At the Walter Schottky Institute (WSI-TUM) we recently launched a research project directed to the exploration of new types of high-efficiency solar cell systems based on 3D-structured III-V semiconductor nanowires.

Conventional single-cell photovoltaic devices are known to have performance limits due to large thermal and spectral losses, light trapping issues and charge carrier losses. To overcome these problems 3D-structured nanowire (NW) solar cells have emerged as promising systems with improved light trapping and absorption properties beyond the ray-optic limit, as well as better carrier collection efficiencies.

The goal of this M.Sc. project is to exploit the advantages of 3D-structured III-V semiconductor NWs and work towards a novel hot carrier solar cell (HCSC), which allows to selectively cool charge carriers and reduce thermal losses. Hereby, you will be closely working together with two PhD students to first design proper bottom-up III-V NW heterostructures from the group-III-V family of semiconductors. Exploiting the full geometrical and energy-selective parameter space, the design will be directly guided by in-depth simulations for enhanced photoabsorption and effective carrier thermalization properties. NW heterostructures on lithographically patterned substrates should then be realized by top-down/bottom-up nanofabrication processes and further characterized by various optical spectroscopy methods (photoluminescence, FTIR, and UV-Vis-NIR absorption spectroscopy). Finally, the goal is to identify correlations between array-geometry, NW dimensions, and electronic properties of the selected heterostructure material (band gap and strain) and the corresponding optical and charge carrier responses.

You will gain & learn:

• Knowledge in electromagnetic (FDTD) and electronic band structure simulations (nextnano)
• Advanced lithography / clean-room processes for state-of-the art 3D structured NWs
• Diverse optical spectroscopy (micro-Photoluminescence, FTIR, UV-Vis-NIR absorption)
• Correlated microscopy methods (SEM, He-Ion Microscopy)

Experience in the area of clean room fabrication, optical spectroscopy or nanoanalytics, as well as experience in simulations is a benefit, but secondary to motivation and commitment. Applications should be sent to Gregor.Koblmueller@wsi.tum.de and Jonathan.Finley@wsi.tum.de. Please include your CV, and a transcript of records (Bachelor & Master).

May 2019

Vector Mesons interactions with nucleons are not known at all in a quantitative way. A new method developed in our TUM group, allows to make use of the copius data collected at the LHC with the ALICE experiment to identify vector mesons as phi and omega together with protons produced in pp and pPb collisions at energiey of the center of mass of 13 and 5 TeV.

The femotscopy technique allows then to extract the scattering parameters that governs the vector meson-nucleon interaction.

This kind of measurements have been not yet carried out by any experimental group yet but are highly important to undertand low energy QCD and hence strong interaction among hadrons.

The work implies programming in c++ but no prior experience is requested.

With solvent effects being central to several scientific disciplines like biology or (electro-)chemistry, computationally affordable methods are crucial to accurately simulate solvated systems. Implicit solvation models are widely used due to their simplicity and practical applicability in these kind of many-body problems. Here only the solute is explicitly modeled while the interaction with the solvent is coarse-grained into a continuum dielectric response, instead of considering individual solvent molecules. However, simply using the solvent medium’s experimental bulk dielectric constant neglects the fact that the behaviour of the solvent differs, sometimes drastically, in the vicinity of the solute compared to the bulk. Existing corrections to account for these entropic effects fail for charged systems and lack scientific foundation. These deficits of correctly accounting for multiple conformations in solution lead to great difficulties when calculating dissociation
constants (pKa values) or modeling other electrochemical processes using implicit solvation models.

