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| 3. |
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| 5. |
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| 6. |
- Bird, D. M., et al.
(författare)
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Dynamics of the spin transition in the adsorption of hydrogen atoms on metals
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 566-568:1-3 part 2, s. 761-766
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Tidskriftsartikel (refereegranskat)abstract
- The time-dependent, mean-field Newns-Anderson model is solved in the wide-band limit. Equations for the time-evolution of the occupation of the spin-dependent adsorbate levels and for the rate of non-adiabatic energy transfer from adsorbate to substrate are derived. Numerical solutions are obtained in the region of space close to the transition point between spin-polarised and non-polarised ground states, for model parameters that correspond to an H-atom incident on the Cu(111) surface. Away from the spin transition the non-adiabatic energy transfer is in close agreement with the nearly-adiabatic limit. Near the transition, non-adiabatic effects are large and the nearly-adiabatic approximation fails.
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| 7. |
- Bjork, J., et al.
(författare)
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STM fingerprint of molecule-adatom interactions in a self-assembled metal-organic surface coordination network on Cu(111)
- 2010
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:31, s. 8815-8821
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
- Dalmar, Abdirisak Ahmed, et al.
(författare)
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Rebuilding research capacity in fragile states : the case of a Somali-Swedish global health initiative
- 2017
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Ingår i: Global Health Action. - Abingdon : Informa UK Limited. - 1654-9716 .- 1654-9880. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an initiative to revive the previous Somali-Swedish Research Cooperation, which started in 1981 and was cut short by the civil war in Somalia. A programme focusing on research capacity building in the health sector is currently underway through the work of an alliance of three partner groups: six new Somali universities, five Swedish universities, and Somali diaspora professionals. Somali ownership is key to the sustainability of the programme, as is close collaboration with Somali health ministries. The programme aims to develop a model for working collaboratively across regions and cultural barriers within fragile states, with the goal of creating hope and energy. It is based on the conviction that health research has a key role in rebuilding national health services and trusted institutions.
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| 10. |
- Donovan, P., et al.
(författare)
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Unexpected Deformations Induced by Surface Interaction and Chiral Self-Assembly of Co-II-Tetraphenylporphyrin (Co-TPP) Adsorbed on Cu(110): A Combined STM and Periodic DFT Study
- 2010
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Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 16:38, s. 11641-11652
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Tidskriftsartikel (refereegranskat)abstract
- In a combined scanning tunnelling microscopy (STM) and periodic density functional theory (DFT) study, we present the first comprehensive picture of the energy costs and gains that drive the adsorption and chiral self-assembly of highly distorted Co-II-tetraphenylporphyrin (Co-TPP) conformers on the Cu(110) surface. Periodic, semi-local DFT calculations reveal a strong energetic preference for Co-TPP molecules to adsorb at the short-bridge site when organised within a domain. At this adsorption site, a substantial chemical interaction between the molecular core and the surface causes the porphyrin macrocycle to accommodate close to the surface and in a flat geometry, which induces considerable tilting distortions in the phenyl groups. Experimental STM images can be explained in terms of these conformational changes and adsorption-induced electronic effects. For the ordered structure we unambiguously show that the substantial energy gain from the molecule surface interaction recuperates the high cost of the induced molecular and surface deformations as compared with gas phase molecules. Conversely, singly adsorbed molecules prefer a long-bridge adsorption site and adopt a non-planar, saddle-shape conformation. By using a van der Waals density functional correction scheme, we found that the intermolecular pi-pi interactions make the distorted conformer more stable than the saddle conformer within the organic assembly. These interactions drive supramolecular assembly and also generate chiral expression in the system, pinning individual molecules in a propeller-like conformation and directing their assembly along non-symmetric directions that lead to the coexistence of mirror-image chiral domains. Our observations reveal that a strong macrocycle surface interaction can trigger and stabilise highly unexpected deformations of the molecular structure and thus substantially extend the range of chemistries possible within these systems.
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| 11. |
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| 12. |
- Dyer, M. S., et al.
(författare)
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The nature of the observed free-electron-like state in a PTCDA monolayer on Ag(111)
- 2010
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- A free-electron-like band has recently been observed in a monolayer of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) molecules on Ag(111) by two-photon photoemission (Schwalb et al 2008 Phys. Rev. Lett. 101 146801) and scanning tunneling spectroscopy (Temirov et al 2006 Nature 444 350). Using density functional theory calculations, we find that the observed free-electron-like band originates from the Shockley surface state band being dramatically shifted up in energy by the interaction with the adsorbed molecules, while it also acquires a substantial admixture with a molecular band.
