Master Theses

Possible topics for master theses.

Where can you do research in a motivating environment? Implement your own ideas? In the field of Material Physics of course. Below are several current topic possibilities for your Master thesis:

Thermodynamic fluctuation theory for grain boundaries. Our team recently presented a regular procedure for the calculation of equilibrium fluctuations in systems, which even includes fluctuation of excess properties of the grain boundaries (GBs). However, the conventional molecular dynamics (MD) simulation is restricted by conservation of the total energy. The flexibility of MD can be greatly enhanced by simulations in contact with a heat bath.  To obtain this, temperature and pressure of the system must be controlled appropriately. The goals of this study are the following: New thermostats shall be integrated into an existing MD code. The thermodynamic fluctuation theory for GBs shall be investigated by proving fluctuation calculated in MD simulations. (Supervisor: Sebastian Eich)

Fabrication and TEM characterization of a high performance ferritic alloy. The ferritic Fe-Cr-Ni-Al-Ti alloys have shown to be a promising candidate and cheap alternative to nickel-based superalloys as a material for high-temperature applications. Superior creep resistance, as compared to conventional ferritic steels, is obtained by precipitation of nano-scaled NiAl/Ni2TiAl-phases during a controlled heat treatment and by controlling the amount of Ti, which has a strong influence on the chemistry and morphology of the precipitates. Our goal is to fabricate three model alloys differing in the amount of Ti and to analyze the influence of the heat treatment on the growth and morphology of these precipitates through TEM analysis. (Supervisors: Robert Lawitzki, Guido Schmitz)

Solder wetting on miniaturized chip metallization. Wetting of metals by liquid solders is a prerequisite of reliable materials joints. The project tries to reduce the size of an individual solder joint from the present technical standard of about 50 µm down to 1µm. Metallic lines of that small size will be prepared by optical lithography. In-situ investigation of the solder flow proceeds inside a special SEM that allows operation at almost atmospheric pressure and is equipped with a small furnace. In addition, a dedicated nano-tweezer must be put into operation to handle the small solder droplets. (supervisors: Samuel Griffith, Guido Schmitz) 

MgH2-Al/LiBH4/Li solid state battery.  Current investigations of the fast Li ion conductivity in LiBHenvisage its use as an electrolyte in all solid state batteries. Whereas powders are commonly investigated, thin films offer the potential of better reliability, interface permeation and also provide a tool for examining the Li transport. Based on our previous development of a production route of LiBH4 films by melt-freezing, focus will be now given to a full solid-state battery. The choice of electrodes is delicate due to reactions with the LiBH4 electrolyte, but MgH2 is a promising candidate. The battery function will be characterized by electrochemical methods. A structural characterization of the system with SEM/FIB/XPS will give further insight to the system. (Supervisor: Efi Hadjixenophontos)

Hydrogen Diffusion in metallic bi-layers. Hydrogen diffusion/storage into metals is of great interest to satisfy increasing energy demands. In this work, we compare different metal coatings that are deposited on Ti films by ion-beam sputtering. The Ti films function as a probe for the hydrogen uptake. That means, the kinetics of TiH2formation is determined by in-situ XRD and then evaluated in terms of the diffusion through the coating on top.  We start by investigating Pd, Fe, Al and Ni in isothermal measurements (at a constant hydrogen flow of about 1bar). Further structural characterization and the stability of the layers will be evaluated by SEM, FIB and TEM.  (Supervisor: Efi Hadjixenophontos)

Electrochromism of NaxMn2O4In prior studies, we concentrated on the possibilities of optical switching by Li intercalation into typical battery electrode materials and found that LiMn2O4 shows a very attractive variation of the reflectivity spectrum. This may be used in future photonic integrated circuits. Since a bigger ion than Li+ may introduce more electrons, we would like to now test, whether charging with Naions results in different optical activity. LiMn2O4 layers will be sputter-deposited, the Li ions will be electrochemically replaced by Na, while the variation of the optical spectrum is measured. The studies will be complemented by TEM to clarify possible microstructural transformations. (Supervisors: Yug Joshi/Guido Schmitz)

