This thesis project focuses on communication processes between cells in the context of pattern formation from a statistical physics point of view. The class of Ising/Potts models provides a simple framework for studying the interplay of direct contact interactions with an external signal. This class of models originated in the context of magnetism, but its basic assumptions also fit the minimal requirements  for some interactions between biological cells. In this thesis, the Ising/Potts model will be studied numerically on biologically inspired lattices with or without the presence of spatially inhomogeneous external signals. The results of this simulations will then be analysed and interpreted with the help of tools from statistical physics and information theory. Prior knowledge in biophysics and information theory is not required, but a solid background in statistical physics is necessary.

Anforderung

• Ÿ  Abgeschlossenes 5. Fachsemester im Bachelor Studiengang Physik
• Ÿ  Spezialisierung Kondensierte Materie (KM) oder Kern-, Teilchen- und Astrophysik (KTA) sinnvoll

Stand der Wissenschaft und Technik

Lithium-Ionen Akkumulatoren kommen in Handys, Laptops und Akkuwerkzeugen als Energiespeicher zum Einsatz. Die Lebenszeit und Ladegeschwindigkeit dieser modernen Akkus sind allerdings durch physikalische als auch chemische Alterungsprozesse begrenzt, die vor allem an den Elektroden stattfinden.

Aufgaben

Ziel dieser Bachelorarbeit ist es, den Alterungsprozess von Graphit-basierte Elektroden zu untersuchen und die Einlagerung von immobilisiertem Lithium in den Elektroden während des Auf- und Entladens tiefenabhängig nachzuverfolgen, um so die die Alterungsprozesse besser zu verstehen und die Lebenszeit künftiger Lithium-Ionen-Batterien zu verlängern. Im Rahmen der Arbeit werden die Tiefenprofile mit dem N4DP Instrument an der Neutronenleiterhalle des Forschungsreaktors München (FRM II) in Garching vermessen.

Wir bieten

Ein interessantes Arbeitsthema, welches die Materialforschung der Kondensierten Materie mit Grundlagen der Kern- und Teilchenphysik kombiniert.

Hybrid solar cells have promising potential for playing a major role in renewable energy transition. They provide the possibility of flexible and light weighted photovoltaic in a large scale roll-to-roll fabrication, by combining the advantages of organic and inorganic semiconductors. For improved device performance, the morphological structure of the system has a crucial influence. This experimental bachelor thesis aims for a novel approach in templating desired hierarchical structure of the inorganic part, using environmentally friendly, non-toxic biopolymers such as proteins. Thin films of protein/semiconductor composites will be fabricated by spray coating for further structural investigations with the help of scanning electron and atomic force microscopy. Besides the laboratory work, the project also involves a literature review.

Lithium ion microbattery is the type of battery where all components (electrodes, membrane, and packaging) are in the thin film format. The need for such types of batteries is to provide light-weight and shape flexible solid-state energy sources for some miniature medical devices, such as implantable pumps, biosensors, and wireless capsule endoscopes. Membrane based on mixing both lithium slat and polyelectrolyte block copolymers will be prepared and investigated using small-angle X-ray scattering and impedance spectroscopy. The effect of a third component such as inorganic SiO₂ nanoparticles on the morphology and conductivity of the prepared thin film membranes will be studied. The best performing membrane will be assembled between two electrodes to probe the performance of a complete assembly of a solid-state lithium battery. The project will involve a literature review, sample preparation, x-ray scattering and impedance spectroscopy.

1.           Problemstellung/ Forschungskontext

Brennstoffzellen werden in der Automobilindustrie derzeit als mögliche Alternative zu Verbrennungsmotoren mittlerweile in Serien- und Vorserienprodukten vermarktet. Den Kern des Brennstoffzellenautos bildet ein Stapel bestehend aus einigen hundert einzelnen Brennstoffzellen. Aufgrund der Serienschaltung dieser Zellen führt der Ausfall einer einzelnen Zelle bereits zum Versagen des Systems. Ausfälle einzelner Zellen entstehen u. a. aufgrund inhomogener Verteilungen von Temperatur, Strom, Gasen und Druck. Elektrochemische Impedanzspektroskopie ist eine Methode mit der aus dem elektrischen Signal einer Brennstoffzelle auf grundlegende physikalische und chemische Vorgänge innerhalb der Zelle geschlossen werden kann. Folglich ist eine Überwachung der oben genannten Betriebsparameter mit dieser Messmethode prinzipiell möglich.

