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Prof. Dr. Ernst Meyer

Department of Physics
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Projects & Collaborations

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Optical beam-deflection atomic force microscopy system at low temperature

Research Project  | 2 Project Members

This project aims to develop an advanced optical beam-deflection atomic force microscope (AFM) integrated in a low-temperature cryostat and an ultra-high vacuum system. The system will enable precise study of individual molecules and complex 2D molecular systems. The cryostat, optimized for low helium consumption and long hold times, will support extended experiments, while the vacuum environment will allow in-situ preparation of samples through methods like thermal evaporation and electrospray deposition. The AFM, built at the University of Basel, will include a preamplifier to extend bandwidth and enable faster data acquisition, supporting advanced AFM modes such as multimode AFM. The system will also feature precise positioning of the AFM probe on 2D materials and quantum dot devices, using optical microscopy and large-area scanning. Controlled electrostatic potentials and back-gate voltages will allow for quantum dot confinement and charge density manipulation, facilitating experiments like 2D or 3D force spectroscopy. Molecules will be studied at submolecular resolution, allowing for manipulation and measurement of lateral forces. Examples include investigating molecular knots and nanographene, with a focus on processes like dehydrogenation. Frictional forces on different substrates will also be explored. Finally, high-resolution AFM and Kelvin probe force microscopy (KPFM) will be used to map charge distributions in electron donor-acceptor systems, including those in excited states, offering new insights into molecular interactions and dynamics.

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Molecular Nanorovers: A roadmap to molecular superlubricity

Research Project  | 2 Project Members

Understanding and choreographing the dance of molecules is a matter of utmost complexity as not only requires a detailed knowledge of their intricate internal dynamics but also how the latter affects and is influenced by its surroundings. Fueled by the practical interest of controlling molecular motion/diffusion in organic synthesis, catalysis, ... , throughout history we witnessed ever ingenious ways to control/activate the motion of molecules: from the plain old heating and stirring, up to microwave and laser guided molecular streams[1]. Yet, a seemingly control of molecular motion at solid interfaces has thus far remained elusive. The challenge stems from understanding how an external stimuli (e.g. light, electrical or chemical energy) can be harnessed to induce structural modifications or alter molecule-surface interactions in such way that generates motion. Such understanding would benefit not only the surface chemistry at large (e.g. on-surface synthesis[2] and catalysis[3]) but also the growing community of nanoscale synthetic molecular machines[4,5] since most their biomolecular counterparts operate at interfaces[6]. The difficulty to direct the motion of molecules over surfaces is perhaps best realized considering that in the 1st nanocar/molecular race[7] only two out of 7 world class research groups were able to meet the challenge. This consisted in propelling a molecule (each team could bring its "best contender") along 100nm in less than 30h!! The sole molecules crossing the finish line required a large amount of time (considering the distance), were very small molecules and used extremely energy inefficient propelling mechanisms. In this project we propose a novel strategy consisting in a bottom-up chemical design of molecules that explore recent advances in superlubricity and physical chemistry allowing to decrease the energy dissipated during the motion by one order of magnitude. Whats more, this will enable to remotely/autonomously propel the molecules along well defined directions using simply an external uniform electric field. To meet this ambitious goal we resort to a synergetic approach combining state of the art 5K Ultra High Vacuum Scanning Probe Microscopy (UHV-SPM) experiments with all atom molecular dynamics simulation (MD) with parameters derived a priory from Quantum Mechanical (QM) calculations. This Spark project will enable the transition of molecular propelling from pulses to fields (STM pulses to uniform electric fields).

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Neue Einsichten in die Sonden-Proben-Wechselwirkung bei den Rastersondenmethoden

Research Project  | 4 Project Members

This 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.

