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Institute of Solid State Physics

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Master Projects

Indexation of grazing incidence x-ray diffraction pattern

The solution of crystal structures from thin films is a contemporary problem in crystallography. A combined experimental / theoretical approach is used where the first step is a grazing incidence x-ray diffraction experiment. The diffraction patterns have to be indexed, which requires the assignment of Laue indices to individual Bragg peaks. The result of the indexation procedure is the geometry of the crystallographic unit cell in terms of lattice constants a, b, c, and the angles α , β , γ. For that purpose, a computer code has to be developed which performs an indexation procedure for grazing incidence diffraction pattern.

Central question of the master thesis:

How is it possible to index a diffraction pattern which arises from two different types of crystal lattices?


There are two avenues to answer this question:
A) Separation of two crystal lattices by neuronal networks. A large number (> several thousand) of diffraction patterns will be calculated and combined into a superposition of two crystal lattices. Neuronal networks will use these examples for for training, and then be applied to (experimentally obtained) diffraction patterns

B) indexation of a single phase by using a specular diffraction peak. Result: 3 real values and two integers besides the individual Laue Indices for each peak Boundary conditions: restricted volume, restricted lattice constants, find solutions for a reduced number of reflections, neglecting of one or more peaks which cannot be explained. In a subsequent step indexation of a single phase without using a specular diffraction peak will be performed.

Contact: Oliver Hofmann (o.hofmann@tugraz.at) / Roland Resel (roland.resel@tugraz.at)

Joanneum Research in Weiz: Investigation on Laser-Lift-Off for the making of opto-electronic devices

A process for lifting semiconductor layers will be investigated. In particular laser processes will be applied. Those processes will be experimentally tested and the processed material will be characterised in order to evaluate the feasibility of the laser-lift-off for making opto-electronic devices.
• Literature research on laser-lift-off for III-V semiconductors
• Fabrication of test-structures by applying laser-lift-off
• Characterisation of materials and defect analysis
• Fabrication and characterisation of test devices made by laser-lift-off

https://www.joanneum.at/lernen-sie-uns-kennen/karriere/offene-diplomarbeiten-dissertationen-praktika/masterarbeit-materials-untersuchung-von-laser-lift-off-fuer-die-herstellung-von-opto-elektronischen-bauteilen.html

The position will be limited to a term of six or nine months, the scope of employment is 100 % of the applicable standard working time of 38,5 hours per week and your monthly gross wages will be € 1.310,- payable in 14 (aliquot) instalments per year. An attractive, team-oriented working environment with state-of-the-art infrastructure and flexible working time completes this attractive job offer.

Please send your application by e-mail to:
Mrs. Anita Steinwender
JOANNEUM RESEARCH Forschungsgesellschaft mbH
MATERIALS – Institute for Surface Technologies and Photonics
Franz-Pichler-Straße 30, 8160 Weiz
materials@joanneum.at

Contact Peter Hadley (p.hadley@tugraz.at) for more information.

Modelling thermal transport in organic semiconductors

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
Contact:
Natalia Bedoya Martinez (bedoyamartinez@tugraz.at, Tel.:873-8465)
Egbert Zojer (egbert.zojer@tugraz.at; Tel.: 873-8475)

Charge Transfer at Mixed Physisorbed/Chemisorbed Interfaces

Inorganic/Organic interfaces are of great relevant to a large variety of applications, ranging from catalysis and corrosion protection to appliances such as large-area OLED-TVs. Of particular interest is the charge-transfer across the interface, which typically governs the overall performance of the system. Depending on the strength of the interaction between substrate and adsorbate, two archetypes for charge-transfer are commonly observed. For strongly interacting, chemisorbed molecules, new bonds are formed and each molecule at the surface becomes fractionally charged. Conversely, if the interaction is weak, i.e. the molecule physisorbs, some molecules acquire an integer electron while others remain neutral.