(English description: Fuel cells are currently considered to be a possible alternative to conventional combustion engines within the automotive industry. Heart of a fuel cell electric vehicle is the fuel cell stack consisting of several hundreds of single fuel cells. Due to the electrical series connection of these cells the failure of a single one leads to failure of the whole system. Failures of single cells are often due to inhomogeneous distribution of operational parameters like temperature, current, gases and pressure. Electrochemical impedance spectroscopy is a method that uses electrical signals of each cell and connects it to basic physical/chemical mechanisms within the electrodes of the cell. Hence, monitoring of fuel cells using impedance spectroscopy is in principle possible.)

2.           Fragestellung und Ziel der Arbeit

Elektrochemische Impedanzspektroskopie an Brennstoffzellen kann Aufschluss über elektrochemische Vorgänge innerhalb der Elektroden geben. Die elektrochemischen Vorgänge innerhalb einer Zelle wiederum werden stark durch die Potentiale der Elektroden beeinflusst. Zyklische Voltammetrie ist eine Methode um diese Vorgänge gezielt Potentialabhängig zu analysieren. Ziel der Arbeit ist es, mittels zyklischer Voltammetrie und Impedanzspektroskopie grundlegende Vorgänge in Brennstoffzellen aufzuklären.

(English description: Electrochemical impedance spectroscopy can give information of electrochemical mechanisms within fuel cell electrodes. These mechanisms are in turn strongly influenced by the potential of the electrodes. Cyclic voltammetry is a method to directly analyze potential dependent mechanisms. Goal of this work is to combine cyclic voltammetric and impedance measurements of fuel cells in different operational points to determine fundamental mechanisms in automotive fuel cell operation.

3.           Material und Methoden

Für die Arbeit steht ein Prüfstand zum Betreiben von Laborzellen und/oder automobilen Brennstoffzellen zu Verfügung. Die Analysen werden an kommerziellen Zellen durchgeführt, deren Zellhardware ebenfalls vorhanden ist. Folgende Messmethoden sollen angewandt werden.

(English description. For the bachelor thesis a test rig for lab cells and automotive fuel cells is provided. The analysis will be done using commercial cells. The single cell hardware will be provided as well. The following methods are planned to be used):

·         Linear sweep voltammetry

·         Cyclic voltammetry

·         Hydrogen/air EIS

·         Polarization measurements

In the field of solar cells and energy-storage new materials and solution processing technologies emerge which allow the fabrication of thin and flexible devices. The chosen substrate materials will have a major influence on the performance and the overall mechanical properties of these devices. Light-weight paper-based materials have the potential to be a low-cost solution in many different applications. In this project, we will prepare electrical conductive paper as a composite material based on varying amounts of nanostructured cellulose and conducting polymers by spray deposition methods. The sheet resistance of the achieved films and the relation to the morphology of films will be investigated.  Key aspect of the work will be the structural evolution of the films during the deposition process investigated with in situ x-ray scattering techniques.

Weiterentwicklung eines 3-D Druckers

Ein bereits vorhandenes Gerät soll evaluiert und notwendige Verbesserungen sollen integriert werden. Neben Software Modifikationen sind Anpassungen des mechanischen Aufbaues notwendig. Das Projektlastenheft wird gemeinsam erarbeitet.

Kontakt: Rainer Stoepler 089/ 28914272 oder 0162 2944773 rstoepler@tum.de

Organic solar cells have gained significant improvements via novel organic synthesis methods and optimized fabrication routes, especially with respect to their potential roll-to-roll processing for large-area device manufacturing. Printing technique, such as slot-die printing, allows for up-scaling to industrial-oriented scale which is not the case for laboratory deposition techniques like spin coating. This experimental bachelor thesis aims at understanding organic solar cell working principle and the corresponding fabrication process of solar cell via advanced slot-die printing technique. Besides, the relationship between its efficiency and morphology will be investigated by different measuring technique, such as AFM and small angle x-ray scattering. The project will involve a literature review, sample preparation process, data analysis and result exhibition.

