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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- 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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| 6. |
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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
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