Some material combinations exhibit two distinct structures, where one is physisorbed and the other chemisorbed. Experimentally, a transition between these can be triggered – on a single molecule basis – e.g. via voltage pulses STM tips. The main objective of this thesis is to investigate how the electronic structure / charge-transfer mechanism evolves for phases where physisorbed and chemisorbed molecules coexist by using density functional theory calculations. Furthermore, the possibility of using other, more readily available impulses (such as electric fields or optical excitations) to switch between chemisorption and physisorption will be explored.

Contact:
Oliver Hofmann
Email: o.hofmann@tugraz.at
Tel: 0316 873 8465
http://www.if.tugraz.at/web.php?85

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.

Contact:
Oliver Hofmann
Email: o.hofmann@tugraz.at
Tel: 0316 873 8465
http://www.if.tugraz.at/web.php?85

Deposition and Characterization of Dielectric Bragg Reflectors


Dielectric Bragg Reflectors (DBR) are commercially manufactured onto rigid substrates, using inorganic materials (e.g. SiO2, TiO2). Recently, organic DBR are under investigation because they allow creation of tunable optical properties. During the wet fabrication processes, the choice of polymers that can be alternated is limited by the condition that the solvents of the alternating materials need to be orthogonal. Our goal is to deposit the organic DBR completely from the vapor phase by an innovative technique called initiated Chemical Vapor Deposition (iCVD). iCVD does not require the use of solvent and allows precise control over layer thickness by coupling with laser interferometry. The polymers that will be alternated will have a large refractive index contrast, as for example Teflon (n≈1.38) and polystyrene (n≈1.59), so to achieve high reflectivity with a limited number of layers. The surface roughness, interfacial roughness, the thickness and the electron densities of each layer will be characterized by X-ray reflectivity (XRR). The results will be compared with ellipsometry and microscopy data.

Compensation: 6 month / 440€ per month


Contacts:
Dr. Anna Maria Coclite, Assistant Professor
anna.coclite@tugraz.at
Dr. Roland Resel, Associate Professor
roland.resel@tugraz.at

Quantum-Mechanical Modelling of Materials

We are currently seeking Master students to work on on the following topics:

* Modeling electronic and structural properties as well as growth of molecules interacting strongly with metal surfaces.
* Design of novel self-assembled monolayers (SAMs) for modifying electrode properties in organic electronic devices.
* Understanding transport through and polarization effects in self-assembled monolayers through quantum-mechanical modelling.
* Computationally designing hybrid systems consisting of nanopatterned ferroelectrics and layered semiconducting materials for novel device applications.
* Impact of Monolayers Inhomogenieties for Hot Spot Formation in Organic Electronic Devices.
* Employing post DFT techniques for reliably modelling charge distribution and electrostatic screening in molecular materials.
* Understanding the electronic properties of weakly coupled hybrid interfaces.
* Predicting the structure of organic adsorbates from first principles.
For further details just come bye and we can identify the topic most interesting to you.
Start: anytime

Contact: Dr. Oliver T. Hofmann (o.hofmann@tugraz.at), Prof. Egbert Zojer (egbert.zojertugraz.at)
Compensation: 440 € per month (Forschungsbeihilfe) for 6-8 months
Additional aspects: work in an internationally very well established group in the area of atomistic modelling of interfaces; publishing in high impact journals; participation in international conferences.

Indizierung von Röntgenbeugungsbildern: Entwicklung numerischer Verfahren für hochtexturierte dünne Schichten

Indizierung von Beugungsbildern bedeutet die Zuordnung von Laue Indizes zu den einzelnen Beugungspeaks. Mit dem Wissen der Indizes kann die kristallographische Einheitszelle bestimmt werden, und ausgehend davon können Kristallstrukturen gelöst werden. Im Rahmen der Arbeit soll eine numerische Routine für die Zuordnung der Laue Indizes entwickelt werden unter Zuhilfenahme analytischer Gleichungen und unter der Vorgabe von Randbedingungen. Das numerische Verfahren ist mittels eines MATLAB- (oder PYTHON-) codes zu realisieren. Diese Arbeit ist ein wichtiger Beitrag für einen international aktuellen Forschungsschwerpunkt zum Thema Kristallstrukturlösung von dünnen Filmen.
Kontakt: Roland Resel