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| 13. |
- Dyer, M. S., et al.
(författare)
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Understanding the Interaction of the Porphyrin Macrocycle to Reactive Metal Substrates: Structure, Bonding, and Adatom Capture
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 5:3, s. 1831-1838
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the absorption and conformation of free-base porphines on Cu(110) using STM, reflection absorption infrared spectroscopy, and periodic DFT calculations in order to understand how the central polypyrrole macrocycle, common to all porphyrins, interacts with a reactive metal surface. We find that,the-macrocycle forms a chemisorption bond with the surface,, arising from electron donation into down-shifted, and nearly degenerate unoccupied porphine orbitals accompanied with electron back-donation from molecular pi-orbitals. Our calculations show that van der Waals interactions give rise to an overall Increase in the adsorption energy but only minor changes in the adsorption geometry and electronic structure. In addition, we observe copper adatoms being weakly attracted to adsorbed porphines at specific molecular sites. These results provide important insights into porphyrin-surface interactions that ultimately, will govern the design of robust surface mounted molecular devices based on this important class of molecules.
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| 14. |
- Fatayer, Shadi, et al.
(författare)
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Reorganization energy upon charging a single molecule on an insulator measured by atomic force microscopy
- 2018
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 13:5, s. 376-380
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular single-electron transfer on electrically insulating films is a key process in molecular electronics 1-4 and an important example of a redox reaction 5,6 . Electron-transfer rates in molecular systems depend on a few fundamental parameters, such as interadsorbate distance, temperature and, in particular, the Marcus reorganization energy 7 . This crucial parameter is the energy gain that results from the distortion of the equilibrium nuclear geometry in the molecule and its environment on charging 8,9 . The substrate, especially ionic films 10 , can have an important influence on the reorganization energy 11,12 . Reorganization energies are measured in electrochemistry 13 as well as with optical 14,15 and photoemission spectroscopies 16,17 , but not at the single-molecule limit and nor on insulating surfaces. Atomic force microscopy (AFM), with single-charge sensitivity 18-22 , atomic-scale spatial resolution 20 and operable on insulating films, overcomes these challenges. Here, we investigate redox reactions of single naphthalocyanine (NPc) molecules on multilayered NaCl films. Employing the atomic force microscope as an ultralow current meter allows us to measure the differential conductance related to transitions between two charge states in both directions. Thereby, the reorganization energy of NPc on NaCl is determined as (0.8 ± 0.2) eV, and density functional theory (DFT) calculations provide the atomistic picture of the nuclear relaxations on charging. Our approach presents a route to perform tunnelling spectroscopy of single adsorbates on insulating substrates and provides insight into single-electron intermolecular transport.
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| 15. |
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| 16. |
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| 17. |
- Forster, M., et al.
(författare)
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Assembly of Chiral Amino-Acids at Surfaces from a Single Molecule Perspective: Proline on Cu(110)
- 2011
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 54:1-4, s. 13-19
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Tidskriftsartikel (refereegranskat)abstract
- We present a molecule-by-molecule mapping of an amino-acid monolayer on a Cu(110) surface in which individual molecular configuration, bonding and adsorption footprints are identified. This detailed mapping provides direct evidence that the (4 x 2) structures of enantiopure and racemic proline are governed by a strict heterochiral adsorption footprint template. For the racemic system this has an interesting consequence, namely that it leads to a 2-D random solid solution, a situation that is rarely encountered in 3-D.
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| 18. |
- Forster, M., et al.
(författare)
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Mapping Complex Chiral Adlayers: A Truly Random 2-D Solid Solution of (RS)-3-Pyrroline-2-Carboxylic Acid on Cu(110)
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:4, s. 1180-1185
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The characterization of chiral molecular adlayers remains a considerable challenge, ultimately requiring detailed knowledge of the molecular chirality, the chemical form, molecular orientation, and interaction with the surface for each molecule within the assembly. In this work, we show that the (4 x 2) organization of a racemic mixture of the amino acid derivative 3-pyrroline-2-carboxylic acid (PCA) on Cu(110) may be analyzed at the single-molecule level in which the molecular chirality and adsorption footprints of each molecule are identified. Such a detailed mapping reveals the surprising outcome that within the racemic (4 x 2) organization the adlayer does not form either the 2-D racemic compound or racemic conglomerate. Instead, both the molecular chirality and adsorption footprints are randomly distributed, creating a truly random solid solution in which both molecular chirality and footprint chirality are scrambled.
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| 19. |
- Forster, M., et al.