The goal of this M.Sc. project is to introduce a better description that accounts for the orientational behaviour of solvent modecules, based on findings from previous extensive Molecular Dynamics simulations. The student will learn how to perform DFT calculations using implicit solvation and, in a second step, will compute the interaction of the interfacial water structure with the electric field obtained from these simulations. Basic knowledge of UNIX based operating systems and some experience with programming (and/or scripting) languages (preferably Python) is desirable, but not mandatory.
1

This Thesis is based on Deep Neural Networks (DNN) applied to generate new organic semiconductor (OS) molecules. Deep learning models project input data through several layers of nonlinearity and learn different levels of abstraction generating a link between the inputs and specific target outputs (or labels). Recently, there has been a fundamental work about using DNN algorithms for synthesising in-silico new OS [1] grounded on the seminal work by Gomez-Bombarelli et al. [2] and Kusner et al. [3] on the Grammar Variational AutoEncoders (GVAE) method. The thesis is focused on implementing a GVAE and further developing the method to include bigger molecules. The DNN will be applied to some realistic OS in order to evaluate the efficiency and accuracy in generating new molecules.

[1] P. B. Jørgensen et al., J. Chem. Phys., 148, 241735 (2018)

[2] R. Gómez-Bombarelli et al., Nat. Mat., 15, 1120-1128 (2016)

[3] M. J. Kusner, B. Paige, J. M. Hernández-Lobato, Grammar Variational Autoencoder, arXiv:1703.01925v1 [stat.ML] (2017)

PERC (Proton Electron Radiation Channel) is a new neutron decay facility that is currently being constructed at the FRM II research reactor. PERC is a versatile source of decay electrons and protons and allows the measurement of several correlation coefficients of the neutron decay with an order of magnitude improvement in precision over current experiments. Measurements of these coefficients are a sensitive probe to investigate the mechanisms of the weak interaction.

The core component of PERC is an 8 m long superconducting magnet. Electrons and protons produced by neutrons decaying inside the magnet are guided along the magnetic field lines to the main detector system behind the spectrometer. Our group has previously used scintillator-based electron detectors for precision measurements of neutron decay correlations. Building on this experience, we plan to use similar devices to detect backscattering in PERC. The purpose of these backscattering detectors is to identify events where the decay electron only deposits a fraction of its energy in the main detector.

The objective of this thesis is the design and demonstration of the backscattering detectors for PERC, including the development of a new read-out system for electron spectroscopy with plastic scintillators and silicon photomultipliers (SiPMs).

Tasks

• Familiarize yourself with neutron decay studies and particle-tracking simulations.

• Optimize the design of the backscattering detectors for PERC based on simulation data.

• Develop and test a SiPM-based read-out system for plastic scintillators suitable for precision electron spectroscopy.

• Construct and test a prototype of the backscattering detectors.

What we offer

We offer you an interesting opportunity to participate in the development of a new high-profile experiment, allowing you to gain diverse experiences in the fields of detector physics, electronics, and low-energy particle physics!

Für die Entwicklung von Theraphieansätzen ist es notwendig, die Wirkung von Medikamenten auf Organe zu untersuchen. Zu diesem Ziel werden inzwischen Organoide verwendet - das sind Organ ähnliche Zellverbände, die in einer 3d Zellkultur wachsen. Trotz der immensen Erfolge, sind ganz zentrale Fragen zu der Entwicklung dieser Strukturen weitestgehend ungeklärt. Im Rahmen der Arbeit sollen die physikalsichen Eigenschaften der Umgebung auf das Organoid-Wachstum untersucht werden. Es werden Mikrorehologische und Mikroskopsiche Methoden entwickelt und verwendet um die Abhängigkeit von Mikro-Umgebung auf Organoidentwicklung zu quantifizieren. 

Angular momentum transport in magnetically ordered insulators is carried by magnetic excitation quanta in contrast to magnetic conductors, where mobile charge carrier also carry angular momentum. In magnetically ordered insulator/normal metal hybrids it is possible to study the transport of angular momentum by all-electrical means via the spin Hall and inverse spin Hall effect in the normal metal. The focus of this project is the investigation of possibilities to manipulate the angular momentum transport in the magnetically ordered insulator by electrical means and by finite size effects. In addition, another goal is the enhancement of the sensitivity of the currently existing measurement setup and the realization of new measurement protocols in hard- and software.

