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Design and control of electron transport properties of single molecules
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
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2009 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 36, 15259-15263 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate in this joint experimental and theoretical study how one can alter electron transport behavior of a single melamine molecule adsorbed on a Cu (100) surface by performing a sequence of elegantly devised and well-controlled single molecular chemical processes. It is found that with a dehydrogenation reaction, the melamine molecule becomes firmly bonded onto the Cu surface and acts as a normal conductor controlled by elastic electron tunneling. A current-induced hydrogen tautomerization process results in an asymmetric melamine tautomer, which in turn leads to a significant rectifying effect. Furthermore, by switching on inelastic multielectron scattering processes, mechanical oscillations of an N-H bond between two configurations of the asymmetric tautomer can be triggered with tuneable frequency. Collectively, this designed molecule exhibits rectifying and switching functions simultaneously over a wide range of external voltage.

Place, publisher, year, edition, pages
2009. Vol. 106, no 36, 15259-15263 p.
Keyword [en]
hydrogen tautomerization, melamine molecules, rectifying effect, switching property, negative differential-resistance, scanning tunneling microscope, total-energy calculations, wave basis-set, conformational-changes, azobenzene, dissociation, efficiency, melamine, device
URN: urn:nbn:se:kth:diva-18741DOI: 10.1073/pnas.0903131106ISI: 000269632400033ScopusID: 2-s2.0-70349304456OAI: diva2:336788
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-05-24Bibliographically approved
In thesis
1. Understanding the Structure and Reaction of Single Molecules on Metal surfaces from First Principles
Open this publication in new window or tab >>Understanding the Structure and Reaction of Single Molecules on Metal surfaces from First Principles
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The study of surface adsorption and reaction is not only interesting from a scientific point of view, but also important in many application fields such as energy, environment, catalysis, corrosion, electronic device, and sensor. Theoretical calculations are essential in these studies.

In this thesis, first principles studies for the structure and reaction of some important single molecules on the surface are presented. Dehydrogenation of single trans-2-butene molecule on a Pd(110) surface is the first example. The adsorption configurations of both reactant and produce are assigned and the whole dehydrogenation pathway is revealed. Our calculations show that the reactant, i.e. trans-2-butene molecule, undergoes a rotation before dehydrogenation occurs, which is an important detail that cannot be observed directly in scanning tunneling microscopy (STM) experiments. The dissociation and rotation processes of single oxygen molecule on a Pt(111) surface have been a subject of extensive studies in the past. A new intermediate state with a peculiar configuration is identified. The puzzled adsorption site is well explained. The calculated energy barriers agree well with experimental results for both dissociation and rotation processes.

Another aspect addressed in this thesis is the mechanism of molecular electronic switches induced by molecular structural changes. By carefully examining the tautomerization process of a naphthalocyanine molecule, an intermediate state is located on the potential surface of the tautomerization. Our calculations indicate that the experimentally observed switching involves four-states, rather than the two-state as proposed by the experimentalists. In a joint experimental and theoretical study the dehydrogenation, tautomerization, and mechanical switching processes of a single melamine molecule on a Cu(100) surface have been comprehensively examined. A new dual-functional molecular device with integrated rectifying and switching functions is made for the first time. In collaborating with another experimental group, we have simulated the switching process of a single 1,1,2,3,4,5-hexaphenylsilole molecule on a Cu(111) surface. The role of the orientation of the molecule is carefully examined and a new switching mechanism is proposed.

Switching processes are strongly associated with the inelastic electron tunneling. We have proposed a statistical model that allows explaining the non-integer exponent in the power-law relationship between the switching rate and tunneling current. In this model, the importance of the randomness in inelastic electron excitations and the lifetime of the immediate state are emphasized. It has shown that the inelastic electron tunneling is a collection of various n-electron processes with different statistical weight.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xii, 72 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2011:16
National Category
Theoretical Chemistry
urn:nbn:se:kth:diva-33565 (URN)978-91-7415-978-3 (ISBN)
Public defence
2011-06-10, FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
QC 20110524Available from: 2011-05-24 Created: 2011-05-10 Last updated: 2011-05-24Bibliographically approved

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