Analysis of the Dynamics of Adsorbed Organic Molecules

Die vorliegende Arbeit analysiert die Dynamik einzelner organischer Moleküle auf einer Kupfer (111) Oberfläche. Wenn Kupfer-Phthalocyanin (CuPc) mit dem Tieftemperatur-Rastertunnelmikroskop (STM) abgebildet wird, erscheint das an ein vierblättriges Kleeblatt erinnernde Molekül verrauscht. Das Phänomen tritt selektiv auf zwei der vier Kleeblätter auf und äußert sich durch zufällige Sprünge im Messsignal, die sich als ’statistisches Telegraphen-Rauschen’ identifizieren lassen. Dieses Rauschen entspricht einem Schalten zwischen zwei Zuständen verschiedener Leitfähigkeit und enthält somit wertvolle Informationen über dynamische Phänomene einzelner Moleküle. Zur Analyse dieses Informationskanals fehlte bislang eine praktikable Methode, die in Echtzeit Schaltereignisse aus dem Messsignal herausfiltert und quantitativ auswertet, während die volle Ortsauflösung des verwendeten STM erhalten bleibt. Dies leistet die im Rahmen dieser Arbeit entwickelte Rauschmikroskopie und -Spektroskopie Methode. Die damit erzielten Ergebnisse zeigen im Detail, wo und mit welcher Frequenz die Fluktuationen auftreten und darüber hinaus, wie groß die Amplituden der Sprungereignisse sind und in welchem Besetzungsverhältnis die beiden Leitfähigkeitszustände zueinander stehen. Die Messergebnisse zeigen, dass das CuPc Molekül eine frustrierte Rotation (auch: Libration) innerhalb seiner Adsorptionsebene ausführt, stimuliert durch ins Molekül injizierte Tunnelelektronen. Die Rauschspektroskopie zeigt, dass die Anregung durch einen Ein-Elektronen-Prozess geschieht und detektiert die energetische Lage der Molekülorbitale LUMO, HOMO und HOMO-1. Zur Unterstützung der Erklärung werden dichtefunktionaltheoretische Simulationen präsentiert. Diese reproduzieren die STM Daten und die gemessene Orbitalstruktur. Darüber hinaus beschreibt eine simulierte Potentialfläche den molekularen Rotor, der sich nach einer Anregung aus seinem Grundzustand in einem von zwei rotierten Zuständen befinden kann. Der Anregungsmechanismus durch inelastisch tunnelnde Elektronen wird schließlich verwendet, um eine Anregungskarte für das Molekül zu simulieren. Das Ergebnis entspricht den experimentellen Beobachtungen.This thesis presents the analysis of the dynamics of an adsorbed organic molecular species on a metal surface. When individual copper phthalocyanine molecules (CuPc) on Cu(111) are imaged by low-temperature scanning tunneling microscopy (STM), fluctuations which can be identified as ’random telegraph noise’ are observed. The noise manifests itself in jumps of the tunneling current and documents bi-stable dynamics on the nanometer scale. A new method of detection is presented, which allows to analyze random telegraph noise during ongoing STM experiments in real-time. The strength of the ’scanning noise microscopy and spectroscopy’ technique (SNM, SNS) relies on the fact that it provides a full characterization of the noise with the same lateral resolution as provided by the STM. The results for the studied system show in great detail where the switching events are localized and provide the corresponding rates. Furthermore, the amplitude of the current jumps, as well as the relative occupation of the two observed states, are being detected. From the new information, a model for the underlying molecular dynamics is deduced: The molecule performs a frustrated rotation, a so called libration, within its adsorption plane, excited by the injected tunneling electrons. Furthermore, the spectroscopy mode reveals a one-electron process for the rotational excitation and gives access to the contributing orbital structure: The LUMO, HOMO and HOMO-1 states are detected. The geometry and electronic properties of the organic-metallic system are also addressed by density functional theory (DFT). As a result, the molecular rotor can be described by a potential energy surface exhibiting potential wells for a ground state and two rotated configurations of the molecule. In addition, the experimental orbital structure and the STM images are reproduced and finally, the simulation of the excitation mechanism yields a calculated excitation map, which corresponds well to the experimental observations

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

Multi-Sektor-Kopplung - Modellbasierte Analyse der Integration erneuerbarer Stromerzeugung durch die Kopplung der Stromversorgung mit dem Wärme-, Gas- und Verkehrssektor