(författare)
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Probing Conformer and Adsorption Footprint Distributions at the Single-Molecule Level in a Highly Organised Amino-Acid Assembly of (S)-Proline on Cu(110)
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:29, s. 10173-10181
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Tidskriftsartikel (refereegranskat)abstract
- Establishing the nanoscale details of organized amino acid assemblies at surfaces is a major challenge in the field of organic-inorganic interfaces. Here, we show that the dense (4 x 2) overlayer of the amino acid, (S)-proline on a Cu(110) surface can be explored at the single-molecule level by scanning tunneling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), and periodic density functional theory (DFT) calculations. The combination of experiment and theory, allied with the unique structural rigidity of proline, enables the individual conformers and adsorption footprints adopted within the organized assembly to be determined. Periodic DFT calculations find two energetically favorable molecular conformations, projecting mirror-image chiral adsorption footprints at the surface. These two forms can be experimentally distinguished since the positioning of the amino group within the pyrrolidine ring leads each chiral footprint and associated conformer to adopt very different ring orientations, producing distinct contrasts in the STM images. DFT modeling shows that the two conformers can generate eight possible (4 x 2) overlayers with a variety of adsorption footprint arrangements. STM images simulated for each structural model enables a direct comparison to be made with the experiment and narrows the (4 x 2) overlayer to one specific structural model in which the juxtaposition of molecules leads to the formation of one-dimensional hydrogen bonded prolate chains directed along the [1 (1) over bar0] direction.
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| 20. |
- Forster, M., et al.
(författare)
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Tailoring Homochirality at Surfaces: Going Beyond Molecular Handedness
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:40, s. 15992-16000
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Tidskriftsartikel (refereegranskat)abstract
- Chirality can be bestowed upon a surface by the adsorption of molecules and is usually discussed in terms of the molecular handedness. However, the adsorption process often leads to a new manifestation of chirality in the form of the adsorption footprint, which can also be chiral and generate mirror-images in 2-D. Therefore, in describing the chirality of the interface, one must consider both the handedness and the adsorption 'footedness' of the system. Specifically, the creation of a truly homochiral surface must ensure that a single chirality is expressed for each aspect, and requires not only the control of molecule handedness but also direct control over footedness. Here, we demonstrate the ability to engineer homochiral footedness by a structural modification of enantiopure (S)-proline, which normally creates a (4 x 2) organization on a Cu(110) surface with heterochiral footedness. This modification of proline via the addition of a double bond within the pyrrolidine ring, yielding 3-pyrroline-2-carboxylic acid (PCA), is sufficient to drive the footprints of the entire (4 x 2) assembly from heterochiral to homochiral, leading to the creation of a truly homochiral interface The effects of modifications upon the footprint arrangements were characterized at the single-molecule level by scanning tunnelling microscopy, reflection absorption infrared spectroscopy and periodic density functional theory calculations. The control of adsorption footprints is not only pivotal to tailoring chirality at surfaces but also plays a key role in dictating the organization, the outward facing functionalities and the response of the organic-inorganic interface.
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| 21. |
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| 22. |
- Gustafsson, Jan-Eric, 1949, et al.
(författare)
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School, Learning and Mental Health : A systematic review
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rapporten presenterar resultaten från en systematisk översikt av forskning om skola, lärande och barns psykiska hälsa. Kungliga Vetenskapsakademiens Hälsoutskottet har givit uppdraget att genomföra en sådan översikt till en arbetsgrupp som har arbetat med uppdraget från hösten 2008 till mars 2009. Det första syftet med översikten är att genomföra en kartläggning av forskning inom det breda fält som behandlar frågor om skola, lärande och barns och ungdomars psykiska hälsa. Det andra syftet är att genomföra en narrativ syntes av forskning som undersökt orsaksförhållanden mellan psykisk hälsa å ena sidan och skolresultat och lärande å den andra sidan. Det tredje syftet är att redovisa resultat från forskning som har studerat svenska barns och ungdomars erfarenheter och upplevelser av skola och undervisningssituationer. För att uppnå de första två syftena genomfördes systematiska litteratursökningar i bibliografiska databaser av artiklar publicerade i vetenskapliga internationella tidskrifter inom olika discipliner. Det tredje syftet undersöktes med litteratursökningar av kvalitativa svenska studier i bibliografiska databaser. Slutsatser På grundval dels av kartläggningen av forskning om skola, lärande och psykisk hälsa, dels av de två fördjupade översikterna kan följande slutsatser dras: • Omfattningen av forskning som undersöker relationerna mellan olika aspekter av skola och psykisk hälsa är begränsad och i synnerhet gäller detta forskning som undersöker organisationsfaktorer och undervisnings-faktorer, aktiviteter, läroplaners utformning, resurser, specialpedagogiskt stöd, och olika former av betyg och bedömning. • Tidiga svårigheter i skolan och i synnerhet läs- och skrivsvårigheter kan orsaka internaliserande och externaliserande psykiska problem. • Svårigheter i