Nanoelectronics – theory and simulation

Archive: Research highlights and news

21 October 2014 – Vibrations at Surfaces (VAS15)

The 15th International Conference on Vibrations at Surfaces (VAS15) will be celebrated in Donostia-San Sebastian during the week June 22-26, 2015. We are working hard to set up an exciting program for next year!

Information about the event is continously being added to the conference web page at vas15.dipc.org.


16 April 2014 – Research paper published in Nature Communications
Chemical control of electrical contacts to sp2 carbon atoms
by T. Frederiksen, G. Foti, F. Scheurer, V. Speisser, and G. Schull

NatCommun-artwork.png Carbon-based nanostructures are attracting tremendous interest as components in ultrafast electronics and optoelectronics. The electrical interfaces to these structures play a crucial role for the electron transport, but the lack of control at the atomic scale can hamper device functionality and integration into operating circuitry. Here we study a prototype carbon-based molecular junction consisting of a single C60 molecule and probe how the electric current through the junction depends on the chemical nature of the foremost electrode atom in contact with the molecule. We find that the efficiency of charge injection to a C60 molecule varies substantially for the considered metallic species, and demonstrate that the relative strength of the metal-C bond can be extracted from our transport measurements. Our study further suggests that a single-C60 junction is a basic model to explore the properties of electrical contacts to meso- and macroscopic sp2 carbon structures.

Nat. Commun. 5, 3659 (2014)



13-16 May 2013 – Workshop on Controlled Atomic Dynamics on Solid Surfaces: Atom and Molecular Manipulation (UEBA13)

Nicolás Lorente (CIN2), Magnus Paulsson (Linnaeus University), and I thank all the participants of the workshop on Controlled Atomic Dynamics on Solid Surfaces: Atom and Molecular Manipulation dedicated to Prof. Ueba for contributing to a stimulating and dynamic meeting.

UEBA13-lowres

The workshop webpage is this one: http://dipc.ehu.es/ws_presentacion.php?id=91.


14 March 2013 – Announcement of Workshop on Controlled Atomic Dynamics on Solid Surfaces: Atom and Molecular Manipulation

Together with Nicolás Lorente (CIN2) and Magnus Paulsson (Linnaeus University) I am organizing a workshop to be held on May 13-16, 2013 at the DIPC. The topics include STM manipulation, current-induced reactions, dynamics on surfaces, excitations at surfaces, action spectroscopy, inelastic electron tunneling, atom-by-atom construction of nano systems, etc. The workshop is dedicated to Prof. Hiromu Ueba and to all of his contributions to these fields.

More information about the workshop can be found here: http://dipc.ehu.es/ws_presentacion.php?id=91.


24 February 2012 – TStutorial moved to the dipc web server

The TStutorial wiki, a user-driven introduction/tutorial to the TranSIESTA quantum transport program, was moved today to http://dipc.ehu.es/frederiksen/tstutorial/ due to discontinued hosting service at dreamhosters.com.


1 February 2012 – Science communication on H-atom relays published in Elhuyar magazine

A science communication on H-atom relays, recently published in Nature Materials, was given in Elhuyar Science and Technology magazine. The article can be found here (in basque).


7 December 2011 – Research paper published in PRL

Engineering Negative Differential Conductance with the Cu(111) Surface State
by B. W. Heinrich, M. V. Rastei, D.-J. Choi, T. Frederiksen, and L. Limot C60-tip images

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate electron tunneling from a C60-terminated tip into a Cu(111) surface. Tunneling between a C60 orbital and the Shockley surface states of copper is shown to produce negative differential conductance (NDC) contrary to conventional expectations. NDC can be tuned through barrier thickness or C60 orientation up to complete extinction. The orientation dependence of NDC is a result of a symmetry matching between the molecular tip and the surface states. Phys. Rev. Lett. 107, 246801 (2011).


27 November 2011 – Research paper accepted in Nature Materials

H-atom relay reactions in real space
by T. Kumagai, A. Shiotari, H. Okuyama, S. Hatta, T. Aruga, I. Hamada, T. Frederiksen, and H. Ueba
H2O-OH-OH.jpg
Hydrogen bonds are the path through which protons and hydrogen atoms can be transferred between molecules. The relay mechanism, in which H-atom transfer occurs in a sequential fashion along hydrogen bonds, plays an essential role in many functional compounds. Here we use the scanning tunnelling microscope to construct and operate a test-bed for real-space observation of H-atom relay reactions at a single-molecule level. We demonstrate that the transfer of H-atoms along hydrogen-bonded chains assembled on a Cu(110) surface is controllable and reversible, and is triggered by excitation of molecular vibrations induced by inelastic tunnelling electrons. The experimental findings are rationalized by ab initio calculations for adsorption geometry, active vibrational modes and reaction pathway, to reach a detailed microscopic picture of the elementary processes. Nature Materials AOP, doi:10.1038/nmat3176


14 November 2010 – Research paper published in Nature Nanotechnology

Atomic-scale engineering of electrodes for single-molecule contacts

by Guillaume Schull, Thomas Frederiksen, Andres Arnau, Daniel Sanchez-Portal, and Richard Berndt
nnano.2010.215.png
The transport of charge through a conducting material depends on the intrinsic ability of the material to conduct current and on the charge injection efficiency at the contacts between the conductor and the electrodes carrying current to and from the material. According to theoretical considerations, this concept remains valid down to the limit of single-molecule junctions. Exploring this limit in experiments requires atomic-scale control of the junction geometry. Here we present a method for probing the current through a single C60 molecule while changing, one by one, the number of atoms in the electrode that are in contact with the molecule. We show quantitatively that the contact geometry has a strong influence on the conductance. We also find a crossover from a regime in which the conductance is limited by charge injection at the contact to a regime in which the conductance is limited by scattering at the molecule. Thus, the concepts of ‘good’ and ‘bad’ contacts, commonly used in macro- and mesoscopic physics, can also be applied at the molecular scale. Nature Nanotechnology 6, 23–27 (2011).



