Bachelor’s Thesis in Physics

Optomechanics is an extremely exciting field where the tiniest motions of mechanical resonators are measured with the help of laser light. So far, most of these experiments have been done with beams and cantilevers, in other words with one-dimensional structures. In the Quantum Technologies Lab we have just build a new setup, where we can measure the vibrations of 2D mechanical systems.

The goal of this project is to explore the world of 2D optomechanics. For this, we have two kinds of samples in mind: one is made from silicon nitride, which is a material with extremely high quality factors. This material is not only used in the manufacturing process of chips, but is also a great material to do optomechanics with. The other direction is to use materials that are just a few atoms thick: This includes graphene, boron nitride, and sandwiches of these true 2D materials. For this, we collaborate with the Karlsruhe Institute of Technology.

We will make the samples for you in the cleanroom, and it will be your goal to measure them with our new setup. This includes their optical characterization, as well as electrical measurements in the time domain (oscilloscope) and in the frequency domain (network- and spectrum analyzer). For the measurement and data processing, we already have a range of computer programs available in our group, so that you can start measuring right away. Depending on your preferences, the project could be completely experimental, or also contain a modelling component.

The project is envisioned with students in Applied and Engineering Physics (AEP) and Condensed Matter Physics (KM) in mind, but if you follow another track we are still interested to hear from you. Being curious and wanting to get a feeling for what doing real research is about, is the most important factor. There are no formal requirements on courses taken.

Pattern formation in cell layers is experimentally studied in both biological and synthetic systems. For instance, in developmental biology, the correct relative positioning of different cell types is essential to ensure that the organism functions correctly. This project will explore some of the underlying physical concepts with a theoretical approach. Whilst many models for pattern formation exist, the focus here is on cellularized systems with interactions only between neighboring cells. This form of communication has previously received less attention from theoretical research than e.g. long-range diffusible signals as a means of communication. Our goal is to explore fundamental limits and patterning concepts with a simple top-down model based on cellular automata. Building on previous work, the project will concentrate on exploring mechanisms of pattern formation with the goal of investigating how cell division and cell death can influence pattern formation in tissues and how tissue regeneration following damage can be achieved. Successful work on this project requires some background in the concepts and methods of statistical physics, as well as skills in computational problem solving.

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.

Josephson junctions (JJs) represent a fundamental building block of modern quantum circuits such as superconducting qubits or Josephson parametric amplifiers. The JJs are conventionally fabricated with Al while the surrounding quantum circuits are often made of Nb. Henceforth, there is a need of galvanic connection between them which includes removing Nb oxide via ion milling.  As a consequence, one needs to develop a careful milling and fabrication technique in order to preserve a low-loss microwave environment in the close vicinity of JJs. This task is of paramount importance for achieving high coherence times of the related quantum devices.

The goal of this Master project is to develop a fabrication technique for Al/Nb superconducting circuits which will include Ar/O2 milling. This also includes cryogenic microwave studies of fabricated superconducting circuits (such as Josephson parametric amplifiers and transmon qubits) and participation in experiments towards quantum information processing with superconducting devices.

Planar superconducting microwave resonators are key for the ultra-sensitive detection of spin properties. We employ planar microwave resonators fabricated from various superconducting materials like Nb, NbN and NbTiN and test their performance with respect to field and temperature stability. With your help, we aim to improve our existing variable temperature setup operating between 1.5 and 300K. In detail, you shall assemble a new measurement inset including a cryogenic microwave amplifier, and asses the overall performance of the setup using electron spin resonance. Moreover, you shall further optimize microwave resonators to improve their quality factors.