Our quantum sensor of choice, the nitrogen-vacancy center in diamond, is on its way to become the world's smallest MRI scanner. It could give a 3D image of a single bio molecule while simultaneously resolving the chemical components. One limiting problem on this way is the reliable preparation of nitrogen-vacancy centers with long coherence times. We provide a state-of-the art measurement setup and a handful of ideas how to approach this task. We are looking for an enthusiastic student to try several preparation approaches and to perform quantum measurements on the coherence properties of the resulting single quantum sensors. Favorable personality qualities: interest in quantum information science, fun with handicrafts and no fear of software (python)

Machine learning, especially deep learning, has recently shown to be a very powerful tool in the fields of image classification, speech recognition, video activity recognition, machine translation, game playing and so on. The basic idea is to train a machine with large datasets such that it can thereafter process and characterize new data. The main goal of this project is to apply deep learning techniques to characterize quantum states. 

For quantum technology it is very important to have sources for single photons. One of the techniques that can be used to create these, is called spontaneous parametric down conversion, or SPDC for short. Here photons with a high frequency can split into two daughter photons with about half the frequency. An important point in this technique is so-called phase matching: the low and high frequency photons should travel at the same speed through the nonlinear material. This is often achieved by using special crystals that have to be oriented carefully. For applications we want to integrated these sources on photonic chips. In this project we will expore the phase matching in waveguides using photonic simulations of waveguides.

Responsive Blockcopolymere mit hydrophoben Endblöcken und hydrophilen Mittelblöcken (Telechele) zeigen großes Potential für die Anwendung in intelligenten Membranen, Gelen und selbstheilenden Materialien. Durch Verwendung von responsiven Blöcken hängen die Eigenschaften des Telechels stark von Parametern wie dem pH-Wert und der Temperatur ab.

In dieser Bachelorarbeit soll ein solches Polymer im dünnen Film untersucht werden. Es soll zunächst ermittelt werden, wie dünne, defektfreie Filme präpariert werden können. Diese sollen mit verschiedenen Methoden charakterisiert werden. Anschließend wird das Quellverhalten der Filme in Wasserdampf durch Messung der spektralen Reflexion bestimmt.

Nach einer Literaturrecherche sollen die Probenpräparation, die Messungen und die Datenanalyse durchgeführt werden. Für weitere Informationen melden Sie sich bitte bei Prof. Christine Papadakis, papadakis@tum.de.

Abgesehen von der kosmischen Hintergrundstrahlung sagt das Urknallmodell der
Kosmologie auch einen kosmischen Neutrinohintergrund voraus, mit einer etwas
niedrigeren Temperatur. Obwohl dieser bisher nicht direkt nachgewiesen werden
kann, gibt es starke indirekte Hinweise auf dessen Existenz im frühen
Universum. Zu späten Zeiten beeinflussen kosmische Neutrinos die
Strukturbildung. Dieser Effekt hängt von der Summe der Neutrinomassen ab,
die bisher unbekannt sind. Sein Nachweis stellt eines der zentralen Ziele
der nächsten Generation von kosmologischen Beobachtungen dar.

Ziele: In dieser Arbeit wird zunächst die Erzeugung des Neutrinohintergrunds
im frühen Universum basierend auf thermodynamischen und kosmologischen
Argumenten erarbeitet. Anschliessend wird der Effekt des Neutrinohintergunds
auf die Strukturbildung theoretisch modelliert und durch numerische Methoden
der Einfluss auf das Powerspektrum der kosmologischen Dichtefluktuationen
(eine zentrale Observable in der Kosmologie) in linearer Näherung in einem
2-Komponenten-Modell berechnet.

Grundlagen: Statistische Physik und Thermodynamik, KTA, theoretische Mechanik

Methoden: Lösen von gewöhnlichen, gekoppelten linearen
Differentialgleichungen mit numerischen Methoden, Analytische Herleitungen
basierend auf Boltzmanngleichungen und thermodynamischen Größen.

The scrambling of quantum information in closed many-body systems has lately received considerable attention. A hydrodynamical description has emerged from considering random local circuits, aspects of which are conjectured to be universal to ergodic many-body systems, even without randomness. In this project, the focus will be on local random unitary circuits with certainly symmetries (e.g., the SU(2) symmetry). 