23 September 2010 – Interview published in local newspaper
In connection to the present celebrations of the 10 years anniversary of the DIPC and the forthcoming Passion for Knowledge conference Ricardo Díez Muiño, Pedro Miguel Etxenike and I gave interview to the local newspaper Gara: "Una gran locura que se ha convertido en un gran invento".



8 September 2010 – DIPC workshop on "Inelastic Transport Phenomena"

The Donostia International Physics Center hosted a workshop on Inelastic Transport Phenomena in the city of Donostia-San Sebastián on September 1-3, 2010. The workshop aimed at the identification and promotion of the common elements developed in experimental and theoretical studies of inelastic transport phenomena, which are fundamental for the development of nanoelectronics. The program of this 3-day workshop was built around several invited talks and a poster session covering some important recent contributions in the field. The workshop was organized by Dr. Aran Garcia-Lekue and myself together with the steering committee of Prof. Andres Arnau, Dr. Nicolas Lorente, Prof. Stephan Roche, and Dr. Daniel Sanchez-Portal.

2010-workshop-lowres

Workshop webpage: http://dipc.ehu.es/ws_presentacion.php?id=54.


8 June 2010 – CECAM workshop on "Transport Phenomena in Molecular Nanostructures"
The CECAM workshop "Transport Phenomena in Molecular Nanostructures" will be held in Zurich, Switzerland, in the days June 22-25, 2010. The objective of the workshop is to provide a platform where computational scientists interact with mathematically and experimentally oriented experts in the different subfields such as Mesoscopic Physics, Surface Science, and Material Science. Organizers: Thomas Frederiksen (DIPC), Ferdinand Evers (Karlsruhe Institute of Technology, Germany), and Kyungwha Park (Virginia Tech, USA).
Workshop webpage: http://www.cecam.org/workshop-434.html.



6 June 2010 – Video competition

Within the framework of the activities to mark the 10th anniversary of the Donostia International Physics Center (DIPC), the Elhuyar Foundation and the DIPC are organising a home video competition designed to communicate science and technology. First prize: 3,000 euros, Second prize: 2,000 euros, Third prize: 1,000 euros. Registration: from 3 May until 15 October, 2010.
Full information is available here: http://www.onzientzia.tv/?lang=EN.


7 January 2010 – TStutorial wiki available
A three-day school on the TranSIESTA code took place in Barcelona on December 14-16, 2009. The organizers of this event were Frederico D. Novaes, M. Paulsson and T. Frederiksen. Everything related to the course (presentations, exercises, etc.) is contained in this wiki, which is intended to be a user-driven introduction/tutorial to the TranSIESTA quantum transport program.
TStutorial webpage: http://wiki.tstutorial.dreamhosters.com/wiki/Main_Page.


29 December 2009 – Inelastica 1.1 released
Inelastica-1.1 is released with a number of improvements and bug fixes. It can be downloaded here.


13 November 2009 – Cover illustration of PRL

prl-cover Images from Passing Current through Touching Molecules is selected for the cover of PRL volume 103, number 20.










12 November 2009 – In the media
The research publication "Passing Current through Touching Molecules" is mentioned in several news media, including Universia.es (spanish), UPV/EHU (spanish), UPV/EHU (basque), EurekAlert, ScienceDaily.com, nanowerk.com, sciencecodex.com, nanotech-now.com, basqueresearch.com, Internetchemie.info, nanotecnologica.com (spanish), pressrelations.de (german), and idw-online.de (german).



30 October 2009 – PRL and Focus article
Physical Review Focus article "Molecular Currents" on the publication
Passing Current through Touching Molecules
by Guillaume Schull, Thomas Frederiksen, Mads Brandbyge, and Richard Berndt
C60 molecule on tip The charge flow from a single C60 molecule to another one has been probed. The conformation and electronic states of both molecules on the contacting electrodes have been characterized using a cryogenic scanning tunneling microscope. While the contact conductance of a single molecule between two Cu electrodes can vary up to a factor of 3 depending on electrode geometry, the conductance of the C60-C60 contact is consistently lower by 2 orders of magnitude. First-principles transport calculations reproduce the experimental results, allow a determination of the actual C60-C60 distances, and identify the essential role of the intermolecular link in bi- and trimolecular chains. Phys. Rev. Lett. 103, 206803 (2009).



13 October 2009 – Release of Inelastica 1.0
Inelastica-1.0 released on SourceForge
Inelastica logo
Inelastica is the name of a Python package related to the SIESTA / TranSIESTA DFT codes. It is written together with Magnus Paulsson and is freely available for download here:

https://sourceforge.net/projects/inelastica/

For more information please have a look at the project wiki.