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  • 1.
    Ahsan, Aisha
    et al.
    Univ Basel, Switzerland.
    Mousavi, S. Fatemeh
    Univ Basel, Switzerland.
    Nijs, Thomas
    Univ Basel, Switzerland.
    Nowakowska, Sylwia
    Univ Basel, Switzerland.
    Popova, Olha
    Univ Basel, Switzerland.
    Wackerlin, Aneliia
    Univ Basel, Switzerland.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Gade, Lutz H.
    Heidelberg Univ, Germany.
    Jung, Thomas A.
    Paul Scherrer Inst, Switzerland.
    Phase Transitions in Confinements: Controlling Solid to Fluid Transitions of Xenon Atoms in an On-Surface Network2019In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 15, no 3, article id 1803169Article in journal (Refereed)
    Abstract [en]

    This study reports on "phase" transitions of Xe condensates in on-surface confinements induced by temperature changes and local probe excitation. The pores of a metal-organic network occupied with 1 up to 9 Xe atoms are investigated in their propensity to undergo "condensed solid" to "confined fluid" transitions. Different transition temperatures are identified, which depend on the number of Xe atoms in the condensate and relate to the stability of the Xe clustering in the condensed "phase." This work reveals the feature-rich behavior of transitions of confined planar condensates, which provide a showcase toward future "phase-transition" storage media patterned by self-assembly. This work is also of fundamental interest as it paves the way to real space investigations of reversible solid to fluid transitions of magic cluster condensates in an array of extremely well-defined quantum confinements.

  • 2.
    Ahsan, Aisha
    et al.
    Univ Basel, Switzerland.
    Mousavi, S. Fatemeh
    Univ Basel, Switzerland.
    Nijs, Thomas
    Univ Basel, Switzerland.
    Nowakowska, Sylwia
    Univ Basel, Switzerland.
    Popova, Olha
    Univ Basel, Switzerland.
    Wackerlin, Aneliia
    Univ Basel, Switzerland.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Gade, Lutz H.
    Heidelberg Univ, Germany.
    Jung, Thomas A.
    Univ Basel, Switzerland; Paul Scherrer Inst, Switzerland.
    Watching nanostructure growth: kinetically controlled diffusion and condensation of Xe in a surface metal organic network2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 11, p. 4895-4903Article in journal (Refereed)
    Abstract [en]

    Diffusion, nucleation and growth provide the fundamental access to control nanostructure growth. In this study, the temperature activated diffusion of Xe at and between different compartments of an on-surface metal organic coordination network on Cu(111) has been visualized in real space. Xe atoms adsorbed at lower energy sites become mobile with increased temperature and gradually populate energetically more favourable binding sites or remain in a delocalized fluid form confined to diffusion along a topological subset of the on-surface network. These diffusion pathways can be studied individually under kinetic control via the chosen thermal energy kT of the sample and are determined by the network and sample architecture. The spatial distribution of Xe in its different modes of mobility and the time scales of the motion is revealed by Scanning Tunneling Microscopy (STM) at variable temperatures up to 40 K and subsequent cooling to 4 K. The system provides insight into the diffusion of a van der Waals gas on a complex structured surface and its nucleation and coarsening/growth into larger condensates at elevated temperature under thermodynamic conditions.

  • 3.
    Badr, Hussein O.
    et al.
    Drexel Univ, PA 19104 USA.
    El-Melegy, Tarek
    Drexel Univ, PA 19104 USA.
    Carey, Michael
    Drexel Univ, PA 19104 USA.
    Natu, Varun
    Drexel Univ, PA 19104 USA.
    Hassig, Mary Q.
    Drexel Univ, PA 19104 USA.
    Johnson, Craig
    Drexel Univ, PA 19104 USA.
    Qian, Qian
    Drexel Univ, PA 19104 USA.
    Li, Christopher Y.
    Drexel Univ, PA 19104 USA.
    Kushnir, Kateryna
    Worcester Polytech Inst, MA 01609 USA.
    Colin-Ulloa, Erika
    Worcester Polytech Inst, MA 01609 USA.
    Titova, Lyubov V
    Worcester Polytech Inst, MA 01609 USA.
    Martin, Julia L.
    Worcester Polytech Inst, MA 01609 USA.
    Grimm, Ronald L.
    Worcester Polytech Inst, MA 01609 USA.
    Pai, Rahul
    Drexel Univ, PA 19104 USA.
    Kalra, Vibha
    Drexel Univ, PA 19104 USA.
    Karmakar, Avishek
    Drexel Univ, PA 19104 USA.
    Ruffino, Anthony
    Drexel Univ, PA 19104 USA.
    Masiuk, Stefan
    Drexel Univ, PA 19104 USA.
    Liang, Kun
    Tulane Univ, LA 70118 USA.
    Naguib, Michael
    Tulane Univ, LA 70118 USA.
    Wilson, Olivia
    Drexel Univ, PA 19104 USA.
    Magenau, Andrew
    Drexel Univ, PA 19104 USA.
    Montazeri, Kiana
    Drexel Univ, PA 19104 USA.
    Zhu, Yucheng
    Drexel Univ, PA 19104 USA.
    Cheng, Hao
    Drexel Univ, PA 19104 USA.
    Torita, Takeshi
    Murata Mfg Co Ltd, Japan.
    Koyanagi, Masashi
    Murata Mfg Co Ltd, Japan.
    Yanagimachi, Akimaro
    Murata Mfg Co Ltd, Japan.
    Ouisse, Thierry
    Univ Grenoble Alpes, France.
    Barbier, Maxime
    Univ Grenoble Alpes, France; European Synchrotron Radiat Facil ESRF, France.
    Wilhelm, Fabrice
    European Synchrotron Radiat Facil ESRF, France.
    Rogalev, Andrei
    European Synchrotron Radiat Facil ESRF, France.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hu, Yong-Jie
    Drexel Univ, PA 19104 USA.
    Barsoum, Michel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA.
    Bottom-up, scalable synthesis of anatase nanofilament-based two-dimensional titanium carbo-oxide flakes2022In: Materials Today, ISSN 1369-7021, E-ISSN 1873-4103, Vol. 54Article in journal (Refereed)
    Abstract [en]

    Two-dimensional (2D) materials offer advantages that their 3D counterparts do not. The conventional method for the bulk synthesis of 2D materials has predominantly been through etching layered solids. Herein, we convert - through a bottom-up approach - 10 binary and ternary titanium carbides, nitrides, borides, phosphides, and silicides into 2D flakes by immersing them in a tetramethylammonium hydroxide solution at temperatures in the 25-85 degrees C range. Based on X-ray diffraction, density functional theory, X-ray photoelectron, electron energy loss, Raman, X-ray absorption near edge structure spectroscopies, transmission and scanning electron microscope images and selected area diffraction, we conclude that the resulting flakes are carbon containing anatase-based layers that are, in turn, comprised of approximate to 6 x 10 angstrom(2) nanofilaments in cross-section some of which are few microns long. Electrodes made from some of these films performed well in lithium-ion and lithium-sulphur systems. These materials also reduce the viability of cancer cells thus showing potential in biomedical applications. Synthesizing 2D materials, at near ambient conditions, with non-layered, inexpensive, green precursors (e.g., TiC) is paradigm shifting and will undoubtedly open new and exciting avenues of research and applications.

  • 4.
    Barragan, Ana
    et al.
    IMDEA Nanosci Inst, Spain.
    Nicolas-Garcia, Tomas
    IMDEA Nanosci Inst, Spain.
    Lauwaet, Koen
    IMDEA Nanosci Inst, Spain.
    Sanchez-Grande, Ana
    IMDEA Nanosci Inst, Spain; Czech Acad Sci, Czech Republic.
    Urgel, Jose I
    IMDEA Nanosci Inst, Spain.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Perez, Emilio M.
    IMDEA Nanosci Inst, Spain.
    Ecija, David
    IMDEA Nanosci Inst, Spain.
    Design and Manipulation of a Minimalistic Hydrocarbon Nanocar on Au(111)2023In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 62, no 6, article id e202212395Article in journal (Refereed)
    Abstract [en]

    Nanocars are carbon-based single-molecules with a precise design that facilitates their atomic-scale control on a surface. The rational design of these molecules is important in atomic and molecular-scale manipulation to advance the development of molecular machines, as well as for a better understanding of self-assembly, diffusion and desorption processes. Here, we introduce the molecular design and construction of a collection of minimalistic nanocars. They feature an anthracene chassis and four benzene derivatives as wheels. After sublimation and adsorption on an Au(111) surface, we show controlled and fast manipulation of the nanocars along the surface using the tip of a scanning tunneling microscope (STM). The mechanism behind the successful displacement is the induced dipole created over the nanocar by the STM tip. We utilized carbon monoxide functionalized tips both to avoid decomposition and accidentally picking the nanocars up during the manipulation. This strategy allowed thousands of maneuvers to successfully win the Nanocar Race II championship.

  • 5.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Formation mechanisms of covalent nanostructures from density functional theory2016In: Proceedings of International Workshop on On-Surface Synthesis, Cham: Springer, 2016, p. 269-287Conference paper (Refereed)
    Abstract [en]

    In this chapter, it is demonstrated how electronic structure calculations, with focus on density functional theory, can be used to gain insight about on-surface reactions. I first give a brief introduction to how density functional theory can be used to study reactions. The focus is then shifted to two different types of on-surface reactions, highlighting the theoretical work that has been performed to gain detailed atomistic insight into them. First, the state of the art of the theory behind on-surface Ullmann coupling is described. In this reaction, molecular building blocks dehalogenate, which enables them to covalently couple. The most crucial reaction parameters are identified—the diffusion and coupling barriers of surface-supported radicals—and the potential for theory to optimize these is discussed. We then concentrate on the homo-coupling between terminal alkynes, a rudimentarily different process where molecules initially couple before undergoing a dehydrogenation step. The theory of the mechanism behind this coupling strategy is less developed than that of the on-surface Ullmann coupling, where fundamental questions remain to be unraveled. For example, by the subtle change of substrate from Ag to Au, the on-surface alkyne chemistry is completely altered from the homo-coupling to a cyclodehydrogenation reaction for the same molecular building block, of which origin remains unknown. The main objective of the chapter is to give an impression of what kind of information theory can obtain about reaction on surface, as well as to motivate and inspire for future theoretical studies, which will be needed to turn on-surface synthesis into a more predictive discipline.