An ambitious master student with good analytical skills is required to carry out these experiments on all-electrical magnon transport. One part of the thesis is the fabrication of nanometer sized devices for the experiments via electron beam lithography and UHV sputtering. The properties of these devices will be analyzed using magnetotransport experiments in superconducting magnet cryostats. Another important aspect is the realization of more sophisticated measurement methods, aiming for a enhancement in sensitivity, a better signal-to-noise ratios and a higher versatility of the measurement protocols

Zur Verbesserung der Effizienz des Myontriggersystems des ATLAS-Detektors am Large Hadron Collider (LHC) werden neue schnelle Triggerdetektoren (Resistive Plate Chambers) gebaut, die sehr hohe Untergrundzaehlraten aushalten und hoehere Lebensdauer und Zeitaufloesung als bisher aufweisen. Die Eigenschaften dieser Detektoren werden in vorhandenen Testaufbauten und im Teststrahl am CERN systematisch untersucht.

Using hydrogen as a fuel would provide a sustainable and worldwide accessible energy system based on abundant resources and zero emission. But in order to let the dream of a hydrogen economy become true, suitable and high-performing catalysts have to be identified and developed. Commonly, theoretical models and calculations are employed to gather information on the geometric structure of an optimal catalyst and its active sites. In our group, we developed as an experimental supplement, the use of a conventional scanning tunneling microscope (STM) to in-situ identify active sites.

Content of this experimental Master thesis is to apply this technique on different materials and to ideally achieve atomic resolution. Experience with STM is helpful, but not required. Good academic background but also haptic sensitivity are desirable. If you’re interested, please send an e-mail with a short introduction of your person and scientific background.

Contact: Regina Kluge (regina.kluge@ph.tum.de)

One of topical issues of the modern condensed matter physics is the interplay between superconducting and insulating instabilities of the normal metallic state in materials with strong electronic correlations. Organic metals and superconductors, thanks to their high crystal quality, simple conduction bands, and a great diversity of electronic states, offer a perfect laboratory for studying fundamental problems of the correlated electron physics. A member of the κ-(ET)₂X family to be studied in this Master thesis is believed to represent a novel state of matter, quantum spin liquid at ambient pressure. Under a moderate pressure of about 3 kbar the material becomes metallic and superconducting.

The aim of the work is to trace the evolution of the electronic properties, particularly, of correlation effects, in close proximity to the metal-insulator phase boundary. The position with respect to the phase boundary will be precisely tuned by applying quasi-hydrostatic pressure. Magnetoresistance and especially its quantum oscillations in strong magnetic fields will be used to probe the electronic properties of the system. Observation of the oscillations requires sufficiently low temperatures which will be achieved by use of a ³He cryostat (down to 0.4 K) and of a ³He-⁴He dilution refrigerator (down to below 100 mK). A part of the experiment will be done at the European Magnetic Field Laboratory in steady fields up to 30 T or in pulsed fields up to 80 T. The experimental results will be analyzed in comparison with recent theoretical predictions of correlation effects and violations of the Fermi-liquid behavior in proximity to the spin-liquid Mott-insulating state.

Physics: Correlated electron systems; metal-insulator transition; magnetic quantum oscillations; unconventional superconductivity.

Techniques: Strong magnetic fields; high pressures; cryogenic (liquid ⁴He; ³He; dilution fridge) techniques; high-precision magnetoresistance measurements.

Contact person: Mark Kartsovnik (mark.kartsovnik@wmi.badw.de)

The field of magnonics deals with exploiting the collective spin dynamics (spin waves) of magnetically ordered materials for computational purposes. Efficient and scalable schemes for controlling spin waves in thin film ferromagnets thus have large application relevance. The magnetic torques arising due to the spin-orbit interaction allow to control spin waves by electric currents and acoustic waves at GHz frequencies. We are particularly interested in a spatially-resolved study of the interaction of spin waves with acoustic and current-induced torques in nanopatterned devices with application potential for spintronics.

