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Nanomechanik (Meyer)

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Nanopatterning and precision-polymer doping: towards single dopant quantum devices

Research Project  | 1 Project Members

Our objective is to develop and experimentally validate a new combination of nanopatterning and deterministic doping of phosphorous (P) in silicon (Si) that is required for the manufacturing of quantum devices. Our approach is based on thermal scanning probe lithography (t-SPL), directed self-assembly of block-copolymers (DSA-BCP), monolayer/polymeric-precision doping (MLD/PPD) and rapid thermal annealing (RTA) to create micro and nanopatterns of P-doped areas in Si, down to single atom doping control. The project will first fabricate test patterns (1 um – 20 nm) having variable geometries and dopant concentration inside the Si crystal, e.g. 1D, 2D arrays, with multiple dopant patterns, that allow us to assess the local dopant profile, and to optimize the process by varying systematically fabrication parameters. To ensure single P dopant control, molecule-receiving holes of around 5 nm are needed, which will be achieved using t-SPL and advanced dry etching to create a 20 nm guide pattern, which will subsequently be reduced by DSA of BCP. Inside these holes we will perform P doping by MLD/PPD using molecules of various kinds and sizes with P moieties. The doping patterns will be characterized by advanced surface analysis techniques, e.g. by Kelvin Probe Force Microscopy (KPFM). Results from the KPFM will be used in an iterative way to optimize design and process flow and to achieve single dopant control in a deterministic way. In a second phase, besides continuing to optimize the doping process, we will begin exploring the use of the single doping technology towards concrete quantum devices. We aim to demonstrate that the technology can be incorporated into the standard process flow for donor-based semiconductor devices as for example, single atom point contact transistors, artificial lattices in semiconductors and deterministic doping for semiconducting qubits. Each PhD topic will be aligned to one of the configurations according to status of the advances we can make. The proposed work requires expertise in nanofabrication, self-assembly and ultra-high-resolution surface and device characterization, The project team with members from EPFL, UniBasel and CNM-Barcelona has been assembled to gather the most advanced skill set in the respective project parts present. Our research project will train four new PhD students in a timely topic related to nanomanufacturing and quantum technology.


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Nanoscale friction control of layered transition metal dichalcogenides

Research Project  | 4 Project Members

Layered 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.

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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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SHEAR: Sheath Role in plasma-surface interactions: applications to unipolar arcs, mirrors cleaning and plasma heating

Research Project  | 2 Project Members

The understanding of plasma sheath, a charged layer that arises in the vicinity of any material surface immersed in plasmas, is crucial in order to control plasma-surface interactions. If the sheath mechanisms are well known in unmagnetized plasmas, even in Radio Frequency (RF) environments, a universal model for a sheath in a tilted magnetic field and more especially with a RF source does not yet exist. The SHEAR project primarily aims at developing and validating such models, by the comparison between simulations and highly resolved measurements in dedicated devices. The issues raised by sheath and plasma potential formation in such plasmas is crucial for the understanding of many nonlinear phenomena encountered in particle confinement, particle acceleration, localized high-energy flux and transport barriers. Here can be mentioned a wide range of fields from laboratory to space, the acceleration of ions in plasma thrusters, the charging of satellites or the additional ion or plasma heating in fusion devices. In RF plasmas in particular, this understanding is important for numerous applications based on high density plasmas, such as magnetically enhanced reactive ion etching, plasma ion assisted deposition (PIAD), or impurity control in fusion plasmas.... SHEAR is a joined research project between 3 academic partners: the Jean Lamour Institute (University of Lorraine, France), the Physics Department of the Basel University (Switzerland) and the Swiss Plasma Center (EPFL, Switzerland). The simulations carried out by French partners will be cross-compared with experimental measurements in a variety of B-field angle and magnitude (0-3.5 T) configurations, in various devices hosted by the three project's partners. In addition, dedicated simulations will directly aim at refining the interpretation of probe measurements, which will be further cross-validated with optical measurements. Therefore, the physics of diagnostics has a central place in the SHEAR project. The SHEAR work program is organized into 5 inter-related scientific work packages (WP) based on coherent theoretical, modelling and experimental approaches. The first WP aims principally at developing accurate interpretation models for probe measurements in magnetized RF plasmas. The second WP focuses on the description of the coupling between RF wave and magnetized plasmas. The third WP aims at understanding the heat and particle flux patterns on surfaces immersed in such plasmas, with a view to control these fluxes for various applications. The fourth WP focuses specifically on the improvement of one of these applications, the cleaning of mirrors in magnetic fusion devices. The last WP is devoted to the understanding of the influence of surface properties and plasma conditions on the triggering and dynamics of unipolar arcs, in order to suppress or to tame them in various applications.

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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.