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Inelastic Electron Tunneling Spectroscopy of Gold-Benzenedithiol-Gold Junctions: Accurate Determination of Molecular Conformation
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.ORCID iD: 0000-0003-0007-0394
2011 (English)In: ACS NANO, ISSN 1936-0851, Vol. 5, no 3, 2257-2263 p.Article in journal (Refereed) Published
Abstract [en]

The gold benzenedithiol gold junction is the classic prototype of molecular electronics. However, even with the similar experimental setup, it has been difficult to reproduce the measured results because of the lack of basic information about the molecular confirmation inside the junction. We have performed systematic first principles study on the inelastic electron tunneling spectroscopy of this classic junction. By comparing the calculated spectra with four different experimental results, the most possible conformations of the molecule under different experimental conditions have been successfully determined. The relationship between the contact configuration, and the resulted spectra is revealed. It demonstrates, again that one should always combine the theoretical and experimental inelastic electron tunneling spectra to determine the molecular conformation in a junction. Our simulations have also suggested that in terms of the reproducibility and stability, the electromigrated nanogap technique is much better than the mechanically controllable break junction technique.

Place, publisher, year, edition, pages
2011. Vol. 5, no 3, 2257-2263 p.
Keyword [en]
inelastic electron tunneling, molecular junctions, molecular conformations, density functional theory, vibrations
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-32041DOI: 10.1021/nn103522kISI: 000288570600085ScopusID: 2-s2.0-79952931567OAI: diva2:408120
Swedish Research Council
QC 20110404Available from: 2011-04-04 Created: 2011-04-04 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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