|Current Workshop | Overview||Back | Home | Search ||
Transport through Single Molecules
Monday, 7 March 9:15 am.
"Experimental approaches in transport through single molecules"
Herre van der Zant
There are several methods to contact single molecules. Each of them has its advantages and disadvantages. A reliable method suitable for a large variety of molecules does not exist. Scanning-probe techniques and mechanical break junctions offer mechanical control, but the incorporation of a third, gate electrode is difficult. Three-terminal molecular junctions have been made using standard (e-beam) fabrication techniques. In combination with electro-chemical methods, atomic control over the gap distance has been obtained, but the electrochemistry itself is complex. In the electromigration technique a small wire is broken by passing a large current through it. This widely used technique has the disadvantage that small gold grains are formed near the gap region masking single molecule behavior. A recent development is the use of nanotube as leads to contact small molecules, but in this case the nanotube itself can add spectroscopic features as well. Despite these shortcomings, many exciting experiments on single molecule transport have been performed. An overview will be given, highlighting the experimental approaches.
Tuesday, 8 March 9:00 am.
"Introduction to the theory of electron transport in molecular systems"
Tuesday, 8 March 2:00 pm.
"What can we learn about a naojunction from current and voltage"
Wednesday, 9 March 9:00 am.
"Carbon Nanotubes Nanocomposites – Quasi 1-Dimensional Structures for Electron Transfer"
Dirk M. Guldi, Jeff Ramey
Universität Erlangen-Nürnberg, Germany
University of Notre Dame, USA
Universität Erlangen-Nürnberg , Germany
Nikos Tagmatarchis, Maurizio Prato
Università di Trieste, Italy
Nanoscale carbon materials (i.e., fullerenes and nanotubes) are attractive platforms for applications in photovoltaics. These nanoscale materials have extended, delocalized π-electron systems, which, in combination with photoexcited electron donors, may make them useful for managing charge transfer within novel, ultra-high efficient photoelectrochemical cells for water splitting and reduction of CO2 to fuels.
Single wall carbon nanotubes (SWNT) may also serve as the electron acceptor component in donor-acceptor ensembles, just as fullerenes have been the electron acceptors in much recent research. Notably, the expected electrical conductivity behavior associated with the tubular structure and good chemical stability opens new promising scenarios for their use as “molecular wires” with high surface areas in the design of electro- and photoactive ensembles. However, there are several obstacles in the way of integrating SWNT into functional donor-acceptor constructs and their use in practical applications. Controlled modification of their surface with multifunctional groups – chromophores, electron donors, biomolecules, etc. – is required to fully realize their potential.
I will discuss recent advances in the design, synthesis, purification, characterization, and examination of the potential for applications of new multifunctional SWNT materials as two- or three-dimensional architectures for high mechanical strength and electron donor-acceptor chemistry.
For example, we reported recently on the photoinduced electron transfer within a novel single wall carbon nanotube – ferrocene nanohybrid (SWNT-Fc), which yields a long-lived charge-separated (SWNT)•–-(Fc)•+ state. The presence of SWNT•–, detected by laser flash photolysis, has been confirmed by time-resolved pulse radiolysis and steady-state bulk electrolysis.
In complementary work we tested the coulomb complex formation of water-soluble SWNT grafted with poly(sodium 4-styrenesulfonate) (SWNT-PSS) and a 5,10,15,20-tetrakis-(2’,6’-bis-(N-methylene-(4’’-tert-butylpyridinium))-4’-tert-butylphenyl)porphyrin octabromide salt (H2P8+) en route to versatile donor-acceptor ensembles. Photoexcitation of the porphyrin chromophore in SWNT-PSSn- / H2P8+ is followed by a rapid and efficient intra-ensemble charge separation to generate a charge-separated state that lives for tens of microseconds.
Wednesday, 9 March 2:00 pm.
"Supramolecular Engineering at Surfaces: Control of Matter at the Nanoscale"
Thursday, 10 March 9:20 am.
Title to be announced
CEA Saclay, France
Thursday, 10 March 2:00 pm.