  • 6.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Reaction mechanisms for on-surface synthesis of covalent nanostructures2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 8, p. 083002-Article, review/survey (Refereed)
    Abstract [en]

    In recent years, on-surface synthesis has become an increasingly popular strategy to form covalent nanostructures. The approach has great prospects for facilitating the manufacture of a range of fascinating materials with atomic precision. However, the on-surface reactions are enigmatic to control, currently restricting its bright perspectives and there is a great need to explore how the reactions are governed. The objective of this topical review is to summarize theoretical work that has focused on comprehending on-surface synthesis protocols through studies of reaction mechanisms.

  • 7.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Thermodynamics of an Electrocyclic Ring-Closure Reaction on Au(111)2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 38, p. 21716-21721Article in journal (Refereed)
    Abstract [en]

    We have computationally studied the effects of temperature on the reaction pathway of an electrocyclic ring-closure reaction on the Au(111) surface, particularly focusing on thermodynamic aspects of the reaction. The electrocyclic ring closure is accompanied by a series of dehydrogenation steps, and while it is found that temperature, in terms of vibrational entropy and enthalpy, has a reducing effect on most energy barriers, it does not alter the qualitative appreciation of the reaction kinetics. However, it is found that the way the abstracted hydrogen atoms are treated is crucial for the thermodynamics of the reaction. The overall reaction is highly endothermic but becomes thermodynamically favorable due to the entropy gain of the hydrogen byproducts, which desorb associatively from the surface as H2. The study provides new outlooks for the theoretical treatment of reactions related to on-surface synthesis, anticipated to be instructive for future studies.

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  • 8.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Zhou, Jie
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Predicting chemical exfoliation: fundamental insights into the synthesis of MXenes2023In: NPJ 2D MATERIALS AND APPLICATIONS, ISSN 2397-7132, Vol. 7, no 1, article id 5Article in journal (Refereed)
    Abstract [en]

    The factors controlling the top-down synthesis of MXenes, by selectively removing the A elements from parent MAX phases, is still under debate. In particular, understanding why some MAX phases can be used for creating MXenes, while others cannot, is of immense interest and would greatly support computational screening and identification of new two-dimensional materials that could also be created by chemical exfoliation. Here we computationally study the etching of MAX phases in hydrofluoric acid, considering the complete exfoliation process and competing processes during the initial steps of the synthesis. The results are compared to experiments and MAX phases successfully converted to MXenes, as well as so far unsuccessful attempts, including previously unpublished experimental data, rationalizing why some MAX phases are exfoliable while others are not. Our results provide an improved understanding of the synthesis of MXenes under acid conditions, anticipated to be vital for our ability to discover novel two-dimensional materials.

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  • 9.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hanke, Felix
    Accelrys, 334 Science Park, Cambridge, CB4 0WN, United Kingdom.
    Towards Design Rules for Covalent Nanostructures on Metal Surfaces2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 4, p. 928-934Article in journal (Refereed)
    Abstract [en]

    The covalent molecular assembly on metal surfaces is explored, outlining the different types of applicable reactions. Density functional calculations for on-surface reactions are shown to yield valuable insights into specific reaction mechanisms and trends across the periodic table. Finally, it is shown how design rules could be derived for nanostructures on metal surfaces.

  • 10.
    Björk, Jonas
    et al.
    University of Liverpool, UK.
    Hanke, Felix
    University of Liverpool, UK.
    Palma, Carlos-Andres
    University de Strasbourg, France.
    Samorì, Paolo
    University de Strasbourg, France.
    Cecchini, Marco
    University de Strasbourg, France.
    Persson, Mats
    University of Liverpool, UK.
    Adsorption of Aromatic and Anti-Aromatic Systems on Graphene through π−π Stacking2010In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 1, p. 3407-3412Article in journal (Refereed)
    Abstract [en]

    The adsorption of neutral (poly)-aromatic, antiaromatic, and more generally π-conjugated systems on graphene is studied as a prototypical case of π-π stacking. To account for dispersive interactions, we compare the recent van der Waals density functional (vdw-DF) with three semiempirical corrections to density functional theory and two empirical force fields. The adsorption energies of the molecules binding to graphene predicted by the vdw-DFwere found to be in excellent agreement with temperature desorption experiments reported in litera- ture,whereas the results of theremaining functionals andforce fields only preserve the correct trends. The comparison of the dispersive versus electrostatic contribu- tions to the total binding energies in the aromatic and antiaromatic systems suggests that π-π interactions can be regarded as being prevalently dispersive in nature at large separations, whereas close to the equilibrium bonding distance, it is a complex interplay between dispersive and electrostatic Coulombic interactions. Moreover our results surprisingly indicate that the magnitude of π-π interactions normalized both per number of total atoms and carbon atoms increases signifi- cantly with the relative number of hydrogen atoms in the studied systems.

  • 11.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hanke, Felix
    Surface Science Research Centre, University of Liverpool, UK.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Mechanisms of halogen-based covalent self-assembly on metal surfaces2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 15, p. 5768-5775Article in journal (Refereed)
    Abstract [en]

    We computationally study the reaction mechanisms of halogen-based covalent self-assembly, a major route for synthesizing molecular nanostructures and nanographenes on surfaces. Focusing on biphenyl as a small model system, we describe the dehalogenation, recombination, and diffusion processes. The kinetics of the different processes are also investigated, in particular how diffusion and coupling barriers affect recombination rates. Trends across the periodic table are derived from three commonly used close-packed (111) surfaces (Cu, Ag, and Au) and two halogens (Br and I). We show that the halogen atoms can poison the surface, thus hindering long-range ordering of the self-assembled structures. Finally, we present core-level shifts of the relevant carbon and halogen atoms, to provide reference data for reliably detecting self-assembly without the need for atomic-resolution scanning tunneling microscopy.

  • 12.
    Björk, Jonas
    et al.
    University of Liverpool, UK.
    Matena, Manfred
    University of Basel, Switzerland.
    Dyer, Matthew S.
    University of Liverpool, UK.
    Enache, Mihaela
    University of Basel, Switzerland.
    Lobo-Checa, Jorge
    University of Basel, Switzerland.
    Gade, Lutz H.
    University of Heidelberg, Germany.
    Jung, Thomas A.
    Paul-Scherrer-Institute, Villigen, Switzerland.
    Stöhr, Meike
    University of Basel, Switzerland.
    Persson, Mats
    University of Liverpool, UK.
    STM fingerprint of molecule-adatom interactions in a self-assembled metal-organic surface coordination network on Cu(111)2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, p. 8815-8821Article in journal (Refereed)
    Abstract [en]

    A novel approach of identifying metal atoms within a metal-organic surface coordination network using scanning tunnelling microscopy (STM) is presented. The Cu adatoms coordinated in the porous surface network of 1,3,8,10-tetraazaperopyrene (TAPP) molecules on a Cu(111) surface give rise to a characteristic electronic resonance in STM experiments. Using density functional theory calculations, we provide strong evidence that this resonance is a fingerprint of the interaction between the molecules and the Cu adatoms. We also show that the bonding of the Cu adatoms to the organic exodentate ligands is characterised by both the mixing of the nitrogen lone-pair orbitals of TAPP with states on the Cu adatoms and the partial filling of the lowest unoccupied molecular orbital (LUMO) of the TAPP molecule. Furthermore, the key interactions determining the surface unit cell of the network are discussed.

  • 13.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Functionalizing MXenes by Tailoring Surface Terminations in Different Chemical Environments2021In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 33, no 23, p. 9108-9118Article in journal (Refereed)
    Abstract [en]

    Two-dimensional metal carbides and nitrides-MXenes-represent a group of materials which have attained growing attention over the last decade due to their chemical versatility, making them highly promising in areas such as energy storage, superconductivity, and heterogenous catalysis. Surface terminations are a natural consequence of the MXene synthesis, conventionally consisting of O, OH, and F. However, recent studies have extended the chemical domain of the surface terminations to other elements, and they should be considered as an additional parameter governing the MXene properties. There is a shortfall in the understanding of how various chemical species could act as terminations on different MXenes. In particular, there is limited comprehension in which chemical environments different terminations are stable. Here, we present an extensive theoretical study of the surface terminations of MXenes in different atmospheres by considering in total six experimentally achieved MXenes (Ti2C, Nb2C, V2C, Mo2C, Ti3C2, and Nb4C3) and twelve surface terminations (O, OH, N, NH, NH2, S, SH, H, F, Cl, Br, and I). We consider fully terminated (single termination) MXenes and also the impact of substituting individual terminations. Our study provides insights into what terminations are stable on which MXenes in different chemical environments, with predictions of how to obtain single-termination MXenes and which MXenes are resilient under ambient conditions. In addition, we propose synthesis protocols of MXenes which have not yet been realized in experiments. It is anticipated that alongside the development of new synthesis routes, our study will provide design rules for how to tailor the surface terminations of MXenes.

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  • 14.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Sanchez-Sanchez, Carlos
    Swiss Fed Labs Mat Sci & Technol, Switzerland; Inst Mat Sci Madrid ICMM CSIC, Spain.
    Chen, Qiang
    Max Planck Inst Polymer Res, Germany; Univ Oxford, England.
    Pignedoli, Carlo A.
    Swiss Fed Labs Mat Sci & Technol, Switzerland.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Ruffieux, Pascal
    Swiss Fed Labs Mat Sci & Technol, Switzerland.
    Feng, Xinliang
    Tech Univ Dresden, Germany; Tech Univ Dresden, Germany.
    Narita, Akimitsu
    Max Planck Inst Polymer Res, Germany; Okinawa Inst Sci & Technol Grad Univ, Japan.
    Mullen, Klaus
    Max Planck Inst Polymer Res, Germany.
    Fasel, Roman
    Swiss Fed Labs Mat Sci & Technol, Switzerland; Univ Bern, Switzerland.
    The Role of Metal Adatoms in a Surface-Assisted Cyclodehydrogenation Reaction on a Gold Surface2022In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 61, no 49, article id e202212354Article in journal (Refereed)
    Abstract [en]

    Dehydrogenation reactions are key steps in many metal-catalyzed chemical processes and in the on-surface synthesis of atomically precise nanomaterials. The principal role of the metal substrate in these reactions is undisputed, but the role of metal adatoms remains, to a large extent, unanswered, particularly on gold substrates. Here, we discuss their importance by studying the surface-assisted cyclodehydrogenation on Au(111) as an ideal model case. We choose a polymer theoretically predicted to give one of two cyclization products depending on the presence or absence of gold adatoms. Scanning probe microscopy experiments observe only the product associated with adatoms. We challenge the prevalent understanding of surface-assisted cyclodehydrogenation, unveiling the catalytic role of adatoms and their effect on regioselectivity. The study adds new perspectives to the understanding of metal catalysis and the design of on-surface synthesis protocols for novel carbon nanomaterials.

