In the following, selected possible master's or bachelor's theses will be presented. However, this list is not complete. If you are interested in working with us, please do not hesitate to contact us.
Investigation of the growth behavior of organic molecules on metallic surfaces with scanning tunneling microscopy
Suitable combinations of certain organic molecules result in systems with metallic properties, e.g. electrical conductivity or even superconductivity. By means of a selective variation of the molecules, there are many possibilities to modify the electronic properties and to synthesize new compounds. Even small changes can have a great influence on the physical behavior of organic molecular systems.
An example of such molecular systems are organic charge transfer salts. Within the scope of the Collaborative Research Centre (SFB / TR 49) the growth behavior on metallic substrates and the electronic structure of organic charge transfer salts are investigated by means of scanning tunneling microscopy and spectroscopy. The metallic substrate has an influence on the growth, and thus also on the electronic properties.
The aim of this master thesis is to investigate and compare the growth and electronic structure of organic charge transfer salts on different metallic surfaces.
Organic semiconductors on ferromagnetic surfaces
A further class of organic molecules, so-called organic semiconductors, allow to manipulate the effective spin polarization of magnetic surfaces. An increase in the spin polarization is of great advantage for the development of tunnel magnetoresistance elements, which are used, among other things, in sensors and hard disk reader heads. The development of magnetic random access memory modules for computers (MRAM) is also based on such tunneling magnetoresistance elements. Investigations of copper phthalocyanine (CuPc), a molecule which is primarily used as a dye (e.g. in solar cells), were carried out in our group. It has been shown that a significant part of the observed magnetoresistance originates from the formation of so-called hybridized interface states in the density of states of the surface-adsorbed molecule.
The growth of these molecules on iron substrate as well as its spin-transport properties were investigated using spin-polarized scanning tunnel microscopy in combination with spin-polarized photoemission (TU Kaiserslautern, AG Aeschlimann) and theoretical calculations (Crann Institut, Dublin, Ireland, AG Sanvito).
The topic of this work would be to investigate further molecules regarding their spin-transport properties.
Spin-polarized STM studies on ultra-magnetic magnetic layers
The investigation of the spin-reorientation transition (SRT) has led to substantial new insights in the field of thin-film magnetism. However, many phenomena can still only be explained to a very limited extent. For the understanding of magnetic properties it is essential to also study these properties in nanoscale systems, where morphology and structure have a great influence on the magnetic behavior. So far, the SRT has mainly been investigated using laterally integrating measuring methods. In this master thesis we use spin-resolved scanning tunnel microscopy. With this technique, it is possible to achieve a resolution in the atomic range. The aim of the project is to gain a microscopic understanding of the SRT by investigating the layer thickness-dependence and temperature-dependence in epitaxial Fe / Mo (110) and Co / Mo (110) films. Special attention is given to the temperature-dependent SRT, since the temperature can be varied continuously as opposed to the layer thickness.
Investigation of ultra-thin iron-vanadium alloy layers
Since the beginning of modern storage technology, it has been possible to store larger amounts of data on even smaller storage media.
The increase in the storage density is accompanied by a miniaturization of the data-storing component, leading to the fields of micro- or nanotechnology. The properties of nanostructures cannot be derived simply from the properties of corresponding macroscopic structures. For example, in a macroscopic alloy of iron and cobalt, the Curie temperature increases compared to pure iron, whereas the same alloy shows an entirely different behavior as an atomic monolayer on tungsten (110), namely a rapid decrease in the Curie temperature with increasing cobalt admixture. The alloy of iron and chromium shows a similar behavior, but the Curie temperature initially remains constant with a low chromium percentage in the alloy. Iron-vanadium is a unique ferromagnetic alloy with a very pronounced scattering behavior and the smallest measured magnetic damping.
The layers are deposited using molecular beam epitaxy, i.e. by thermal evaporation of the metals and deposition on a substrate surface. The growth of the layers, as well as the electronic properties, are investigated with scanning tunneling microscopy and -spectroscopy and low-energy electron diffraction (LEED). The magnetic properties of the alloy layers are investigated using Kerr magnetometry. This simple method allows the investigation to be carried out at different applied external magnetic fields as well as at different temperatures. It is possible to determine the temperature dependence of important magnetic variables such as remanence and saturation magnetization. An objective of this work is to investigate the dependence of the Curie temperature of iron vanadium alloy monolayers on tungsten (110).
Growth and magnetic properties of MnBi-films
Spin-based electronics (spintronics) is currently a hot topic in solid-state physics because it provides the opportunity for a new generation of multifunctional electronic components that combine traditional microelectronics with spin-dependent phenomena.Ideal components for such parts are ferromagnetic semimetals. These are materials, which show a band gap at the Fermi level for spin-down electrons similar to semiconductors, whereas the majority spin-up electrons ensure a metallic conductivity. In addition to the intensive experimental investigation of the Heusler alloys for which this behavior has been predicted, great efforts are being made to find further materials with semi-metallic properties. Epitaxial growth on suitable substrates opens up new possibilities for stabilizing materials in crystal structures which are metastable in the volume. According to theoretical predictions, MnBi is a true ferromagnetic semimetal in such a metastable structure. In addition to the semi-metallic properties, MnBi has been investigated as a storage medium for magneto-optical data storage media for some time. For volume samples from MnBi, one of the greatest Kerr effects of all known materials was found. So far, attempts to prepare thin films of this material on SiO2 substrates have had limited success. The task of this master thesis is to find suitable preparation parameters for the epitaxial growth of MnBi layers on tungsten substrate. The characterization of structural and magnetic properties can be done by low-energy electron diffraction (LEED), scanning tunneling microscopy and Kerr magnetometry.
For further information please contact:
Prof. Dr. Hans-Joachim Elmers
Institute of Physics - Johannes Gutenberg University in Mainz
(3rd floor, room 03 623, North wing)
Phone: +49 6131 39-24150