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Mixed Self-Assembled Monolayers of Ferrocene-Terminated and Unsubstituted Alkanethiols on Gold: Surface Structure and Work Function
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialfysik)
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialfysik)
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialvetenskap)
2009 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 5, 1972-1979 p.Article in journal (Refereed) Published
Abstract [en]

Mixed self-assembled monolayers of 11-ferrocene-1-undecanethiol (FcC11) and decanethiol (C10) were prepared by two different methods: from a mixed solution and by subsequent immersion. These preparations result in self-assembled monolayers (SAMs) with different portions of FcC11 molecules, orientations, and degrees of order in the SAM. The structure of these layers was studied by high-resolution X-ray photoelectron spectroscopy (HRXPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and their effect on the surface electronic properties was investigated by Kelvin probe. The fraction of FcC11 in C10 thiol could be estimated from the intensity of the HRXPS Fe 2p3/2 peaks. The SAM prepared from the mixed solution was of high quality, and the portion of FcC11 molecules in this film was about 60%. The interaction of neighboring ferrocene moieties indicated phase separation between FcC11 and C10 species in the film. For the SAMs prepared by subsequent immersion in C10 and FcC11 solutions, the portion of FcC11 molecules varied from 35% to 55% dependent on the immersion times in the C10 solution. The degree of orientational order of the alkyl chains increased with increasing immersion time in C10. In addition, the adsorption of C10 decreased the work function of the gold surface while the adsorption of FcC11 increased this value. By varying the fraction of FcC11 in the SAMs with different preparation schemes, the work function of the gold surface could be varied in a controllable way

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2009. Vol. 113, no 5, 1972-1979 p.
National Category
Condensed Matter Physics Physical Chemistry
Research subject
Physics
Identifiers
URN: urn:nbn:se:kau:diva-2866DOI: 10.1021/jp808938dOAI: oai:DiVA.org:kau-2866DiVA: diva2:54463
Funder
Swedish Research Council
Available from: 2008-10-16 Created: 2008-10-16 Last updated: 2012-12-11Bibliographically approved
In thesis
1. Structure of Self-Assembled Monolayers on Gold Studied by NEXAFS and Photoelectron Spectroscopy
Open this publication in new window or tab >>Structure of Self-Assembled Monolayers on Gold Studied by NEXAFS and Photoelectron Spectroscopy
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Self-assembled monolayers (SAMs) provide well-defined and ordered films of molecules spontaneously chemisorbed on a surface. By designing molecules with desired functionalities, such molecular film can be interesting for a range of applications from molecular electronics to catalysis. Important parameters for SAM applications are the film structure and quality, which are dependent on the structure of molecular constituents, the substrate, and the self-assembly process. In this work, SAMs on Au(111) of a variety of functionalized molecules, with thiol and silane headgroups, have been studied using high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Infrared reflection absorption spectroscopy (IRRAS), contact angle measurements and Kelvin probe measurements. In particular, the effects of varying the size of the backbone, varying the headgroup, inclusion of a porphyrin tailgroup, different ways of deprotection of the headgroups, and mixed molecular layers have been investigated.

The first part of thesis work is focused on SAMs of oligo(phenyleneethynylene) (OPE) derivatives. First the effect of the extent of the conjugated system on the structure of SAM was investigated. As the lateral π-system in the OPE backbone increases, molecular surface densities become lower and molecular inclinations larger. Subsequently, a bulky porphyrin tailgroup was added onto the OPE molecule. Porphyrin-functionalized OPE with several headgroups were compared and the thioacetyl anchor group was found to form a high quality SAM.

In the second part of the work, the molecular orientation of thiol-derivatized tetraphenylporphyrin layers was studied. The geometry of the molecular layer and the number of linkers that bind to the gold surface depend strongly on preparation schemes, i.e. whether or not the acetyl protection groups on the thiol were removed before adsorption.

Finally, mixed SAMs of a ferrocene-terminated alkanethiol and alkanethiols were studied. By diluting the ferrocene-functionalized molecules in unfunctionalized alkanethiols, the orientational order and the packing density improved. The geometrical structure and the fraction of the ferrocene-terminated molecules can be tuned by controlling the parameters in the preparation scheme.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2008. 69 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:40
Keyword
Self-assembled monolayer (SAMs), X-ray photoelectron spectroscopy (XPS), Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Infrared reflection absorption spectroscopy (IRRAS), contact angle measurements, Kelvin probe measurements, oligo(phenyleneethynylene) (OPE), Porphyrin-functionalized OPE, Tetraphenylporphyrin, Ferrocene-terminated alkanethiol, thiol, silane, Au(111)
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-2723 (URN)978-91-7063-200-6 (ISBN)
Public defence
2008-11-07, 21A 342, Karlstad University, 13:15 (English)
Opponent
Supervisors
Available from: 2008-10-20 Created: 2008-09-25 Last updated: 2011-12-21Bibliographically approved

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Publisher's full texthttp://pubs.acs.org/doi/full/10.1021/jp808938d

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Watcharinyanon, SomsakulMoons, EllenJohansson, Lars S.O.

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