skola och psykiska problem tenderar att vara stabila över tid. • Skolrelaterade hälsoproblem tenderar att minska när eleverna börjar på gymnasiet och får tillgång till nya områden av aktiviteter, roller och valmöjligheter. • Att genomföra stora ansträngningar utan att detta leder till resultat är relaterat till utveckling av depression. Problem i skolan med skolresultat och prestationer orsakar inter-naliserande symptom för flickor under tonåren. • Det finns samband mellan olika typer av psykiska problem och de är också relaterade till ett brett spektrum av somatiska och psykosomatiska symptom. • Internaliserande och externaliserande psykiska problem har negativa effekter på skolprestationer genom mekanismer som är delvis ålders- och genusspecifika. • Kompetenser och prestationer i skolan är relaterade till psykisk hälsa. • Goda resultat i skolan har en positiv effekt på självuppfattning. • En god självuppfattning bidrar inte direkt till bättre resultat, men andra faktorer som är relaterade till självuppfattning (motivation och upplevd inre/yttre kontroll) påverkar lärande och resultat • Relationer med klasskamrater och lärare bidrar till processer som kopplar skolmisslyckande till psykisk ohälsa. Relationer med kamrater och lärare kan också skydda mot utvecklingen av psykiska problem. • Jämförelser med klasskamrater påverkar självuppfattningen, med effekter som varierar beroende på gruppsammansättning och typ av skola.
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| 23. |
- Hanke, F., et al.
(författare)
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Heat-to-Connect: Surface Commensurability Directs Organometallic One-Dimensional Self-Assembly
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 5:11, s. 9093-9103
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Tidskriftsartikel (refereegranskat)abstract
- Recent experiments demonstrated the assembly of unfunctionalized porphyrin molecules into organometallic wires on the Cu(110) surface through the formation of stable C-Cu-C bonds involving Cu adatoms. The remarkable properly of the observed structures is that they adopt a dear direction, despite the lack of functional ligands to direct the assembly. Here we use density functional theory calculations and scanning tunneling microscopy to clarify the mechanism for the highly one-dimensional assembly of the observed nanostructures. An energetic preference for the formation of C-Cu-C bonds is found In several lattice directions, but self-assembly critically relies on the commensurability of appropriate adsorption sites for the Cu atoms involved-in the coupling. The experimentally observed structures arise from a geometric self-limitation of the assembly process, which proceeds in the energetically and geometrically most preferred direction. A further extension of the structure in the orthogonal dimension to form 2D assemblies is prevented by the lattice mismatch between the repeat lengths in the and directions of the underlying (110) lattice and the apparent rigidity of the molecules involved. However, the fusing of two parallel chains is geometrically allowed and leads to some of the energetically most favorable configurations. Finally, the role of van der Waals forces is investigated for the covalent couplings and chemisorbed interactions found in this system.
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| 24. |
- Hanke, F., et al.
(författare)
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Structure and stability of weakly chemisorbed ethene adsorbed on low-index Cu surfaces: performance of density functionals with van der Waals interactions
- 2012
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:42, s. Article Number: 424217 -
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the performance of popular density functionals that include van der Waals interactions for the experimentally well-characterized problem of ethene (C2H4) 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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| 25. |
- Haq, S., et al.
(författare)
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Clean Coupling of Unfunctionalized Porphyrins at Surfaces To Give Highly Oriented Organometallic Oligomers
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:31, s. 12031-12039
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Tidskriftsartikel (refereegranskat)abstract
- The direct coupling of complex, functional organic molecules at a surface is one of the outstanding challenges in the road map to future molecular devices. Equally demanding is to meet this challenge without recourse to additional functionalization of the molecular building blocks and via clean surface reactions that leave no surface contamination. Here, we demonstrate the directional coupling of unfunctionalized porphyrin molecules-large aromatic multifunctional building blocks-on a single crystal copper surface, which generates highly oriented one-dimensional organometallic macromolecular nanostructures (wires) in a reaction which generates gaseous hydrogen as the only byproduct. In situ scanning tunneling microscopy and temperature programmed desorption, supported by theoretical modeling, reveal that the process is driven by C-H bond scission and the incorporation of copper atoms in between the organic components to form a very stable organocopper oligomer comprising organometallic edge-to-edge porphyrin-Cu-porphyrin connections on the surface that are unprecedented in solution chemistry. The hydrogen generated during the reaction leaves the surface and, therefore, produces no surface contamination. A remarkable feature of the wires is their stability at high temperatures (up to 670 K) and their preference for 1D growth along a prescribed crystallographic direction of the surface. The on-surface formation of directional organometallic wires that link highly functional porphyrin cores via direct C-Cu-C bonds in a single-step synthesis is a new development in surface-based molecular systems and provides a versatile approach to create functional organic nanostructures at surfaces.