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. In addition, you will fabricate and optimize microwave resonators and perform the microwave spectroscopy measurements. 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

The extreme environment in a fusion plasma reactor, especially the heavy load with hydrogen, leads to various unexpected effects. The Plasma Component Interaction research group at the Max Planck Institute for Plasma Physics (IPP) investigates these effects. One material system of interest is the Fe-W system, which exhibits tungsten enrichment on the surface under hydrogen bombardment. In order to separate the underlying mechanisms and their contribution, well-characterised model samples will be prepared and treated (annealed, ion beam bombarded) and their response to these treatments will be analysed by ion beam analyses and scanning electron microscopy. This thesis should contribute to answering the question: Does ion- and/or hydrogen-enhanced segregation exist in the system Fe-W?

Contact: Dr. Martin Balden

Porennetzwerk in porösen Medien sind integraler Baustein von Reaktionszellen, die den Kern für Photokatalyse, Gassensorik und Lithium-Ionen-Batterien in Brennstoffzellen bilden. Der Transport durch ungeordneten porösen Medien wird durch die exponentielle Verteilung von Strömungsgeschwindigkeiten grundlegend eingeschränkt, da in großen Bereichen nur geringe Strömungsgeschwindigkeit vorliegt. Mit dem Ziel gezielt Strömung durch poröse Medien zu verbessern soll hier ein geometrisches Mass für die  Unordnung in porösen Medien gefunden werden. Dazu werden Sie laminier Strömungen in porösen Medien mit einfachen Matlab Programmen simulieren und quantifizieren, wie sich Änderungen im Porennetzwerk auf Strömungen auswirken. Einfache analytische Modelle zu Strömungen in Porennetzwerken werden Ihnen dabei helfen ein Mass für die Unordnung in porösen Medien zu finden.

Pore networks in porous media are integral components of reaction cells, which form the core for photocatalysis, gas sensor technology and lithium-ion batteries in fuel cells. The transport through disordered porous media is fundamentally restricted by the exponential distribution of flow velocities, since only low flow velocity is present in large areas. With the aim of improving the flow through porous media, a geometric measure for the disorder in porous media is to be found here. For this purpose you will simulate laminated flows in porous media with simple Matlab programs and quantify how changes in the pore network affect flows. Simple analytical models of flows in pore networks will help you to find a measure for the disorder in porous media.

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.

Pattern formation in cell layers is experimentally studied in both biological and synthetic systems. For instance, in developmental biology, the correct relative positioning of different cell types is essential to ensure that the organism functions correctly. This project will explore some of the underlying physical concepts with a theoretical approach. Whilst many models for pattern formation exist, the focus here is on cellularized systems with interactions only between neighboring cells. This form of communication has previously received less attention from theoretical research than e.g. long-range diffusible signals as a means of communication. Our goal is to explore fundamental limits and patterning concepts with a simple top-down model based on cellular automata. Building on previous work, the project will concentrate on investigating how the interaction range between cells can influence the ability to realiably create typical biological patterns such as a heterogeneous stripe-pattern. Successful work on this project requires some background in the concepts and methods of statistical physics, as well as skills in computational problem solving.

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.

The Backbone of state of the art ultrafast metrology measurements is the high-harmonic-generation (HHG).

This process is driven by a few-cycle laser pulse being focused into a gas. In doing so, several harmonic orders

of the used light are generated and can thus be used for a variety of experiments. The maximum (aka. Cut-off)

energy reachable via this process depends on a variety of factors, e.g. the used gas or the chosen focussing.

The main part of the work will be the investigation of these factors in order to reach a higher Cut-off.

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.

Für den Betrieb des MADMAX Experimentes wurden Piezo Motoren entwickelt, die bei kryogenen Temperaturen (4 K) funktionieren und einen Hub von bis zu 1 m haben. Die ersten gelieferten Prototypmotoren müssen bei kryogenen Temperaturen getestet und auf verschiedene Betriebsparameter untersucht werden. Qualification of Piezo motors at cryogenic temperatures for the MADMAX axion dark matter experiment In the context of the MADMAX dark matter axion search experiment Piezo motors have been developed for operation at cryogenic temperatures (4 K) for a stroke of up to 1 m. The first prototype motors that have been delivered will need to be tested at cyrogenic temperatures and several parameters need to be investigated.

