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Scanning tunneling microscopy study of metal-free phthalocyanine monolayer structures on graphite
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
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2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 11, 114702- p.Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
2007. Vol. 127, no 11, 114702- p.
Keyword [en]
adsorption, annealing, density functional theory, evaporation, graphite, molecular electronic states, monolayers, organic compounds, scanning tunnelling microscopy
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95721DOI: 10.1063/1.2770732ISI: 000249667400050OAI: oai:DiVA.org:uu-95721DiVA: diva2:170040
Available from: 2007-04-13 Created: 2007-04-13 Last updated: 2017-12-14
In thesis
1. Electronic and Geometrical Structure of Phthalocyanines on Surfaces: An Electron Spectroscopy and Scanning Tunneling Microscopy Study
Open this publication in new window or tab >>Electronic and Geometrical Structure of Phthalocyanines on Surfaces: An Electron Spectroscopy and Scanning Tunneling Microscopy Study
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Core- and Valence Photoelectron Spectroscopy (PES), X-ray- and Ultraviolet-Visible Absorption Spectroscopy (XAS and UV-Vis), Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) calculations are used to study the electronic and geometrical structure of a class of macro-cyclic molecules, Phthalocyanines (Pc), on surfaces. These molecules are widely studied due to their application in many different fields.

Multilayer and monolayer coverages of Iron Phthalocyanine (FePc) and metal-free Phthalocyanine (H2Pc) deposited on different surfaces are investigated in order to get insight in the electronic and geometrical structure of the obtained overlayers, of crucial importance for the understanding of the film functionality. Sublimation of molecular thick films on Si(100) and on conducting glass results in films with molecules mainly oriented with their molecular plane orthogonal to the surface. Ex-situ deposited H2Pc films on conductive glass show different molecular orientation and morphology with respect to the vacuum sublimated films.

We study the monolayer adsorption structure of FePc and H2Pc and compare our results with other Pc’s adsorbed on graphite. We find that the molecular unit cell and the superstructure is characteristic for each Pc adsorbed on graphite, even if the geometrical size of the compared molecules is the same. The PE- and XA- spectra of FePc on graphite are essentially identical for the mono- and multilayer preparations, evidencing weak intermolecular and molecular-substrate interactions of van der Waals nature.

Furthermore, we characterize Pc’s on InSb (001)-c(8x2). The substrate In rows are observed to be the adsorption site for Pc’s. We find that the growth of the two-dimensional islands of FePc is prolonged in the [-110] direction, in contrast to ZnPc adsorbed on the same substrate at room temperature. We interpret this result as an indication that the adsorption is controlled by the substrate corrugation observed at 70 K.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 291
Keyword
Physics, PhotoElectron Spectroscopy (PES), X-ray Absorption Spectroscopy (XAS), UltraViolet-Visible absorption spectroscopy (UV-Vis), Scanning Tunneling Microscopy (STM), Phthalocyanine (Pc), Iron Phthalocyanine (FePc), metal-free Phthalocyanine (H2Pc), Zinc Phthalocyanine (ZnPc), Graphite (HOPG), Indium Antimony (InSb), Surface science, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-7802 (URN)978-91-554-6856-9 (ISBN)
Public defence
2007-05-04, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2007-04-13 Created: 2007-04-13 Last updated: 2012-03-28Bibliographically approved
2. Phthalocyanines on Surfaces: Monolayers, Films and Alkali Modified Structures
Open this publication in new window or tab >>Phthalocyanines on Surfaces: Monolayers, Films and Alkali Modified Structures
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 61 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 342
Keyword
Atomic and molecular physics, Phthalocyanines, Surface Science, X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS), Scanning Tunneling Microscopy (STM), Density Functional Theory (DFT), Metal-free Phthalocyanine, Iron Phthalocyanine, Zinc Phthalocyanine, Gold, Graphite, Aluminium, Indium Antimony, Molecular adsorption, Monolayer, Film, Alkali, Geometrical structure, Electronic structure, Doping, Atom- och molekylfysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-8209 (URN)978-91-554-6966-5 (ISBN)
Public defence
2007-10-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2007-09-21 Created: 2007-09-21 Last updated: 2011-07-08Bibliographically approved

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Brena, BarbaraMårtensson, NilsPuglia, Carla

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