Conductance calculations for small molecules
Technical University of Denmark, Lyngby, Denmark
The conductance of a several different small molecules have been calculated based on density-functional theory. The calculations are carried out using a Green function technique based on maximally localized and partly occupied Wannier functions. The Wannier functions are convenient for the calculations because they combine high accuracy with a local chemical intuitive representation. The latter aspect allows for a detailed orbital analysis of the mechanisms behind the transport.
We have focused on the structure, dynamics and tranport of reasonably small molecules many of which have also been investigated experimentally. Some of the results are for the following systems.
Hydrogen molecule between Pt electrodes: Different possible structures and vibrational modes are identified as a function of contact strain together with calculations of the coherent transport. The findings support the previous suggestion of a molecule bridging between two electrodes and it is shown that the molecular antibonding state is responsible for the nearly open conductance channel.
CO between Pt electrodes: A single CO molecule is found to bind to Pt contacts with several different geometries. During the breaking of the contact the molecule switches from being bound through the carbon atom to both electrodes to a more bridge-like configuration which has a conductance close to half a quantum unit. This may explain the recently observed half-integer peak in experiments performed in Leiden.
Results for (nitro-)benzene and bipyridine will also be presented with particular focus on the connection between bonding and transport as the bonding geometry and electrode material is changed.
Friday, 11 March 9:00 am.
"Molecular Electronics: The Organic Chemists' Viewpoint"
Friday, 11 March 2:00 pm.
"Wet molecular junctions"
Saturday, 12 March 9 am.
"Scanning tunneling spectroscopy of single magnetic adatoms and complexes at surfaces"
MPI Stuttgart, Germany
The spin of individual magnetic atoms and molecules at surfaces is of fundamental interest and may play an important role in future atomic-scale technologies. Starting from a study of the behaviour of single cobalt adatoms on noble metal surfaces by low temperature STM and STS, we demonstrate the ability to manipulate the spin state and the associated magnetic properties of individual adatoms by the controlled attachment of molecular ligands. The spin state of the resulting complexes is determined via the Kondo resonance, which appears in STS spectra. Spectroscopic results are complemented by a study of the spatial dependence of the Kondo resonance. This novel imaging mode allows to map the spin centers of magnetic molecules with atomic precision. Spin detection and mapping via the Kondo Effect is compared to other SPM-related techniques offering spin contrast.
"Liquid gating of single molecules in break junctions"
either on Thursday or on Friday,
"Electrical transport through DNA molecules under stretching"
Theoretical calculations have demonstrated that the charge transport through the DNA will be strongly influenced by conformational transitions. To probe this effect, we have measured the resistance of DNA molecules under stretching with the help of the mechanically controllable break junction technique (MCB). Using the break junctions, we are able to fabricate electrodes with nanometer separation and fine-tune the tunneling gap between electrodes. In our experiments, we used 10-nm-long (30 base pairs) DNA with thiol groups at both ends, and stretched continuously the trapped molecules by means of MCB. A discrete two-level resistance switching behavior is observed when changing the distance of the electrodes.
"C60 in gated nanogaps"
I shall describe our recent unpublished experiments with deposition of fullerenes in metallic nanogaps prepared on top of electrostatic gate made of oxidized aluminium.
"One-way switching of photochromic molecules on gold"
Sense Jan van der Molen, D. Dulic, T. Kudernac, H.T. Jonkman, J.J.D. de Jong, T.N. Bowden, J. van Esch, B.L. Feringa, and B.J. van Wees
Groningen, The Netherlands
Single-molecule electronics provides an interesting pathway for further miniaturization of electronic devices. We concentrate on creating a molecular switch that can be manipulated with light. For this, we investigate photochromic molecules (1,2-bis[5’-(5”-acetylsulfanylthien-2”-yl)-2’-methylthien-3’-yl]) that are synthesized in the chemical department of our institute. In solution, these organic molecules can be switched reversibly between a conjugated, ‘conductive’ state and a non-conjugated, ‘insulating’ state by using light of the proper wave lengths (conjugated to non-conjugated: l » 550 nm; non-conjugated to conjugated: l » 330 nm).
