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TDAE chemisorbed on gold
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
2008 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 31Article in journal (Refereed) Published
Abstract [en]

DFT calculations on tetrakis(dimethylamino)ethylene (TDAE) interacting with a gold surface have been performed. A monolayer of TDAE deposited on a gold surface creates an interface dipole, which decreases the barrier for electron injection from a gold contact into an (organic) electroactive material. This was studied by simulating the complex in two different ways, using a slab model and using a gold cluster surface. These approaches are shown to be complementary: the cluster results apply to the situation of isolated molecules and the slab results describe the case of interacting TDAE molecules on the gold surface. We found that there is a transfer of around one electronic charge per TDAE to the gold in the limit of non-interacting TDAE molecules. This charge transfer results in the formation of an interface dipole and a corresponding lowering of the work function of the surface. The lowering of the work function increases with increasing coverage and is as large as 2.4 eV for a monolayer of TDAE on gold. Due to depolarization effects, the charge transfer in this state is reduced to 0.56 times the electronic charge.

Place, publisher, year, edition, pages
Bristol, United Kingdom: Institute of Physics Publishing (IOPP), 2008. Vol. 20, no 31
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-13872DOI: 10.1088/0953-8984/20/31/315008ISI: 000257759600025OAI: oai:DiVA.org:liu-13872DiVA: diva2:22057
Available from: 2006-06-28 Created: 2006-06-28 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Molecular Electronics: A Theoretical Study of Electronic Structure of Bulk and Interfaces
Open this publication in new window or tab >>Molecular Electronics: A Theoretical Study of Electronic Structure of Bulk and Interfaces
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. The materials studied include molecular crystals of pentacene and DNA, which are used as active material in field-effect transistors and as tentative molecular wires, respectively. The molecular magnet compound TCNE and surface modification by means of chemisorption of TDAE on gold are also studied.

Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field-effect transistors. The conduction process in field-effect transistors applications occurs in a single layer of the molecular crystal. Hence, in studies of transport properties molecular crystals of pentacene can be considered as a two dimensional system. An open question of these system is if the charge transport is bandlike or if as a result of disorder is a hopping process. We address this question in two of the included papers, paper I and paper II.

The conducting properties of DNA are of interest for a broad scientific community. Biologist for understanding of oxidatively damaged DNA and physicist and the electronics community for use as a molecular wire. Some reports on the subject classifies DNA as a conductor while other report insulating behavior. The outcome of the investigations are heavily dependent on the type of DNA being studied, clearly there is a big difference between the natural and more or less random sequence in, e.g., λ-DNA and the highly ordered syntethic poly(G)-poly(C) DNA. It has been suggested that long-range correlation would yield delocalized states, i.e., bandlike transport, in natural DNA, especially in the human chromosome 22. In paper III we show that this is not the case. In general our results show that DNA containing an approximately equal amount of the four basis is an insulator in a static picture.

An emerging research field is spintronics. In spintronic devices the spin of the charge carrier is as important as the charge. One can envision a device where spin alone is the carrier of information. In realizing spintronic devices, materials that are both magnetic and semiconducting are needed. Systems that exhibit both these properties are organic-based magnets. In paper IV the electronic structure of the molecular magnet compound TCNE is studied, both experimentally and theoretically.

The injection of carriers from metal contacts to organic semiconductors is central to the performance of organic based devices. The interface between the metal contact and the organic material has been pointed out to be one of the device parameters that most significantly influences the device performance. This relates to the process of injection of charge carriers in to the organic material. In some contact and organic material combinations the energy barrier for charge injection can be very high. The barrier can be reduced by modify the interface dipole, this is achieved by a monolayer of adsorbed molecules at the interface. The molecule TDAE chemisorbed on gold is studied in paper V.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 991
Series
Keyword
molecular electronics, electron transport, disorder, localization, long-range correlation, organometallic magnets, interface dipole
National Category
Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-6938 (URN)91-85457-82-5 (ISBN)
Public defence
2006-01-13, Planck, Fysikhuset, IFM, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2006-06-28 Created: 2006-06-28 Last updated: 2009-06-08
2. Molecular electronics : a theoretical study of electronic structure in molecular crystals and surfaces
Open this publication in new window or tab >>Molecular electronics : a theoretical study of electronic structure in molecular crystals and surfaces
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

  

This thesis deals with theoretical studies of the electronic structures of molecules in organic crystal and molecules adsorbed on metal surfaces. Both studies with first principle calculations and classical mechanics were performed. The materials include pentacene and bis(9-cyclohexylimino-l-oxyphenalenyl)boron and the

Tetrakis( dimethylamino )ethylene (TDAE) molecule chemisorbed on a gold surface. Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field effect transistors, and are therefore suitable to be the active material in such devices. The increase in conductivity obtained experimentally by doping with alkali metals showed great promise, and we therefore performed calculations on pentacene crystals doped with potassium. Phase transitions occured upon doping, and the herringbone arrangement of the pristine pentacene molecules relaxes towards a 1r stacked structure. Charge transfer between the crystal and the potassium occurs, which shifts the Fermi level into the lowest unoccupied molecular orbitals bands and turns the crystal metallic. The study of bis(9-cyclohexylimino-l-oxyphenalenyl)boron, a biphenalenyl based neutral radical, was performed in order to investigate the electronic properties since experimental studies had shown simultaneous electrical, optical and magnetical bistability. The system is quasi one-dimensional, as shown from band structure calculations.. The injection of charge carriers from metals to organic semiconductors is one of the most central processes when it comes to the performance of organic devices. The interface between the metal and the semiconductor is one of the device parameters that will significantly influence the device performance. The addition of a molecular layer on the interface can, by the introduction of a dipole, reduce the energy barrier for charge injection. ·we found that a molecular layer of TDAE deposited on a gold surface results in a charge transfer from the molecule to the surface which reduced the charge injection barrier by as much as 2.4 eV.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2007. 34 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1315
Series
LIU-TEK-LIC, 24
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-38440 (URN)44368 (Local ID)978-91-85831-76-0 (ISBN)44368 (Archive number)44368 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-14

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Unge, MikaelStafström, SvenBöhlin, Johan

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