Thermoelectric (TE) materials can be used in TE generators to convert a temperature gradient directly into electrical energy. Therefore they are of great interest in terms of waste heat recovery or the use of solar thermal energy. To be qualified as good TE materials, polymers should have a high Seebeck coefficient S and electrical conductivity σ. In this bachelor thesis polymer films will be post-treated with different methods in order to increase S and σ, leading to a novel efficient TE generator. This project will involve a literature review, polymer film preparation/treatment and TE measurements of the fabricated films.

Planar superconducting microwave resonators are key for the ultra-sensitive detection of spin properties using magnetic resonance techniques. In this thesis you will compare the performance of planar microwave resonators fabricated from various superconducting materials regarding their frequency stability and Q-factors when magnetic fields are applied. In particular, their performance close to the transition temperature of the superconducting phase to the normal conducting phase shall be investigated, as this imposes a stringent limit for the application of those microwave resonators.

Your bachelor thesis will bring you in touch with state-of-the art microwave spectroscopy tools like vector network analyzers, as well as cryogenic measurement environments. Moreover, the careful data analysis of the magnetic field dependent datasets will put you in the position to make a meaningful impact on microwave resonator technology.

Contact: Stefan.Weichselbaumer@wmi.badw.de, Hans.Huebl@wmi.badw.de

Organic photovoltaics are a promising alternative to conventional silicon solar cells as they offer several potential advantages e.g. low weight, high mechanical flexibility and low-cost production. The chemical structure of the polymer donor and the non-fullerene acceptor molecule as well as their ratio have an impact on the structure and performance of an organic solar cell. Printing of active layers with a slot-die-coating technique enables up-scaling of organic solar cells devices. This experimental bachelor thesis aims at the basic understanding of the printing process and the properties of the active material as well as the construction of an organic solar cell. Active layers are printed with different donor:acceptor ratios and post-characterized by methods such as UV/Vis spectroscopy, optical microscopy and scanning electron microscopy. The project will involve a literature review, sample preparation and post-characterization of the films.

Responsive polymers are water-soluble at low temperatures, but become water-insoluble above a certain temperature, the so-called cloud point, and form large aggregates. Applying pressure, their hydration behavior can be modified, which, in turn, allows controlling their aggregation behavior.

In the bachelor project, the phase behavior and the self-assembly behavior of novel self-assembling thermoresponsive block copolymers shall be investigated under high pressure using turbidimetry and dynamic light scattering.

After a literature research, samples will be prepared and measured, and data analysis will be carried out. For more information, please contact Prof. Christine Papadakis, papadakis@tum.de.

SgrA*, at the location of supermassive black hole (SMBH) at the center of our Milky Way, shows rapid brightness fluctuations (high states called “flares”) in different wavelength ranges including the infrared. The Interferometer GRAVITY on the Very Large Telescope (VLT) observes the Galactic center since 2016 which resulted in the first successful test of Einstein’s general relativity near SMBH and the most detailed observations of material orbiting close to a black hole. The acquisition camera for GRAVITY instrument observes this region with all four VLT telescopes in H-band. The goal of this master/bachelor thesis is to use standard photometry techniques, to measure the H-band flux of the brightest flares, observed with GRAVITY. The thesis shall take existing data from the Gravity acquisition camera, and perform photometry on SgrA* and stars close to SMBH. The goal is to separate Sgr A* from the nearby stars and correct its flux for the flux contribution of nearby stars.