Amphiphilic block copolymers having a permanently hydrophobic block and a thermo-responsive block form nanoparticles, or rather core-shell micelles, in aqueous solution. The structure of these micelles is controllable by changing the temperature or the ratio between the hydrophobic and the hydrophilic block. These properties enable amphiphilic block copolymers as candidates for a wide variety of applications, such as drug delivery. The main goal of this thesis is to investigate above which polymer concentration micelles form and to characterize the size of the micelles by fluorescence correlation spectroscopy.  For more information, please contact Prof. Christine Papadakis, papadakis@tum.de.

In nature, quarks and gluons cannot exist as free particles. They are always confined into hadrons. Unfortunately, the equations of the strong interaction that governs the behavior of quarks and gluons cannot be directly solved at energy scales where hadrons form. Hence theoretical predictions of hadron properties such as their masses and decay modes are very difficult. This is in particular true for hadrons that are made of the three lightest quarks: „up“, „down“, and „strange“. Also on the experimental side much confusion exists on what concerns masses, decay widths, and the assignment of quantum numbers of some observed hadrons, let alone the interpretation of their internal structure.

Our group participates in the COMPASS experiment at CERN, where we study the production of mesons (hadrons with integer spin) in the scattering of a 190 GeV pion beam off a stationary proton target. The produced highly excited mesons have extremely short life times of the order of 10^-24 seconds and can hence be measured only via their decay products. Our group employs and develops mathematically involved statistical analysis tools in order to identify the produced mesons with high sensitivity and to measure their properties with high precision. We have recently found a new meson with surprising properties and also did groundbreaking work on precision measurements of the properties of the pion. This science addresses one of the last open questions of the Standard Model of particle physics, which is the understanding of the strong force at large distances and low energies.

We offer thesis topics, which cover a wide range of subjects in strong-interaction physics, statistics, and/or computer science. The thesis work can start at different levels within the analysis chain: from the selection of a reaction process itself up to the final fitting process leading to scientific publications. The topic can be chosen according to personal preference and interest.

Experience in computer programming is helpful, but not required.

Contact: Boris Grube bgrube@tum.de, room PH1 3574, Tel. 089 289 12588

Outline, calculation and design of a purification cryostat to produce isotopically pure He-4 out of natural helium in a continuous manner based on the superfluid heat flush principle.

The FRM II is presently testing and will subsequently install a source to produce ultra-cold neutrons (UCN) in the reactor. In the central section of this UCN source, helium is used for cooling. By passing through, the cooling agent helium will be irradiated by neutrons, which create radioactive tritium out of the He-3 portion. This negative side effect can be avoided respectively reduced to a permissible level if isotopically purified He-4 with no traceable He-3 content is used.

Sources for isotopically pure He-4 are scarce and availability varies with market demand. In order to ensure continuous operation of the UCN source the availability must be secured. For this reason such an isotopic purifier shall be build.

In this thesis the thermodynamical properties of the purifier shall be simulated with COMSOL.

Contact / Supervisor:

Dr. Andreas Frei, Tel. 089 289 14260, andreas.frei@tum.de

Magnetic Weyl semi-metals combine magnetic order and a topological electronic band structure. It is expected that mutual spin-to-charge conversion is particularly efficient in these materials. We will study mutual spin-to-charge conversion using methods of ferromagnetic resonance.

The improvements of Silicon photo-multipliers (SiPM) over the last years qualify them as promising replacements for classical photo-multiplier tubes (PMT). This is particularly interesting for cases where the high voltages and large dimensions of PMTs are difficult to afford, such as for space applications. For the simplest version of gamma-ray detectors, a scintillator crystal read out by SiPMs, the size of the scintillator determines the sensitivity, and thus should stay large. This suggests an Anger camera principle as the most efficient way for a gamma-ray detector in space: a mosaic of sparsely distributed single-cell SiPMs instead of the coverage of the full scintillator area.