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| 26. |
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| 27. |
- Honkela, M. L., et al.
(författare)
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Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces
- 2012
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 14:16, s. 5849-5854
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 28. |
- Inganaes, Olle, et al.
(författare)
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Alternating fluorene copolymer-fullerene blend solar cells
- 2005
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Ingår i: Optical Science and Engineering. ; 99, s. 387-402
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Tidskriftsartikel (refereegranskat)abstract
- We present a new class of alternating fluorene copolymers, which can be combined with a fullerene acceptor, to make polymer blends suitable for photovoltaic energy conversion. By choice of comonomers in the polymer, it is possible to engineer the optical absorption spectrum and to cover the wavelength range down to 900 nm. The transport properties of the polymers investigated so far are competitive with other polymers used in polymer solar cells and the mixing of polymers with acceptors in the form of fullerenes is extensive. These polymers are therefore of interest in the future developments of high-performance polymer solar cells. [on SciFinder (R)]
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| 29. |
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| 30. |
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| 31. |
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| 32. |
- Kumagai, T., et al.
(författare)
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Controlling intramolecular hydrogen transfer in a porphycene molecule with single atoms or molecules located nearby
- 2014
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Ingår i: Nature Chemistry. - 1755-4349 .- 1755-4330. ; 6:1, s. 41-46
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Tidskriftsartikel (refereegranskat)abstract
- Although the local environment of a molecule can play an important role in its chemistry, rarely has it been examined experimentally at the level of individual molecules. Here we report the precise control of intramolecular hydrogen-transfer (tautomerization) reactions in single molecules using scanning tunnelling microscopy. By placing, with atomic precision, a copper adatom close to a porphycene molecule, we found that the tautomerization rates could be tuned up and down in a controlled fashion, surprisingly also at rather large separations. Furthermore, we extended our study to molecular assemblies in which even the arrangement of the pyrrolic hydrogen atoms in the neighbouring molecule influences the tautomerization reaction in a given porphycene, with positive and negative cooperativity effects. Our results highlight the importance of controlling the environment of molecules with atomic precision and demonstrate the potential to regulate processes that occur in a single molecule.
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| 33. |
- Kumagai, T., et al.
(författare)
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Quantum tunneling in real space: Tautomerization of single porphycene molecules on the (111) surface of Cu, Ag, and Au
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 148:10
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Tidskriftsartikel (refereegranskat)abstract
- Tautomerization in single porphycene molecules is investigated on Cu(111), Ag(111), and Au(111) surfaces by a combination of low-temperature scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. It is revealed that the trans configuration is the thermodynamically stable form of porphycene on Cu(111) and Ag(111), whereas the cis configuration occurs as a meta-stable form. The trans → cis or cis → trans conversion on Cu(111) can be induced in an unidirectional fashion by injecting tunneling electrons from the STM tip or heating the surface, respectively. We find that the cis → cis tautomerization on Cu(111) occurs spontaneously via tunneling, verified by the negligible temperature dependence of the tautomerization rate below ∼23 K. Van der Waals corrected DFT calculations are used to characterize the adsorption structures of porphycene and to map the potential energy surface of the tautomerization on Cu(111). The calculated barriers are too high to be thermally overcome at cryogenic temperatures used in the experiment and zero-point energy corrections do not change this picture, leaving tunneling as the most likely mechanism. On Ag(111), the reversible trans → cis conversion occurs spontaneously at 5 K and the cis → cis tautomerization rate is much higher than on Cu(111), indicating a significantly smaller tautomerization barrier on Ag(111) due to the weaker interaction between porphycene and the surface compared to Cu(111). Additionally, the STM experiments and DFT calculations reveal that tautomerization on Cu(111) and Ag(111) occurs with migration of porphycene along the surface; thus, the translational motion couples with the tautomerization coordinate. On the other hand, the trans and cis configurations are not discernible in the STM image and no tautomerization is observed for porphycene on Au(111). The weak interaction of porphycene with Au(111) is closest to the gas-phase limit and therefore the absence of trans and cis configurations in the STM images is explained either by the rapid tautomerization rate or the similar character of the molecular frontier orbitals of the trans and cis configurations.