Elastic stress-strain relation in cylindrical core/shell nanowires of NbO cores and TiO, ZnO or Al2O3 shells. We investigate the aspects of growth including structural and mechanical properties (elastic stress-strain relations) of core/shell nanowires grown on Nb wires on the mesoscale. Determination of the mechanical properties as e.g. "effective" Young modulus is carried out by using a nanomanipulator and force sensor within an SEM. Additionally, TEM, in combination with EDX, facilitate the identification of the constitutive phases in the nanowires. Characteristics of the core-shell nanowires also implicate their potential for energy storage utilized in the field of nano-robots. (Supervisor: Gábor Csiszár)

Systematic tuning of segmented magnetic nanowires made out of Fe/Cu and Fe/Pt. The magnetic properties of the NWs can be tuned by changing segment-length of a ferromagnetic/anti-ferromagnetic core to yield remarkable new properties in the field of biomedical applications (hyperthermia). The proposed diamagnetic /paramagnetic spacer between the ferromagnetic bits allows the initiation of how, fundamentally, the magnetic landscape depends on segment length in the range of 100nm (soft magnetic) to 10 nm (hard magnetic) in length. The individual nanowire is to be imaged by using SEM, TEM EDX and XRD, while the single-domain structure is rigorously examined by means of MFM. (Supervisor: Gábor Csiszár)

New generation of lithium ion batteries based on 1D Cu/Cr sharply segmented nanowires? Conventionally, the intercalation compounds rely on vacant sites for the insertion of lithium into the crystal structure. As an alternative, we propose a system incorporating a high amount of lattice-mismatch-induced dislocations providing pathways, as well as lattice sites for fast migration and storage of lithium. The project will incorporate the fabrication via electrodeposition, and subsequently, the electrochemical de/-intercalation procedure. Various electrochemical activity-governing aspects such as wire thickness, segment-length, effect of atmosphere etc. will be examined. (Supervisor: Gábor Csiszár)

Correlative study of grain boundary segregation in nanocrystalline Cu-Ni alloys. Nanomaterials raise new challenges in characterizing and understanding their chemical and physical behavior. Preferred enrichment of a certain element in the grain boundaries leads to changes in thermodynamic stability of the alloy. In this project, we want to analyze grain boundary segregation in Cu-Ni alloys by atom probe tomography (APT). With the same sample, the crystallographic orientation of the adjacent grains should be determined in a correlative study. For this, electron backscatter diffraction (EBSD) in a high resolution scanning microscope is used. Results of orientation-dependent grain boundary segregation shall be compared to predictions of atomistic studies already available in our team. (Rüya Duran, Guido Schmitz)

Catalysis by metallic wires. In today’s catalytic converters, platinum is a key catalytic component to oxidize hazardous gases like CO and CxHx. To reduce the costs of the catalytic converters, it would be beneficial to use a Palladium/Platinum alloy instead of pure Pt. The addition of Pd will change the properties of the catalytic process and the stability of the catalytic component. Our goal is to investigate the oxidation of Pt/Pd alloy particles by atom probe tomography and to get an insight into the material changes during the catalytic process. (Supervisor: Yoonhee Lee, Guido Schmitz)

Lattice structure information in atom probe data. Atom Probe Tomography (APT) is a high-resolution analysis method that provides three-dimensional materials analysis at atomic resolution. While the chemical contrast is clear, structural information is still difficult to access. However, especially with segregation phenomena, the orientation relationship between grains is of fundamental importance. We will try to extract lattice structure information from the measured data by a new algorithm based on Fourier transformations. Since 108 atoms have to be evaluated, fast graphic card processing will be used. Once the corresponding lattice planes have been identified, local orientation relationships are to be determined. (Supervisor: Patrick Stender)

Pulse-probe experiments in atom probe tomography. In Atom Probe Tomography (APT), very fine samples are evaporated as tiny molecule fractions by superposition of high electric field and short laser pulses. Especially with organic matter, the size and the charge state of the evaporated fractions have not been understood, yet. Likewise, oxygen and nitrogen can be lost due to insufficient ionization. The aim of the project is to investigate whether a second, subsequent laser pulse, that hits the species right after leaving the sample surface, can positively influence the level of ionization and the fragmentation through multi-photon ionization. This requires laser powers > 1020W/cm2, which we plan to obtain with ultra-short (40 fs), highly focused laser pulses (Supervisor: Patrick Stender)

Further information and consultation:

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Prof. Dr. Dr. h.c.

Guido Schmitz

Chair Professor

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