Two ways of contacting are chosen, both based on the Au-S bond. First, we use the mechanically controllable break junction (MCBJ) technique, which allows us to manipulate the distance between two gold electrodes with sub-Angstrom precision. Second, we study a diluted self-assembled monolayer (SAM), i.e. dodecanethiol containing a low concentration of the switch, using scanning tunneling microscopy (STM). In both experiments, we observe switching from the ‘conductive’ to the ‘insulating’ state. However, we do not observe the reverse process, which should occur upon illumination with UV light. An independent optical absorption experiment using a solution of gold colloids covered by switchable molecules confirms this observation: once connected to gold, the molecule can switch from conjugated to non-conjugated, but it cannot switch back. We attribute this effect to quenching of the excited state of the non-conjugated molecule by the presence of gold [1,2]. Finally, we discuss a possible way out of this problem, using newly synthesized organic molecules.
 D. Dulic, S.J. van der Molen, T. Kudernac, H.T. Jonkman, J.J.D. de Jong, T.N. Bowden, J. van Esch, B.L. Feringa, and B.J. van Wees,
Phys. Rev. Lett. 91 (20), 207402 (2003)
 R. Hania, A. Pugzlys, T. Kudernac, H.T. Jonkman and K. Duppen
Proceedings of 14th International Conference on Ultrafast Phenomena,
July 25-30, 2004 Toki Messe, Convention Center Niigata, Japan.
"Coordination complexes with redox active TTF-type ligands"
Designing molecule-based materials, which possess synergy or interplay between two or more properties such as electrical conductivity with magnetism or spin cross-over …, is currently a challenging target and it have been attracting great interests from chemists and physicists for both application to devices or for fundamental science. For the particular class of materials combining electrical conductivity and magnetic interactions, it is hopped to achieve magnetic coupling between the localized spin of the inorganic part through the mobile electrons of the organic part via the so-called p-d interactions . We present in this contribution some of our results according to the idea consisting in the synthesis of paramagnetic coordination complexes [2,3] containing TTF’s as ligands as well as their radical cation salts .
 L. Ouahab, T. Enoki, Eur. J. Inorg. Chem., 2004, 931
 F. Iwahori et al. Inorg. Chem., 2001, 40, 6541
 L. Ouahab et al Synthetic Metal, 2003, 133-134, 505
 F. Setifi et al. Inorg. Chem., 2003, 42, 1791
"Intramolecular Electron Transfer in Organic Radical Ions"
Prof. J. Veciana
"Single Molecule Transport Measurements through Transition Metal Complexes"
Mario Ruben 1,Aitor Landa 1, Heiko Weber 1, Jan Würfel1, Marcel Mayor1
Institute of Nanotechnolgy,Research Centre Karlsruhe, P.O. 3640,D-76021 Karlsruhe
Electronic transport through single molecules is a driving new direction in the science and technology of nano-metre-scale electronic systems. Especially, the use of the mechanically controlled break junction techniques has been proven to a powerful tool, since it enables a symmetrical connection to both electrodes by well defined covalent, mostly Au-S, bonds. Herein, we describe the use of terpyridine molecules incorporating a transition metal and having attached fully conjugated, conformationally rigid organic linkers in I-V measurements in break junctions.
The class of transition metal–bis(terpyridyl) complexes exhibits a broad variety of highly interesting properties. In particular, the complexes containing Ru2+ have been shown to act as photo- and electrochemically driven molecular switches in a multitude of supramolecular devices. In order to to determine the electronic and photophysical properties of this class of complexes at the single molecule level, we have synthesized taylor-made molecule 1 and investigated its I-V characteristics in a mechanically controlled break junction set-up.
Thereby, we have found that the spatial symmetric of 1 is reflected in rather symmetric I-V characteristics. The molecule 1 exhibits a single-molecule conductance of G = 10-8 S. Further details of the electronic characteristics will be discussed.
We would like to acknowledge the support by the BMBF-FZK network project MOLMEM (13N8360) of the German Ministry of Education and Research.