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  • 15.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Adsorption of large hydrocarbons on coinage metals: a van der Waals density functional study2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 13, p. 2851-2858Article in journal (Refereed)
    Abstract [en]

    The adsorption of organic molecules onto the close-packed facets of coinage metals is studied, and how accurately adsorption heights can be described by using recent advances of the van der Waals density functional (vdWDF), with optPBE/vdWDF, optB86b/vdWDF, vdWDF2, and rev/vdWDF2 functionals is illustrated. The adsorption of two prototypical aromatic hydrocarbons is investigated, and the calculated adsorption heights are compared to experimental literature values from normal incident X-ray standing wave absorption and a state-of-the-art semi-empirical method. It is shown that both the optB86b/vdWDF and rev/vdWDF2 functionals describe adsorption heights with an accuracy of 0.1 Å, compared to experimental values, and are concluded as reliable methods of choice for related systems.

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  • 16.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hanke, Felix
    University of Liverpool.
    Zipping Up: Cooperativity Drives the Synthesis of Graphene Nanoribbons2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 38, p. 14884-14887Article in journal (Refereed)
    Abstract [en]

    We investigate the cooperative effects controlling the synthesis of a graphene nanoribbon on the Au(111) surface starting from an anthracene polymer using density functional calculations including van der Waals interactions. We focus on the high-temperature cyclodehydrogenation step of the reaction and find that the reaction proceeds by simultaneously transferring two H-atoms from the anthracene units to the Au surface, leaving behind a C C bond in the process. This step is significantly more favorable than the three other potential reaction paths. Moreover, we find that successive dehydrogenations proceed from one end of the polyanthracene and propagate step-by-step through the polymer in a domino-like fashion.

  • 17.
    Björk, Jonas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Zhang, Yi-Qi
    Technische Universität München, Garching, Germany.
    Klappenberger, Florian
    Technische Universität München, Garching, Germany.
    Barth, Johannes V.
    Technische Universität München, Garching, Germany.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Unraveling the Mechanism of the Covalent Coupling Between Terminal Alkynes on a Noble Metal2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 6, p. 3181-3187Article in journal (Refereed)
    Abstract [en]

    The mechanism of the newly reported route for surface-assisted covalent coupling of terminal alkynes on Ag(111) is unraveled by density functional theory based transition state calculations. We illustrate that the reaction path is fundamentally different from the classical coupling schemes in wet chemistry. It is initiated by the covalent coupling between two molecules instead of single-molecule dehydrogenation. The silver substrate is found to play an important role stabilizing the intermediate species by chemical bonds, although it is hardly active electronically in the actual coupling step. The dimer intermediate is concluded to undergo two subsequent dehydrogenation processes expected to be rate-limiting according to the comparatively large barriers, which origin is discussed.

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  • 18.
    Bronner, Christopher
    et al.
    Heidelberg Univ, Phys Chem Inst, D-69120 Heidelberg, Germany ; Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Tegeder, Petra
    Heidelberg Univ, Phys Chem Inst, D-69120 Heidelberg, Germany ; Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany.
    Tracking and removing Br during the on-surface synthesis of a graphene nanoribbon2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 1, p. 486-493Article in journal (Refereed)
    Abstract [en]

    The fabrication of graphene nanoribbons (GNRs) requires a high degree of precision due to the sensitivity of the electronic structure on the edge shape. Using Br-substituted molecular precursors, this atomic precision can be achieved in a thermally induced two-step reaction following Br dissociation on a Au(111) surface. Using DFT, we find evidence that the Br atoms are bound to the intermediate polyanthrylene chains. We employ temperature-programmed desorption to demonstrate the associative desorption of HBr and molecular hydrogen during the final cyclodehydrogenation step of the reaction. Both processes are found to have similar activation barriers. Furthermore, we are able to remove Br atoms from the polyanthrylene chains by providing molecular hydrogen. The subsequent formation of GNR via a cyclodehydrogenation demonstrates that Br does not influence this part of the overall reaction.

  • 19.
    Cai, Liangliang
    et al.
    Tongji Univ, Peoples R China.
    Yu, Xin
    Tongji Univ, Peoples R China.
    Liu, Mengxi
    Natl Ctr Nanosci and Technol, Peoples R China.
    Sun, Qiang
    Tongji Univ, Peoples R China.
    Bao, Meiling
    Tongji Univ, Peoples R China.
    Zha, Zeqi
    Natl Ctr Nanosci and Technol, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Pan, Jinliang
    Natl Ctr Nanosci and Technol, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Ma, Honghong
    Tongji Univ, Peoples R China.
    Ju, Huanxin
    Univ Sci and Technol China, Peoples R China.
    Hu, Shanwei
    Univ Sci and Technol China, Peoples R China.
    Xu, Liang
    Tongji Univ, Peoples R China.
    Zou, Jiacheng
    Tongji Univ, Peoples R China.
    Yuan, Chunxue
    Tongji Univ, Peoples R China.
    Jacob, Timo
    Ulm Univ, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Zhu, Junfa
    Univ Sci and Technol China, Peoples R China.
    Qu, Xiaohui
    Natl Ctr Nanosci and Technol, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Xu, Wei
    Tongji Univ, Peoples R China.
    Direct Formation of C-C Double-Bonded Structural Motifs by On-Surface Dehalogenative Homocoupling of gem-Dibromomethyl Molecules2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 8, p. 7959-7966Article in journal (Refereed)
    Abstract [en]

    Conductive polymers are of great importance in a variety of chemistry-related disciplines and applications. The recently developed bottom-up on-surface synthesis strategy provides us with opportunities for the fabrication of various nanostructures in a flexible and facile manner, which could be investigated by high-resolution microscopic techniques in real space. Herein, we designed and synthesized molecular precursors functionalized with benzal gem-dibromomethyl groups. A combination of scanning tunneling microscopy, noncontact atomic force microscopy, high-resolution synchrotron radiation photoemission spectroscopy, and density functional theory calculations demonstrated that it is feasible to achieve the direct formation of C-C double-bonded structural motifs via on-surface dehalogenative homocoupling reactions on the Au(111) surface. Correspondingly, we convert the sp(3)-hybridized state to an sp(2)-hybridized state of carbon atoms, i.e., from an alkyl group to an alkenyl one. Moreover, by such a bottom-up strategy, we have successfully fabricated poly(phenylenevinylene) chains on the surface, which is anticipated to inspire further studies toward understanding the nature of conductive polymers at the atomic scale.

  • 20.
    Cao, Nan
    et al.
    Tech Univ Munich, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Corral-Rascon, Eduardo
    Tech Univ Munich, Germany.
    Chen, Zhi
    Karlsruhe Inst Technol, Germany; Shenzhen Univ, Peoples R China.
    Ruben, Mario
    Karlsruhe Inst Technol, Germany; Univ Strasbourg, France; Karlsruhe Inst Technol, Germany.
    Senge, Mathias O.
    Tech Univ Munich, Germany.
    Barth, Johannes V.
    Tech Univ Munich, Germany.
    Riss, Alexander
    Tech Univ Munich, Germany.
    The role of aromaticity in the cyclization and polymerization of alkyne-substituted porphyrins on Au(111)2023In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349Article in journal (Refereed)
    Abstract [en]

    Aromaticity is an established and widely used concept for the prediction of the reactivity of organic molecules. However, its role remains largely unexplored in on-surface chemistry, where the interaction with the substrate can alter the electronic and geometric structure of the adsorbates. Here we investigate how aromaticity affects the reactivity of alkyne-substituted porphyrin molecules in cyclization and coupling reactions on a Au(111) surface. We examine and quantify the regioselectivity in the reactions by scanning tunnelling microscopy and bond-resolved atomic force microscopy at the single-molecule level. Our experiments show a substantially lower reactivity of carbon atoms that are stabilized by the aromatic diaza[18]annulene pathway of free-base porphyrins. The results are corroborated by density functional theory calculations, which show a direct correlation between aromaticity and thermodynamic stability of the reaction products. These insights are helpful to understand, and in turn design, reactions with aromatic species in on-surface chemistry and heterogeneous catalysis. While aromaticity is a useful concept for assessing the reactivity of organic compounds, the connection between aromaticity and on-surface chemistry remains largely unexplored. Now, scanning probe experiments on cyclization reactions of porphyrins on Au(111) show that the peripheral carbon atoms outside of the aromatic 18-& pi; electron pathway exhibit a higher reactivity.

  • 21.
    Cao, Nan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Tech Univ Munich, Germany.
    Yang, Biao
    Tech Univ Munich, Germany.
    Riss, Alexander
    Tech Univ Munich, Germany.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Barth, Johannes V.
    Tech Univ Munich, Germany.
    On-surface synthesis of enetriynes2023In: Nature Communications, E-ISSN 2041-1723, Vol. 14, no 1, article id 1255Article in journal (Refereed)
    Abstract [en]

    Belonging to the enyne family, enetriynes comprise a distinct electron-rich all-carbon bonding scheme. However, the lack of convenient synthesis protocols limits the associated application potential within, e.g., biochemistry and materials science. Herein we introduce a pathway for highly selective enetriyne formation via tetramerization of terminal alkynes on a Ag(100) surface. Taking advantage of a directing hydroxyl group, we steer molecular assembly and reaction processes on square lattices. Induced by O-2 exposure the terminal alkyne moieties deprotonate and organometallic bis-acetylide dimer arrays evolve. Upon subsequent thermal annealing tetrameric enetriyne-bridged compounds are generated in high yield, readily self-assembling into regular networks. We combine high-resolution scanning probe microscopy, X-ray photoelectron spectroscopy and density functional theory calculations to examine the structural features, bonding characteristics and the underlying reaction mechanism. Our study introduces an integrated strategy for the precise fabrication of functional enetriyne species, thus providing access to a distinct class of highly conjugated pi-system compounds. Enetriynes, which belong to the enyne family, are characterized by a distinct electron-rich carbon-bonding scheme. Here, the authors report the formation of enetriynes with high selectivity by tetramerization of terminal alkynes on Ag(100).

