Advanced image processing algorithms for coherent x-ray nanoCT

Ptychographic nanotomography is a recently developed coherent imaging technique, which yields 3D measurements of the electron density distribution in the investigated specimen with nanometer resolution and high sensitivity. This new technique is relevant in many research fields such as biomedicine and materials science.

The focus of this project lies on the implementation and on the improvement of advanced image processing algorithms for ptychographic phase projections. These algorithms include phase-unwrapping and alignment routines. The algorithms developed by the student will be applied to existing data as well as to data taken in future synchrotron experiments.

For more information, please contact: Bjoern Enders (benders@ph.tum.de), Dr. Pierre Thibault (pierre.thibault@ph.tum.de), or Dr. Irene Zanette (irene.zanette@ph.tum.de).

Dünne Schichten für spin-kaloritronische Experimente / Thin Film Fabrication for Spin Caloritronic Experiments

Bereich: Laser-MBE, Spin Caloritronics

Magnetic ferrites such as zinc ferrite (Zn_xFe_3-xO₄), cobalt ferrite (Co_xFe_3-xO₄), or yttrium iron garnet (Y₃Fe₅O₁₂ or YIG for short) are expected to display large caloric effects in spin transport experiments. Using laser molecular beam epitaxy (laser-MBE), epitaxial thin films as well as heterostructures of such materials shall be deposited on suitable, differently oriented single-crystalline substrates (e.g., MgO). The thin film samples will then be characterized structurally using high-resolution X-ray diffraction (XRD), and magnetically via superconducting quantum interference device (SQUID) magnetometry and magneto-optical Kerr effect (MOKE) measurements.

Advisors: Dipl. Phys. Matthias Althammer, Dr. Matthias Opel, Prof. Rudolf Gross.

Ferroische Emitter für spinpolarisierte Elektronenemission / Ferroic emitters for spin-polarized electron emission

Area: laser molecular beam epitaxy, thin film technology

Spin-polarized electron emission is important for applications, e.g. in materials' analysis. We plan to follow a novel approach where magnetic thin films shall be integrated into existing ferroelectric electronic emitter devices in collaboration with the TU Dresden. To this end, we will deposit integrated multi-functional thin film structures -- consisting of the ferromagnetic insulators NiFe₂O₄, CoFe₂O₄, or Y₃Fe₅O₁₂ and the ferroelectric materials [Pb(Mg_1/3Nb_2/3)O₃]_1-x[PbTiO₃]_x (PMN-Pt) or BaTiO₃ -- using laser molecular beam epitaxy at the WMI (E23). The work will contain the fabrication and patterning of these multilayer structures as well as their structural, magnetic, and ferroelectric characterization and optimization. It represents the basis for the future electron emission experiments in Dresden.

Advisors: Dr. Stephan Geprägs, Dr. Matthias Opel, Prof. Rudolf Gross.

Implementation and application of a phython-based fast CT reconstruction algorithm for high-energy phase-contrast imaging

Phase-contrast x-ray computed tomography is a recently developed x-ray imaging technique, which yields enhanced soft-tissue contrast for biomedical samples. In order to develop this approach toward potential future clinical applications, the method will be tested with high x-ray energies in the 60-80 keV range. This work will deal with the implementation and application of a phython-based fast CT reconstruction package for high-energy phase-contrast imaging on larger biomedical samples. The work will also include the development and application of multimodal bilateral filters and 2D regularized integration schemes to improve image quality.

Interactions Between UMo/Al Fuel and Diffusion Barriers Under Thermal Treatment

Research reactors worldwide are preparing to convert their fuel from high enriched Uranium (HEU) to Uranium with lower enrichment. Currently, FRM II uses a fuel highly enriched in U²³⁵ and the research on the replacement of HEU with adjusting the fuel is highly emphasized. One of the most promising candidates for a future nuclear fuel is UMo particles embedded in an Aluminium matrix. However, there is a strong interaction between UMo and Al. This interaction has been considered as the major cause of the failure of UMo fuel during the in-pile irradiation test. Studies on eliminating the interaction phenomenon therefore attract great interests. It is observed that the growth of the interaction layer during in-situ irradiation can be suppressed by adding a diffusion barrier element. Niobium and titanium nitride as diffusion barriers have shown great effect on suppressing the interaction layer growth after heavy ion irradiation (iodine ion with 80 MeV energy and fluence 1×10¹⁷/cm²). Further annealing test for niobium and titanium nitride samples is expected to exhibit evidences of interactions among UMo, diffusion barrier and aluminium under long heat treatment. Characterizations as SEM, EDX and XRD will be applied and the growth relation of interaction layer under annealing should be generated.