This Master thesis shall test and optimize a 5x5 cm^2 sized CeBr3 scintillator read out with a mosaic of SiPMs. Measurements of the spatial and spectral resolution as well as efficiency (noise) and power consumption are foreseen, and form the basic parameters for the trade-off study. The set-up has two potential applications: (i) in the ComPol Cubesat mission pursued within the Origins Cluster of Excellence, and (ii) the POLAR-2 gamma-ray burst polarisation mission developed within the SFB "Neutrinos and Dark Matter".

Interest in electronics and ASIC readout is required, and some background in astrophysics is advantegeous. The lab-work will be done at MPP Freimann, shared with Prof. S. Mertens group.
 
Contact: Jochen Greiner, jcg@mpe.mpg.de, MPE Room 1.3.13, Tel. 30000-3847

Disorder has a drastic influence on transport properties. In the presence of a random potential, a system of electrons can become insulating; a phenomenon known as many-body localization (MBL) that has been envisioned by the Nobel laureate Phil Anderson. However, even beyond the vanishing transport such systems have very intriguing properties. For example, many-body localization describes an exotic state of matter, in which fundamental concepts of statistical mechanics break down. In this project we will explore these exciting aspects of many-body localization.

Thermoresponsive block copolymer thin films can be applied in vapor sensors detecting water and organic cosolvents. As sensitive layers, they exhibit characteristic swelling kinetics steered by cosolvent mediated effective interactions between individual polymer chains. This bachelor thesis will cover the fundamentals of responsive polymers and the cononsolvency effect. The experimental part revolves around thin film preparation and swelling behavior analysis in our vapor chamber. The project will include a brief literature review.

PEN ist ein industriell hergestelltes Plastikmaterial, das das Interesse als Szintillator für Experimente der Teilchenphysik auf sich gezogen hat. PEN szintilliert im blauen Regime, ideal für viele Photosensoren. Zusätzlich hat PEN exzellente mechanische Eigenschaften. Ausserdem konnte eine sehr extrem niedrige Belastung surch natürliche Radiositope nachgewiesen werden. Dies macht PEN als strukturelles, szintillierendes Material für Experimente zur Suche nach extrem seltenen Ereignissen interessant. In diesem Zusammenhang wurden PEN Platten für das LEGEND200 Experiment zur Suche nach neutrinolosem Doppelbetazerfall hergestellt. Im Rahmen dieser Arbeit sollen die optischen Eigenschaften diser Platten vermessen werden. Es sollen verschiedene PEN Samples mit einem existierenden Messaufbau auf Emissions- und Absorbtionsspektrum, sowie Lichtausbeute und Attenuierungslänge untersucht werden.

PEN is an industrial plastic that  has drawn the interest as a new type of plastic scintillator material. PEN scintillates in the blue regime, which is ideal for most photosensor devices. In addition, PEN has excellent mechanical properties and very good radiopurity has been achieved, which makes it an ideal candidate as an active structural scintillator material in low-background physics experiments. In this context, PEN plates have been produced for use in the LEGEND200 experiment for the search of neutrinoless double beta decay. The goal of this thesis will be the measurement of the main optical properties of PEN. The emission and absorption spectrum, attenuation length, and light output will be measured for several PEN samples using existing setups.

Amphiphilic block copolymers having a permanently hydrophobic block and a responsive block form core-shell micelles in aqueous solution. The structure of these micelles is controllable by changing the temperature or pH value. These properties enable amphiphilic block copolymers as candidates for a wide variety of applications, such as drug delivery. The main goal of this thesis is to investigate the effect of the pH value on the transition temperature and the micellar size. At this, differential scanning calorimetry (DSC) and dynamic light scattering will be used. For more information, please contact Prof. Christine Papadakis, papadakis@tum.de.