"The relationship between bonding and conductance in a bipyridine molecular contact"
Inspired by recent experiments, where the forces and conductances through bipyridine nano-junctions have been measured simultaneously, we performed total energy and conductance calculations based on density functional theory. Our study focuses on a variation of the surface geometry of the gold leads, to which the molecules are connected, and on the effect that this has on the binding energy and the electron transmission through the molecule. We find that the binding energy depends linearly on the coordination number of the gold atom the molecule is connected to and can be explained in terms of the interaction between the HOMO and the Au-s-states. The conductance is mediated by the LUMO only, which shifts in its energetic position relative to the metal's Fermi level depending on its surface geometry. We explain the resulting conductance behaviour using a simple one-level model.
"Characterization of electromigration-induced gold nanogaps"
Trouwborst M.L., Van der Molen S.J., Dulic D., Van Wees B.J.
Groningen, the Netherlands
One of the challenges in single-molecule electronics, is the development of stable electrodes, with gaps in the (sub)nanometer range. In the past years, some creative solutions have been found for manufacturing such nanojunctions. One of the fastest methods is fabrication with the help of electromigration . We have created electromigration-induced gaps, approximately 0 to 2 nm in width, and have investigated the breaking process.
Our samples are fabricated using electron-beam lithography, and consist of a gold wire with a constriction in the middle with a thickness of 12 nm and a with of 100 nm. The gaps are formed by sending a current through the wire. When the current density exceeds a certain value, the electromigration process will start, finally leading to the formation of a gap.
We have investigated the electromigration process at constant voltage and made a comparison with simulations performed by Mahadevan et.al.  We have found that the data fits well with stimulation, except for the initial part and the part just before breaking. For the first part, we observe a resistance decrease prior the narrowing of the gap. We ascribe this initial resistance decrease to a pushing away of impurities and vacancies in the bulk, by the high current density in the wire. This behavior is especially present at the room temperature data. For the data at 4.2 Kelvin, this “cleaning” effect has not been observed. This is as expected since at lower temperatures it is harder for the impurities to diffuse.
For the last part of the electromigration process, the conductance is expected to decrease logarithmically with time. However, we observe steps in the conductance just prior the breaking. This behavior is expected, when considering a small number of atoms present in the constriction, starting to dominate the total resistance. The observed conductance steps are in the order of 1-8 times the conductance quantum 2*e2/h.
These conductance plateaus are investigated at different voltages. At voltages higher than 0.8 Volt, the conductance is no longer quantized, but starts to vary at non-integer values of 2*e2/h. This value for the critical voltage is also observed by Mizobata et al , and is not yet completely understood.
 H. Park et al, Appl. Phys. Lett. 75, 301 (1999)
 M. Mahadevan, R.M. Bradley, Phys. Rev. B. 59, 11037 (1999)
 J. Mizobata et al, Phys. Rev. B. 68, 155428 (2003)
Fig.1 Electromigration sample.
Constriction in the middle is ~12×100 nm (h×w)
"Application of nanoparticle arrays in molecular electronics"
A great challenge in molecular electronics is to overcome the huge size mismatch between a molecule and an electronic device. An alternative approach is to use colloidal particles as a media to interconnect molecules to external leads. Herein, 2D nanoparticle arrays were prepared by self-assembly on water surface and acted as breadboards for mesurement of molecules. Molecular wires (OPE and OPV) were inserted to connect neighboring nanoparticles by molecular exchange. This method can give average information of molecular transport properties.
"The electron conduction of photosynthetic protein complexes embedded in a membrane"
Universiteit Leiden, Netherlands
"Simulating electron transport in atomic-scale systems from first principles"
In this talk we concentrate on our results for the transport channels of single atom wide metal contacts. We consider contact systems of different metals connecting perfect bulk electrodes where detailed experimental data is available . The odd-even behaviour of the conductance of monovalent atomic chains as a function of chain-length is investigated  as well as the effect of impurities present in the chains. We discuss the forces acting on the contact atoms due to the non-equilibrium situation in the electronic subsystem, i.e. in the presence of an electronic current .