This work will be focused on the experimental part of annealing test and theoretical growth relation deduction. Students can have the opportunity of accessing to large scale facilities in Europe: FRM II (Germany) and MLL-tandem accelerator (Germany).

Contact: Ms. Hsin-Yin Chiang

Magnetic and structural properties of Fe-doped \(\mathrm{TiO}_2\)

Long range coupling of local moments of a transition metal diluted in an insulating parent, such as \(\mathrm{TiO}_2\), is a matter of recent research. Dilute ferromagnetic oxides can be an obvious choice for spintronics as the Curie temperature exceeds the dream limit of 300 K. 

Thin-films are to be grown in oxidizing conditions, optimized for non-segregation of the magnetic species from the host. Magnetometric studies complemented with polarized neutron reflectometry and x-ray absorption spectroscopy (in collaboration with SLRI-Thailand) will be implemented in the investigation of such magnetic oxides at a nanometric scale. Our particular interest will be to observe the in-situ variation of magnetic domain structures (in the micron range) by GISANS and off-specular neutron scattering techniques as we grow the films under optimal preconditions. 

Supervision: Dr. Amitesh Paul, Prof. Dr. Peter Böni

MicroCT and X-Ray Vector Radiography Imaging Experiments on Vertebral Bones

The detailed micro-structure of human vertebral bones reflect the load it usually experiences in daily life. The stability of vertebraes mainly depends on the orientational distribution of the trabeculae and can be assessed by high-resolution 3D microCT measurements. This master thesis will focus on experiments that correlate 3D microCT data to x-ray vector radiography imaging results on phantom and human vertebral samples.

Direct supervision: Andreas Malecki & Dr. Guillaume Potdevin

Moiré Interferometry at Compact X-ray Synchrotron Sources

Clinical x-ray imaging presently relies on x-ray generators that deliver a broad polychromatic spectrum. Large-scale sources, on the other hand, can provide monochromatic brilliant x-rays, resulting in significantly improved image quality at lower dose. This project focuses on beam quality characterisation at new compact x-ray synchrotron sources using Moiré Interferometry. The project is embedded as a core activity into the excellence cluster “Munich Advanced Photonics” (MAP) and the future “Centre for Advanced Laser Applications” (CALA).

The main aim of the project is the identification of the main x-ray source stability parameters and the quantitative analysis of grating based Moiré interferometry data from a compact x-ray synchrotron source.

For more information, please contact Simone.Schleede@tum.de or Martin.Bech@tum.de.

Schaltprozesse in thermoresponsiven Polymergelen / Switching processes in thermoresponsive polymer gels

Thermoresponsive Polymere ändern ihr Volumen stark beim Erwärmen über die lower critical solution temperature. Wir untersuchen selbstassemblierte Hydrogele aus thermoresponsiven Polymeren. Wichtige Fragen sind hierbei die strukturelle Änderungen beim Schalten sowie deren Kinetik und Reversibilität.

In der Master-/Diplomarbeit sollen Hydrogele aus neuartigen thermoresponsiven Polymeren präpariert werden und die von ihnen gebildeten Strukturen untersucht werden. Hierzu werden moderne Streumethoden, auch am Forschungsreaktor FRM II eingesetzt.

Spezielle Vorkenntnisse sind nicht zwingend erforderlich.

Betreuer: Prof. C.M. Papadakis, K. Kyriakos

Suche nach ungetriggerten Gamma-ray Bursts in den Fermi/GBM Daten / Search for untriggered GRBs in Fermi/GBM data

Fermi/GBM is a Gamma-ray Burst detector build at MPE, and operating on NASA's Fermi mission since 2008. It detects about 250 GRBs per year by a sophisticated triggering algorithm. Yet, several burst-like features escape the trigger algorithm. The task is to derive a software tool which allows easy manual inspection of the GBM data, and to determine the fraction of untriggered events.

Contact: J. Greiner (jcg@mpe.mpg.de)

Requirements: fun in writing software

Training effect and exchange bias

Exchange bias between an antiferro-feromagnet is an integral part of magnetoelctronics. Traning is described as the loss of exchange bias effect after the first field cycling. We intend to investigate the possible recovery of the training effect in the exchange biased \(\mathrm{CoO}\)-\(\mathrm{Co}\) system. Magnetometric techniques will be complemented with polarized neutron reflectometry in investigating the interfacial modifications.

Supervision: Dr. Amitesh Paul, Prof. Dr. Peter Böni