8. Oct. 2020

Michal Horák from CEITEC BUT received an award for the best dissertation this year from the Czechoslovak Microscopic Society. In his work he dealt with the use of electron microscopy and spectroscopy in plasmonics. In addition to the dissertation itself, some of Horák's articles have already been awarded in the past.

When the FEI Titan transmission electron microscope was installed at CEITEC BUT, Michal Horák, a new doctoral student, knew what the topic of his dissertation would be. "It was necessary to do science on this device. And when I was looking for a doctorate topic, I quickly knew I wanted to work on it. I left the specific focus of the work to my supervisor. And because professor Šikola leads the plasmonic group, it was more or less decided, " describes Dr. Michal Horák the beginnings.

At the same time, he points out that he basically started from scratch. It took him the first year and a half to find out how to properly prepare a sample, how to measure, process and evaluate the results obtained by electron energy loss spectroscopy (EELS). "I had to learn to work with the device first. Most was a trial and error method. I read a little in foreign publications or consulted with foreign researchers. Subsequently, I tried to apply it," confirms Horák. 

The first major result of his efforts came in 2018. “At that time, we were able to publish an article in Scientific Reports that compared the response of plasmon antennas measured by EELS. The antennas were made by either ion or electron lithography," describes Michal Horák the first pillar of his dissertation.

This was followed by a study of the limits of Babinet's principle and an article from 2019 dealing with disks and apertures. "The third part of the dissertation was focused on antennas that concentrate electric or magnetic fields, which are bowtie or diabolo antennas. Again, we measured the electric field distribution by EELS. Babinet's principle relates the electric field of a direct structure, ie particles, and the magnetic field of a complementary structure, the so-called aperture. This means that we have shown the possibility of qualitative measuring of the magnetic field with these methods on these structures, even though EELS is not sensitive to it," adds Horák. The research results were published by the team from CEITEC BUT in the professional journal Nanophotonics this year.

The last part of the dissertation summarized the results of cooperation with the Institute of Biophysics of the Czech Academy of Sciences. "Specifically, the cooperation concerned silver amalgam, which was invented by a team from the Czech Academy of Sciences as an alternative to mercury electrodes in electrochemistry. They decided to nanostructure the amalgam, which means making nano and microparticles out of an alloy of silver and mercury. Our task was then to determine whether the particles are plasmonically active. Which means whether there will be any possibility to combine plasmonics and electrochemistry, "explains Horák. The obtained amalgam nanoparticles were examined again in a transmission electron microscope. "I found that they are polycrystalline and have a relatively homogeneous ratio of mercury to silver. We have also proven that they are plasmonically active and with their size, the resonant energy can be tuned from near ultraviolet radiation to the infrared region, which is a very nice result," added Michal Horák.

Although the described researches ended with the completion of the dissertation, Michal Horák will definitely not be bored in the future. He continues his work on similar topics. An example is research comparing the effect of mono and polycrystalline gold on plasmon resonances. "We explore, if we observe the damping at the grain boundaries. Or if it makes sense for us to bother with the production of monocrystalline structures, or if the polycrystalline ones are good enough. The first results show that the polycrystalline structures are good enough," explains Horák the ongoing research.

In general, he thinks that today the team from CEITEC BUT is already at the world level in the field of electron microscopy and spectroscopy of plasmonic antennas. "And as for the application of the Babinet principle, then we get world-unique results," he adds. That these are excellent and unique results is confirmed not only by the shared first place for the best doctoral thesis from the Czechoslovak Microscopic Society, but also by the first prize in 2019 in the competition for the best professional work of young authors in spectroscopy organized by the Jan Marek Marci Spectroscopic Society, or an honorable mention from the Czech Physical Society in the competition for the Milan Odehnal Award in 2020. The current work of Michal Horák is also supported by a prestigious two-year scholarship from ThermoFisher Scientific and the Czechoslovak Microscopic Society 2019.

Author: Zuzana Hübnerová


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