Projects & Collaborations 5 foundShow per page10 10 20 50 Nanoscale friction control of layered transition metal dichalcogenides Research Project | 4 Project MembersLayered 2D materials have a wide range of tunable physical properties that offer many potential applications in areas such as photovoltaics, hydrogen evolution catalysis, transistors, DNA detection, nanoelectromechanical systems and tribological applications. Transition metal dichalcogenides (TMDs) are particularly useful in this regard due to their flexible chemistry and stoichiometry. However, the manipulation and assembly of free-standing TMD layers into devices requires a deep understanding and control of their frictional properties at the nanoscale. To address this challenge, the aim of this project is to develop a thorough theoretical and experimental understanding of how to control friction in TMD-based systems at the nanoscale. This will involve identifying the most promising TMD-based heterostructures with targeted functionalities and establishing protocols for designing new tribological materials with tailored frictional properties. The specific scientific objectives of this project are to develop a deep understanding of how to control friction in TMD-based systems on demand, and to identify the best electrical and optical stimuli that can be used as external 'knobs' for users to control friction. Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden Research Project | 4 Project MembersThis research proposal focuses on the progress in the study of local interactions by Scanning Probe Methods (SPM). The research in this field is only possible due to our longstanding experience and equipment:Nanolino: STM/AFM force microscopy in ultrahigh vacuumLT-SPM: Combined low temperature scanning tunneling and force microscopyThe following research topics will be addressed in this period:a) High resolution tunneling and force spectroscopy of Majorana bound statesIn this research, we pursue our investigations of magnetic chains on superconductors, grown by self-assembly or atom-by-atom via tip manipulations, with a particular focus on growing perfect chain structures. Their characterizations will be conducted with advanced SPM techniques in order to disentangle electronic properties, spin texture and atomic structure. We are acquiring a new ultra-low temperature tuning fork microscope operated at 900 mK under a variable magnetic field of ± 3T with He holding times of about 150 hours that will be set up during this research period. Beside the topological chains, we also investigate new condensed-matter systems to realize synthetic topological superconductors based on two dimensional materials and potentially hosting Majorana fermions (MFs). We thus focus on the on-surface synthesis of doped graphene nano-structures as well as the epitaxy of silicene atomic layers. Not appropriate for Pb substrates due to its low melting temperature, these synthesis will be transferred to atomically-cleaned niobium surfaces prepared in ultra-high vacuum.b) Pulling of molecular wires along surfacesOur main focus for this research period is on the pulling of single molecular wires with predefined mechanical properties. For this purpose, we will exploited the manipulation techniques developed in our group these last years. The metallic STM tip is approached to one end of the wire until a bond is formed. Then the tip is retracted in the vertical direction to detach the molecular wires unit after unit while recording its mechanical responses. These experiments are in analogy with our previous ones using graphene nanoribbons (GNRs) and poly-fluorene chains. In the case of poly-pyrenylene-chains, we are particularly interest in detecting and controlling the effects of steric hindrance between consecutive sub-units of the chains. From ab initio calculations, it is expected that the free poly-pyrenylene molecules naturally promotes large twists about the single C-C bonds of ±40°, as a result of steric repulsions between adjacent hydrogen atoms. In a second phase, we wish to design new molecular chains with selected peripheral side groups or sub-units. The concept is to promote new mechanical dynamics upon lifting/sliding with different sub-units twist angles of the equilibrium form of the molecular chains. Consequently, we expect that cryo-force spectroscopic measurements observe different adhesive forces to detach the molecular units. In analogy to the pyrenylene case, we might observe variations of the maximum detachment force depending on the twisting direction (clock- vs. anti-clock wise).c) Friction and contact forces with large molecules prepared by electrospray depositionWe will use electrospray deposition to deposit large molecules, such as the hexadodecylhexabenzo-coronene, and extend this study to graphylene-1, also called the spoked wheel molecule. Several questions are to be addressed: 1) Do the molecules assemble on metallic and insulating substrates? The assembly on insulators is of importance for applications in optics and molecular electronics, where optical and electronic decoupling of the molecules from metallic substrates are required. 