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Phthalocyanine interfaces: the monolayer region
KTH, School of Information and Communication Technology (ICT), Material Physics.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Organic molecules adsorbed on inorganic substrates are the topics of interest in this thesis. Interfaces of this kind are found in dye sensitized solar cells that convert solar energy to electricity, a promising environmentally friendly energy source which might provide a route to replace fossil fuels. Another field where these interfaces play a role is in molecular electronics, an approach to solve the down scaling in the ever increasing hunt for miniaturized electronic devices. The motivation for this work lies among other in these applications and surface science is a suitable approach to investigate the electronic and morphologic properties of the interfaces as it provides detailed knowledge on an atomic level.

Phthalocyanines are the organic molecules investigated and the inorganic substrates range from wide band gap via narrow band gap semiconductors to metals. Photoelectron and X-ray spectroscopy experiments are performed to shed light on the electronic properties of the adsorbed molecules and the substrate, as well as the chemical interaction between adsorbate and substrate at the interface. The ordering of the adsorbate at the interface is important as ordered molecular thin films may have other properties than amorphous films due to the anisotropic electronic properties of the organic molecules; this is investigated using scanning tunneling microscopy.

We find that the phthalocyanines are affected by adsorption when the substrate is TiO2 or Ag, where charge transfer from the molecule occurs or an interface state is formed respectively. The molecules are adsorbed flat on these surfaces giving a large contact area and a relatively strong bond. On Ag, ordered structures appear with different symmetry depending on initial coverage. The reactivity of the TiO2 surface is not ideal in the solar cell application and by modifying the surface with a thin organic layer, the negative influence on the adsorbed phthalocyanine is reduced. ZnO is not as reactive as TiO2, thanks maybe to the upright adsorption mode of the phthalocyanines. The semiconductor InSb is less reactive leading to self-assembled molecular structures on the (001) surface, either homogenously distributed in a one monolayer thick film or in strands along the reconstruction rows. InAs on the other hand has a larger influence on the adsorbed molecules resulting in a metallic film upon thermal treatment.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , 68 p.
Series
Trita-ICT/MAP, 2007:10
Keyword [en]
phthalocyanine, III-V semiconductor, transition metal oxides, adsorption, self-assembly
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-4571ISBN: 978-91-7178-784-2 (print)OAI: oai:DiVA.org:kth-4571DiVA: diva2:12916
Public defence
2007-12-18, N2, electrum 3, Isafjordsgatan 28, Kista, 10:00
Opponent
Supervisors
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2010-08-12
List of papers
1. Bonding of metal-free phthalocyanine to TiO2(110) single crystal
Open this publication in new window or tab >>Bonding of metal-free phthalocyanine to TiO2(110) single crystal
2006 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 90, no 20, 3602-3613 p.Article in journal (Refereed) Published
Abstract [en]

The metal-free phthalocyanine interface formation on rutile TiO2(110) is investigated using scanning tunneling microscopy and photoelectron spectroscopy. The molecules are adsorbed flat on the surface, centered on the substrate oxygen rows. High-resolution core-level C1s spectroscopy indicates a strong difference between the second layer and the first monolayer bonding to the surface. The C1s core-level from the second layer has a bulk-like line shape whereas the first layer shows a strongly modified line profile. Upon thermal treatment, changes in the N1s core level line profile points to dehydrogenation of the center of the molecule.

Keyword
Adsorption; Metal-free phthalocyanine; Titanium dioxide; Dehydrogenation; Heat treatment; Scanning tunneling microscopy; Single crystals; Titanium oxides; X ray photoelectron spectroscopy; Metal-free phthalocyanine; Monolayer bonding; Substrate oxygen; Nitrogen compounds
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7778 (URN)10.1016/j.solmat.2006.06.054 (DOI)000241483200011 ()2-s2.0-33749134840 (Scopus ID)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
2. Band bending and structure dependent HOMO energy at the ZnO(0001)-titanyl phthalocyanine interface
Open this publication in new window or tab >>Band bending and structure dependent HOMO energy at the ZnO(0001)-titanyl phthalocyanine interface
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2007 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 18, 4222-4226 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the initial stages of titanyl phthalocyanine (TiOPc) growth on single crystalline ZnO(0 0 0 1). This organic-semiconductor interface is self-organizing as a 2 x 1 pattern appears in a low energy electron diffraction upon deposition of the molecules. To achieve this pattern, the TiOPc is suggested to adsorb standing with the edge of the molecule along the substrate atomic rows. Photoelectron spectroscopy is used to further analyze the interface; a relatively large upwards band bending amounting to 0.5 eV is found and a splitting of the molecules highest occupied molecular orbital occurs after thermal treatment, indicating that the molecules are lying down.

Keyword
Single crystal; Synchrotron radiation photoelectron spectroscopy; Titanyl phthalocyanine; ZnO; Crystal growth; Photoelectron spectroscopy; Single crystals; Synchrotron radiation; Titanium compounds; Zinc oxide; Band bending; Synchrotron radiation photoelectron spectroscopy; Titanyl phthalocyanine; Interfaces (materials)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7779 (URN)10.1016/j.susc.2007.04.113 (DOI)000250414600117 ()2-s2.0-34548810178 (Scopus ID)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
3. Interface properties in organic thin films: FePc on TiO2(110)
Open this publication in new window or tab >>Interface properties in organic thin films: FePc on TiO2(110)
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(English)In: Journal of Physical Chemistry, ISSN 1932-7447Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:kth:diva-7780 (URN)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2010-08-12Bibliographically approved
4. Changing adsorption mode of FePc on TiO2(110) by surface modification with bipyridine
Open this publication in new window or tab >>Changing adsorption mode of FePc on TiO2(110) by surface modification with bipyridine
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2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 7, 074707- p.Article in journal (Refereed) Published
Abstract [en]

