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Institute of Solid State Physics

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Master Projects

Chirality of molecules due to surface crystallisation

The work is related to the optical properties of chiral molecules within thin films. Thin films of the chirial molecule (R,R)-PyrSQ-C1 will be grown by physical vapor deposition on various optically transparent substrates like glass, potassium chloride, sapphire, indium-tin coated glass, a.o. Pre-studies are already performed. https://onlinelibrary.wiley.com/doi/10.1002/chir.23213 The crystallographic properties of the films will be investigated by classical X-ray diffraction methods. The optical properties will be studied by electronic circular dichroism using Müller Matrix approach. The work should resolve the optical properties of the films in terms of birefringence and determination of type of chirality. The work will be performed in close collaboration with Prof. Manuele Schiek, University Linz.

COMPENSATION: 440€ per month / 6 months
CONTACT: Roland Resel (roland.resel@tugraz.at)

Preparation of a photonic single crystal

The first part of the work is the preparation of a photonic single crystal by 3D printing technique. 3-dimensional stacking of piles will provide a periodic lattice with periodicity in the range of 1 µm, a characteristic length comparable with the wavelength of visible light. In a subsequent step en experimental set-up have to be built to perform diffraction experiments using visible light. Geometries of classical X-ray diffraction techniques will be used using white light (Laue diffraction) or monochromatic light (single crystal diffraction by using a four circle goniometer).
additional information:

COMPENSATION: 440€ per month / 6 months
CONTACT: Roland Resel (roland.resel@tugraz.at)

Memory effect in thin film crystallization from the melt

The work is related to the fundamental question why specific polymorphs reappear after recrystallization from the melt. It is shown for the molecule PEG-BTBT (see chemical structure left) that specific thin film preparation parameters cause metastable crystal structures which are considerably different from the thermodynamic stable phase. First experiments shown that heating of the thin films above the melting temperature and subsequent recrystallization causes the appearance of the initially present metastable phase. This observation will be studied at different metastable phases, at different substrate surfaces by varying the temperature range of investigation. The crystalline properties of the thin films will be characterized by X-ray diffraction techniques. For that purpose, grazing incidence X-ray diffraction experiments will be performed at the beamline XRD1, synchrotron Elettra, Trieste.

COMPENSATION: 440€ per month / 6 months
CONTACT: Roland Resel (roland.resel@tugraz.at)

Setup of in-situ monitoring of liquid intrusion into paper observed with micro-CT

This master project aims at designing and installing a setup to finely and remotely dose controlled amounts of liquids to paper during micro-CT measurements. Such measurements reveal in-situ changes in the microstructure during the incorporation of the liquid with a spatial resolution of less than a micrometer. The project will comprise of designing a remotely controlled humidity chamber and suitable samples, test measurements at a synchrotron or laboratory micro-CT-machines, and the analysis of the scanned image data.

COMPENSATION: 440€ per month / 6 months

Contact: Karin Zojer (karin.zojer@tugraz.at; Tel.: 873-8974),
Eduardo Machado Charry (machadocharry@tugraz.at; Tel.: 873-8465)

Charge mobility in organic semiconductors and covalent organic frameworks using the newly developed transient localization theory

Despite the fact that organic semiconductors (OSCs) have been known and extensively investigated for several decades, the mechanism of charge transport in these materials is still hotly debated. Nevertheless, it is increasingly accepted that the charge carrier dynamics in organic semiconductors is strongly determined by a coupling to low frequency inter-molecular phonons. Due to the similar energy scales of the phononic relaxation of charge carriers and the inter-molecular electronic coupling strengths, the charge carrier dynamics in OSCs is hard to model properly. Recently, a new approach – the transient localization model - has been introduced and successfully applied to various important OSCs. An advantage of this approach is that by avoiding an explicit consideration of quantum dynamics, it becomes tractable also for rather complex systems. The goal of this Master thesis is to first implement this model and to benchmark it against reported results for organic semiconductors. Subsequently, it shall for the first time be applied to covalent organic frameworks, a highly promising class or materials that is related to organic semiconductors, but consists of a fully covalently linked, porous network. From these studies unprecedented insight into the charge carrier dynamics in these advanced materials can be expected. Notably, the input parameters needed for the transient localization model (the electronic structure of the OSCs and COFs as well as the properties of phonons in these materials) are commonly calculated in our group and can be provided by other group members.

We are looking for: Highly motivated, self-propelled students with an interest in solid state physics, quantum mechanics, and computational material science. Basic programming skills are required (Matlab, Python).

