The following projects can be conducted in our group:
- 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.
- Effect of the Precise Cantilever Geometry on Oscillation Modes
An atomic force microscope (AFM) is usually operated in a dynamic mode, i.e., the cantilever is mechanically excited to oscillations. The frequency-dependent properties critically depend on the cantilever geometry. Particularly the precise determination of the cantilever thickness (a few μm) is challenging. In this project a measurement method based on interferences in the optical infrared range is evaluated and compared to state-of-the-art models. The relationship between frequency spectra and geometry is analyzed for various cantilevers.
- Anharmonic Effects in Dynamic Atomic Force Microscopy
Cantilever oscillations in atomic force microscopy (AFM) are usually treated within the model of the harmonic oscillator. However, in vicinity of a surface the resulting potential is strongly nonlinear. This project aims at characterizing the nonlinear dynamics of the cantilever-surface system. By measuring the frequency spectrum for varying tip-sample distance and oscillation amplitude, regimes of stable and unstable, chaotic oscillations are identified. By analyzing higher harmonics of the cantilever oscillation the interaction force can be characterized for different surfaces.
- Orientation of Dipole Transition Moments in Molecular Aggregates
Experimental determination of the internal structure of molecular nanostructures is a challenging task. However, the orientation of dipole transition moments is closely connected to the molecule orientation, and it is relatively simple to measure. Such data can be used to isolate remaining possible intermolecular arrangements. In this project a modified fluorescence microscope is used for polarization-dependent excitation and detection of molecule luminescence at each pixel of the images, yielding the respective dipole orientations.
- Correlation of Morphology and Luminescence of Cells in Liquids
Scanning ion conductance microscopy (SICM) allows us to measure the 3D morphology of nano- and micro-objects without exerting any disturbing forces. It is well-suited for the investigation of biologic species such as cells. In this project the connection between cell morphology and the spatial distribution of adhesion proteins is investigated. The latter are identified by fluorescence markers imaged in a fluorescence microscope simultaneously with the SICM measurements.
- Mechanisms Contributing to the Ion Current in the Vicinity of Living Pacemaker Cells
With scanning ion conductance microcopy (SICM) the ion current above living cells in an electrolytic buffer solution can be monitored as a function of time. This project aims at identifying the mechanisms that contribute to the ion current of living cardiomyocytes. Besides geometric variations due to the periodic beating behavior possible contributions from the electric action potential and ion redistribution are investigated.
- Degeneration of Albumin in Artificial Joints Assessed by AFM
Wear and lubrication are an important topic for artificial joints, e.g. in the human knee. In this project the situation of forces is mimicked on the nanoscale using an atomic force microscope (AFM) under tapping conditions. The analysis of force-distance curves of Albumin (an abundant protein) before and after the AFM treatment can provide insight in structural changes and degeneration.
- 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 migration, initial physical or chemical binding, rearrangements in the cells surface region, and spreading. 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.