university of L'Aquila, Italy.
    Cesare, Grazioli
    CNR-ISM, Italy.
    Zhang, Teng
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ieva, Bidermane
    Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz Zentrum Berlin.
    Lüder, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Monica, de Simone
    CNR-IOM, Italy.
    Marcello, Coreno
    CNR-ISM, Italy.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luca, Lozzi
    Department of physical and chemical sciences, university of L'Aquila, Italy.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Electronic structure investigations of biphenylene filmsArticle in journal (Refereed)
    Abstract [en]

    Photoelectron Spectroscopy (PES) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The obtained results have been compared to previous gas phase spectra and single molecule density functional theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, NEXAFS measurements allowed characterizing the variation of the molecular arrangement with the film thickness and helped to clarify the substrate- molecule interaction. 

  • 50.
    Saak, Clara-Magdalena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Unger, Isaak
    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.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, DE-22607 Hamburg, Germany.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Site-specific X-ray induced dynamics in liquid methanol2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 28, p. 15478-15486Article in journal (Refereed)
12 1 - 50 of 66
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