TUČEK, M. Frekvenční rapid-scan EPR na organických radikálech [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2018.

Posudek vedoucího

Neugebauer, Petr

Marek Tuček se ve své diplomové práci, psané v angličtině, zabývá aktuální tematikou implementace a metodikou rychlého rozmítání (rapid scan) frekvence v elektronové paramagnetické rezonanci (EPR). Práce obsahuje šest kapitol. Po obecném úvodu do magnetické rezonance autor přechází k obecné teorii EPR založené na Zeemanově jevu. Popisuje jednotlivé možné magnetické interakce pomocí spin Hamiltonianu, následně rozebírá makroskopický popis magnetizace pomocí Blochových rovnic, a tak zavádí relaxační časy T1 a T2. Velice stručně popisuje současné metody měření – kontinuální a pulsní EPR techniku, než přejde k technice rychle rozmítané frekvence/pole, které věnuje celou kapitolu. Následuje popis experimentálního uspořádání s popisem experimentu a použitých testovaných vzorků. V páté kapitole se zabývá samotným experimentem a analýzou obdržených dat, která jsou velice kvalitní. Zde je nutno podotknout, že zmíněný vysoko frekvenční “Rapid Scan” experiment byl zde demonstrován poprvé! Marek Tuček v práci prokázal schopnost analýzy experimentálních dat s extrakcí velice důležitého relaxačního času T2. Pokud bych měl něco vytknout, tak trošku odbyté kritické zamyšlení nad dosaženými T2 časy a literaturou, zde si myslím, že autor by měl být schopen lepší kritiky. Marek Tuček během své diplomové práce pracoval samostatně, cílevědomě využíval veškeré zázemí a znalosti starších kolegů pro dosažení co nejlepších výsledků. Jako vedoucí jeho diplomové práce jsem s prací spokojen a navrhuji jeho práci k obhajobě.

Posudek oponenta

Marko, Andriy

The master thesis with a title ‘Frequency-swept rapid-scan EPR spectroscopy’ composed by Mr Marek Tuček presents a very interesting scientific work. This worked was done under the supervision of Dr Petr Neugebauer in Central European Institute of Technology (CEITEC) of Brno University of Technology (BUT) and in the University of Stuttgart. At the beginning of the master thesis project during his ERASMUS+ period, Mr Marek Tuček was accepted in the University of Stuttgart in the groups of Dr. Petr Neugebauer and Prof Joris van Slageren in whose Lab the rapid-scan EPR experiments were performed. While preparing this master thesis Mr Marek Tuček had also an intensive scientific collaboration with Dr Oleksii Laguta (Postdoc in the research group of Dr Petr Neugebauer at the University of Stuttgart) who has a great experience in microwave technology. The master thesis of Marek Tuček is well written and gives generally a good description of the investigated topic. It starts with an introductory chapter containing the information about the history of the rapid scan development and current method state of the art. Also, the goals and the meaning of the carried out project are clearly defined in the introduction. The next chapter describes the basic theoretical concepts which are necessary for setting up the experiments described later. By writing this chapter Mr Marek Tuček demonstrates a good understanding of the theoretical background of EPR. In the third chapter ‘Rapid Scan EPR’, the theory is further described although it is here more specified for the rapid scan. However, (this can be considered as a minor criticism) in order to improve the structure of the work presentation, these two theoretical chapter could be united into one chapter under a different title. My arguments for this are: (i) both chapters deal with the theory (ii) the chapter title ‘General theory of EPR’ does not fully reflect or rather overstates the chapter content, which described mainly basic theoretical EPR concepts that is fairly justified in the content of this thesis. My other minor criticism is related to the accuracy of the equation presented in the theoretical section. In some cases, consistent notations of the same physical values are lacking. For example, in Eq. (2.14), the electron spin operator is noted as S , whereas in Eq. (2.36) the electron spin operator is noted as a bold S. Furthermore, in Eq. (2.14) the author uses for magnetic field the notation with a hat B , which is rather unusual in physics or magnetic resonance. Again in Eq. (2.36) there is no hat over magnetic field. The forth chapter provides the details to the experiments performed in this work. Two organic radicals BDPA and LiPc, which were here examined by means of the frequency swept rapid scan EPR spectroscopy, are well described. This chapter contains also a comprehensive schematic description of the home-built EPR spectrometer which was used for experiments in the University of Stuttgart. In the fifth chapter the measurement results followed by the data analysis are presented. In Figs. 5.2 - 5.5 four datasets recorded with two different values of magnetic field for both samples mentioned above are shown. In each dataset the variation of the signal form is observed depending on the rate of the frequency sweep. Further the Fourier deconvolution algorithm is applied to transform one signal from each data set into the corresponding slow scan signals (See Figs. 5.8 - 5.11). The measured data were also used to estimate T2 relaxation times for BDPA at 8.1 T and for LiPc at 8 T employing the experimental signals recorded with a sweep rate of 2460 THz/s and with a sweep rate of 46000 THz/s, respectively. Considering the fact, that the obtained values of the relaxation times obtained here differ much from the values reported in literature for similar systems, the estimates of T2 relaxation times employing the rapid scan signals with other sweep rates would be useful to report in the thesis. Although, an exact clarification of this discrepancy would probably require additional research which can go beyond the scope of this thesis. In the last ‘Conclusion’ section Mr Marek Tuček demonstrates all advantages of the frequency-swept rapid-scan method and summarizes the work that has been done in the project. In my opinion he has greatly contributed to the extension of the rapid scan method to high magnetic fields and high frequencies and deserves a very high rating of his master thesis despite several minor criticisms.

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