Surface modification of reactive oxide substrates to obtain a less strongly interacting template for dye adsorption may be a way to enhance performance in dye-sensitized solar cells. In this work, we have investigated the electronic and structural properties of 4,4(')-bipyridine (bipy) as modifier adsorbed on the TiO2(110) surface. The modified surface is then coated with iron phthalocyanine (FePc) and the properties of this heterostructure are investigated with synchrotron based photoelectron spectroscopy, x-ray absorption spectroscopy, and scanning tunneling microscopy. We find that a saturated monolayer consisting of standing bipy molecules with one nitrogen atom pointing outward is formed on the oxide surface. FePc adsorb in molecular chains along the [001] direction on top of bipy and ordered in a tilted arrangement with adjacent molecules partially overlapping. Already from the first layer, the electronic properties of FePc resemble those of multilayer films. FePc alone is oxidized on the TiO2(110) surface, but preadsorbed bipy prevents this reaction. The energy level lineup at the interface is clarified.

Keyword
Direct energy conversion; Solar cells; Solar energy; Bipyridine; Dye adsorption; Dye-sensitized solar cells; Electronic and structural properties; Oxide substrates; Surface modifications; Adsorption; 4, 4' bipyridine; 4, 4'-bipyridyl; ferrous ion; indole derivative; iron phthalocyanine; pyridine derivative; titanium; titanium dioxide; unclassified drug; adsorption; article; artificial membrane; chemistry; electron; surface property; Electrons; Ferrous Compounds; Indoles; Membranes, Artificial; Pyridines; Surface Properties; Titanium
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7781 (URN)10.1063/1.2969081 (DOI)000258643300041 ()19044792 (PubMedID)2-s2.0-50249106920 (Scopus ID)
Note
QC 20100812. Uppdaterad från Submitted till Published 20100812.Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
5. Self-ordering of metal-free phthalocyanine on InAs(100) and InSb(100)
Open this publication in new window or tab >>Self-ordering of metal-free phthalocyanine on InAs(100) and InSb(100)
2006 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 48, 10707-10723 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption and surface ordering of metal-free phthalocyanine (H2PC) on InAs(100)(4 x 2)/c(8 x 2) and InSb(100) c(8 x 2) is investigated using scanning tunnelling microscopy (STM) and synchrotron based photoelectron spectroscopy. The two systems show structural similarities; at submonolayer coverage the preferred adsorption site of H2PC is on top of the In rows, and above 1 monolayer and after thermal treatment the first molecular layer is ordered in a densely packed 'x3' structure observed with both low energy electron diffraction and STM.

The electronic properties and the surface bonds of the two systems are quite different: the InAs-H2PC interface is semiconducting after room temperature adsorption but becomes metallic upon thermal treatment whereas InSb(100) H2PC is semiconducting at all preparations. These differences are reflected in pronounced differences in the C 1s line shape between the two systems. N 1s core level spectra from both surfaces reveal deprotonation of the molecules, i.e. the central hydrogen atoms are lost upon thermal treatment.

Keyword
Adsorption; Crystalline materials; Electron diffraction; Electronic properties; Heat treatment; Photoelectron spectroscopy; Scanning tunneling microscopy; Semiconducting indium compounds; Surface chemistry; Adsorption sites; Deprotonation; Phthalocyanine; Surface bonds; Pigments
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7782 (URN)10.1088/0953-8984/18/48/001 (DOI)000242650600002 ()2-s2.0-33846096421 (Scopus ID)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
6. STM and XPS characterization of Zinc Phthalocyanine on InSb(001)
Open this publication in new window or tab >>STM and XPS characterization of Zinc Phthalocyanine on InSb(001)
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2008 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, no 2, 452-459 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Indium antimonide; Scanning tunneling microscopy; X-ray photoelectron spectroscopy; Zinc phthalocyanine; Annealing; Electronic structure; Monolayers; Scanning tunneling microscopy; X ray photoelectron spectroscopy; Elevated temperatures; Indium antimonide; Zinc phthalocyanine; Nitrogen compounds
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7783 (URN)10.1016/j.susc.2007.10.052 (DOI)000253277900008 ()2-s2.0-38349136764 (Scopus ID)
Note
QC 20100812. Uppdaterad från In press till Published 20100812.Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
7. STM investigation of FePc on InSb(001)c8x2
Open this publication in new window or tab >>STM investigation of FePc on InSb(001)c8x2
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(English)Manuscript (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7784 (URN)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2010-08-12Bibliographically approved
8. Thermal effects on order at organic/inorganic interfaces: TiOPc on IOnSb(001)c(8x2)
Open this publication in new window or tab >>Thermal effects on order at organic/inorganic interfaces: TiOPc on IOnSb(001)c(8x2)
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2007 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528Article in journal (Other academic) Submitted
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7785 (URN)
Note
QS 20120319Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
9. Adsorption site of phthalocyanines on the InSb(001)c(8x2) surface
Open this publication in new window or tab >>Adsorption site of phthalocyanines on the InSb(001)c(8x2) surface
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(English)Manuscript (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7786 (URN)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2010-08-12Bibliographically approved
10. Charge transfer and band alignment at the InSb(111)B-TiOPc interface
Open this publication in new window or tab >>Charge transfer and band alignment at the InSb(111)B-TiOPc interface
Show others...
(English)Manuscript (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7787 (URN)
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2010-08-12Bibliographically approved
11. Ordered phthalocyanine structures on Ag(110)
Open this publication in new window or tab >>Ordered phthalocyanine structures on Ag(110)
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2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Other academic) Submitted
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-7788 (URN)
Note
QS 20120319Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved

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