2) How is the assembly depending on the temperature? First evidence is found that large molecules with alkyl chains have temperature dependent inter-molecular spacing, which correspond to very large thermal expansion coefficients of the order of 10-4/°K.In the second period, individual large molecules will be moved by the probing tip and the frictional forces will be determined as a function of orientation, adsorption location and loading force. How do the frictional forces scale with the size of the molecules? Can we heat the molecules by exposure to tunneling currents or laser light? Does this increase the mobility or reduce the frictional forces. In the same spirit, we will prepare carbon onions and graphene nanoribbons, which will continue some the previous experiments on larger scales. Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden Research Project | 6 Project MembersThis research proposal focuses on the progress in the study of local interactions by Scanning Probe Methods (SPM). The here proposed plan is only possible due to our long-standing experience and equipment: Nanolino: Combined STM/AFM force microscopy in ultrahigh vacuum Nanolab: High resolution STM and XPS measurements in ultrahigh vacuum The following research topics will be addressed in this period: 1. High-resolution force microscopy and spectroscopy The electronic and mechanical properties of self-assembled metallic nanowires as well as molecular chains are investigated by combined tunneling and force microscopy. Evidence for bound states of Majorana fermions will be searched in Fe wires deposited on superconductive surfaces. It is expected that the zero bias peak of tunneling spectroscopy will show these bound states. High resolution force microscopy gives access to the atomic structures of the Fe chains and possibly provides further evidence of the bound states. On-surface chemistry will be used to assemble molecular chains or ribbons, which will be investigated by high resolution force microscopy, where the submolecuar structure is revealed by a CO-terminated probing tip. In addition, the molecular chains will be picked up by the metallic probing tip and moved across the surface to probe their mechanical properties. Quantitative data about adhesion and friction will be gained with the help of these well characterized mechanical junctions. Questions about the effect of commensurability of molecular wires in relation to the substrate will be addressed. A new strand of research is the combination of Kelvin force microscopy of single molecules with light exposure. We plan to investigate charge transfer mechanisms within single molecules as a function of wave length. 2. Electrons, atoms and molecules in porous on-surface networks: Properties in local and periodic confinement Novel phenomena and properties emerging from the cooperative interaction of electrons and adsorbates within confinements and in periodic arrays thereof are to be investigated. Scanning tunneling microscopy and spectroscopy shall be used for the high resolution mapping of the host-guest architectures and the electronic states. Complementary photon and photoelectron spectroscopies shall reveal the present chemical states and bonds. Well-established and new to be developed porous on-surface / sample architectures shall be investigated in their property to serve as hosting body for the atom-by-atom investigation of condensation and for their capability to form regular and irregular arrangements of quantum-boxes by interaction with the substrate electronic states. The atom-by-atom condensation experiments performed with one or more components like Ne, Xe, allow for unprecedented insight into condensation physics in comparison to numerical models. In collaboration with Nanolino also the forces acting involved in the formation of the confined condensates shall be investigated. The 2D quantum box arrays also provide a unique platform to investigate the coupling between nanometer confined quantum states by controlled patterning of these "quantum breadboards". Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden Research Project | 10 Project MembersThis research proposal focuses on the progress in the study of local interactions by Scanning Probe Methods (SPM). The research in this field is only possible due to our long-standing experience and equipment: Nanolino: Combined STM/AFM at room temperature and Friction Force Microscope nc-AFM at 4K: Force microscopy at low temperature Nanolab: STM in ultrahigh vacuum (UHV) combined with MBE and ESCA The following research topics will be addressed in this period: 1. High-resolution force microscopy experiments: To further improve the stability and knowledge about the electronic and the structural properties at molecular and atomic scale we will continue developing improved techniques of detection as well as increase the understanding of the short range interaction in nc-AFM. For that purpose we concentrate our research on mainly three topics, the analysis of the short range interaction determined by multimodal nc-AFM, the development of enhanced analytical models to quantify the measured signals as well as the further analysis of the growth and the structural properties of organic molecules on insulating surfaces. The gap between contact measurements and noncontact measurements is becoming continuously smaller so that we expect to get detailed information on the contact formation as well as on frictional properties by both techniques. 2. Electrons, atoms and molecules in supramolecular porous networks: Properties in local and periodic confinement We propose to use specifically designed surface mounted supramolecular porous networks as templates to build complex and functional architectures at the surface. It is the study of site specific adsorption of molecules, their diffusion/libration within the confinement of the pores, as well as cooperative effects mediated by electronic or mechanic coupling between neighbouring sites across the two-dimensional (2D) network which provides the scientific focus of this proposal. Importantly these studies are performed in dependence of both, the sample temperature and in dependence of variable, local forces and fields through the local probe (Scanning Tunneling Microscopy (STM), tf-Atomic Force Microscopy (AFM) and nc-AFM), i.e. in dependence of the tip-sample interaction. Complementary Low Energy Electron Diffraction (LEED), Photo-Electron Spectroscopy (PES) and X-ray Standing Wave (XSW) experiments are performed to assess structural features of the supramolecular networks on the surface. This research aims at understanding increasingly complex supramolecular systems towards the design of novel functional surface properties, also by collaboration with theory. Molecular assemblies on semiconductors and insulating surfaces Research Project | 5 Project MembersThe main aim of the project is to investigate processes taking place around the molecular assemblies formed on insulating and semiconducting substrate under irradiation by photons. The molecular assemblies grown either by evaporation or by electro-spray deposition will be examined by scanning probe methods, especially non contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) in order to determine dependence of the electrical properties of the assemblies of their morphology, and exploit that dependence to control the electrical properties of the assemblies. Within the project a number of molecule/substrate systems will be tested in order to find the most suitable ones for examination of the evolution of excitation in the assemblies induced by the incoming light. As the result we hope to gain deeper understanding of charge evolution and transport in the assembly which is crucial in many fields of the nanotechnology and research related to development of light-harvesting media. 1 1
Nanoscale friction control of layered transition metal dichalcogenides Research Project | 4 Project MembersLayered 2D materials have a wide range of tunable physical properties that offer many potential applications in areas such as photovoltaics, hydrogen evolution catalysis, transistors, DNA detection, nanoelectromechanical systems and tribological applications. Transition metal dichalcogenides (TMDs) are particularly useful in this regard due to their flexible chemistry and stoichiometry. However, the manipulation and assembly of free-standing TMD layers into devices requires a deep understanding and control of their frictional properties at the nanoscale. To address this challenge, the aim of this project is to develop a thorough theoretical and experimental understanding of how to control friction in TMD-based systems at the nanoscale. This will involve identifying the most promising TMD-based heterostructures with targeted functionalities and establishing protocols for designing new tribological materials with tailored frictional properties. The specific scientific objectives of this project are to develop a deep understanding of how to control friction in TMD-based systems on demand, and to identify the best electrical and optical stimuli that can be used as external 'knobs' for users to control friction.
Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden Research Project | 4 Project MembersThis research proposal focuses on the progress in the study of local interactions by Scanning Probe Methods (SPM). The research in this field is only possible due to our longstanding experience and equipment:Nanolino: STM/AFM force microscopy in ultrahigh vacuumLT-SPM: Combined low temperature scanning tunneling and force microscopyThe following research topics will be addressed in this period:a) High resolution tunneling and force spectroscopy of Majorana bound statesIn this research, we pursue our investigations of magnetic chains on superconductors, grown by self-assembly or atom-by-atom via tip manipulations, with a particular focus on growing perfect chain structures. Their characterizations will be conducted with advanced SPM techniques in order to disentangle electronic properties, spin texture and atomic structure. We are acquiring a new ultra-low temperature tuning fork microscope operated at 900 mK under a variable magnetic field of ± 3T with He holding times of about 150 hours that will be set up during this research period. Beside the topological chains, we also investigate new condensed-matter systems to realize synthetic topological superconductors based on two dimensional materials and potentially hosting Majorana fermions (MFs). We thus focus on the on-surface synthesis of doped graphene nano-structures as well as the epitaxy of silicene atomic layers. Not appropriate for Pb substrates due to its low melting temperature, these synthesis will be transferred to atomically-cleaned niobium surfaces prepared in ultra-high vacuum.b) Pulling of molecular wires along surfacesOur main focus for this research period is on the pulling of single molecular wires with predefined mechanical properties. For this purpose, we will exploited the manipulation techniques developed in our group these last years. The metallic STM tip is approached to one end of the wire until a bond is formed. Then the tip is retracted in the vertical direction to detach the molecular wires unit after unit while recording its mechanical responses. These experiments are in analogy with our previous ones using graphene nanoribbons (GNRs) and poly-fluorene chains. In the case of poly-pyrenylene-chains, we are particularly interest in detecting and controlling the effects of steric hindrance between consecutive sub-units of the chains. From ab initio calculations, it is expected that the free poly-pyrenylene molecules naturally promotes large twists about the single C-C bonds of ±40°, as a result of steric repulsions between adjacent hydrogen atoms. In a second phase, we wish to design new molecular chains with selected peripheral side groups or sub-units. The concept is to promote new mechanical dynamics upon lifting/sliding with different sub-units twist angles of the equilibrium form of the molecular chains. Consequently, we expect that cryo-force spectroscopic measurements observe different adhesive forces to detach the molecular units. In analogy to the pyrenylene case, we might observe variations of the maximum detachment force depending on the twisting direction (clock- vs. anti-clock wise).c) Friction and contact forces with large molecules prepared by electrospray depositionWe will use electrospray deposition to deposit large molecules, such as the hexadodecylhexabenzo-coronene, and extend this study to graphylene-1, also called the spoked wheel molecule. Several questions are to be addressed: 1) Do the molecules assemble on metallic and insulating substrates? The assembly on insulators is of importance for applications in optics and molecular electronics, where optical and electronic decoupling of the molecules from metallic substrates are required. 2) How is the assembly depending on the temperature? First evidence is found that large molecules with alkyl chains have temperature dependent inter-molecular spacing, which correspond to very large thermal expansion coefficients of the order of 10-4/°K.In the second period, individual large molecules will be moved by the probing tip and the frictional forces will be determined as a function of orientation, adsorption location and loading force. How do the frictional forces scale with the size of the molecules? Can we heat the molecules by exposure to tunneling currents or laser light? Does this increase the mobility or reduce the frictional forces. In the same spirit, we will prepare carbon onions and graphene nanoribbons, which will continue some the previous experiments on larger scales.
Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden Research Project | 6 Project MembersThis research proposal focuses on the progress in the study of local interactions by Scanning Probe Methods (SPM). The here proposed plan is only possible due to our long-standing experience and equipment: Nanolino: Combined STM/AFM force microscopy in ultrahigh vacuum Nanolab: High resolution STM and XPS measurements in ultrahigh vacuum The following research topics will be addressed in this period: 1. High-resolution force microscopy and spectroscopy The electronic and mechanical properties of self-assembled metallic nanowires as well as molecular chains are investigated by combined tunneling and force microscopy. Evidence for bound states of Majorana fermions will be searched in Fe wires deposited on superconductive surfaces. It is expected that the zero bias peak of tunneling spectroscopy will show these bound states. High resolution force microscopy gives access to the atomic structures of the Fe chains and possibly provides further evidence of the bound states. On-surface chemistry will be used to assemble molecular chains or ribbons, which will be investigated by high resolution force microscopy, where the submolecuar structure is revealed by a CO-terminated probing tip. In addition, the molecular chains will be picked up by the metallic probing tip and moved across the surface to probe their mechanical properties. Quantitative data about adhesion and friction will be gained with the help of these well characterized mechanical junctions. Questions about the effect of commensurability of molecular wires in relation to the substrate will be addressed. A new strand of research is the combination of Kelvin force microscopy of single molecules with light exposure. We plan to investigate charge transfer mechanisms within single molecules as a function of wave length. 2. Electrons, atoms and molecules in porous on-surface networks: Properties in local and periodic confinement Novel phenomena and properties emerging from the cooperative interaction of electrons and adsorbates within confinements and in periodic arrays thereof are to be investigated. Scanning tunneling microscopy and spectroscopy shall be used for the high resolution mapping of the host-guest architectures and the electronic states. Complementary photon and photoelectron spectroscopies shall reveal the present chemical states and bonds. Well-established and new to be developed porous on-surface / sample architectures shall be investigated in their property to serve as hosting body for the atom-by-atom investigation of condensation and for their capability to form regular and irregular arrangements of quantum-boxes by interaction with the substrate electronic states. The atom-by-atom condensation experiments performed with one or more components like Ne, Xe, allow for unprecedented insight into condensation physics in comparison to numerical models. In collaboration with Nanolino also the forces acting involved in the formation of the confined condensates shall be investigated. The 2D quantum box arrays also provide a unique platform to investigate the coupling between nanometer confined quantum states by controlled patterning of these "quantum breadboards".
Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden Research Project | 10 Project MembersThis research proposal focuses on the progress in the study of local interactions by Scanning Probe Methods (SPM). The research in this field is only possible due to our long-standing experience and equipment: Nanolino: Combined STM/AFM at room temperature and Friction Force Microscope nc-AFM at 4K: Force microscopy at low temperature Nanolab: STM in ultrahigh vacuum (UHV) combined with MBE and ESCA The following research topics will be addressed in this period: 1. High-resolution force microscopy experiments: To further improve the stability and knowledge about the electronic and the structural properties at molecular and atomic scale we will continue developing improved techniques of detection as well as increase the understanding of the short range interaction in nc-AFM. For that purpose we concentrate our research on mainly three topics, the analysis of the short range interaction determined by multimodal nc-AFM, the development of enhanced analytical models to quantify the measured signals as well as the further analysis of the growth and the structural properties of organic molecules on insulating surfaces. The gap between contact measurements and noncontact measurements is becoming continuously smaller so that we expect to get detailed information on the contact formation as well as on frictional properties by both techniques. 2. Electrons, atoms and molecules in supramolecular porous networks: Properties in local and periodic confinement We propose to use specifically designed surface mounted supramolecular porous networks as templates to build complex and functional architectures at the surface. It is the study of site specific adsorption of molecules, their diffusion/libration within the confinement of the pores, as well as cooperative effects mediated by electronic or mechanic coupling between neighbouring sites across the two-dimensional (2D) network which provides the scientific focus of this proposal. Importantly these studies are performed in dependence of both, the sample temperature and in dependence of variable, local forces and fields through the local probe (Scanning Tunneling Microscopy (STM), tf-Atomic Force Microscopy (AFM) and nc-AFM), i.e. in dependence of the tip-sample interaction. Complementary Low Energy Electron Diffraction (LEED), Photo-Electron Spectroscopy (PES) and X-ray Standing Wave (XSW) experiments are performed to assess structural features of the supramolecular networks on the surface. This research aims at understanding increasingly complex supramolecular systems towards the design of novel functional surface properties, also by collaboration with theory.
Molecular assemblies on semiconductors and insulating surfaces Research Project | 5 Project MembersThe main aim of the project is to investigate processes taking place around the molecular assemblies formed on insulating and semiconducting substrate under irradiation by photons. The molecular assemblies grown either by evaporation or by electro-spray deposition will be examined by scanning probe methods, especially non contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) in order to determine dependence of the electrical properties of the assemblies of their morphology, and exploit that dependence to control the electrical properties of the assemblies. Within the project a number of molecule/substrate systems will be tested in order to find the most suitable ones for examination of the evolution of excitation in the assemblies induced by the incoming light. As the result we hope to gain deeper understanding of charge evolution and transport in the assembly which is crucial in many fields of the nanotechnology and research related to development of light-harvesting media.
