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PhD Defence Alexandros Papanikolopoulos: A light scattering study of molecular assemblies in high magnetic fields

Date of news: 9 November 2021

Wednesday 10 November, Alexandros Papanikolopoulos successfully defended his doctoral thesis. He focused on the growth of different molecular assemblies in the presence of high magnetic fields, and the emergent phenomena accompanying them. The observations led either to a construction of a simplified theory on the basis of thermodynamics and statistical physics, or provided a steppingstone towards that.

When it comes to fabricating material at the nanoscale there are two approaches; the high cost top-down approach and the bottom-up approach, which lacks a long-range order. A special case of a bottom-up technique is the self-assembly approach, the ability of structures to spontaneously organize bottom-up into more complex objects, shapes and systems. In directed self-assembly (DSA) an external force is used to tune the assembly into a desired and predictable form. DSA is considered one of the potential techniques for next generation lithography. Commonly used external forces vary from thermal, to optical, to electric, to pressure and others. Magnetic fields have been proven successful in directing the self-assembly while offering the advantages of being easily tunable in magnitude, homogeneous, well-defined and contact free.

Understanding the mechanism that leads to a specific structure through DSA is the holy grail when it comes to manipulating matter at nanoscale. It is however a daunting task since the meso structures usually dealt with are operating at room temperature and are in solution. The self-assembled macrocycles are intrinsically heterogeneous, with complex interactions across different length scales, and slow dynamics, making their overall behaviour very hard to predict. There exists no fundamental theory that encompasses all systems that self-assemble, rather each system is unique and needs to be studied as its own special case.

It is therefore essential that the use of more than one technique takes place in order to obtain specific information and to understand the behaviour of the studied system. Such a course of thinking is sustained throughout Papanikolopoulos’ thesis. The studied systems are subjected to a magnetic field and their response is measured with the aid of several techniques. The techniques are employed either consecutively, or in parallel.

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Promotor prof. dr. Peter Christianen and dr. Alexandros Papanikolopoulos. Behind them co-promotor dr. Hans Engelkamp (left) and the jury.

Papanikolopoulos: "the novelty of the lab and the elaborate techniques available were the main reason for me to do my promotion at HFML-FELIX. My research was all about trying to figure out what happens to matter in extreme conditions. This lab is one of the very few places you can do this type of experiments. It wasn’t always easy. If you choose an experimental study, you never know what the outcome will be. Trying to understand more about DSA is a high risk, high gain topic. I guess that attracted me. The good atmosphere in the lab also helped. If I was hitting my head against a wall there was always someone to cool down with."

Dr. Papanikolopoulos is now working at ASML as design engineer.

Promotor: prof. dr. P.C.M. Christianen
Co-promotor: dr. H. Engelkamp