Im Projekt MuSeKo wird der kombinierte Einsatz unterschiedlicher Flexibilitäten und Sektorenkopplungen in einem künftigen Energiesystem mit einem hohen Anteil erneuerbarer Energien modellbasiert untersucht. Die Analyse erfolgt mit einem zeitlich und räumlich aufgelösten, techno-ökonomischen Ansatz. Anhand dessen Ergebnissen werden unterschiedliche energiewirtschaftliche Rahmenbedingungen im Hinblick auf Investitionen und den Anlageneinsatz bewertet. Der Neuheitswert des Projekts liegt einerseits in der Fokussierung auf die Ausgestaltung der Kopplung von Strom- und Gassystem und andererseits auf der Kombination der gesamtwirtschaftlichen mit der betriebswirtschaftlichen Perspektive. Die Projektergebnisse zeigen einerseits die Chancen einer engeren Verzahnung der Strom-, Wärme- und Gasversorgung, und andererseits die damit einhergehenden regulatorischen Herausforderungen für die Anreizung systemdienlicher Investitionen und Anlageneinsätze. Die Arbeiten bieten in den erweiterten Methoden und erhobenen Daten eine wichtige Grundlage zur weiteren Erforschung der Umsetzung der flexiblen Sektorenkopplung in der Energiewende

Integrating system and operator perspectives for the evaluation of power-to-gas plants in the future German energy system

In which way, and in which sectors, will renewable energy be integrated in the German Energy System by 2030, 2040, and 2050? How can the resulting energy system be characterised following a −95% greenhouse gas emission reduction scenario? Which role will hydrogen play? To address these research questions, techno-economic energy system modelling was performed. Evaluation of the resulting operation of energy technologies was carried out from a system and a business point of view. Special consideration of gas technologies, such as hydrogen production, transport, and storage, was taken as a large-scale and long-term energy storage option and key enabler for the decarbonisation of the non-electric sectors. The broad set of results gives insight into the entangled interactions of the future energy technology portfolio and its operation within a coupled energy system. Amongst other energy demands, CO2 emissions, hydrogen production, and future power plant capacities are presented. One main conclusion is that integrating the first elements of a large-scale hydrogen infrastructure into the German energy system, already, by 2030 is necessary for ensuring the supply of upscaling demands across all sectors. Within the regulatory regime of 2020, it seems that this decision may come too late, which jeopardises the achievement of transition targets within the horizon 2050

Integrating System and Operator Perspectives for the Evaluation of Power-to-Gas Plants in the Future German Energy System

In which way, and in which sectors, will renewable energy be integrated in the German Energy System by 2030, 2040, and 2050? How can the resulting energy system be characterised following a −95% greenhouse gas emission reduction scenario? Which role will hydrogen play? To address these research questions, techno-economic energy system modelling was performed. Evaluation of the resulting operation of energy technologies was carried out from a system and a business point of view. Special consideration of gas technologies, such as hydrogen production, transport, and storage, was taken as a large-scale and long-term energy storage option and key enabler for the decarbonisation of the non-electric sectors. The broad set of results gives insight into the entangled interactions of the future energy technology portfolio and its operation within a coupled energy system. Amongst other energy demands, CO2 emissions, hydrogen production, and future power plant capacities are presented. One main conclusion is that integrating the first elements of a large-scale hydrogen infrastructure into the German energy system, already, by 2030 is necessary for ensuring the supply of upscaling demands across all sectors. Within the regulatory regime of 2020, it seems that this decision may come too late, which jeopardises the achievement of transition targets within the horizon 2050

Progress in Power-to-Gas Energy Systems

Hydrogen is expected to become a key component in the decarbonized energy systems of the future [...

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

Current Legislative Framework for Green Hydrogen Production by Electrolysis Plants in Germany

(1) The German energy system transformation towards an entirely renewable supply is expected to incorporate the extensive use of green hydrogen. This carbon-free fuel allows the decarbonization of end-use sectors such as industrial high-temperature processes or heavy-duty transport that remain challenging to be covered by green electricity only. However, it remains unclear whether the current legislative framework supports green hydrogen production or is an obstacle to its rollout. (2) This work analyzes the relevant laws and ordinances regarding their implications on potential hydrogen production plant operators. (3) Due to unbundling-related constraints, potential operators from the group of electricity transport system and distribution system operators face lacking permission to operate production plants. Moreover, ownership remains forbidden for them. The same applies to natural gas transport system operators. The case is less clear for natural gas distribution system operators, where explicit regulation is missing. (4) It is finally analyzed if the production of green hydrogen is currently supported in competition with fossil hydrogen production, not only by the legal framework but also by the National Hydrogen Strategy and the Amendment of the Renewable Energies Act. It can be concluded that in recent amendments of German energy legislation, regulatory support for green hydrogen in Germany was found. The latest legislation has clarified crucial points concerning the ownership and operation of electrolyzers and the treatment of green hydrogen as a renewable energy carrier