Contact: Maryam Habibi <mhabibi@mpe.mpg.de>

A superconducting vortex consists of a normal conducting core carrying the magnetic field, screened by a superconducting current. The macroscopic continuity of the wavefunction of the cooper pairs leads to the quantization of flux and renders superconductivity a textbook example of a macroscopic quantum effect. Therefore, superconducting vortices resemble countable, impartible entities that can be assigned with particle-like properties which take over the role as building blocks of a novel kind of matter denoted “vortex matter”. Similar to atoms that condense to a crystal also the superconducting vortices arrange themselves in a vortex lattice which corresponds to a two-dimensional Bravais lattice, reflecting the minimal free energy landscape, where a regular hexagonal symmetry is obtained for isotropic superconductors within the Ginzburg-Landau theory.
Analogous to condensed matter a large variety of phases is also observed for vortex matter. Besides long range ordered vortex lattices, vortex glasses and vortex liquids have been identified. Vortex matter is governed by a multitude of different interactions on the vortices: The energy associated with the expulsion of the magnetic flux leads to a repulsive interaction, while for some superconducting materials, the reduction of energy of overlapping vortex cores can lead to a long range attractive force.
Using neutron scattering, we have carefully examined the phase transitions and domain formation processes of the vortex lattice in the model superconductor Niobium. Topic of this Bachelors thesis is to develop and implement 2D molecular dynamic simulations of superconducting vortex matter. The phase transitions and the domain formation process of the vortex matter shall be simulated considering the various inter-vortex interactions, the presence of pinning and the influence of temperature and magnetic field. The results of the simulations can be directly compared to and fitted to the existing experimental data.
These tasks require both a strong interest in programming and a solid background in condensed matter physics, in particular superconductivity.
The work will be performed together with the SANS-1 team @ MLZ and offers the unique possibility to work at an internationally leading large scale neutron facility like the MLZ.

Contact:
Dr. Sebastian Mühlbauer, sebastian.muehlbauer@frm2.tum.de, 089 289 10784
Alexander Backs, alexander.backs@frm2.tum.de, 089 289 54825

In diesem Projekt sollen Methoden entwickelt werden, mit denen eine in vitro erzeute RNA an Latex-Kügelchen gekoppelt, und so für Strukturuntersuchungen in einem Laserfallen-Mikroskop verwendet werden kann. (Enge Anbindung an Gruppe Prof. M. Rief.)

Low energy quantum electrodynamics is the most successful physical
theory owing to the availability of accurate theoretical predictions and
extremely precise experimental measurements. Nonetheless, certain observables,
such as electron anomalous magnetic moment or the proton radius,
disclose some tension between the theory and the experiment. Therefore, both the
theory and the experiments should be further scrutinized to ensure
consistent and correct determination of fundamental constants.

In this project, the student will explore the problem of the determination of
fundamental constants in low energy experiments. Using perturbation
theory in quantum mechanics and solving numerically the Schroedinger equation
they will determine how finite charge distribution of the proton
changes the spectrum of the hydrogen atom, including the simplest possible
radiative corrections.  No prior knowledge of quantum electrodynamics is
required.

Small-angle neutron scattering (SANS) is a powerful technique to study correlations of condensed matter samples in the range of 20–2000 Å. As an extension of a standard SANS setup, TISANE (Time Involved Small Angle Neutron Scattering) is a new neutron scattering technique for time resolved kinetic neutron scattering. TISANE is able to resolve dynamic processes up to microsecond time-scales. The setup is based on two counter-rotating chopper disks installed at a standard small angle neutron scattering beamline.
Such a TISANE setup has recently been installed at the SANS-1 beamline at MLZ, jointly operated by TUM and Helmholtz Zentrum Geesthacht. An AC-field setup allows to apply AC fields up to 10 kHz and static fields to the sample, providing an ideal tool for the investigation of the dynamical properties of ferrofluid samples. A ferrofluid is a colloidal liquid made of nanoscale ferromagnetic particles in a carrier fluid. Ferrofluids are used for various applications like damping, speakers, liquid sealings but also in cancer therapy.
The task of this Bachelors thesis is the characterization of ferrofluid samples on a time-scale up to 10 kHz by means of time-resolved small angle neutron scattering. It includes the preparation of the samples, their characterization by means of measurements of susceptibility and magnetization, the neutron experiment and the subsequent data analysis. A solid background in solid state physics, in particular magnetism, but also mechanical skills are required. The work will be performed together with the SANS-1 team @ MLZ and offers the unique possibility to get hands on experience at an internationally leading large scale neutron facility like the MLZ.

Contact: Dr. Sebastian Mühlbauer, sebastian.muehlbauer@frm2.tum.de, 089 289 10784

The truncated Wigner approach allows to approximate the dynamics of quantum systems out of equilibrium. The main goal of the project is to apply this method to coupled chains, which are relevant for recent experiments using cold atoms.