| 1. |
- Ahlund, John, et al.
(författare)
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Molecular growth determined by surface domain patterns
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:17, s. 6887-6890
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Tidskriftsartikel (refereegranskat)abstract
- The growth of iron phthalocyanine (FePc) on InSb(001) c(8 x 2) at submonolayer coverage has been investigated with scanning tunneling microscopy (STM). FePc adsorbs flat centered on the In rows both at 70 K and at room temperature (RT). However, the shapes of the two-dimensional molecular islands are fundamentally different; while the RT growth results in chainlike structures along the [I 10] direction, as already observed for other Pc's adsorbed on the same surface, the islands are prolonged along [110], i.e., perpendicular to the substrate rows, at 70 K. These observations are explained on the basis of a recently observed new surface phase at low temperature, resulting in structural domains on the surface. The molecular growth front follows the propagating domain boundary that freezes at low temperature.
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| 2. |
- Alfredsson, Ylvi, et al.
(författare)
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Electronic structure of a vapor-deposited metal-free phthalocyanine thin film
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:21
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.
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| 3. |
- Alfredsson, Ylfi, et al.
(författare)
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Phase and molecular orientation in H2Pc on conducting glass : characterization of two deposition methods
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 493:1-2, s. 13-19
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Tidskriftsartikel (refereegranskat)abstract
- In this study, metal-free phthalocyanine has been deposited on a conducting glass surface by two methods: by spreading the molecular powder directly on the substrate in air and by vapor sublimation under ultra-high vacuum conditions (evaporation). The films have been characterized by means of core level X-ray Photoemission Spectroscopy, X-ray Absorption Spectroscopy (XAS) and Ultra Violet and Visible absorption spectroscopy (UV-Vis). Our results show that the two deposition methods produce molecular overlayers in different polymorphic phases; the UV-Vis measurements indicate that the film obtained by powder deposition is of x-phase type whereas sublimation leads to an α-polymorph structure. The XAS results show that in the powder deposited film the molecules are mainly oriented parallel to the surface. This is opposite to the case of the vapor deposited film, where the molecules mainly are oriented orthogonal to the surface.
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| 4. |
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| 5. |
- Berner, Simon, et al.
(författare)
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Electronic and structural studies of immobilized thiol-derivatized cobalt porphyrins on gold surfaces
- 2007
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 253:18, s. 7540-7548
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Tidskriftsartikel (refereegranskat)abstract
- The immobilisation of thiol-derivatized cobalt porphyrins on gold surfaces has been studied in detail by means of combined scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). S-thioacetyl has been used as a protective group for the thiol. Different routes for deprotection of the acetyl groups were performed in acidic and in basic conditions. The results show the formation of monolayer films for the different preparation schemes. The immobilisation of the molecules on the gold surface takes place through the thiol-linkers by the formation of multiple thiolate bonds. In the case of layers formed with protected porphyrins approximately 60% of the linkers are bonded to the gold surface whereas for deprotected layers the amount of bonded linkers is increased up to about 80%. STM measurements revealed that the molecules arrange in a disordered overlayer and do not exhibit mobility on the gold surface. Annealing experiments have been performed in order to test the stability of the porphyrin layers. Disordered patterns have been observed in the STM images after annealing at T = 400 °C. XPS revealed that the sulphur content disappeared completely after annealing at T = 180 °C and that the molecules did undergo significant modifications.
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| 6. |
- Brena, Barbara, et al.
(författare)
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Equivalent core-hole time-dependent density functional theory calculations of carbon 1s shake-up states of phthalocyanine
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:19, s. 195214-
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Tidskriftsartikel (refereegranskat)abstract
- The shake-up transition energies of the carbon 1s photoelectron spectrum of metal-free phthalocyanine (H2Pc) have been calculated by means of time-dependent density functional theory, for which an equivalent core approximation is adopted. Model calculations for the C 1s shake-up states of benzene are in excellent agreement with the latest experimental results. The complex C 1s shake-up structures associated with the aromatic and pyrrole carbons in the phthalocyanine are computed, as well as their ionization potentials. They allow us to determine the origin of the anomalous intensity ratio between the pyrrole and benzene carbons in a high resolution C 1s photoelectron spectrum measured for a H2Pc film, as due to a benzene-related shake-up contribution, hidden under the pyrrole main intensity feature.
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| 7. |
- Brena, Barbara, et al.