 M. Brandbyge, J. Taylor, K. Stokbro, J-L. Mozos, and P. Ordejon, Phys. Rev. B 65, 165401 (2002).
 J. M. Soler, E. Artacho, J. D. Gale, A. Garcia, J. Junquera, P. Ordejon, and D. Sanchez-Portal, J. Phys. C 14, 2745 (2002).
 S. K. Nielsen, M. Brandbyge, K. Hansen, K. Stokbro, J. M. Van Ruitenbeek, and F. Besenbacher, Phys. Rev. Lett. 89, 66804 (2002).
 Y. J. Lee, M. Brandbyge, M. J. Puska, J. Taylor, K. Stokbro, and R. M. Nieminen, Phys. Rev. B 69, 125409 (2004).
 M. Brandbyge, K. Stokbro, J. Taylor, J. L. Mozos, P. Ordejon, Phys. Rev. B 67, 193104 (2003).
"A Statistical Approach for the Investigation of Charge Carrier Transport through Single Molecules"
Emanuel Lörtscher*, Heiko B. Weber+ and Heike Riel*
* IBM Research GmbH, Rueschlikon, Switzerland
+ University of Erlangen-N¨urnberg, Germany
A fundamental understanding of conductance through metal-molecule-metal junctions is a key challenge of molecular electronics and a requirement for future applications. However, for any implementation into circuits, the contacting of single molecules by symmetric electrodes remains challenging and charge carrier transport through single molecules can be dominated by the nature of the contact between molecule and electrodes.
Statistical investigation of charge carrier transport through metal-moleculemetal junctions is performed by a mechanically controllable break-junction (MCBJ) technique . Our system is designed to acquire data automatically during the stepwise opening and closing of the junction. This approach requires an excellent mechanical stability which is testified by consistently observable quantized conductance of quantum point contacts at room temperature. Analysis tools provide the basis for statistical examination of comprehensive data sets to perform e.g. conductance spectra at different voltage points.
A model system consisting of one, two, three and four phenyl units terminated symmetrically by acetyl protected thiol groups [a] has been investigated. We report an extensive data set of reproducible and stable current-voltage curves reflecting the characteristics of the individual molecule. Conductance studies at different temperatures will be compared to results achieved by other techniques [3,4] and theoretical predictions.
[a]Courtesy of the Institut fuer Nanotechnologie, Forschungszentrum Karlsruhe, Germany
 J. Moreland and J. Elkin, J. Appl. Phys. 58, 3888 (1985).
 C. J. Muller, J. M. van Ruitenbeek, and L. de Jongh, Physica C 191, 485 (1992).
 S. Hong, R. Reifenberger, W. Tian, S. Datta, J. Henderson, and C. P. Kubiak, Superlattices and Microstructures 28, 289 (2000).
 M. A. Reed, C. Zhou, C. Muller, T. Burgin, and J. Tour, Science 278, 252 (1997).
Inelastic scattering in atomic junctions
"Inelastic transport in atomic gold wires - a first principles approach"
Technical University of Denmark, Lyngby, Denmark
We describe a method for calculating the conductance of nanosized systems taking into account inelastic effects related to local vibrations in the junction. This method combines Density Functional Theory (DFT) for the electronic structure and vibrational modes with non-equilibrium Green's functions (NEGF) for the steady current and power flow. The electron-vibration interaction is treated within the self-consistent Born approximation (SCBA). The scheme is applied to atomic gold wires for which comparison with experimental results can be made. We show results for a four-atom wire under two different states of strain, and discuss mode selectivity as well as signatures of phonon heating.
"Theoretical description of electrical conduction through platinum wires"
"Electronic Interactions in a New p-Extended Tetrathiafulvalene Dimer"
Marta C. Díaz,a Beatriz M. Illescas,a Nazario Martína,* Igor F. Perepichka,b Martin R. Bryce,b,* and Eric Levillain,c
a Universidad Complutense, Madrid, Spain.
bUniversity of Durham, Durham,United Kingdom.
c CNRS UMR 6200, Angers, France
To study the electronic interactions between the two redox centers in extended TTF molecules (exTTF) we synthesized compound D-D in which two exTTF units linked together.
