Electron Transport at Surfaces and Interfaces

Here we present two techniques which give insight on transport phenomena with atomic resolution. Ballistic electron emission microscopy is used to study the ballistic transport through layered heterogeneous systems. The measured ballistic fraction of the tunneling current provides information about lossless transport channels through metallic layers and organic adsorbates. The transport characteristics of Bi(111)/Si Schottky devices and the influence of the organic adsorbates perylene tetracaboxylic dianhydride acid and C60 on the ballistic current are discussed. Scanning tunneling potentiometry gives access to the lateral transport along a surface, thus scattering processes within two-dimensional electron systems for the Bi(111) surface and the Si(111)(?3 × ?3)-Ag surface could be visualized

Tunneling electron induced rotation of a copper phthalocyanine molecule on Cu(111)

The rates of a hindered molecular rotation induced by tunneling electrons are evaluated using scattering theory within the sudden approximation. Our approach explains the excitation of copper phthalocyanine molecules (CuPc) on Cu(111) as revealed in a recent measurement of telegraph noise in a scanning tunneling microscopy experiment. A complete explanation of the experimental data is performed by computing the geometry of the adsorbed system, its electronic structure, and the energy transfer between tunneling electrons and the molecule's rotational degree of freedom. The results unambiguously show that tunneling electrons induce a frustrated rotation of the molecule. In addition, the theory determines the spatial distribution of the frustrated rotation excitation, confirming the striking dominance of two out of four molecular lobes in the observed excitation process. This lobe selectivity is attributed to the different hybridizations with the underlying substrate. © 2013 American Physical Society.J.S., A.S., C.A.B., and R.M. gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft through the SFB616 ‘Energy Dissipation at Surfaces.’ N.L. is supported by the ICT-FET Integrated Project AtMol (http://www.atmol.eu). M.C.C. thanks the Studienstiftung desdeutschen Volkes.Peer Reviewe

Probing the electronic transport on the reconstructed Au/Ge(001) surface

By using scanning tunnelling potentiometry we characterized the lateral variation of the electrochemical potential $\mu _{ec}$ on the gold-induced Ge(001)-c(8 × 2)-Au surface reconstruction while a lateral current flows through the sample. On the reconstruction and across domain boundaries we find that $\mu _{ec}$ shows a constant gradient as a function of the position between the contacts. In addition, nanoscale Au clusters on the surface do not show an electronic coupling to the gold-induced surface reconstruction. In combination with high resolution scanning electron microscopy and transmission electron microscopy, we conclude that an additional transport channel buried about 2 nm underneath the surface represents a major transport channel for electrons

Anreizsysteme - Eine Möglichkeit zur Verbesserung der universitären Lehre?

Eingeleitet wird das Journal mit dem Beitrag "Anreize für gute Lehre" von Kiefer, Niederhaus, Balzani, Bobisch, Gerharz, Kruggel-Emden, Schwarz, Thielbörger & Weiss, Mitgliedern der Global Young Faculty. In ihrer Umfrage in den UMAR-Universitäten gingen sie der Frage nach "Was motiviert Lehrende qualitativ gute Lehre anzubieten?". Ihre Ergebnisse überraschen und zeigen, welchen Stellenwert nach Meinung der Interviewten Lehre generell einnimmt

Following the steps of a reaction by direct imaging of many individual molecules

The dehydrogenation and dechlorination of FeOEP-Cl on Cu(111) has been studied in detail by scanning tunneling microscopy. Although, it is not possible to follow the reaction of an individual molecule, the complete pathway of the reaction with 22 inequivalent intermediate states and the rates of the involved processes are revealed. This is achieved by combining the analysis of a large data set showing thousands of molecules in the different stages of the reaction with numerical simulations

Following the steps of a reaction by direct imaging of many individual molecules

et al.The dehydrogenation and dechlorination of FeOEP-Cl on Cu(111) has been studied in detail by scanning tunneling microscopy. Although, it is not possible to follow the reaction of an individual molecule, the complete pathway of the reaction with 22 inequivalent intermediate states and the rates of the involved processes are revealed. This is achieved by combining the analysis of a large data set showing thousands of molecules in the different stages of the reaction with numerical simulations.C. A. Bobisch acknowledges financial support from the Deutsche Forschungsgemeinschaft (DFG). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).Peer Reviewe

A chemically inert Rashba split interface electronic structure of C60, FeOEP and PTCDA on BiAg2/Ag(111) substrates

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.The fields of organic electronics and spintronics have the potential to revolutionize the electronics industry. Finding the right materials that can retain their electrical and spin properties when combined is a technological and fundamental challenge. We carry out the study of three archetypal organic molecules in intimate contact with the BiAg2 surface alloy. We show that the BiAg2 alloy is an especially suited substrate due to its inertness as support for molecular films, exhibiting an almost complete absence of substrate-molecular interactions. This is inferred from the persistence of a completely unaltered giant spin-orbit split surface state of the BiAg 2 substrate, and from the absence of significant metallic screening of charged molecular levels in the organic layer. Spin-orbit split states in BiAg2 turn out to be far more robust to organic overlayers than previously thought. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.This work is supported by the Spanish Ministerio de Economia y Competitividad (MAT2010-21156-C03-01, PIB2010US-00652), by the Basque Government (IT-257-07), and the Deutsche Forschungsgemeinschaft through the SFB 616 ‘Energy Dissipation at Surfaces’. MCC additionally thanks the Studienstiftung des deutschen Volkes for support. MCC, JS, CAB and RM would like to thank the DFG for support within the program ‘open access publizieren’.Peer Reviewe

Surface-induced dechlorination of FeOEP-Cl on Cu(111)

To be or not to be chlorinated: When octaethylporphyrin iron(III) chloride (FeOEP-Cl) molecules are sublimated onto Cu(111) surfaces, two different molecular species are observed through scanning tunneling microscopy, showing either a protrusion or a depression at the center. In combination with van der Waals-corrected density functional calculations, our experiments reveal that one species corresponds to FeOEP-Cl molecules with the chlorine atom pointing away from the surface, whereas the other species has been dechlorinated.Financial support is acknowledged from the Deutsche Forschungsgemeinschaft through SFB616: Energy Dissipation at Surfaces.Peer Reviewe

Interplay between Forward and Backward Scattering of Spin–Orbit Split Surface States of Bi(111)

The electronic structure at the surface of Bi(111) enables us to study the effect of defects scattering into multiple channels. By performing scanning tunneling spectroscopy near step edges, we analyze the resulting oscillations in the local density of electronic states (LDOS) as function of position. At a given energy, forward and backward scattering not only occur simultaneously but may contribute to the same scattering vector Δ<b>k</b>. If the scattering phase of both processes differs by π and the amplitudes are almost equal, the oscillations cancel out. A sharp dip in the magnitude of the Fourier transform of the LDOS marks the crossover between forward and backward scattering channels