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  • 22.
    Cirera, B.
    et al.
    IMDEA Nanosci, Spain.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Otero, R.
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain.
    Gallego, J. M.
    CSIC, Spain.
    Miranda, R.
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain.
    Ecija, D.
    IMDEA Nanosci, Spain.
    Efficient Lanthanide Catalyzed Debromination and Oligomeric Length-Controlled Ullmann Coupling of Aryl Halides2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 14, p. 8033-8041Article in journal (Refereed)
    Abstract [en]

    Lanthanide elements play a vital role in a broad range of high-tech applications, and there is an increasing interest in their catalytic activity, particularly in organo-metallics. However, their catalytic role on surfaces remains unexplored. Here, we present a scanning tunneling microscopy and density functional theory study of the debromination, contacting, and coupling of dibromine terphenyl species with Dy (f-block element) and Ag (d-block element) adatoms, respectively. We show that Dy debrominates the targeted species more efficiently than Ag adatoms at room temperature, promoting the formation of unprecedented C-Dy-C organo-metallic supramolecules versus C-Ag-C parallel chains for the Ag case. DFT calculations corroborate our results showing an almost spontaneous debromination process with Dy compared to Ag. Upon annealing, for samples containing Dy, the formation of C-Ag-C organometallic bonds and concomitant C-C coupling is inhibited, giving rise to a self-assembly of debrominated monomers, showing only a minority number of covalent dimes species. For samples without Dy covalent chains of irregular length are promoted. Our studies open new avenues for using lanthanide elements as efficient dehalogenation catalysts. Furthermore, we illustrate their potential as inhibitors of uncontrolled C-C coupling reactions, of great relevance for fine-tuning the length of polymeric compounds.

  • 23.
    Cirera, Borja
    et al.
    IMDEA Nanoscience, c/Faraday 9, Cantoblanco,Madrid, Spain.
    Giménez-Agulló, Nelson
    Institute of Chemical Research of Catalonia, Barcelona Institute of Science and Technology, Avinguda Pa¨ısos Catalans 16, Tarragona, Spain.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Martínez-Peña, Francisco
    IMDEA Nanoscience, c/Faraday 9, Cantoblanco,Madrid, Spain..
    Martin-Jimenez, Alberto
    IMDEA Nanoscience, c/Faraday 9, Cantoblanco,Madrid, Spain..
    Rodriguez-Fernandez, Jonathan
    Departamento de F´ısica de la Materia Condensada, Universidad Auto´noma de Madrid, c/Francisco Toma´s y Valiente.
    Pizarro, Ana M.
    IMDEA Nanoscience, c/Faraday 9, Cantoblanco,Madrid, Spain..
    Otero, Roberto
    IMDEA Nanoscience, c/Faraday 9, Cantoblanco, 28049 Madrid, Spain,Universidad Auto´noma de Madrid, c/Francisco Toma´s y Valiente.
    Gallego, José M.
    Instituto de Ciencia de Materiales de Madrid, c/ Sor Juana Ine´s de la Cruz 3, Cantoblanco,Madrid, Spain..
    Ballester, Pablo
    Institute of Chemical Research of Catalonia, Barcelona Institute of Science and Technology, Avinguda Pa¨ısos Catalans 16, Tarragona, Spain/Catalan Institutionfor Research and Advanced Studies, Passeig Lluis Companys 23, Barcelona, Spain..
    Galan-Mascaros, José R.
    Institute of Chemical Research of Catalonia, Barcelona Institute of Science and Technology, Avinguda Pa¨ısos Catalans 16, Tarragona, Spain/Catalan Institutionfor Research and Advanced Studies, Passeig Lluis Companys 23, Barcelona, Spain..
    Ecija, David
    IMDEA Nanoscience, c/Faraday 9, Cantoblanco, Madrid, Spain.
    Thermal selectivity of intermolecular versus intramolecular reactions on surfaces2016In: Nature Communications, E-ISSN 2041-1723, Vol. 7, no 11002Article in journal (Refereed)
    Abstract [en]

    On-surface synthesis is a promising strategy for engineering heteroatomic covalent nanoarchitectures with prospects in electronics, optoelectronics and photovoltaics. Here we report the thermal tunability of reaction pathways of a molecular precursor in order to select intramolecular versus intermolecular reactions, yielding monomeric or polymeric phthalocyanine derivatives, respectively. Deposition of tetra-aza-porphyrin species bearing ethyl termini on Au(111) held at room temperature results in a close-packed assembly. Upon annealing from room temperature to 275 °C, the molecular precursors undergo a series of covalent reactions via their ethyl termini, giving rise to phthalocyanine tapes. However, deposition of the tetra-aza-porphyrin derivatives on Au(111) held at 300 °C results in the formation and self-assembly of monomeric phthalocyanines. A systematic scanning tunnelling microscopy study of reaction intermediates, combined with density functional calculations, suggests a [2+2] cycloaddition as responsible for the initial linkage between molecular precursors, whereas the monomeric reaction is rationalized as an electrocyclic ring closure.

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  • 24.
    Cirera, Borja
    et al.
    IMDEA Nanosci, Spain.
    Trukhina, Olga
    University of Autonoma Madrid, Spain.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bottari, Giovanni
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain; University of Autonoma Madrid, Spain.
    Rodriguez-Fernandez, Jonathan
    University of Autonoma Madrid, Spain.
    Martin-Jimenez, Alberto
    IMDEA Nanosci, Spain.
    Islyaikin, Mikhail K.
    Ivanovo State University of Chemistry and Technology, Russia.
    Otero, Roberto
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain.
    Gallego, Jose M.
    CSIC, Spain.
    Miranda, Rodolfo
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain.
    Torres, Tomas
    IMDEA Nanosci, Spain; University of Autonoma Madrid, Spain; University of Autonoma Madrid, Spain.
    Ecija, David
    IMDEA Nanosci, Spain.
    Long-Range Orientational Self-Assembly, Spatially Controlled Deprotonation, and Off-Centered Metalation of an Expanded Porphyrin2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 40, p. 14129-14136Article in journal (Refereed)
    Abstract [en]

    Expanded porphyrins are large-cavity macro cycles with enormous potential in coordination chemistry, anion sensing, photodynamic therapy, and optoelectronics. In the last two decades, the surface science community has assessed the physicochemical properties of tetrapyrrolic-like macrocydes. However, to date, the sublimation, self-assembly and atomistic insights of expanded porphyrins on surfaces have remained elusive. Here, we show the self-assembly on Au(111) of an expanded aza-porphyrin, namely, an "expanded hemi-spatially-controlled porphyrazine", through a unique growth mechanism based on deprotonation long-range orientational self-assembly. Furthermore, a spatially controlled "writing" protocol on such self-assembled architecture is presented based on the STM tip-induced deprotonation of the inner protons of individual macrocydes. Finally, the capability of these surface-confined macrocydes to host lanthanide elements is assessed, introducing a novel off-centered coordination motif. The presented findings represent a milestone in the fields of porphyrinoid chemistry and surface science, revealing a great potential for novel surface patterning, opening new avenues for molecular level information storage, and boosting the emerging field of surface-confined coordination chemistry involving f-block elements.

  • 25.
    Esau, Derek
    et al.
    Queens Univ, Canada.
    Schuett, Fabian M.
    Ulm Univ, Germany.
    Varvaris, K. Liam
    Queens Univ, Canada.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Jacob, Timo
    Ulm Univ, Germany; Helmholtz Inst Ulm HIU Electrochem Energy Storage, Germany; KIT, Germany.
    Jerkiewicz, Gregory
    Queens Univ, Canada.
    Controlled-Atmosphere Flame Fusion Growth of Nickel Poly-oriented Spherical Single Crystals-Unraveling Decades of Impossibility2020In: Electrocatalysis, ISSN 1868-2529, E-ISSN 1868-5994, Vol. 11, no 1Article in journal (Refereed)
    Abstract [en]

    Experimental research using monocrystalline electrodes has been a hallmark of interfacial electrochemistry and electrocatalysis since 1980. However, it has been limited to mainly noble metals because of the challenges encountered when using non-noble metals. We report on the development of controlled-atmosphere flame fusion that enables the growth of spherical single crystals of non-noble metals in controlled gaseous atmosphere and without the formation of surface or bulk oxides. The set-up is used to grow nickel single crystals the structure of which is verified using Laue X-ray back-scattering and scanning electron microscopy (SEM). The equilibrium shape of the nickel single crystals calculated using Wulff construction agrees with the actual shape determined using SEM. Electrochemical measurements in aqueous NaOH solution using the monocrystalline Ni electrodes reveal cyclic voltammetry features unique to their surface structure. The methodology, transferrable to other metals, creates enormous research opportunities in interfacial electrochemistry, electrocatalysis, surface science, gas-phase catalysis, and corrosion science.