(författare)
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InSb-TiOPc interfaces : Band alignment, ordering and structure dependent HOMO splitting
- 2009
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 603:20, s. 3160-3169
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of titanyl phthalocyanine (TiOPc) have been adsorbed on InSb(1 1 1) (3 x 3) and InSb(1 0 0) c(8 x 2) surfaces and studied with respect to their electronic structure using photoemission (PES), density functional theory (DFT) and scanning tunneling microscopy (STM). The interface chemical interaction is weak in both cases; no adsorbate induced surface band bending is observed and the energy level alignment across the interface is determined by the original position of the substrate Fermi level and the charge neutrality level of the molecule. Room temperature adsorption results in disordered films on both surfaces. The behaviors after annealing are different; on InSb(1 0 0) well-ordered molecular chains form along and on top of the In-rows, whereas on (1 1 1) no long range order is observed. The disorder leads to intermolecular interactions between the titanyl group and neighboring benzene rings leading to a split of TiOPc HOMO (highest occupied molecular orbital) by as much as 0.8 eV.
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| 8. |
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| 9. |
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| 10. |
- Nilson, Katharina, 1977-
(författare)
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Phthalocyanines on Surfaces : Monolayers, Films and Alkali Modified Structures
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Phthalocyanines (Pc’s) are a group of macro-cyclic molecules, widely investigated due to the possibility to use them in a variety of applications. Electronic and geometrical structure investigations of molecular model systems of Pc’s adsorbed on surfaces are important for a deeper understanding of the functionality of different Pc-based devices. Here, Pc’s monolayers and films, deposited on different surfaces, were investigated by X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS) and Scanning Tunneling Microscopy (STM). In addition Density Functional Theory (DFT) simulations were performed. For molecular films of Metal-free (H2Pc) and Iron (FePc) Pc’s, on surfaces, it is found that the intermolecular interaction is weak and the molecules arrange with their molecular plane mainly perpendicular to the surface. Several monolayer systems were characterized, namely H2Pc and FePc adsorbed on Graphite, ZnPc on InSb(001)-c(8x2), H2Pc on Al(110) and on Au(111). For all the studied monolayers it was found that the molecules are oriented with their molecular plane parallel to the surface. The electronic structure of the molecules is differently influenced by interaction with the surfaces. For H2Pc adsorbed on Graphite the nearly negligible effect of the surface on the molecular electronic structure allowed STM characterization of different molecular orbitals. A strong interaction is instead found in the case of H2Pc on Al(110) resulting in molecules strongly adsorbed, and partly dissociated. Modifications of the electronic and geometrical structure induced by alkali doping of H2Pc films and monolayers were characterized. It is found both for the H2Pc film on Al(110) and monolayer adsorbed on Au(111), that the molecular arrangement is changed upon doping by Potassium and Rubidium, respectively. Potassium doping of the H2Pc films results in a filling of previously empty molecular orbitals by a charge transfer from the alkali to the molecule, with significant modification of the molecular electronic structure.
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| 11. |
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| 12. |
- Nilson, Katharina, et al.
(författare)
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Rubidium Doped Metal-Free Phthalocyanine Monolayer Structures on Au(111)
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:28, s. 12166-12172
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) studies of monolayer of metal-free phthalocyanine (H2Pc) adsorbed on Au(111) have shown ordered arrangement of the molecules on the surface. Evaporation of H2Pc onto the Au(111) surface and post annealing of the sample to 670 K results in a densely packed structure of the molecules. The monolayer is characterized by molecules adsorbed with the molecular plane parallel to the substrate surface in a square adsorption unit cell. Furthermore, the high resolution images revealed the orientation of individual molecules. The H2Pc/Au(111) system has also been doped by rubidum and compared to the undoped layers. The Rb affects the molecular adsorption geometry, and a hexagonal unit cell is found for the coadsorption of H2Pc and Rb. Upon doping, highly ordered Rb-induced protrusions are observed at the benzene site of adsorbed molecules.
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| 13. |
- Nilson, Katharina, et al.