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ULTRADISS

Research Project  | 2 Project Members

Dissipation spectroscopy: Nanomechanical dissipation, experienced by oscillating tip-based Force Microscopy (AFM) instruments, provides an innovative probe of the physics of classical and quantum materials, solids, surfaces. My group made, in the last decade, well-recognized experimental and conceptual advances by exploiting and adapting advanced AFM techniques, especially the ultra-sensitive pendulum-AFM, (p-AFM, dissipation sensitivity ~0.1 aW, force sensitivity ~ 10-12N) detecting collective phenomena and phase transitions including structural, electronic, magnetic. This dissipation spectroscopy was applied so far mostly at the equilibrium physics of 3D classical solids. The challenge: I propose to extend nanomechanical dissipation spectroscopy to pick up much weaker effects caused by non-equilibrium perturbations, by nanomanipulations, and by quantum effects in carefully picked case studies. Such as measuring the imperceptible wind force exerted on a noncontact tip by a thermal or electrical current in the surface below, or the minute mechanical cost of creating and dismantling a single spin Kondo state, or a topological surface state. Risks, benefits, relevance: None of this was done before, so despite our experience and good feasibility estimates there is some risk. The benefits however will be substantial. Thermal and electrical migration of defects and impurities is important in materials, and electrical contacts. The dragging, peeling, sensing of 2D systems like graphene nanoribbons and twisted bilayers is hot. And quantum dissipation is pertinent to the limiting factor of quantum information processes. To do all this by nanomechanics will be unique. The opportunity: My group is ready to put its expertise in these exciting new problems, once I can through an Advanced Grant secure the instrumental and experimental human resources, as well as the theoretical support of additional beneficiary SISSA, indispensable in such a frontier context. 1Instructions

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111_Etude de consommation électrique du m1

Research Project  | 1 Project Members

L'objectif global de cette étude est l'optimisation énergétique d'un système ferroviaire urbain. Les résultats sont attendus sur deux points : il s'agit d'une part d'améliorer les véhicules de la ligne m1 et d'autre part d'établir des critères d'efficacité énergétique pour le futur tram lausannois. Pour y parvenir, les tl prévoient tout d'abord de quantifier la consommation en électricité des véhicules du m1 pour l'ensemble des consommateurs internes (traction, chauffage, éclairage, ...), ainsi que leur bilan calorifique. Il s'agira ensuite d'établir un diagnostic d'efficacité de ces consommateurs et de proposer une série d'améliorations et des moyens de contrôle de fonctionnement. Finalement, une sélection de mesures sera réalisée sur les véhicules m1, et une autre sera intégrée au cahier des charges des véhicules à acheter ainsi que du plan d'exploitation du futur tram lausannois. Les tl attendent de ce projet des options concrètes en termes d'économie d'énergie et de gestion des véhicules. Les mesures seront effectuées par une équipe reconnue dans le domaine et les résultats seront régulièrement partagés avec les intéressés du domaine en Suisse. Für die Messungen wird eine massgeschneiderte automatische Messanlage entwickelt und in das Fahrzeug eingebaut, welche die Daten regelmässig via Mobilfunk an einen Server sendet. Die dort gespeicherten Langzeitdaten werden ausgewertet um Massnahmen für eine bessere Energieeffizienz zu finden. Neben Energiedaten werden auch eine Vielzahl weiterer Daten erfasst wie Innen‐ Aussentemperatur/ Feuchte, Sonneneinstrahlung, CO2‐Konzentration, Türöffnungen und GPS‐Daten.

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Q-AFM / Quantum Limited Atomic Force Microscopy

Research Project  | 2 Project Members

We aim to make a radical improvement in the speed of acquisition and information content of Scanning Probe Microscopy (SPM) images by developing a new type of resonant mechanical force sensor. By the end of the project we realize a Quantum-limited Atomic Force Microscope (Q-AFM), where the force sensor is working at the fundamental limit of action and reaction set by quantum physics. Achieving this limit will result in three orders of magnitude improvement in force sensitivity and five orders of magnitude in measurement bandwidth, beyond the current state-of-the-art. This huge gain in performance will translate to a radical increase in imaging speed and in the information content of images. Our sensor will lead to a revolution in SPM, where multi-dimensional data sets are acquired in seconds, as opposed to several days as is the current practice. The key to reaching quantum-limited sensitivity lies in the the electro-mechanical coupling between the resonant mechanical force transducer and the readout circuit. While our ideas are based on well-established theories and some proof-of-concept measurements, but there is still a high risk that we can not reach the desired strong-coupling regime with an appropriate SPM sensor design. To mitigate this high risk we will pursue two different sensor designs, one based on electrostatic coupling and the other based on piezoelectric coupling. Our work plan includes medium and low risk stages of development, each of will result in major gains in performance SPM. The project brings together three university research groups from KTH, Uni Basel and TU Wien, with one SME Intermodulation Products. Together they bring the diverse and complementary expertise necessary to carry out this project such as: superconducting quantum circuits, low temperature AFM, piezoelectric MEMS, and advanced analog and digital electronic design and low-level programming.