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Self-ordering of metal-free phthalocyanine on InAs(100) and InSb(100)
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
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.

Place, publisher, year, edition, pages
2006. Vol. 18, no 48, 10707-10723 p.
Keyword [en]
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: urn:nbn:se:kth:diva-7782DOI: 10.1088/0953-8984/18/48/001ISI: 000242650600002Scopus ID: 2-s2.0-33846096421OAI: oai:DiVA.org:kth-7782DiVA: diva2:12909
Note
QC 20100812Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2010-11-22Bibliographically approved
In thesis
1. Phthalocyanine interfaces: the monolayer region
Open this publication in new window or tab >>Phthalocyanine interfaces: the monolayer region
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
phthalocyanine, III-V semiconductor, transition metal oxides, adsorption, self-assembly
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-4571 (URN)978-91-7178-784-2 (ISBN)
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
2. Initial stages of metal- and organic-semiconductor interface formation
Open this publication in new window or tab >>Initial stages of metal- and organic-semiconductor interface formation
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This licentiate thesis deals with the electronic and geometrical properties of metal-semiconductor and organic-semiconductor interfaces investigated by photoelectron spectroscopy and scanning tunneling microscopy.

First in line is the Co-InAs interface (metal-semiconductor) where it is found that Co is reactive and upon adsorption and thermal treatment it alloys with the indium of the substrate to form metallic islands, about 20 nm in diameter. The resulting broken bonds causes As entities to form which are loosely bond to the surface and evaporate upon thermal treatment. Thus, the adsorption of Co results in a rough interface.

Secondly the metal-free phthalocyanine (H2PC) - titanium dioxide interface (organic-semiconductor) is investigated. Here it is found that the organic molecules arrange themselves along the substrate rows upon thermal treatment. The interaction with the TiO2 is mainly with the valence Π-electrons in the molecule causing a relatively strong bond, but this interaction is short range as the second layer of molecules retains their molecular character. This results in an ordered adsorption but limited mobility of the molecules on the surface prohibiting well ordered close packed layers. Furthermore, the hydrogen atoms inside the cyclic molecule leave the central void upon thermal treatment.

The third case is the H2PC-InAs/InSb interface (organic-semiconductor). Here ordered overlayer growth is found on both substrates where the molecules are preferentially adsorbed on the In rows in the [110] direction forming one-dimensional chains. The InSb-H2PC interface is found to be weakly interacting and the bulk-like molecular character is retained upon both adsorption and thermal treatment. On the InAs-H2PC interface, however, the interaction is stronger. The molecules are more affected by the surface bond and this effect stretches up a few monolayers in the film after annealing.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 47 p.
Series
Trita-FTE, ISSN 0284-0545 ; 0601
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-3911 (URN)
Presentation
2006-04-07, Sal C1, KTH-Electrum, Isfjordsgatan 22, Kista, 10:15
Opponent
Supervisors
Note
QC 20101122Available from: 2006-04-07 Created: 2006-04-07 Last updated: 2010-11-22Bibliographically approved

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