We are looking for a talented and highly motivated master student who is interested in joining our spin dynamics project. During your thesis, you will use state-of-the-art nanolithography and thin film deposition tools to fabricate hybrid devices that allow for the interaction of spin waves with electrical currents and acoustic waves. You will study spin waves in these devices using optical and microwave spectroscopy methods.

In this project, we aim to fabricate and investigate novel organic-inorganic hybrid materials for thermoelectric applications. The goal is to realize efficient low temperature (T < 100°C) thermoelectric thin films and coatings which can contribute for example to energy efficient buildings. By combining nanostructured inorganic materials with conducting polymers a novel approach for this class of materials shall be realized. Possible inorganic nanomaterial components include Silicon nanocrystals (either undoped, n-type or p-type doped) as well as other nanoparticles. Different polymer materials such as the polymer blends of conjugated polymers, which can be tuned in conductivity and in its nanostructure, shall be used as the organic partner in our hybrid approach.

Organic photovoltaic (OPV) technology has seen a rapid evolution over the last decade. The unique selling points of OPVs, such as excellent light harvesting capability, freedom of form, color and transparency, environmental friendliness, easy scalability and lower manufacturing costs based on roll-to-roll printing methods, position this technology for the mobile power market, and this most properly reflects the state of the art in commercialization. An important milestone towards OPV commercialization has been surpassed by reaching a power conversion efficiency (PCE) of up to 17%. The main limitation in OPVs is due to the intrinsic narrow absorption window (~100-200 nm) of polymers compared to inorganic semiconductors such as Si, which makes it challenging to fully cover the solar spectrum with a single junction device. To overcome the absorption limitation, ternary blend organic solar cells represent one of the dominant strategies that has been explored in the last decade. The outstanding advantage of ternary blends consists of maintaining the simplicity of the processing conditions used for single active layer devices. Interestingly, the open circuit voltage (Voc) is tunable depending on the loading concentration of the ternary compound in both ternary systems compromised of i) two donors and one accepter as well as ii) one donor – two accepters blends.

The origin of the composition-tunability of Voc and the optimal electronic correlations between the components remains as an open question in OPV field. Obviously, it is very challenging to develop a complete model for Voc in ternary systems mainly due to the fact that this model should take all the electronic interactions between the components into account and consider their role in the photogeneration. Moreover, the model should be compositional dependent and accounts for the different microstructures and transport mechanisms operating simultaneously in the system. To this end, a semi-empirical method is required to link the electrical characteristics of ternaries to their morphological properties and draw a comprehensive picture from the morphology models reported in literature as the origin of Voc changes in ternary systems.

This project will focus on solving the aforementioned key challenge by employing a semi-emprical method based on kinetic Monte Carlo (kMC). An existing lattice kinetic Monte Carlo model, previously applied to the modeling of binary polymer:fullerrene solar cells, will be extended to treat ternary blends. This will allow us to correlate nano-morphological features with measured optical properties and obtained Voc, a crucial capability for the design of optimized, high performance ternary solar cells. 

In recent years, the plan of sending human back to the Moon came back to the fore. Some ambitious plans even consider building a permanently inhabited base on the moon. However, the radiation environment on the Moon can be a problematic health issue for the astronauts. Only little data is available from the Moon’s surface and the effect of particles that are produced in the upper layers of the lunar surface by the bombardment of cosmic rays is not yet fully understood. In this thesis, a full simulation of the lunar radiation environment shall be conducted. A detailed simulation of the galactic cosmic-ray background interacting with the Moon’s regolith shall be conducted using the high-energy physics simulation tool Geant4. The outcome of this study shall be used to set requirements for radiation detectors that shall measure all contributing radiation components. These results shall be used to optimize the design of the radiation detector currently under development for the LUVMI-X moon rover. 