  • 26.
    Fritton, Massimo
    et al.
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Duncan, David A.
    Tech Univ Munich, Germany; Diamond Light Source, England.
    Deimel, Peter S.
    Tech Univ Munich, Germany.
    Rastgoo-Lahrood, Atena
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Allegretti, Francesco
    Tech Univ Munich, Germany.
    Barth, Johannes V.
    Tech Univ Munich, Germany.
    Heckl, Wolfgang M.
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lackinger, Markus
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    The Role of Kinetics versus Thermodynamics in Surface-Assisted Ullmann Coupling on Gold and Silver Surfaces2019In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 12, p. 4824-4832Article in journal (Refereed)
    Abstract [en]

    Surface-assisted Ullmann coupling is the workhorse of on-surface synthesis. Despite its obvious relevance, many fundamental and mechanistic aspects remain elusive. To shed light on individual reaction steps and their progression with temperature, temperature-programmed X-ray photoelectron spectroscopy (TP-XPS) experiments are performed for a prototypical model system. The activation of the coupling by initial dehalogenation is tracked by monitoring Br 3d core levels, whereas the C 1s signature is used to follow the emergence of metastable organometallic intermediates and their conversion to the final covalent products upon heating in real time. The employed 1,3,5-tris(4-bromophenyl)benzene precursor is comparatively studied on Ag(111) versus Au(111), whereby intermolecular bonds and network topologies are additionally characterized by scanning tunneling microscopy (STM). Besides the well-comprehended differences in activation temperatures for debromination, the thermal progression shows marked differences between the two surfaces. Debromination proceeds rapidly on Ag(111), but is relatively gradual on Au(111). While on Ag(111) debromination is well explained by first-order reaction kinetics, thermodynamics prevail on Au(111), underpinned by a close agreement between experimentally deduced and density functional theory (DFT) calculated reaction enthalpies. Thermodynamically controlled debromination on Au(111) over a large temperature range implies an unexpectedly long lifetime of surface-stabilized radicals prior to covalent coupling, as corroborated by TP-XPS of C is core levels. These insights are anticipated to play an important role regarding our ability to rationally synthesize atomically precise low-dimensional covalent nanostructures on surfaces.

  • 27.
    Fritton, Massimo
    et al.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Otte, Katrin
    Bavarian Acad Sci and Humanities, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Biswas, Pronay Kumar
    Univ Siegen, Germany.
    Heckl, Wolfgang M.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Schmittel, Michael
    Univ Siegen, Germany.
    Lackinger, Markus
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    The influence of ortho-methyl substitution in organometallic self-assembly - a comparative study on Cu(111) vs. Ag(111)2018In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 70, p. 9745-9748Article in journal (Refereed)
    Abstract [en]

    Metal surface-induced dehalogenation of precursors is known to initiate self-assembly of organometallic networks, where tectons are connected via carbon-metal-carbon (C-M-C) bonds. Even though reversibility of the C-M-C bonds facilitates structural equilibration, defects associated with highly bent organometallic linkages are still commonly observed. By introducing a steric hindrance to reduce the C-M-C bond angle flexibility, we find well ordered organometallic networks of an ortho-methyl substituted 1,3,5-tris(p-bromophenyl)-benzene analogue on Cu(111) after room-temperature (RT) deposition and on Ag(111) after annealing.

  • 28.
    Gottardi, Stefano
    et al.
    University of Groningen, Netherlands.
    Muller, Kathrin
    University of Groningen, Netherlands.
    Bignardi, Luca
    University of Groningen, Netherlands.
    Carlos Moreno-Lopez, Juan
    University of Groningen, Netherlands.
    Tuan Anh Pham; Ivashenko, Oleksii
    University of Groningen, Netherlands.
    Yablonskikh, Mikhail
    Sincrotrone Trieste Scpa, Italy.
    Barinov, Alexei
    Sincrotrone Trieste Scpa, Italy.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Rudolf, Petra
    University of Groningen, Netherlands.
    Stohr, Meike
    University of Groningen, Netherlands.
    Comparing Graphene Growth on Cu(111) versus Oxidized Cu(111)2015In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 2, p. 917-922Article in journal (Refereed)
    Abstract [en]

    The epitaxial growth of graphene on catalytically active metallic surfaces via chemical vapor deposition (CVD) is known to be one of the most reliable routes toward high-quality large-area graphene. This CVD-grown graphene is generally coupled to its metallic support resulting in a modification of its intrinsic properties. Growth on oxides is a promising alternative that might lead to a decoupled graphene layer. Here, we compare graphene on a pure metallic to graphene on an oxidized copper surface in both cases grown by a single step CVD process under similar conditions. Remarkably, the growth on copper oxide, a high-k dielectric material, preserves the intrinsic properties of graphene; it is not doped and a linear dispersion is observed close to the Fermi energy. Density functional theory calculations give additional insight into the reaction processes and help explaining the catalytic activity of the copper oxide surface.

  • 29.
    Grossmann, Lukas
    et al.
    Deutsches Museum, Museumsinsel 1, 80538 München, Germany. markus@lackinger.org; Technische Universität München, Physics Department, James-Franck-Strasse 1, 85748 Garching, Germany.
    Duncan, David A.
    Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK.
    Jarvis, Samuel P
    Lancaster University, Physics Department, Lancaster LA1 4YB, UK.
    Jones, Robert G
    University of Nottingham, Department of Physical Chemistry, School of Chemistry, Nottingham NG7 2RD, UK.
    De, Soumen
    Center of Micro and Nanochemistry and Engineering, Organische Chemie I, Universität Siegen, Adolf-Reichwein-Str. 2, 57068 Siegen, Germany.
    Rosén, Johanna
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Materials design.
    Schmittel, Michael
    Center of Micro and Nanochemistry and Engineering, Organische Chemie I, Universität Siegen, Adolf-Reichwein-Str. 2, 57068 Siegen, Germany.
    Heckl, Wolfgang M
    Deutsches Museum, Museumsinsel 1, 80538 München, Germany. markus@lackinger.org; Technische Universität München, Physics Department, James-Franck-Strasse 1, 85748 Garching, Germany.
    Björk, Jonas
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Materials design.
    Lackinger, Markus
    Deutsches Museum, Museumsinsel 1, 80538 München, Germany. markus@lackinger.org; Technische Universität München, Physics Department, James-Franck-Strasse 1, 85748 Garching, Germany.
    Evolution of adsorption heights in the on-surface synthesis and decoupling of covalent organic networks on Ag(111) by normal-incidence X-ray standing wave2022In: Nanoscale Horizons, ISSN 2055-6764, E-ISSN 2055-6756, Vol. 7, no 1, p. 51-62Article in journal (Refereed)
    Abstract [en]

    Structural characterization in on-surface synthesis is primarily carried out by Scanning Probe Microscopy (SPM) which provides high lateral resolution. Yet, important fresh perspectives on surface interactions and molecular conformations are gained from adsorption heights that remain largely inaccessible to SPM, but can be precisely measured with both elemental and chemical sensitivity by Normal-Incidence X-ray Standing Wave (NIXSW) analysis. Here, we study the evolution of adsorption heights in the on-surface synthesis and post-synthetic decoupling of porous covalent triazine-phenylene networks obtained from 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (TBPT) precursors on Ag(111). Room temperature deposition of TBPT and mild annealing to ~150 C result in full debromination and formation of organometallic intermediates, where the monomers are linked into reticulated networks by C-Ag-C bonds. Topologically identical covalent networks comprised of triazine vertices that are interconnected by biphenyl units are obtained by a thermally activated chemical transformation of the organometallic intermediates. Exposure to iodine vapor facilitates decoupling by intercalation of an iodine monolayer between the covalent networks and the Ag(111) surface. Accordingly, Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS) and NIXSW experiments are carried out for three successive sample stages: organometallic intermediates, covalent networks directly on Ag(111) and after decoupling. NIXSW analysis facilitates the determination of adsorption heights of chemically distinct carbon species, i.e. in the phenyl and triazine rings, and also for the organometallic carbon atoms. Thereby, molecular conformations are assessed for each sample stage. The interpretation of experimental results is informed by Density Functional Theory (DFT) calculations, providing a consistent picture of adsorption heights and molecular deformations in the networks that result from the interplay between steric hindrance and surface interactions. Quantitative adsorption heights, i.e. vertical distances between adsorbates and surface, provide detailed insight into surface interactions, but are underexplored in on-surface synthesis. In particular, the direct comparison with an in situ prepared decoupled state unveils the surface influence on the network structure, and shows that iodine intercalation is a powerful decoupling strategy.

  • 30.
    Grossmann, Lukas
    et al.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    King, Benjamin T.
    Univ Nevada, NV 89557 USA.
    Reichlmaier, Stefan
    Phys Elect GmbH, Germany.
    Hartmann, Nicolai
    Neaspec GmbH, Germany.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Heckl, Wolfgang M.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lackinger, Markus
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    On-surface photopolymerization of two-dimensional polymers ordered on the mesoscale2021In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 13, no 8, p. 730-736Article in journal (Refereed)
    Abstract [en]

    The use of solid supports and ultra-high vacuum conditions for the synthesis of two-dimensional polymers is attractive, as it can enable thorough characterization, often with submolecular resolution, and prevent contamination. However, most on-surface polymerizations are thermally activated, which often leads to high defect densities and relatively small domain sizes. Here, we have obtained a porous two-dimensional polymer that is ordered on the mesoscale by the two-staged topochemical photopolymerization of fluorinated anthracene triptycene (fantrip) monomers on alkane-passivated graphite surfaces under ultra-high vacuum. First, the fantrip monomers self-assemble into highly ordered monolayer structures, where all anthracene moieties adopt a suitable arrangement for photopolymerization. Irradiation with violet light then induces complete covalent cross-linking by [4+4] photocycloaddition to form a two-dimensional polymer, while fully preserving the long-range order of the self-assembled structure. The extent of the polymerization is confirmed by local infrared spectroscopy and scanning tunnelling microscopy characterization, in agreement with density functional theory calculations, which also gives mechanistic insights.

  • 31.
    Grossmann, Lukas
    et al.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Ringel, Eva
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Rastgoo-Lahrood, Atena
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    King, Benjamin T.
    Univ Nevada, NV 89557 USA.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Heckl, Wolfgang M.
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Opris, Dorina
    Empa, Switzerland.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Lackinger, Markus
    Deutsch Museum, Germany; Tech Univ Munich, Germany.
    Steering Self-Assembly of Three-Dimensional Iptycenes on Au(111) by Tuning Molecule-Surface Interactions2022In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 61, no 25, article id e202201044Article in journal (Refereed)
    Abstract [en]

    Self-assembly of three-dimensional molecules is scarcely studied on surfaces. Their modes of adsorption can exhibit far greater variability compared to (nearly) planar molecules that adsorb mostly flat on surfaces. This additional degree of freedom can have decisive consequences for the expression of intermolecular binding motifs, hence the formation of supramolecular structures. The determining molecule-surface interactions can be widely tuned, thereby providing a new powerful lever for crystal engineering in two dimensions. Here, we study the self-assembly of triptycene derivatives with anthracene blades on Au(111) by Scanning Tunneling Microscopy, Near Edge X-ray Absorption Fine Structure and Density Functional Theory. The impact of molecule-surface interactions was experimentally tested by comparing pristine with iodine-passivated Au(111) surfaces. Thereby, we observed a fundamental change of the adsorption mode that triggered self-assembly of an entirely different structure.