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| 34. |
- Kumagai, T., et al.
(författare)
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Thermally and Vibrationally Induced Tautomerization of Single Porphycene Molecules on a Cu(110) Surface
- 2013
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 111:24, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- We report the direct observation of intramolecular hydrogen atom transfer reactions (tautomerization) within a single porphycene molecule on a Cu(110) surface by scanning tunneling microscopy. It is found that the tautomerization can be induced via inelastic electron tunneling at 5 K. By measuring the bias-dependent tautomerization rate of isotope-substituted molecules, we can assign the scanning tunneling microscopy-induced tautomerization to the excitation of specific molecular vibrations. Furthermore, these vibrations appear as characteristic features in the dI/dV spectra measured over individual molecules. The vibrational modes that are associated with the tautomerization are identified by density functional theory calculations. At higher temperatures above similar to 75 K, tautomerization is induced thermally and an activation barrier of about 168 meV is determined from an Arrhenius plot.
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| 35. |
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| 36. |
- Luntz, A.C., et al.
(författare)
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Theoretical evidence for nonadiabatic vibrational deexcitation in H2(D2) state-to-state scattering from Cu(100)
- 2006
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 124:9, s. 091101-
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Tidskriftsartikel (refereegranskat)abstract
- Dynamical calculations are presented for electronically nonadiabatic vibrational deexcitation of H2 and D2 in scattering from Cu(111). Both the potential energy surface and the nonadiabatic coupling strength were obtained from density functional calculations. The theoretically predicted magnitude of the deexcitation and its dependence on incident energy and isotope are all in agreement with state-to-state scattering experiments [on Cu(100)], and this gives indirect evidence for a nonadiabatic mechanism of the observed deexcitation. Direct evidence could be obtained by measuring the chemicurrent associated with the deexcitation, and its properties have been predicted.
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| 37. |
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| 38. |
- Martinez-Castro, Jose, et al.
(författare)
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Electric polarization switching in an atomically thin binary rock salt structure
- 2018
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 13:1, s. 19-23
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Tidskriftsartikel (refereegranskat)abstract
- Inducing and controlling electric dipoles is hindered in the ultrathin limit by the finite screening length of surface charges at metal-insulator junctions 1-3, although this effect can be circumvented by specially designed interfaces 4 . Heterostructures of insulating materials hold great promise, as confirmed by perovskite oxide superlattices with compositional substitution to artificially break the structural inversion symmetry 5-8 . Bringing this concept to the ultrathin limit would substantially broaden the range of materials and functionalities that could be exploited in novel nanoscale device designs. Here, we report that non-zero electric polarization can be induced and reversed in a hysteretic manner in bilayers made of ultrathin insulators whose electric polarization cannot be switched individually. In particular, we explore the interface between ionic rock salt alkali halides such as NaCl or KBr and polar insulating Cu2N terminating bulk copper. The strong compositional asymmetry between the polar Cu2N and the vacuum gap breaks inversion symmetry in the alkali halide layer, inducing out-of-plane dipoles that are stabilized in one orientation (self-poling). The dipole orientation can be reversed by a critical electric field, producing sharp switching of the tunnel current passing through the junction.
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| 39. |
- Matena, Manfred, et al.
(författare)
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Aggregation and contingent metal/surface reactivity of 1,3,8,10-tetraazaperopyrene (TAPP) on Cu(111)
- 2010
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 16:7, s. 2079-2091
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 40. |
- Matena, M., et al.
(författare)
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On-surface synthesis of a two-dimensional porous coordination network: Unraveling adsorbate interactions
- 2014
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 90, s. 125408-125415
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 41. |
- Mizielinski, M. S., et al.
(författare)
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Electronic nonadiabatic effects in the adsorption of hydrogen atoms on metals
- 2005
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 122:8
-
Tidskriftsartikel (refereegranskat)abstract
- The time-dependent, mean-field Newns-Anderson model for a spin-polarized adsorbate approaching a metallic surface is solved in the wide-band limit. Equations for the time evolution of the occupation of the spin dependent adsorbate states and for the nonadiabatic and nearly adiabatic adsorbate-surface energy transfer rates are derived. Numerical solutions are obtained using characteristic parameters derived from density functional theory calculations for the H/Cu(111) system. The time evolution of the model system is shown to be strongly nonadiabatic in the vicinity of the transition point between spin-polarized and nonpolarized ground states. Away from the spin transition the nonadiabatic energy transfer is in close agreement with the nearly adiabatic limit. Near the transition, nonadiabatic effects are large and the nearly adiabatic approximation fails.