Tasks

• Acquire the necessary theoretical understanding of the radiation environment in space and the interactions of cosmic rays with matter.
• Set up a simulation written in C++, based on the Geant4 simulation framework.
• Analyze and interpret the simulated radiation environment.
• Optimize the design of a particle detector that can efficiently measure the lunar radiation environment.  

Prerequisites 

Experience in C++ programming is helpful, but not required.

Contact

Thomas Pöschl, Room PH1 3257, Thomas.poeschl@ph.tum.de

Martin Losekamm, Room PH1 3257, m.losekamm@tum.de

Prof. Stephan Paul, Room PH1 3263, stephan.paul@tum.de

In vielen wichtigen elektrochemischen Prozessen (wie zB der Reduktion von CO₂) vermutet man Prozesse, bei denen zwei Radikale beteiligt sind. Interessanterweise wurden diese chemischen Elementarprozesse noch nicht beobachtet. In dieser Arbeit soll eine elektrochemische Zelle in ein klassisches Spinresonanz-Spektrometer integriert werden und dann die Signatur solcher Biradikale im Stromtransport beobachtet werden. Sie werden in dieser Masterarbeit hochempfindliche Methoden der magnetischen Resonanz sowie die wichtigsten Askepte der Elektrochemie kennenlernen und an einem Thema an der vordersten Front der Physik und Chemie des Klimawandels forschen.   

Optomechanics provides extremely sensitive methods to measure the displacement of mechanical resonators. However, the forces are much smaller in optomechanics compared to those in nanoelectromechanical systems (NEMS). The goal of the project is to make, and measure opto-electromechanical devices which have strong electrostatic interactions. This includes the electrostatic spring effect where the resonance frequency depends strongly on the applied voltage. The next step is trying to measure the potential by measuring the ringdown of different mechanical modes. The devices will be made using advanced nanofabrication techniques such as electron beam lithography and reactive ion etching.

See http://www.groups.ph.tum.de/en/qtech/openings/ for a detailed description of this project.

Der Large Hadron Collider (LHC) bietet eine einzigartige Gelegenheit, nach Teilchen der Dunklen Materie zu suchen. Sie machen sich im Detektor durch sogenannte fehlende Energie bemerkbar. Zusaetzlich muessen jedoch bekannte Teilchen als Signal erzeugt werden. Dafuer eignen sich besonders gut Hadronjets, die durch Gluonabstrahlung im Anfangszustand haeufig erzeugt werden, aber auch Eichbosonen und sogar das Higgs-Boson. Die Auswahlkriterien fuer solche Ereignisse werden mit Hilfe simulierter Daten optimiert.

The recent detection of gravitational waves (GW) with the advanced LIGO/Virgo instruments in conjunction with a short gamma-ray burst (GRB) has surprised gamma-ray astronomers because of the substantially different properties of the GRB signal as compared to canonical GRBs. This motivates an "open-mind" search for untriggered transient events in the data stream of the gamma-ray burst monitor (GBM) on the Fermi satellite. With two previous Bachelor theses we have developed a physical background model, paving the way for automated searches, and subsequent source and background fitting.

This thesis shall be devoted to establishing a Python program for identifying long-term (> few minutes) transients in Fermi/GBM data, localizing them on the sky, and deriving basic properties (spectrum, light curve). The project includes elements from computational and observational high-energy astrophysics, and will allow for obtaining extensive knowledge on the broad class of high-energy transients.

Some background in astrophysics is advantegeous, but affinity with Python programming is a must.

Contact: Jochen Greiner, jcg@mpe.mpg.de, MPE Room 1.3.13, Tel. 30000-3847

Synchronization is a universal phenomenon that is knows since they days of Huygens. When two or more oscillators with slightly different frequencies are coupled, they will start to move in phase. We can create small mechanical devices using advanced nanofabrication techniques here on campus. By sending light of the right wavelength, they start to oscillate, and when increasing the power the optomechanical coupling synchronizes them. The goal of this project is to synchronize devices made from silicon nitride, which is a special material with a lot of stress in it, and to increase the number of synchronized oscillators. The larger the system becomes, the richer the nonlinear dynamics will become. You will first make the devices in the cleanroom, measure them, and analyze the data.

