Schlüsselwörter
(Englisch)
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electrons; lithography; scanning tunneling microscopy; single-molecule chemistry
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Forschungsprogramme
(Englisch)
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COST-Action CM0601 - Electron Controlled Chemical Lithography - ECCL
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Kurzbeschreibung
(Englisch)
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Electron-induced chemistry performed with the scanning tunneling microscope (STM) tip will be investigated on a fundamental level with small molecules at surfaces. Besides electron-induced decomposition reactions, much emphasis will be given to adding reactants to activated hydrocarbon molecules (hydrogenation and oxidation). Using the STM manipulation along specific surface structures, differences in activation barriers for decomposition and addition of species with respect to different surface sites will be investigated.
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Weitere Hinweise und Angaben
(Englisch)
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Full name of research-institution/enterprise: Eidg. Materialprüfungs- und Forschungsanstalt EMPA Molecular Surface Science Laboratory for Nanoscale Materials Science
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, CH, CZ, DE, DK, ES, FR, IS, NL, PL, PT, RS, SK, TR, UK
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Abstract
(Englisch)
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Adsorbate motions are one of the most fundamental steps in surface chemistry. In particular if collisions with other reaction partners or reactive surface sites are required, they are commonly the rate-determined steps of heterogeneously catalyzed reactions. The role of vibrational molecular modes has been investigated in great detail for the process of adsorption, but is rarely considered for lateral motion on the surface. How the vibronic excitation of a molecule couples to the lateral translation across the surface plane and which state-resolved excitations preferentially support lateral movement or rotation remains an important question. Studying the movement of adsorbates, induced by phonons, photons or electrons, is therefore of paramount interest. Scanning tunneling microscopy (STM) has been developed as a tool beyond imaging, and manipulation of single atoms and molecules with the STM-tip is a well-established procedure. Manipulation experiments have been performed with single molecules of the hydrocarbon propene on a copper(211) surface at 7 K. Depending on the location of the methyl group, propene forms two enantiomorphous pairs of different adsorbate states. Beyond repositioning of the molecules via vertical and lateral manipulations with the STM tip, conversions between the different adsorbate geometries were observed. The role of inelastically tunneled electrons and the electric field in the junction between tip and surface are discussed as origins of adsorbate mode conversion. In addition, we observed a mode-selective dissociation reaction after inelastic multiple electron scatting. Finally, we studied the directed motion of a molecular motor, containing four unidirectional rotor units. A full rotation of a rotor comprises four steps, two helix inversions and two isomerisation reactions. Only when all four motors are synchronized in their rotation direction, linear propulsion is observed. Other isomers cause random walks, since the rotors work against each other.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C07.0081
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