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Assignments of Inelastic Electron Tunneling Spectra of Semifluorinated Alkanethiol Molecular Junctions
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0003-0007-0394
2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 41, 20301-20306 p.Article in journal (Refereed) Published
Abstract [en]

The peculiar experimental inelastic electron tunneling spectra of a series of hexadecanethiol molecular junctions have finally been reproduced by first-principles simulations. It is found that the debated spectral profile around 0.38 eV indeed originated from the C-H stretching vibration associated with at least two terminal methylene groups close to the sulfur atom. The intensity of this spectral peak becomes dominant, as observed in the experiments when the molecule is titled -40 degrees relative to the normal of the electrode surface, which is due to the opening of a new tunneling pathway bypassing the end sulfur atom. The dependence of this strong vibrational feature on the titled angle of the molecule is predicted with the help of the concept of effective coupling energy. The degree of the fluorination on the inelastic electron tunneling spectrum of hexadecanethiol molecules has also been discussed in detail.

Place, publisher, year, edition, pages
2011. Vol. 115, no 41, 20301-20306 p.
Keyword [en]
spectroscopy, transport, simulations, pathways, rules
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-46844DOI: 10.1021/jp206085uISI: 000295700800033ScopusID: 2-s2.0-80054769181OAI: diva2:454399
QC 20111107Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2012-05-15Bibliographically approved
In thesis
1. Theoretical Modeling of Intra- and Inter-molecular Charge Transport
Open this publication in new window or tab >>Theoretical Modeling of Intra- and Inter-molecular Charge Transport
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on theoretical study of charge transportproperties in molecular systems. The understanding of the transportprocess and mechanism in molecular systems is essential forthe design of new functional molecular materials and molecularelectronic devices. The molecular junctions and organic molecularcrystals have been used as the model systems to highlight the usefulnessof theoretical modelling. A molecular junction is a system that consists ofone or several molecules sandwiched between two electrodes.The charge transport in molecular junctions is a very complex processthat is affected by the interaction between molecules and electrodes,the surroundings, as well as electron-electron (e-e) andelectron-phonon (e-p) couplings. When the molecule-electrode couplingis strong, the transport process can be very quick. If the e-p couplingis weak, the inelastic tunneling has only negligible contributions to thetotal current and the elastic electron tunneling plays the dominant role.Furthermore, the hopping process becomes dominant in the case of strong e-pcoupling, for which the geometric relaxation of the molecule needsto be considered. In this thesis, we have examined these three kinds oftransport processes separately.

The first studied system is a molecular junction consisting of aromaticallycoupled bimolecules. Its elastic electron tunneling property is simulatedusing Green's functional theory at density functional theory level.The dependence of the conductance of bimolecular junctions on the vertical distances,horizontal distances and the tilt angles has been systematically studied. Theinelastic electron tunneling spectra (IETS) of molecular junctions have beencalculated for several systems that were experimentally measured with conflictingresults and controversial assignments. Our calculations provide the reliableassignments for the experimental spectra and revealed unprecedented detailsabout the molecular conformations within the junctions under different conditions.It demonstrates that a combined theoretical and experimental IETS study is capableof accurately determining the structure of a single molecule inside the junction.The hopping process is a dominant charge transfer process in organic molecularcrystals. We have studied the charge transport ability of four kinds of n-typeorganic semiconductor materials to find out the related structure-to-propertyrelationship. It is done by adopting the quantum charge transfer rate equationcombined with the random walk approach.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. x, 68 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2012:15
charge transport, molecular junction, organic molecular materials, Green's function, first-principles simulation
National Category
Physical Chemistry
Research subject
SRA - Transport
urn:nbn:se:kth:diva-94103 (URN)978-91-7501-371-8 (ISBN)
Public defence
2012-06-05, FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
TrenOp, Transport Research Environment with Novel Perspectives
QC 20120515Available from: 2012-05-15 Created: 2012-05-07 Last updated: 2012-05-15Bibliographically approved

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