See http://www.groups.ph.tum.de/en/qtech/openings/ for a detailed description of this project.

The broken inversion symmetry at the interface of thin film ferromagnets and normal metals with strong spin-orbit coupling can give rise to chiral magnetic order. These chiral magnetic materials show exotic magnetic properties such as a skyrmion lattice phase and have strong application potential for future spintronic devices. For these applications, a detailed understanding of the magnetization dynamics in these materials is required. The goal of this master thesis is to fabricate such thin film multilayer structures using sputter deposition techniques and analyze their dynamic magnetic properties using broadband ferromagnetic resonance spectroscopy.

We are looking for a highly motivated master student to carry out these experiments on interfacial effects in metallic multilayers. The thesis work will be split up into of the fabrication of these multilayer structures using UHV sputter deposition systems and determining their magnetic properties by broadband ferromagnetic resonance spectroscopy and SQUID magnetometry.

Wavelength-scale coherent optical sources are vital for a wide range of applications in nanophotonics ranging from metrology and sensing to nonlinear frequency generation and optical switching. Since precision metrology and spectroscopy is enabled by the ability to generate phase-stabilized trains of ultrafast laser pulses, it is of particular interest to realize such a technology on-chip. However, the complexity of conventional mode-locked laser systems has so far hindered their realization at the nanoscale. Recently, we demonstrated that subsequently emitted ultrafast laser pulses emitted from incoherently pumped GaAs-AlGaAs core-shell nanowire lasers remain mutually phase coherent over timescales that are approximately ten times longer than the emitted pulse duration¹. A deeper understanding of the factors governing the electron and photon dynamics of NW lasers is now crucial for further developments.

In this project, you will, therefore, investigate the carrier relaxation and gain dynamics of novel quantum confined nanowire laser structures by employing ultrafast pump-probe spectroscopy. Thereby you will explore the influence of composition modulation and low dimensional gain media on the frequency and phase-dependent lasing characteristics. Further, you will have the option of extending the current pump-probe setup in order to study coupling and switching phenomena in NW-based silicon photonic circuits.

You will get experience in performing state-of-the-art ultrafast spectroscopy at room and cryogenic temperatures, and a solid understanding of the physics of semiconductor nanolasers.

In this thesis, you will be closely working with several other student members at WSI. Good knowledge in physics, especially optics, semiconductors, as well as previous experience with lab work related to of nanophotonics or quantum optics are a benefit, but secondary to motivation and commitment. Applications should be sent to Andreas.Thurn@wsi.tum.de, Gregor.Koblmueller@wsi.tum.de, or Jonathan.Finley@wsi.tum.de. Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

[1] Mayer, B. et al. Long-term mutual phase locking of picosecond pulse pairs generated by a semiconductor nanowire laser. Nat. Commun. 8, 15521 (2017)

Our lab is using solid state qubits to build sensors, for instance for magnetic fields. We aim to apply them to various applications, with a particular focus on life sciences.

We are seeking a MSc student to study a novel application, imaging of electric action potentials of neurons, the cells performing computation in the brain. This should involve the development of a new type of sensor, based on solid state quantum materials, smart signal processing by artificial neural networks, or a combination of both.

Techniques:

* You will learn to prepare microscopy samples of both solid state samples and cell cultures. 

* You will design an experiment to detect the weak optical signals from these samples in one of our existing microscope setups. This will involve development of advanced optics and control software.  

Depending on preference you will either

* Study fluoresent quantum materials like red fluorescent diamond and their response to external electric fields. 

* Develop signal processing protocols to enhance these signals in existing devices