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  • 32.
    Hanke, Felix
    et al.
    Surface Science Research Centre, University of Liverpool, UK.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Structure and local reactivity of the Au(111) surface reconstruction2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 23Article in journal (Refereed)
    Abstract [en]

    The close-packed (111) surface of gold is well known to show a 22×√3 reconstruction on single nm lengths with a long-range herringbone pattern on scales of a few hundred nm. Here we investigate the local reconstruction using density functional theory and compare the results to scanning tunneling microscopy experiments. Moreover, we use hydrogen and fluorine as probe atoms to investigate changes in the ability of the Au(111) surface to catalyze the reactions involved in the formation of molecular nanostructures. We find a small variation of the reactivity across different surface sites and link those results to the local coordination environment of the face-centered-cubic (fcc), hexagonal-close-packed (hcp), and ridge regions. Finally, we scrutinize a commonly used approximation in density functional studies, namely that Au(111) is atomically flat and a perfect termination of the fcc lattice.

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  • 33.
    Hanke, Felix
    et al.
    Surface Science Research Centre, University of Liverpool, UK.
    Dyer, Matthew S.
    Surface Science Research Centre, University of Liverpool, UK.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Persson, Mats
    Surface Science Research Centre, University of Liverpool, UK.
    Structure and stability of weakly chemisorbed ethene adsorbed on low-index Cu surfaces: performance of density functionals with van der Waals interactions2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 42, p. 424217-424225Article in journal (Refereed)
    Abstract [en]

    We have investigated the performance of popular density functionals that include van der Waals interactions for the experimentally well-characterized problem of ethene (C(2)H(4)) adsorbed on the low-index surfaces of copper. This set of functionals does not only include three van der Waals density functionals-vdwDF-PBE, vdwDF-revPBE and optB86b-vdwDF-and two dispersion-corrected functionals-Grimme and TS-but also local and semi-local functionals such as LDA and PBE. The adsorption system of ethene on copper was chosen because it is a weakly chemisorbed system for which the vdW interactions are expected to give a significant contribution to the adsorption energy. Overall the density functionals that include vdW interactions increased substantially the adsorption energies compared to the PBE density functional but predicted the same adsorption sites and very similar C-C bonding distances except for two of the van der Waals functionals. The top adsorption site was predicted almost exclusively for all functionals on the (110), (100) and (111) surfaces, which is in agreement with experiment for the (110) surface but not for the (100) surface. On the (100) surface, all functionals except two van der Waals density functionals singled out the observed cross-hollow site from the calculated C-C bonding distances and adsorption heights. On the top sites on the (110) surface and the cross-hollow site on the Cu(100) surface, the ethene molecule was found to form a weak chemisorption bond. On the (111) surface, all functionals gave a C-C bonding distance and an adsorption height more typical for physisorption, in agreement with experiments.

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  • 34.
    Hellwig, Raphael
    et al.
    Tech Univ Munich, Germany.
    Uphoff, Martin
    Tech Univ Munich, Germany.
    Paintner, Tobias
    Tech Univ Munich, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ruben, Mario
    KIT, Sweden; Univ Strasbourg, France.
    Klappenberger, Florian
    Tech Univ Munich, Germany.
    Barth, Johannes V.
    Tech Univ Munich, Germany.
    Ho-Mediated Alkyne Reactions at Low Temperatures on Ag(111)2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 60, p. 16126-16135Article in journal (Refereed)
    Abstract [en]

    Low-temperature approaches to catalytic conversions promise efficiency, selectivity, and sustainable processes. Control over certain coupling reactions can be obtained via the pre-positioning of reactive moieties by self-assembly. However, in the striving field of on-surface synthesis atomistic precision and control remains largely elusive, because the employed coupling reactions proceed at temperatures beyond the thermal stability of the supramolecular templates. Here, utilizing scanning tunneling microscopy, we demonstrate terminal alkyne on-surface reactions mediated by Ho atoms at a weakly reactive Ag(111) substrate at lowtemperatures. Density functional theory calculations confirm the catalytic activity of the involved adatoms. Pre-deposited Ho induces alkyne dehydrogenation starting at substrate temperatures as low as 100 K. Ho arriving at molecularly pre-covered surfaces held at 130 and 200 K produces covalent enyne-linked dimers and initiates cyclotrimerization, respectively. Statistical product analysis indicates a two-step pathway for the latter, whereby the enyne intermediates influence the distribution of the products. High chemoselectivity results from the absence of cyclotetramerization and diyne-forming homocoupling. Our analysis indicates that mainly the arriving Ho adatoms enable the coupling. These findings support the concept of dynamic heterogeneity by single-atom catalysts and pave the way for alternative means to control on-surface reactions.

  • 35.
    Helmer, Pernilla
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Zhou, Jie
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Mohan, Roopathy
    Chemical Physics, Department of Physics, Chalmers University of Technology, Gothenburg.
    Wickman, Björn
    Chemical Physics, Department of Physics, Chalmers University of Technology, Gothenburg.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Investigation of 2D Boridene from First Principles and Experiments2022In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 32, no 14, article id 2109060Article in journal (Refereed)
    Abstract [en]

    Recently, a 2D metal boride - boridene - has been experimentally realized in the form of single-layer molybdenum boride sheets with ordered metal vacancies, through selective etching of the nanolaminated 3D parent borides (Mo2/3Y1/3)2AlB2 and (Mo2/3Sc1/3)2AlB2. The chemical formula of the boridene was suggested to be Mo4/3B2-xTz, where Tz denotes surface terminations. Here, the termination composition and material properties of Mo4/3B2-xTz from both theoretical and experimental perspectives are investigated. Termination sites are considered theoretically for termination species T = O, OH, and F, and the energetically favored termination configuration is identified at z = 2 for both single species terminations and binary termination mixes of different stoichiometries in ordered and disordered configurations. Mo4/3B2-xTz is shown to be dynamically stable for multiple termination stoichiometries, displaying semiconducting, semimetallic, or metallic behavior depending on how different terminations are combined. The approximate chemical formula of a freestanding film of boridene is attained as Mo1.33B1.9O0.3(OH)1.5F0.7 from X-ray photoelectron spectroscopy (XPS) analysis which, within error margins, is consistent with the theoretical results. Finally, metallic and additive-free Mo4/3B2-xTz shows high catalytic performance for the hydrogen evolution reaction, with an onset potential of 0.15 V versus the reversible hydrogen electrode.

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  • 36.
    Honkela, Maija
    et al.
    Aalto University, Finland.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Persson, Mats
    Surface Science Research Centre, University of Liverpool, UK.
    Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 16, p. 5849-5854Article in journal (Refereed)
    Abstract [en]

    The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).

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  • 37.
    Hu, Yong-Jie
    et al.
    Drexel Univ, PA 19104 USA.
    Tandoc, Christopher
    Drexel Univ, PA 19104 USA.
    Barsoum, Michel
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Structural and electronic properties of two-dimensional titanium carbo-oxides2023In: 2D Materials, E-ISSN 2053-1583, Vol. 10, no 1, article id 015019Article in journal (Refereed)
    Abstract [en]

    This work was inspired by new experimental findings where we discovered a two-dimensional (2D) material comprised of titanium-oxide-based one-dimensional (1D) sub-nanometer filaments. Preliminary results suggest that the 2D material contains considerable amounts of carbon, C, in addition to titanium, Ti, and oxygen, O. The aim of this study is to investigate the low-energy, stable atomic forms of 2D titanium carbo-oxides as a function of C content. Via a combination of first-principles calculations and an effective structure sampling scheme, the stable configurations of C-substitutions are comprehensively searched by templating different 2D TiO2 polymorphs and considering a two O to one C replacement scheme. Among the searched stable configurations, a structure where the (101) planes of anatase bound the top and bottom surfaces with a chemical formula of TiC1/4O3/2 was of particularly low energy. Furthermore, the variations in the electronic band structure and chemical bonding environments caused by the high-content C substitution are investigated via additional calculations using a hybrid exchange-correlation functional.

  • 38.
    Karlsson, Max
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Qin, Jiajun
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Niu, Kaifeng
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Luo, Xiyu
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Tsinghua Univ, Peoples R China.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Duan, Lian
    Tsinghua Univ, Peoples R China.
    Xu, Weidong
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Northwestern Polytech Univ, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Role of chloride on the instability of blue emitting mixed-halide perovskites2023In: FRONTIERS OF OPTOELECTRONICS, ISSN 2095-2759, Vol. 16, no 1, article id 37Article in journal (Refereed)
    Abstract [en]

    Although perovskite light-emitting diodes (PeLEDs) have seen unprecedented development in device efficiency over the past decade, they suffer significantly from poor operational stability. This is especially true for blue PeLEDs, whose operational lifetime remains orders of magnitude behind their green and red counterparts. Here, we systematically investigate this efficiency-stability discrepancy in a series of green- to blue-emitting PeLEDs based on mixed Br/Cl-perovskites. We find that chloride incorporation, while having only a limited impact on efficiency, detrimentally affects device stability even in small amounts. Device lifetime drops exponentially with increasing Cl-content, accompanied by an increased rate of change in electrical properties during operation. We ascribe this phenomenon to an increased mobility of halogen ions in the mixed-halide lattice due to an increased chemically and structurally disordered landscape with reduced migration barriers. Our results indicate that the stability enhancement for PeLEDs might require different strategies from those used for improving efficiency.