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| 42. |
- Moberg, Christina, et al.
(författare)
-
De unga gör helt rätt när de stämmer staten : 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
- 2022
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Ingår i: Aftonbladet. - : Aftonbladet. ; :2022-12-07
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Vi, 1 620 forskare samt lärare vid universitet och högskolor, är eniga med de unga bakom Auroramålet: De drabbas och riskerar att drabbas allvarligt av klimatkrisen under sin livstid. De klimatåtgärder vi vidtar i närtid avgör deras framtid. Sverige måste ta ansvar och göra sin rättvisa andel av det globala klimatarbetet. I strid med Parisavtalet ökar utsläppen av växthusgaser i en takt som gör att 1,5-gradersmålet kan överskridas om några år. De globala effekterna blir allt mer synliga med ständiga temperaturrekord, smältande isar, havshöjning och extremväder som torka, förödande bränder och skyfall med enorma översvämningar, som i Pakistan nyligen. Försörjningen av befolkningen utsätts för allvarliga hot i många länder.Minskningen av den biologiska mångfalden är extrem. Klimatkrisen är enligt WHO det största hotet mot människors hälsa i hela världen och barn utgör en särskilt sårbar grupp. Med Sveriges nordliga läge sker uppvärmningen här dubbelt så fort som det globala genomsnittet. Det förskjuter utbredningsområden för växtlighet och sjukdomsbärande insekter och ökar förekomsten av extremväder såsom värmeböljor, skogsbränder och översvämningar samt av många olika sorters infektioner och allergier. När extremväder ökar, ökar även stressen och risken för mental ohälsa. Värmeböljor ökar risken för sjukdom och död hos sårbara grupper som äldre, små barn och personer med kroniska sjukdomar. De negativa effekterna på hälsan kommer att öka i takt med klimatkrisen och barn riskerar att drabbas av ackumulerade negativa hälsoeffekter under hela sina liv. Redan i dag är mer än hälften av unga mellan 12 och 18 år i Sverige ganska eller mycket oroliga för klimat och miljö. Detta är förståeligt när våra beslutsfattare inte gör vad som krävs.Den juridiska och moraliska grunden för arbetet mot klimatförändringarna är att varje land måste göra sin rättvisa andel av det globala klimatarbetet. Centralt i det internationella klimatramverket är att rika länder med höga historiska utsläpp, däribland Sverige, måste gå före resten av världen. Dessa länder måste också bidra till att finansiera klimatomställningen i länderna i det Globala Syd, som är minst ansvariga för klimatkrisen men drabbas hårdast. Denna rättviseprincip är tydlig i Parisavtalet och var en het diskussionsfråga under COP27 i Sharm el-Sheikh, men lyser med sin frånvaro i det svenska klimatarbetet. Sverige har satt mål för att minska sina utsläpp. Men de är helt otillräckliga: minskningstakten är för låg och målen tillåter samtidigt att åtgärder skjuts på framtiden. Dessutom exkluderas merparten av Sveriges utsläpp från de svenska nationella utsläppsmålen; bland annat utelämnas utsläpp som svensk konsumtion orsakar utanför Sveriges gränser, utsläpp från utrikes transporter och utsläpp från markanvändning och skogsbruk, exempelvis utsläpp från förbränning av biobränslen eller utsläpp från dikade våtmarker (Prop. 2016/17:146 s.25-28).Sverige saknar dessutom ett eget mål för att öka upptaget av växthusgaser genom utökat skydd och restaurering av ekosystem, något som krävs för att begränsa de värsta konsekvenserna av klimatkrisen (IPCC s.32). Trots dessa låga ambitioner misslyckas Sverige med att nå sina utsläppsmål, konstaterar både Klimatpolitiska rådet och Naturvårdsverket. En klimatpolitik i linje med Parisavtalet kräver både att alla typer av växthusgasutsläpp minskar samtidigt som – inte i stället för – upptaget av växthusgaser maximeras: i dag misslyckas Sverige på bägge fronter.Slutsatsen är tydlig. Sverige vidtar inte de åtgärder som krävs för att skydda barns och ungdomars rättigheter enligt Europakonventionen till skydd för de mänskliga rättigheterna. Detta medför allvarliga risker för liv och hälsa för unga generationer, människor i andra länder och särskilt utsatta grupper. Detta kan inte fortsätta. Därför ställer vi oss bakom Auroras krav att Sverige börjar göra sin rättvisa andel och omedelbart sätter igång ett omfattande och långtgående klimatarbete som vilar på vetenskaplig grund och sätter rättvisa i centrum.
