PhD theses

Ongoing


"Higher-order correlations in complex liquids"

Michael Dartsch

While the microscopic structure and properties of crystalline matter has been studied for one century the local order of disordered systems remains a challenge. Due to limitations of spatial and temporal resolution, conventional experiments typically allow access to ensemble averaged information only.

With the advent of newest generation of storage ring and FEL sources, different techniques are developed that allow to obtain information of higher order beyond conventional pair correlations. Among those, X-ray Cross Correlation Analysis (XCCA) was demonstrated as a powerful tool to reveal the orientational order of disordered samples.

Within this project, XCCA will be further developed by studying both structural snapshots from simulations and experimental data of soft matter materials. A theoretical model combining widely-used local order parameters studied in simulation such as the Steinhardt parameters and XCCA results will be established. This knowledge will be transferred to experiments where order formation in soft matter systems such as colloidal glasses and crystals or liquid crystals will be investigated.


"All optical switching of nanoscale magnetic domains"

Matthias Riepp

All-optical switching (AOS) is one of the most promising methods for future magnetic recording applications. The switching of a magnetic single domain state by short infrared (IR) laser pulses in ferrimagnetic systems like GdFeCo has been extensively studied in the past years. The underlying mechanism is based on different demagnetization times of the magnetic sublattices (Gd and Fe/Co) and can be triggered by linearly polarized laser pulses.

Recently,  a helicity dependent (HD-) AOS has been found in ferromagnetic multilayers like Co/Pt which is understood to proceed via a two-step process. Namely the nucleation of a reversed magnetic domain which seems to be stochiastic in nature and its helicity dependent growth. However, the detailed switching mechanism is not yet fully understood and has neither been investigated by time-resolved measurements nor on the nanoscale.

This PhD-thesis addresses the understanding of ultrafast processes in thin ferromagnetic films due to electronic excitation by short polarized laser pulses. Therefore, pump-probe magnetic small-angle scattering (mSAXS) experiments are employed at free electron laser (FEL) facilities in order to investigate the onset of HD-AOS on a femtosecond time- and nanometer length-scale.


2021

"Time-resolved rheology on complex fluids"

Verena Markmann



2019

"Development of a compact hard X-ray split-and-delay line for studying ultrafast dynamics at free electron laser sources"

Rustam Rysov


"Structure and Dynamics of Complex Liquids - The Phase Behaviour of Silica-PNIPAm Nanogels"

Lara Frenzel



2018

"Structure of complex fluids under shear flows"

Joana Valerio

Link to thesis


"Structure and Dynamics of Glass-Forming Fluids"

Dina Sheyfer

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2015

"Liquid Jets for Experiments on Complex Fluids"

Ingo Steinke

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2014

"Dynamics of colloids in molecular glass forming liquids studied via X-ray photon correlation spectroscopy"

Heiko Conrad

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2010

"Structure and Dynamics of highly charged colloidal suspensions"

Fabian Westermeier

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2008

"Development of an X-Ray Delay Unit for Correlation Spectroscopy and Pump-Probe Experiments"

Wojciech Roseker

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"Glass transition near the free surface studied by synchrotron radiation"

Marcin Sikorski

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