  • 39.
    Kawai, Shigeki
    et al.
    Namiki, Tsukuba, 305-0044 Ibaraki, Japan/Basel, Switzerland/ Honcho, Kawaguchi, 332-0012 Saitama, Japan.
    Foster, Adam S.
    Aalto University, Finland/Kanazawa University, Kanazawa Japan..
    Björkman, Torbjörn
    Aalto University/Åbo Akademi University, Finland..
    Nowakowska, Sylwia
    University of Basel,Switzerland.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Canova, Filippo Federici
    Aalto University, Finland.
    Gade, Lutz H.
    Universität Heidelberg, Germany.
    Jung, Thomas A.
    University of Basel, Switzerland/Paul Scherrer Institute, Switzerland..
    Meyer, Ernst
    University of Basel, Switzerland..
    Van der Waals interactions and the limits of isolated atom models at interfaces2016In: Nature Communications, E-ISSN 2041-1723, Vol. 7, article id 11559Article in journal (Refereed)
    Abstract [en]

    Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar–Xe, Kr–Xe and Xe–Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal–organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems.

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  • 40.
    Kepčija, Nenad
    et al.
    Technische Universität München, Germany.
    Zhang, Yi-Qi
    Technische Universität München, Germany.
    Kleinschrodt, Martin
    Technische Universität München, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Klyatskaya, Svetlana
    Karlsruhe Institute of Technology, Germany.
    Klappenberger, Florian
    Technische Universität München, Germany.
    Ruben, Mario
    Karlsruhe Institute of Technology, Germany.
    Barth, Johannes V.
    Technische Universität München, Germany.
    Steering On-Surface Self-Assembly of High-Quality Hydrocarbon Networks with Terminal Alkynes2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 8, p. 3987-3995Article in journal (Refereed)
    Abstract [en]

    The two-dimensional (2D) self-assembly of 1,3,5-triethynyl-benzene (TEB) and de novo synthesized 1,3,5-tris-(4-ethynylphenyl)benzene (Ext-TEB) on Ag(111) was investigated by means of scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Both 3-fold symmetric molecules form long-range ordered nanoporous networks featuring organizational chirality, mediated by novel, planar 6-fold cyclic binding motifs. The key interaction for the expression of the motifs is identified as C–H···π bonding. For Ext-TEB, an additional open-porous phase exists with the 3-fold motif. The nature of the underlying noncovalent bonding schemes is thoroughly analyzed by density functional theory (DFT) calculations including van der Waals corrections. The comparison of calculations focusing on isolated 2D molecular sheets and those including the substrate reveals the delicate balance between the attractive molecule–molecule interaction, mediated by both the terminal alkyne and the phenyl groups, and the molecule–substrate interaction responsible for the commensurability and the regularity of the networks. Comparison with bulk structures of similar molecules suggests that these strictly planar cyclic binding motifs appear only in 2D environments.

  • 41.
    Klappenberger, Florian
    et al.
    Technical University of Munich, Germany.
    Zhang, Yi-Qi
    Technical University of Munich, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Klyatskaya, Svetlana
    Karlsruhe Institute Technology, Germany.
    Ruben, Mario
    Karlsruhe Institute Technology, Germany; University of Strasbourg, France.
    Barth, Johannes V.
    Technical University of Munich, Germany.
    On-Surface Synthesis of Carbon-Based Scaffolds and Nanomaterials Using Terminal Alkynes2015In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 48, no 7, p. 2140-2150Article, review/survey (Refereed)
    Abstract [en]

    CONSPECTUS: The covalent linking of acetylene compounds is an important synthetic tool to control carbon carbon bond formation and has been extensively studied for more than a century. Notably, Glaser coupling and subsequently developed refined procedures present an important route for the fabrication of distinct carbon-based scaffolds incorporating units with both sp(2)- and sp-hybridizations, such as carbyne chains, or two-dimensional (2D) graphyne or graphdiyne networks. However, the realization of the envisioned regular low-dimensional compounds and nanoarchitectures poses formidable challenges when following conventional synthesis protocols in solution, which we briefly overview. Now, recent developments in on-surface synthesis establish novel means for the construction of tailored covalent nanostructures under ultrahigh vacuum conditions. Here we focus on the exploration of pathways utilizing interfacial synthesis with terminal alkynes toward the atomically precise fabrication of low-dimensional carbon-rich scaffolds and nanomaterials. We review direct, molecular-level investigations, mainly relying on scanning probe microscopy, providing atomistic insights into thermally activated reaction schemes, their special pathways and products. Using custom-made molecular units, the employed homocoupling, cyclotrimerization, cycloaddition, and radical cyclization processes indeed yield distinct compounds, extended oligomers or 2D networks. Detailed insights into surface interactions such as bonding sites or conformational adaptation, and specific reaction mechanisms, including hierarchic pathways, were gained by sophisticated density functional theory calculations, complemented by X-ray spectroscopy measurements. For the fabrication of regular nanostructures and architectures, it is moreover imperative to cope with spurious side reactions, frequently resulting in chemical diversity. Accordingly, we highlight measures for increasing chemo- and regioselectivity by smart precursor design, substrate templating, and external stimuli. The ensuing preorganization of functional groups and control of side reactions increases product yields markedly. Finally, the electronic band structures of selected cases of novel low-dimensional hydrocarbon materials accessible with the monomers employed to date are discussed with a specific focus on their differences to theoretically established graphyne- and graphdiyne-related scaffolds. The presented methodology and gained insights herald further advancements in the field, heading toward novel molecular compounds, low-dimensional nanostructures, and coherently reticulated polymeric layers, eventually presenting well-defined arrangements with specific carbon carbon bond sequencing and electronic characteristics. The functional properties of these or other foreseeable scaffolds and architectures bear significant prospects for a wide range of applications, for example, in nanoelectronics, photonics, or carbon-based technologies.

  • 42.
    Li, Qing
    et al.
    Soochow Univ, Peoples R China.
    Yang, Biao
    Soochow Univ, Peoples R China.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Zhong, Qigang
    Soochow Univ, Peoples R China; Justus Liebig Univ Giessen, Germany.
    Ju, Huanxin
    Univ Sci and Technol China, Peoples R China.
    Zhang, Junjie
    Soochow Univ, Peoples R China.
    Cao, Nan
    Soochow Univ, Peoples R China.
    Shi, Ziliang
    Soochow Univ, Peoples R China.
    Zhang, Haiming
    Soochow Univ, Peoples R China.
    Ebeling, Daniel
    Justus Liebig Univ Giessen, Germany.
    Schirmeisen, Andre
    Justus Liebig Univ Giessen, Germany.
    Zhu, Junfa
    Univ Sci and Technol China, Peoples R China.
    Chi, Lifeng
    Soochow Univ, Peoples R China.
    Hierarchical Dehydrogenation Reactions on a Copper Surface2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 19, p. 6076-6082Article in journal (Refereed)
    Abstract [en]

    Hierarchical control of chemical reactions is being considered as one of the most ambitious and challenging topics in modern organic chemistry. In this study, we have realized the one-by-one scission of the X-H bonds (X = N and C) of aromatic amines in a controlled fashion on the Cu(lll) surface. Each dehydrogenation reaction leads to certain metal-organic supramolecular structures, which were monitored in single-bond resolution via scanning tunneling microscopy and noncontact atomic force microscopy. Moreover, the reaction pathways were elucidated from X-ray photoelectron spectroscopy measurements and density functional theory calculations. Our insights pave the way for connecting molecules into complex structures in a more reliable and predictable manner, utilizing carefully tuned stepwise on-surface synthesis protocols.

  • 43.
    Li, Xuechao
    et al.
    Soochow Univ, Peoples R China.
    Niu, Kaifeng
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering. Soochow Univ, Peoples R China.
    Duan, Sai
    Fudan Univ, Peoples R China.
    Tang, Yanning
    Soochow Univ, Peoples R China.
    Hao, Zhengming
    Soochow Univ, Peoples R China.
    Xu, Zhichao
    Soochow Univ, Peoples R China.
    Ge, Haitao
    Soochow Univ, Peoples R China.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Zhang, Haiming
    Soochow Univ, Peoples R China.
    Xu, Xin
    Fudan Univ, Peoples R China.
    Chi, Lifeng
    Soochow Univ, Peoples R China.
    Pyridinic Nitrogen Modification for Selective Acetylenic Homocoupling on Au(111)2023In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed)
    Abstract [en]

    On-surface acetylenic homocoupling has been proposed to construct carbon nanostructures featuring sp hybrid-ization. However, the efficiency of linear acetylenic coupling is far from satisfactory, often resulting in undesired enyne products or cyclotrimerization products due to the lack of strategies to enhance chemical selectivity. Herein, we inspect the acetylenic homocou-pling reaction of polarized terminal alkynes (TAs) on Au(111) with bond-resolved scanning probe microscopy. The replacement of benzene with pyridine moieties significantly prohibits the cyclotrimerization pathway and facilitates the linear coupling to produce well-aligned N-doped graphdiyne nanowires. Combined with density functional theory calculations, we reveal that the pyridinic nitrogen modification substantially differentiates the coupling motifs at the initial C-C coupling stage (head-to-head vs head-to-tail), which is decisive for the preference of linear coupling over cyclotrimerization.

  • 44.
    Lin, Tao
    et al.
    Technical University of Munich, Germany.
    Zhang, Liding
    Technical University of Munich, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Chen, Zhi
    Karlsruhe Institute Technology, Germany.
    Ruben, Mario
    Karlsruhe Institute Technology, Germany; University of Strasbourg, France.
    Barth, Johannes V.
    Technical University of Munich, Germany.
    Klappenberger, Florian
    Technical University of Munich, Germany.
    Terminal Alkyne Coupling on a Corrugated Noble Metal Surface: From Controlled Precursor Alignment to Selective Reactions2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 62, p. 15588-15593Article in journal (Refereed)
    Abstract [en]

    Surface-templated covalent coupling of organic precursors currently emerges as a promising route to the atom-precise fabrication of low-dimensional carbon materials. Here, we investigate the adsorption and the coupling reactions of 4,4-diethynyl-1,1:4,1-terphenyl on Au(110) under ultra-high vacuum conditions by using scanning tunneling microscopy combined with density functional theory and kinetic Monte Carlo calculations. Temperature treatment induces both 1,2,4-asymmetric cyclotrimerization and homocoupling, resulting in various reaction products, including a previously unreported, surface-templated H-shaped pentamer. Our analysis of the temperature-dependent relative product abundances unravels that 1,2,4-trimerization and homocoupling proceed via identical intermediate species with the final products depending on the competition of coupling to a third monomer versus dehydrogenation. Our study sheds light on the control of coupling reactions by corrugated surfaces and annealing protocols.