Cyclic voltammetry (CV) of D–D shows two quasi-reversible oxidation waves (Fig. 1). These redox processes can be described either as:
D0–D0 à D2+–D0 à D2+–D2+ (one 2e-process at each step; two exTTF units interacts electronically) or
D0–D0 à D·+–D·+ à D2+–D2+ (two 1e-processes at each step; no electronic interactions between the exTTF units).
To clarify the mechanism of the redox transformations, spectroelectrochemical experiments (SEC) for D–D and the monomeric exTTF D have been performed (Fig. 2). An oxidation of D–D results in a new broad band in the region of 460–540 nm, which is characteristic for the dication D2+ species (as confirmed by comparison with the SEC for the monomeric exTTF D). No long-wavelength absorption in the region of 560–700 nm, where the radical cations of the exTTF expected was observed during the oxidation of D–D (Fig. 2). Good isobestic points leave no room for the existence of D·+ species during the oxidation.
Similar evolution of the spectra was observed at the chemical oxidative titration of D–D by NOSbF6. SEC experiments in thin layer conditions demonstrates the spectral features of D2+–D0 and D2+–D2+ species. All these data point to the electrochemical oxidation of compound D–D occuring as two consecutive 2e processes:
D0–D0 à D2+–D0 à D2+–D2+. With this model, we found a good correlation between the experimental CVs in diffusion conditions at different scan rates and their simulations.
Thus, the oxidation of D–D can be interpreted by two consecutive inverted potentials on each exTTF moiety, which are electronically interacting.
"Nano-meter scale contacts by controlled electromigration"
Kavli Institute of Nanoscience, Delft University of Technology, Netherlands
Electromigration is currently a favourite technique for making molecular-scale electrodes: a high current in a wire 50nm wide by 10-20nm high can move enough material to create a 1-10nm gap, which may be subsequently bridged by a molecule. Typically considered a nuisance in the electronics industry, electromigration has been successfully used to measure conduction through single molecules. It suffers, however, from lack of yield and controllability, making it necessary to often break thousands of samples for a reasonable yield of credible single-molecule transport data. We discuss briefly how electromigration may be controlled to optimize the resistance of the junction and thus increase device yield, and present data on bare gold electrodes and single molecules.
Stretching dependence of the vibration modes of a single-molecule Pt-H2-Pt junction
D. Djukic, C. Untiedt, R.H.M. Smit, and J.M. van Ruitenbeek
Kamerlingh Onnes Laboratorium, Universiteit Leiden, Netherlands
K.S. Thygesen and K.W. Jacobsen
Technical Univiversity Denmark, Lyngby, Denmark
A conducting bridge of a single hydrogen molecule between Pt electrodes is formed in a break junction experiment. It has a conductance near the quantum unit carried by a single channel. Using point contact spectroscopy three vibrational modes are observed and their variation upon stretching and isotope substitution is obtained. The interpretation of the experiment is verified by Density Functional Theory calculations for the stability, vibrational modes and conductance of the PtH2 structure.
Vibrational spectroscomicroscopy of carbon nanostructrures with atomic resolution
L.Vitali, M.Burghard, P.Wahl, M.A.Schneider, K.Kern
Max-Planck-Institute, Stuttgart, Germany
Inelastic Electron Tunneling Spectroscopy (IETS-STM) is an elegant technique to probe the vibrational states of individual molecules adsorbed at surfaces. Moreover it has recently been demonstrated by IETS-STM measurements of HOPG surfaces that the inelastic spectrum is directly proportional to the total density of states.
