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Synthesis of iron oxide nanoparticles from mixed valence precursors

The topic of this thesis is the synthesis of nanoparticles from a metal oleate precursor. The precursor is decomposed in a high boiling solvent at >300°C under inert atmosphere. During the decomposition, monodisperse nanoparticles with an average size of 20nm are formed.
In this thesis, the focus is on the preparation of a mixed valence precursor. The goal is the synthesis of a mixed valence precursor, containing both Fe2+ and Fe3+. From this precursor, nanoparticles are formed. The synthesized particles will be characterized by TEM, XRD, SQUID, and EELS. The focus is on the structure (shape and crystal structure) of the particles. Further information about the group can be found here: Research group nanoparticles

ContactDr. Aladin Ullrich, Room 364 (North building), Phone: (0821) 598-3215

 


 

Temperature-dependent optical properties of Dirac semimetals

Recently, three-dimensional (3D) Dirac materials, such as Dirac semimetals and Weyl semimetals, have attracted significant attention in condensed-matter research area. The 3D Dirac semimetals are considered to be the 3D bulk analogue of some other known 2D counterparts like graphene. Therefore, these materials are good candidates to extend the various applications of graphene to 3D. They are predicted to be a unique parent compounds to the other exotic phases and show peculiar properties.
This Master project will focus on the characterization of the optical properties related to the exotic electronic states in novel Dirac semimetals at low temperature. Optical spectra will be analyzed in terms of the existence of Dirac fermions. Reflectivity measurements in a wide energy range (from far-infrared to visible energy region) on Dirac semimetal samples will be carried out as a function of temperature.

Please also see the project description (PDF).

ContactProf. Dr. Christine Kuntscher, Room 361 (Physics North Building), Phone: (0821) 598-3315

 


 

Optical spectroscopy study on Ir-based magnetic materials

The 5d transition-metal oxides such as iridates are currently in the focus of condensed matter physics as they are promising candidates for the realization of novel quantum states like the quantum spin liquid state. The exotic physical properties are due to the complex interplay between strong spin-orbit coupling, electronic correlations, and crystal field.
This project focuses on honeycomb-type iridates and hexagonal perovskite-type iridates with mixed valence. Their electronic properties and lattice dynamics will be studied by optical spectroscopy. We will also apply external pressure by diamond anvil cells to induce structural or electronic phase transitions, and the emerging novel high-pressure phases will be characterized in terms of the low-energy excitations.

Please also see the project description (PDF).

ContactProf. Dr. Christine Kuntscher, Room 361 (Physics North Building), Phone: (0821) 598-3315

 


 

Optical properties of transition-metal dichalcogenides

Transition-metal dichalcogenides MX2, where M is a transition metal (Nb, Mo, Ti etc.) and X is a chalcogen atom (S, Se or Te) display several interesting electronic phases including charge density wave, superconductivity, and Weyl semimetal with exotic physical properties. Each of these phases has characteristic optical properties, which can be probed by infrared spectroscopy.
The aim of this Master project is to characterize various transition-metal dichalcogenides in terms of their optical properties by temperature-dependent reflectivity measurements. The results give valuable insight into the charge dynamics, lattice vibrations, and interband transitions in these materials.

Please also see the project description (PDF).

ContactProf. Dr. Christine Kuntscher, Room 361 (Physics North Building), Phone: (0821) 598-3315

 


 

Analysis of crack pattern development during pyrolysis of carbon fiber reinforced plastic for manufacturing of ceramic matrix composites (C-C/SiC)

Ceramic matrix composites like C-C/SiC combine the high thermal stability of conventional ceramics with a high fracture toughness, damage tolerance and thermal shock resistance, which makes them ideal for applications in extreme environments.
The matrix material of carbon fiber reinforced plastics is converted into porous carbon during pyrolysis. This induces crack formation within the matrix. The cracks then serve as infiltration paths for liquid silicon (Liquid Silicon Infiltration, LSI). Here, the crack pattern significantly influences the properties of the resulting composite.
In this work, an experimental setup for acoustic emission analysis during pyrolysis will be tested and optimized regarding its transfer properties. Subsequently, samples with different material systems will be tested in this setup with the goal of characterizing the crack formation and identifying influencing factors.

Contact: Bastian Brueck, Room 376 (Physics North Building), 

Phone: (0821) 598-3422

 


 

Testing of a gold evaporation cryostat

To obtain quantitative reflectivity spectra of a material as a function of temperature, the measurement of a perfect reference is mandatory. Such a perfect reference is realized by the intensity reflected from the gold-coated sample under investigation, where the gold coating is achieved by in-situ gold evaporation.
Within this Master project a gold evaporation cryostat will be tested in our Fourier-transform infrared spectrometer. After the successful testing, temperature-dependent reflectivity measurements on transition-metal dichalcogenides will be carried out.

Please also see the project description (PDF).

ContactProf. Dr. Christine Kuntscher, Room 361 (Physics North Building), Phone: (0821) 598-3315

 


 

Magnetic field dependence of the critical temperature behavior as a function of the F1-layer thickness in S/F1/F2-type triplet spin-valves

• Preparation of samples
• Measurements of the critical temperature in different magnetic fields in the low temperature laboratory
• Measurements of the magnetoresistance for different F1-film thicknesses at fixed temperature in the low temperature laboratory
• Measurement of the film thicknesses by Rutherford Backscattering Spectroscopy

Ansprechpartner: Daniel Lenk, Raum 375 Nord, Telefon: (0821) 598-2111

 


 

Examination of the chemical mechanism during thermal treatment of carbon fiber PAN precursors

By synthesis of isotopically labelled PAN precursors (2H, 15N, 13C) including their copolymers (with methylacrylate, itaconic acid?) and examination of the structural changes of them during thermal treatment by means of IR and NMR spectroscopy, DSC measurement and TG/GC/MS analysis the mechanism and elemental chemical reactions for the formation of efficient carbon fibers is worked out.
The knowledge about the detailed reaction pathways leading to most-efficient final carbon fiber material is still very limited. Thus, it is extremely difficult for carbon fiber producers (e. g. SGL Carbon) to systematically improve their products.
The chemically oriented work will include the synthesis and characterization of precursor polymers and copolymers and their thermal treatment as well as the synthesis and analysis of small model compounds.

PAN Precursor

AnsprechpartnerProf. Dr. Klaus Ruhland, Raum 348 Süd, Telefon: (0821) 598-3361