The following projects can be conducted in our group:
Stamping of Molecular Patterns with Amine Termination for Cell Adhesion Studies
Osteoblast adhesion is important for ingrowth of implants. Cell adhesion includes a number of steps such as seeding, migration, settling and spreading. To understand which cues are relevant in migration and anisotropic spreading molecular landscapes of amine-terminated species can be used. In aqueous solution the amine groups become positively charged, thus lateral electric fields will be present on the surface. Micro-contact printing is a method to prepare monolayer patterns of molecules on surfaces. Silicone stamps are produced as molds from glass masters, immersed in the molecule solution and contacted to the substrate in order to transfer molecules from the stamp to the glass. The task is to produce and characterize such molecule landscapes and participate in scanning ion conductance measurements of adhered cells thereon.
Electrochemical Etching of Pt-Ir Tips for Multiprobe Applications
Scanning probe microscopes are known for their extraordinary resolution, even enabling imaging of individual atoms. The most critical component is the tip which must be very sharp, ideally reaching an effective diameter of only a single atom. In most cases the basis for such tips is electrochemical etching yielding a highly defined shape. While this method is routinely used for tungsten tips many applications require inert, non-oxidizing materials. In this project wires made from a Pt-Ir alloy are used for tip etching. Resulting tips are characterized by electron microscopy and by the actual imaging quality "at work" in a multiprobe scanning probe microscope.
Ion-based Films on Insulators for SEM Imaging on Perovskites
Surface charges frequently lead to critical situations in space applications. In a project together with the DLR (German Aerospace Center) we explore mechanisms of charge deposition and charge control on the nanoscale, where the primary tool is a scanning electron microscope (SEM). A promising class of materials are perovskites, due to their extremely large dielectric constant. But they are essentially insulating, giving rise to charge accumulation during electron bombardment. This Bachelor project aims at controlling or neutralizing these charges using a conductive film. The question is if and how surface charges on insulating materials are affected by ion-based films in a scanning electron microscope.
- Immersion Process of Metal Nanoparticles Embedded into thin Polymer Films
Functional mapping in an atomic force microscope (AFM) often suffers from crosstalk between topographic and functional channels. For experiments using optical mapping embedded nanoparticles are a promising system because they exhibit local near fields with little geometric surface corrugation. In this project the embedding process into polymer films is investigated by a combination of AFM, optical microscopy, and/or reflectometry.
- Ink-Jet Printed Molecular Aggregates: Structure and Orientation of Dipole Transition Moments
Drop-casting is one of the simplest methods for preparation molecular aggregates. In collaboration with the group of Prof. Hermann Seitz (Fakultät für Maschinenbau und Schiffstechnik) an ink-jet technique is employed for preparing self-assembled molecular nanostructures on smooth surfaces. In contrast to conventional drop casting the liquid volume is about 100000 times smaller, enabling more controlled conditions and multiple preparations on a single sample. In this project ink-jet printed molecule structures are investigated by optical and atomic force microscopy. In addition fluorescence microscopy is used for polarization-dependent luminescence studies, yielding the respective dipole orientations and thus giving insight in the internal aggregate structure.
- Ion Current in Nanopipettes near Surfaces
In scanning ion conductance microscopy a nanopipette is brought close to a surface, and the ion current in a conductive liquid is used as a probe for nanoscale surface imaging. Due to surface charges inside the pipette, as well as on the surfaces to be investigated, the ion current may be affected in a characteristic way. For example, rectifying behavior is observed in analogy to semiconductor heterojunctions. In this project the ion current is investigated as a function of external parameters such as voltage, ion concentration, pipette dimensions and -material, and the surface material (determining the surface charge). Observations may be analyzed experimentally in view of biological samples (e.g. living cells) or in conjunction with numerical simulations taking into account the essential geometry.
More topics are available upon request.
- Nonlinear Oscillation Dynamics of Atomic Force Microscopy Cantilevers
The amplitude spectrum of a cantilever in an atomic force microscope (AFM) in vicinity to a sample surface is rich in structure if the tip-sample interaction is sufficiently nonlinear. In this project the eigenfrequencies and mixing modes due to external forces for different cantilevers, as well as nonlinear mapping modes are explored.
- Mapping Light-Induced Forces on Nanostructures Samples
Light-matter interaction can lead to various phenomena such as optical forces, photovoltages, and plasmon excitation. In this project the possibility to map such effects with dynamic atomic force microscopy (AFM) is explored on nanostructured surfaces. Possible approaches are Kelvin probe force microscopy (KPFM), amplitude modulated force detection, or tip-induced light scattering in the near field.
- Long-Range Order of Self-Assembled Organic Molecules Prepared in Ultra-High Vacuum
Photoemission electron microscopy (PEEM) enabled simultaneous spatially and energy resolved investigation of the electronic and optical properties of dye molecules adsorbed on a surface. In this project a dedicated ultra-high vacuum (UHV) evaporator for molecular species is being built and used for well-controlled preparation of ultrathin fluorophore layers. The geometric, optical and electronic properties are investigated using atomic force microscopy (AFM), fluorescence microscopy, and PEEM.
- Mapping the Work Function of Heterogeneous Metal-Semiconductor Nanostructures
The spatially dependent work function of metal-semiconductor nanostructures at surfaces contains vital information on the material distribution and the band topology. Using Kelvin probe force microscopy (KPFM) or photoemission electron microscopy (PEEM) the work function can be mapped with high spatial resolution. This capability is applied to nanostructures prepared by evaporation in vacuum or by ex-situ nanolithography.
- Morphology of Live Cells on Structured Surfaces Studied by Scanning Ion Conductance Microscopy (Biophysics)
Adhesion of cells to surfaces can include several steps such as initial physical or chemical binding, rearrangements in the cells surface region, spreading, and migration. The aim is to uncover surface structure dependent interaction mechanisms on the basis of time-dependent morphology studies.
For the State Examination ("Staatsexamen") a variety of projects are available which are closely related to running activities in our research group. Possible topics are:
- Dynamic atomic force microscopy (AFM)
- Growth of molecular nanostructures
- Luminescence properties of dye aggregates on surfaces
- Morphology of metallic nanostructures on surfaces
None at the moment.