The scanning tunneling microscope is also ideally suited to identify and characterize local defects, such as intermolecular junctions and endings of carbon nanotubes. Indeed the predicted signature of these local topological structures on the tube electronic properties has been measured by scanning tunneling spectroscopy. Despite the electronic characterization of these defects from the theoretical and the experimental point of view, little is known with respect to their vibrational properties. In this work, the capability of IETS-STM to probe vibrational features on the atomic scale have been applied to study single wall carbon nanotubes adsorbed on Au substrates. The radial breathing mode (RBM) of isolated tubes has been identified and its linear dependence on the inverse of the tube diameter is demonstrated. Moreover, the high spatial resolution has allowed the unraveling of changes in the local phonon spectrum related to topological defects.
One-dimensional supramolecular ordering of oxalic amidine derivates on a noble metal substrate
F. Klappenberger, Marta Esther Cañas Ventura, Stéphane Pons, Sylvain Clair, Zhi-Rong Qu, Mario Ruben, Roman Fasel, Klaus Kern, Harald Brune, Johannes V. Barth
Scanning tunneling microscopy investigations of an oxalic amidine derivate on a metal surface are presented. The studies were carried out at low temperatures under ultra high vacuum conditions. The oxalic amidine, which was synthesized as organic molecular beam epitaxy compatible base compound for molecular magnetism, self-assembles in linear nanostructures on the Au(111) surface. This supramolecular arrangement indicates intermolecular hydrogen bonds mediated by NH groups. It implies presumably mesomeric state of the ONH group along the supramolecular lines, giving rise to particular electronic properties. The mesoscopic ordering of the molecular chains is influenced by the substrate chevron reconstruction. In addition, first results on metallosupramolecular arrangements obtained by reticulating of the oxalic amidine species with codeposited Fe atoms are shown.
Metallosupramolecular nanocavities and ribbons on fcc (111) noble metal surfaces
Marta Esther Cañas Ventura 1,2, Stéphane Pons 1, Sylvain Clair 1, Florian Klappenberger 1 , Zhi-Rong Qu 3, Mario Ruben 3, Roman Fasel 2, Klaus Kern 1,4, Harald Brune 1, Johannes V. Barth 1,5
1 École Polytechnique Fédérale de lausanne, Institut de Physique des Nanostructures (IPN), Lausanne, Switzerland
2 Swiss federal Laboratories for materials testing and Research (EMPA), Thun, Switzerland
3 Institute of Nanotechnology, Forschungszentrum Karlsruhe, Karlsruhe, Germany
4 Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
5 Advanced Materials and Process Engineering Laboratory, University of British Columbia, Vancouver, Canada
In order to advance the understanding and nanoscale control of molecular self-assembly processes at surfaces, systematic investigations on the adsorption of 1,4-benzenedicarboxylic acid (TPA) on single crystal metal surfaces have been carried out. In situ low-temperature scanning tunneling microscopy (STM) studies under ultra high vacuum provide atomistic insight into the underlying intermolecular and molecule-substrate interactions. The TPA building blocks deposited on Pd (111) produce linear hydrogen-bonded stripes in three orientations (reflecting the substrate symmetry) which do not reticulate. When Fe is subsequently added it decorates the stripe edges and connected networks evolve leading to the formation of nanocavities, which can serve as template for growing new metallic nanstructures. Furthermore, metallosupramolecular ribbons with length of hundreds of nanometers are built when depositing TPA on a pre-patterned Fe/Au (111) surface. In this system the chevron reconstruction of Au (111) plays an important role for nanotexturing.
Electron Transport through the Single Molecule Magnet Manganese-12
Kavli Institute of Nanoscience, Delft University of Technology
The single molecule magnet Manganese-12 (Mn-12) is a well known molecule due to its high spin ground state (S=10). Although the magnetic properties of Mn-12 have been studied extensively, little is known about the interplay between molecular spin and electron transport. We have trapped single Mn12 molecules between two electrodes that are only a few (1-5) nanometers apart. The electrodes are fabricated using a combination of electron beam lithography and electro-migration. For the first time, we measured the transport properties of a molecular magnet in a single molecule transistor geometry. The results will be discussed in the context of recent theoretical calculations.
1. Carlos Arroyo: Au-S-Au junctions
2. J.J. Riquelme: Distribution of channels in superconducting nanocontacts