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| 43. |
- Mohn, Fabian, et al.
(författare)
-
Reversible Bond Formation in a Gold-Atom-Organic-Molecule Complex as a Molecular Switch
- 2010
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 105:26
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the formation of a metal-molecule complex that can be used as a molecular switch. Using a cryogenic scanning tunneling microscope, a covalent bond was formed reversibly between a gold atom and a perylene-3,4,9,10-tetracarboxylic dianhydride molecule supported by a thin insulating film. The bonded and the nonbonded state of the complex were found to be associated with different charge states, and the switching between the two states was accompanied by a considerable change in the tunneling current. Atomic force microscopy molecular imaging was employed to determine precisely the atomic structure of the complex, and the experimental results were corroborated by density functional theory calculations.
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| 44. |
- Nylund, Göran M., 1974, et al.
(författare)
-
The red alga Bonnemaisonia asparagoides regulates epiphytic bacterial abundance and community composition by chemical defence
- 2010
-
Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 71:1, s. 84-93
-
Tidskriftsartikel (refereegranskat)abstract
- Ecological research on algal-derived metabolites with antimicrobial activity has recently received increased attention and is no longer only aimed at identifying novel natural compounds with potential use in applied perspectives. Despite this progress, few studies have so far demonstrated ecologically relevant antimicrobial roles of algal metabolites, and even fewer have utilized molecular tools to investigate the effects of these metabolites on the natural community composition of bacteria. In this study, we investigated whether the red alga Bonnemaisonia asparagoides is chemically defended against bacterial colonization of its surface by extracting surface-associated secondary metabolites and testing their antibacterial effects. Furthermore, we compared the associated bacterial abundance and community composition between B. asparagoides and two coexisting macroalgae. Surface extracts tested at natural concentrations had broad-spectrum effects on the growth of ecologically relevant bacteria, and consistent with this antibacterial activity, natural populations of B. asparagoides had significantly lower densities of epibacteria compared with the coexisting algae. Terminal restriction fragment length polymorphism analysis further showed that B. asparagoides harboured surface-associated bacteria with a community composition that was significantly different from those on coexisting macroalgae. Altogether, these findings demonstrate that B. asparagoides produces surface-bound antibacterial compounds with a significant impact on the abundance and composition of the associated bacterial community.
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| 45. |
- Olsson, Eva, 1960, et al.
(författare)
-
Multiple Charge States of Ag Atoms on Ultrathin NaCl Films
- 2007
-
Ingår i: Phys. Rev. Lett.. ; 98, s. 176803-
-
Tidskriftsartikel (refereegranskat)abstract
- A combined study using density functional calculations and scanning tunneling microscopy experiments shows that individual silver adatoms on ultrathin sodium chloride films on copper surfaces are stable in three different charge states—neutral, negatively, and positively charged adatoms. The charge states of the individual adatoms were manipulated by voltage pulses. The key parameters determining the stability of various charge states are identified and discussed within a simple model.
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Paavilainen, Sami, et al.
(författare)
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Vibrational assignments and line shapes in inelastic tunneling spectroscopy: H on Cu(100)
- 2006
-
Ingår i: Phys. Rev. B. ; 74, s. 085417-
-
Tidskriftsartikel (refereegranskat)abstract
- We have carried out a computational study of the inelastic electron tunnelling spectrum (IETS) of the two vibrational modes of a single hydrogen atom on a Cu(100) surface in a scanning tunnelling microscopy (STM) junction. This study addresses key issues about vibrational assignment and line shape of observed peaks in IETS within the framework of density functional theory calculations and the Lorente-Persson theory for STM-IETS. We argue that the observation of only a single broad peak in the STM-IETS [L. J. Lauhon and W. Ho Phys. Rev. Lett. 85, 4566 (2000)] is not caused by any symmetry restrictions or any cancellation between inelastic and elastic vibrational contributions for one of the two modes but is due to strongly overlapping superposition of the contributions from the two modes caused by the rather large instrumental broadening and the narrow vibrational energy separation between the modes. In particular, we find that this broadening and the large asymmetry of the vibrational line shapes gives rise to substantial apparent vibrational energy shifts of the two modes and decreases their apparent energy separation.
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| 50. |
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