Compensation: € 440,-- Forschungsbeihilfe per month for at least 6 months

Contact: Egbert Zojer (egbert.zojer@tugraz.at; Tel.: 873-8475),
Christian Winkler (christian.winkler@student.tugraz.at)

Understanding the physical origins of the electrical conductivity in Covalent Organic Frameworks

2 MASTER THESES Conductive organic materials have interesting electronic and optoelectronic properties, high mechanical flexibility and can be designed/functionalized quite easily. Thus, they are highly relevant for a huge variety of applications such as transistors, optoelectronic devices, and solar cells. Efficient charge-carrier transport is essential in all these applications.
A related materials class conductive covalent organic frameworks COFs. Their transport properties are, however, much less understood. This makes simulating their electronic structure particularly interesting from a fundamental point of view.
Notably, up to now only very few COFs with high charge carrier mobility exist and understanding of how one could systematically change the charge carrier mobility in these materials is, thus, of paramount importance. The goal of the present project is to start from existing conductive COFs, to calculate their electronic properties by using state of the art DFT models in combination with tight-binding approaches and from that to gaining a fundamental understanding of the relevant transport mechanisms and how they are impacted by the MOF structure. Based on these findings strategies for engineering the structure of the materials to exhibit even higher charge carrier mobilities will be developed.
Both theses will primarily focus on COFs consisting of covalently linked 2D layers, that are held together mostly by van der Waals forces.
The first thesis will focus on understanding, which interactions (exchange, electrostatic, van der Waals …) determine the type of inter-layer stacking, how this impacts charge transport, and how changing the “ideal stacking” can be realized by modifying the structure of the sheets.
The second thesis will systematically study the impact of the intra-layer linking units on intra-layer charge transport as well as the role played by the specific MOF topology.

We are looking for: Highly motivated, self-propelled students with an interest in solid state physics and computational material science. Basic programming skills are required (Matlab, Python).

Compensation: € 440,-- Forschungsbeihilfe per month for at least 6 months

Egbert Zojer (egbert.zojer@tugraz.at; Tel.: 873-8475)
Christian Winkler (christian.winkler@student.tugraz.at)

Modelling thermal transport in organic semiconductors      >> more >>

Goal: Development of atomistically motivated structure-to-property relationships for heat transport in organic semiconductors – a property, that is crucial for device operation, but is still largely unexplored such that the suggested studies can have a huge impact.

Details: The ability of a material to transport heat is of considerable importance even in cases where its main application is not thermal- related. Some examples where this property plays a central role include thermoelectricity, thermal barrier coatings, phase-change memory, heat-assisted magnetic recording, and extends to the general problem of thermal management of a wide variety of de- vices.

The main objective of the master thesis is to develop structure-to-property relation- ships for thermal transport in organic semiconductors, a cutting-edge research direction with potential applications in fields as varied as microelectronics, optoelectronics, catalysis, and porous materials.

The studies will be addressed by combining molecular dynamics and electronic structure calculations. The applicants should be interested in solid state physics, should have strong motivation for computer simulations, and should be willing to develop codes and scripts.

At the end of the master thesis, the students will have expertise in computa- tional methods for modelling thermal transport, and will have practical knowledge in electronic structure calculations and molecular dynamics. These methodologies constitute a powerful tool to study the electronic, structural and thermodynamic properties of materials.

Aside of the academic profits, we offer a very friendly work environment.

Starting date: any time
Compensation: 440 € per month for 6-8 months
Natalia Bedoya Martinez (bedoyamartinez@tugraz.at, Tel.:873-8465)
Egbert Zojer (egbert.zojer@tugraz.at; Tel.: 873-8475)

      >> more >>

The molecule HATCN is a strong electron acceptor that is commercially used in OLEDs to modify the property of metal substrates. Adsorbed on silver, this molecule shows unusual, fascinating physics. At low coverage, the molecule forms honeycomb patterns, which can be exploited as epitaxial growth template. When the coverage is increased, however, the first monolayer rearranges. This drastically changes the material properties, in particular the system’s work function.

At present only very little is known about the geometric and electronic structure of the rearranged, high- coverage phase. This is now at the focus of a joint efforts including the groups of Prof. Resel (TU Graz), and Prof. Fritz (University Jena), which will perform x-ray and low energy electron diffraction experiments and characterize the system via optical spectroscopy. The aim of this thesis is to provide complimentary computational insight to these experiments. Density-functional theory calculations will be performed in order to predict possible geometric structures, characterize the optical and vibrational properties, and understand the driving force that leads to the observed phase transition.

Oliver Hofmann
Email: o.hofmann@tugraz.at
Tel: 0316 873 8465



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