(författare)
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Scanning tunneling microscopy study of metal-free phthalocyanine monolayer structures on graphite
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:11, s. 114702-
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Tidskriftsartikel (refereegranskat)abstract
- Low temperature scanning tunneling microscopy (STM) studies of metal-free phthalocyanine (H2Pc) adsorbed on highly oriented pyrolytic graphite (HOPG) have shown ordered arrangement of molecules for low coverages up to 1 ML. Evaporation of H2Pc onto HOPG and annealing of the sample to 670 K result in a densely packed structure of the molecules. Arrangements of submonolayer, monolayer, and monolayer with additional adsorbed molecules have been investigated. The high resolution of our investigations has permitted us to image single molecule orientation. The molecular plane is found to be oriented parallel to the substrate surface and a square adsorption unit cell of the molecules is reported. In addition, depending on the bias voltage, different electronic states of the molecules have been probed. The characterized molecular states are in excellent agreement with density functional theory ground state simulations of a single molecule. Additional molecules adsorbed on the monolayer structures have been observed, and it is found that the second layer molecules adsorb flat and on top of the molecules in the first layer. All STM measurements presented here have been performed at a sample temperature of 70 K.
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| 14. |
- Nilson, Katharina, et al.
(författare)
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STM and XPS characterization of Zinc Phthalocyanine on InSb(001)
- 2008
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 602:2, s. 452-459
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Tidskriftsartikel (refereegranskat)abstract
- Zinc phthalocyanine (ZnPc) adsorbed on the InSb(0 0 1)-c(8 x 2) surface has been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Coverages from sub-monolayer to monolayer (ML) have been investigated. The molecules form ordered structures on the reconstructed rows of the surface with the molecular plane parallel to the surface. A change in the electronic structure between the sub-ML and higher coverages has been observed. Moreover, in order to study the influence of annealing on the electronic and geometric structures, the samples have been heated to elevated temperatures (about 640 K). In addition, multi-layer ZnPc films have been characterized by XPS measurements.
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| 15. |
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| 16. |
- Åhlund, John, et al.
(författare)
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The adsorption of iron phthalocyanine on graphite : A scanning tunnelling microscopy study
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:17, s. 3661-3667
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Tidskriftsartikel (refereegranskat)abstract
- Different adsorption phases of iron phthalocyanine (FePc) on highly oriented pyrolitic graphite (HOPG) have been characterized by scanning tunnelling microscopy (STM). Evaporation of FePc onto the graphite (0 0 0 1) surface, kept at room temperature, results in the formation of three-dimensional molecular islands.After annealing to 400 °C different two-dimensional features are identified, depending on the initial coverage. At low doses, domains with well defined boundaries have been observed, within which molecules tend to organise in chains. At higher coverage, islands exhibiting well-ordered densely-packed square or hexagonal molecular arrangement have been resolved. For the adsorption structures corresponding to one monolayer islands our results show that the molecules adsorb with the molecular plane parallel to the surface. The high resolution STM images allow us to resolve the orientation of single molecules and subsequently we suggest that the molecular monolayer is stabilized by van der Waals interactions. The characterization of the observed Moiré contrast and a comparison with other similar systems underlines the importance of the central metal in the molecule–molecule and molecule–substrate interactions, which govern the molecular adsorption geometry.
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| 17. |
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| 18. |
- Åhlund, John, et al.
(författare)
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The electronic structure of iron phthalocyanine probed by photoelectron and x-ray absorption spectroscopies and density functional theory calculations
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:3, s. 034709-1-034709-7
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Tidskriftsartikel (refereegranskat)abstract
- A joint experimental and theoretical work to explain the electronic and geometrical structure of an in situ prepared film of iron phthalocyanine (FePc) on silicon (100) is presented. FePc molecular films have been characterized by core and valence photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS), and the results have been interpreted and simulated by density functional theory (DFT) calculations. C1s and N1s PE spectra have been analyzed by taking into account all chemically nonequivalent C and N atoms in the molecule. In the Fe2p(3/2) spectra it has been possible to resolve two components that can be related to the open shell structure of the molecule. By valence PES and N1s XAS data, the geometrical orientation of the FePc molecules in the film could be determined. Our results indicate that for the FePc on Si(100), the molecules within the film are mainly standing on the surface. The experimental N1s XAS spectra are very well reproduced by the theoretical calculations, which are both angle and atomic resolved, giving a detailed description of the electronic and geometric structure of the FePc film. Furthermore, the asymmetry and the intensity angle variation of the first N1s XAS threshold feature could be explained by the presented DFT calculations as due to the chemical nonequivalence of the N atoms and the symmetry character of the lowest unoccupied molecular orbital.
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