  • 45.
    Lischka, Matthias
    et al.
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Fritton, Massimo
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Eichhorn, Johanna
    Tech Univ Munich, Germany; Deutsch Museum, Germany.
    Vyas, Vijay S.
    Max Planck Inst Solid State Res, Germany; Marquette Univ, WI 53233 USA.
    Strunskus, Thomas
    Christian Albrechts Univ Kiel, Germany.
    Lotsch, Bettina V.
    Max Planck Inst Solid State Res, Germany; Nanosyst Initiat Munich, Germany; Ctr NanoSci, Germany; Univ Munich LMU, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Heckl, Wolfgang M.
    Tech Univ Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Ctr NanoSci, Germany.
    Lackinger, Markus
    Tech Univ Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Ctr NanoSci, Germany.
    On-Surface Polymerization of 1,6-Dibromo-3,8-diiodpyrene-A Comparative Study on Au(111) Versus Ag(111) by STM, XPS, and NEXAFS2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 11, p. 5967-5977Article in journal (Refereed)
    Abstract [en]

    The surface chemistry of 1,6-dibromo-3,8-diiodopyrene (Br2I2Py) is comparatively studied on Au(111) versus Ag(111) surfaces under ultrahigh vacuum conditions by a combination of high-resolution scanning tunneling microscopy (STM) and X-ray spectroscopy. The chemical state of the molecular networks, that is, the dehalogenation and the possible formation of organometallic intermediates, is assessed by X-ray photoelectron spectroscopy. In addition, pyrene tilt angles are quantified by carbon K-edge near edge X-ray absorption fine structure experiments. Upon room-temperature (RT) deposition of Br2I2Py onto Au(111), only partial deiodination was found, and STM revealed the coexistence of ordered arrangements of both intact Br2I2Py molecules and organometallic dimers as well as few larger aggregates. Further annealing to 100 C triggered full deiodination followed by the formation of organometallic chains of otherwise still brominated molecules. By contrast, on Ag(111), iodine is fully and bromine is partly dissociated upon RT deposition of Br2I2Py. The initially disordered organometallic aggregates can be reorganized into more ordered structures by mild annealing at 125 degrees C. Yet, the conversion of the organometallic intermediates into well-defined cross-linked quasi 2D covalent networks was neither possible on Au(111) nor on Ag(111). This is attributed to the large steric hindrance in the covalently linked adsorbed state.

  • 46.
    Malina, Tomas
    et al.
    Karolinska Inst, Sweden.
    Hamawandi, Bejan
    KTH Royal Inst Technol, Sweden.
    Toprak, Muhammet S.
    KTH Royal Inst Technol, Sweden.
    Chen, Lin
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Zhou, Jie
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.
    Fadeel, Bengt
    Karolinska Inst, Sweden.
    Tuning the transformation and cellular signaling of 2D titanium carbide MXenes using a natural antioxidant2024In: Matter, ISSN 2590-2393, E-ISSN 2590-2385, Vol. 7, no 1Article in journal (Refereed)
    Abstract [en]

    2D titanium carbide (Ti3C2) MXenes have emerged as promising candidates for biomedical applications. However, the biological properties of these materials are poorly understood. Moreover, MXenes are prone to oxidation under ambient conditions. Here, we show that glutathione (GSH), a natural antioxidant present in millimolar concentrations in the cytosol of most cells, protects MXenes from oxidation in aqueous suspensions while preserving the biocompatibility of the material. Reactive molecular dynamics (RMD) simulations confirm that GSH protects MXenes. Moreover, we provide evidence of the intracellular biotransformation of Ti3C2 MXenes to the rutile form of TiO2, and we show that GSH tunes the transformation process, resulting in the secretion of pro -inflammatory interleukin (IL) -1b through a non -canonical, elastase-dependent pathway. These results are important because they shed new light on the biotransformation of Ti3C2 MXenes and its ramifications for cellular signaling.

  • 47.
    Matena, Manfred
    et al.
    Department of Physics, University of Basel, Basel, Switzerland, Donostia International Physics Center, San Sebastian, Spain .
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. Surface Science Research Centre, Department of Chemistry, University of Liverpool, Liverpool, United Kingdom.
    Wahl, Markus
    Department of Physics, University of Basel, Basel, Switzerland.
    Lee, Tien-Lin
    European Synchrotron Radiation Facility, Grenoble, France.
    Zegenhagen, Jörg
    European Synchrotron Radiation Facility, Grenoble, France.
    Gade, Lutz H.
    Anorganisch-Chemisches Institut, Universität Heidelberg, Heidelberg, Germany.
    Jung, Thomas A.
    Department of Physics, University of Basel, Basel, Switzerland, Laboratory for Micro- and Nanotechnology, Villigen, Switzerland.
    Persson, Mats
    Surface Science Research Centre, University of Liverpool, UK, Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Stöhr, Meike
    Department of Physics, University of Basel, Basel, Switzerland, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    On-surface synthesis of a two-dimensional porous coordination network: Unraveling adsorbate interactions2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, p. 125408-125415Article in journal (Refereed)
    Abstract [en]

    We present a detailed experimental and theoretical characterization of the adsorption of the perylene derivative 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) on Cu(111) and compare it to its threefold dehydrogenated derivative 3deh-DPDI, which forms in a surface reaction upon annealing. While DPDI itself does not give rise to long-range ordered structures due to lack of appropriate functional groups, 3deh-DPDI acts as an exoligand in a Cu-coordinated honeycomb network on Cu(111). The main focus of this work lies on the analysis of intermolecular and molecule-substrate interactions by combining results from scanning tunneling microscopy, x-ray photoelectron spectroscopy, x-ray standing wave measurements, and density functional theory. We show, in particular, that the interactions between metal atoms and organic ligands effectively weaken the molecule-surface interactions for 3deh-DPDI leading to an increase in molecule-substrate distances compared to the DPDI precursor. Our experimental findings also shed light on the applicability of current theories, namely van der Waals corrections to density functional theory.

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  • 48.
    Matena, Manfred
    et al.
    University of Basel, Switzerland.
    Stöhr, Meike
    University of Basel, Switzerland.
    Riehm, Till
    University of Heidelberg, Germany.
    Björk, Jonas
    University of Liverpool, UK.
    Martens, Susanne
    University of Heidelberg, Germany.
    Dyer, Matthew S.
    University of Liverpool, UK.
    Persson, Mats
    University of Liverpool, UK.
    Lobo-Checa, Jorge
    University of Basel, Switzerland.
    Müller, Kathrin
    Paul-Scherrer-Institute, Villigen, Switzerland.
    Enache, Mihaela
    University of Basel, Switzerland.
    Wadepohl, Hubert
    University of Heidelberg, Germany.
    Zegenhagen, Jörg
    European Synchrotron Radiation Facility, Grenoble, France.
    Jung, Thomas A.
    Paul-Scherrer-Institute, Villigen, Switzerland.
    Gade, Lutz H.
    University of Heidelberg, Germany.
    Aggregation and contingent metal/surface reactivity of 1,3,8,10-tetraazaperopyrene (TAPP) on Cu(111)2010In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 7, p. 2079-2091Article in journal (Refereed)
    Abstract [en]

    The structural chemistry and reactivity of 1,3,8,10-tetraazaperopyrene (TAPP) on Cu(111) under ultra-high-vacuum (UHV) conditions has been studied by a combination of experimental techniques (scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy, XPS) and DFT calculations. Depending on the deposition conditions, TAPP forms three main assemblies, which result from initial submonolayer coverages based on different intermolecular interactions: a close-packed assembly similar to a projection of the bulk structure of TAPP, in which the molecules interact mainly through van der Waals (vDW) forces and weak hydrogen bonds; a porous copper surface coordination network; and covalently linked molecular chains. The Cu substrate is of crucial importance in determining the structures of the aggregates and available reaction channels on the surface, both in the formation of the porous network for which it provides the Cu atoms for surface metal coordination and in the covalent coupling of the TAPP molecules at elevated temperature. Apart from their role in the kinetics of surface transformations, the available metal adatoms may also profoundly influence the thermodynamics of transformations by coordination to the reaction product, as shown in this work for the case of the Cu-decorated covalent poly(TAPP-Cu) chains.

  • 49.
    Medeiros, Paulo V. C.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Müller, Kathrin
    Zernike Institute for Advanced Materials, University of Groningen, The Netherlands.
    Jung, Thomas A.
    Laboratory for Micro- and Nanotechnology, Paul-Scherrer-Institute, Switzerland.
    Gade, Lutz H.
    Anorganisch-Chemisches Institut, Universität Heidelberg, Germany.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
    Stöhr, Meike
    Zernike Institute for Advanced Materials, University of Groningen, The Netherlands.
    Self-assembly of a DPDI+PTCDA mixed layer on Ag(111): Theory and experimentsManuscript (preprint) (Other academic)
    Abstract [en]

    We present a combined experimental and theoretical investigation of the self-assembly of a binary mixture of 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) molecules on Ag(111). At a 1:1 ratio, the two molecules intermix to form a long-range ordered bimolecular network stabilized by intermolecular hydrogen bonding. We show, by means of low energy electron diffraction (LEED) measurements, that the self-assembled network is commensurate with the underlying silver surface. Scanning tunneling microscope (STM) measurements and density functional theory (DFT) calculations are combined to unravel the structural configuration of the system. Core-level binding energy shifts for the 1s levels of the O atoms, obtained from both X-ray photoelectron spectroscopy (XPS) measurements and DFT simulations, are reported and compared. Our DFT calculations allow the investigation of the interplay between molecule-molecule and molecule-surface interactions in the network. Our combined experimental-theoretical approach allows a precise characterization of the structural and electronic properties of the studied system.

  • 50.
    Medeiros, Paulo V. C.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 4, p. 041407-1-041407-4Article in journal (Refereed)
    Abstract [en]

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

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