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:

Site-specific enthalpic and entropic contributions to the grain boundary segregation energy. It is a well-known observation that in a binary system, atoms of a certain species preferentially segregate to the grain boundary in order to reduce the total free energy of the system. This reduction in energy, the so-called segregation energy, consists of an enthalpic part and an entropic part, respectively. In this study, these two contributions shall be investigated for the individual grain boundary sites using atomistic simulations and the full composition range shall be explored at several temperatures in order to get a deeper thermodynamic understanding of the segregation process. Eventually, based on the atomistic data, a thermodynamic model shall be applied, which describes the enthalpic and entropic parts for all compositions and temperatures. (Supervisor: Dr. Sebastian Eich)

Simulation study of atomic redistribution at interfaces in single crystalline core/shell nanowires. We elaborate on an atomic level the stress-strain behavior (elastic stress-strain relations) of single crystalline core/shell nanowires. The computer modelling will focus on the interface structure between the core and the shell (LAMMPS/Python). Also, the influence of shell-thickness (e.g. 10 to 100 nm) and surface effects is of interest. Finally, an appropriate mechanical property, e.g. the "effective" Young modulus, or a linear equivalence of it is an ultimate aspiration of the project. (Supervisor: Dr. Gábor Csiszár)

Optimization of phase boundary tensions in high performance ferritic alloys. Ferritic Fe-Cr-Ni-Al-Ti alloys have shown to be a promising economic alternative to nickel-based superalloys 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. Unfortunately, the superior creep strength is lost, when the precipitates grow and the matrix/precipitate interfaces become incoherent. Our goal is to stabilize interface by alloying in order to minimize the interfacial tension. The characterization of the microstructure will be performed by high-end aberration corrected transmission electron microscopy (TEM). (Supervisors: Robert Lawitzki, Prof. Dr. Guido Schmitz)

Li1.33Ti1.667O4 + 1.5 Li2O (or Li2CO3): Phase evolution during battery cycling? Transition metal oxides are known to exhibit variable oxidation states. Due to this effect their use in lithium ion battery is highly preferred. The varied oxidation state may induce different crystal structures. During battery cycling, the oxidation state of the cations in the host changes and thus the crystal structure. In a recent study, we found out that a phase transformation in Li2MnO3-δ is indeed beneficial for the battery performance. The aim of the study is to study the phase evolution in a well-known Li4Ti5O12 battery anode material (exhibiting lithium reordering during battery cycling) when the material is mixed with Li2O (or Li2CO3). (Supervisors: Yug Joshi, Prof. Dr. Guido Schmitz)

Mechanical properties of LiCoO2/LiFePO4 battery electrode in response to de-/lithiation. Due to continued interest in energy storage and the need for safer and faster battery electrode, an understanding of failure mechanism in a battery is required. Henceforth, the study will focus on nano-mechanical testing of LiCoO2/LiFePO4 battery electrodes and the effect of lithium concentration on the elastic stiffness and plastic strength of the material. The study will produce battery electrodes through sputter deposition followed by electrochemical characterization. Subsequently, nano-indentation tests will be undertaken to determine the mechanical properties. (Supervisors: Yug Joshi, Prof. Dr. Guido Schmitz)

Martensite and Perlite reaction in steel nanowires. These reactions are the heart of the dominating role of steel applications in the history of technology. However, how do these reactions appear in nanowires, where the thickness becomes less than a typical perlite lamella or a single Martensite needle. Fe nanowires are produced by electrodeposition in templates? They are carbonized in methane atmosphere. After proper heat treatment the wires are investigated by high resolution electron microscopy. (Supervisors: Dr. Gábor Csiszár, Prof. Dr. Guido Schmitz)

Stabilization of grain size by grain boundary segregation. Nanocrystalline materials suffer from instability against grain growth. In a frequently considered concept grain growth could be stopped by strong impurity segregation in the grain boundaries. Although this concept is established, clear measurements are rare. The study should electrodeposited thick films of a nanocrystalline Cu(Bi). Grain growth will be characterized by XRD and TEM in dependence on the Bi fraction in the alloy. (Supervisors: Dr. Gábor Csiszár, Prof. Dr. Guido Schmitz)

Atomprobe study of tantalum diffusion in TiB2 crystals. For grain refinement in aluminum casting processes TiB2 and Ta are added for grain refinement. To gain insight into the process, the diffusion of Ta in TiB2 crystals should be analyzed using Atom Probe Tomography (APT). Single crystals of TiB2 will be coated by sputter deposition with a thin tantalum layer. Subsequent annealing steps at different temperatures will create the necessary samples for a detailed APT study. APT demand samples of a needle like shape with a radius of curvature of about 50nm. These samples will be created using a Focused Ion Beam assisted Lift-Out procedure. Using the high spatial and chemical resolution of the APT, diffusion processes of Ta should be investigated in detail. The work will be carried out in collaboration with the Montan University Leoben, Austria. (Supervisor: Dr. Patrick Stender)

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, Prof. Dr. Guido Schmitz)

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 yet been understood. 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 > 1020 W/cm2, which we plan to obtain with ultra-short (40 fs), highly focused laser pulses (Supervisor: Dr. Patrick Stender)

Atom probe tomography of III-V semiconductors for light emission and optical sensors. Band gap engineering requires the alloying of the cation sublattice of nitrides (B, Ga, Al, In). However, limited solubility often hinders to obtain the required lattice parameter for a homogeneous alloy. The goal is to produce non-equilibrium alloys and to detect the earliest indication of decomposition by atom probe tomography. Samples are produced by FIB Lift-out to nanometric needles and investigated by laser-assisted atom probe tomography. (Supervisors: Dr. Patrick Stender, Prof. Dr. Guido Schmitz)

Atom probe tomography of carbohydrates. Glucose and other carbohydrates are important materials for living organisms. Atom Probe Tomography has been proven to be a perfect method for hard materials, but the material class of soft matter and liquids is the object of current research. Usually, carbohydrates evaporate under laser illumination and high electrical fields as molecular fragments (CxHy). The dependence of these fragments shall be investigated in dependence on laser wavelength, electrical field and other parameters.  Suitable measurement conditions for the analysis of organic structures should be identified. The project is a demanding high-end experimental study and requires utilization of Atom Probe Tomography, Focused Ion Beam Techniques and Laser. (Supervisors: Dr. Patrick Stender, Prof. Dr. Guido Schmitz)

Development of cryo-APT preparation techniques. Samples for Atom Probe Tomography must be in a needle-like shape with a radius of curvature of 50 nm at the apex. Preparation of conventional materials is available by using Focused Ion Beam Techniques. Currently, liquids are of great interest, with the goal of studying processes at interfaces like cell membranes, viruses or bacteria in atomic resolution. Aqueous solutions are cryo-frozen and transferred into the FIB for tip shaping and finally to the atom probe. The sample must be permanently cooled to preserve them in solid state. To avoid artifacts, crystallization must be prevented. The project shall develop a dedicated ink-jet-printing technique suitable to create frozen droplets of 10-40 um in diameter. The cooling rates achieved should prevent the liquid from crystallization. (Supervisor: Dr. Patrick Stender)

Further information and consultation:

This image shows Guido Schmitz

Guido Schmitz

Prof. Dr. Dr. h.c.

Chair Professor

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