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High frequency electron spin resonance spectroscopy
Hrubý, Jakub ; Perfetti, Mauro (oponent) ; ShangDa, Jiang (oponent) ; Neugebauer, Petr (vedoucí práce)
Electron spin resonance (ESR) is a non-invasive magnetic-resonance-based spectroscopic technique. It is used in many scientific fields such as biology, chemistry, and physics to investigate systems with unpaired electrons. This doctoral thesis deals with high-frequency electron spin resonance (HF-ESR) spectroscopy and its use on paramagnetic coordination compounds. The first part outlines theoretical basics with literature research in this field and shows the HF-ESR applications. Afterwards, methods used to study systems of interest are presented. Herein, the complementary spectroscopic methods (XPS, RS, UV-VIS, AFM, SEM) are described, and the design of a newly built high-vacuum (HV) sublimation chamber was developed for the preparation of thin films of coordination compounds on surfaces. The next part deals with results obtained by HF-ESR on molecular quantum bits [Cu(dbm)2], single-molecule magnets [CoX2(dppf)], [Co(4MeO-L)2Cl2], and vision of graphene-based bolometers for detection of this class of compounds is outlined. The results are further discussed, and their implications are summarised in conclusions. Finally, references and the author's outputs make up the final chapters of this work.
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Problematika bezdrátových sítí
Klein, Lukáš ; Neugebauer, Petr (oponent) ; Kříž, Jiří (vedoucí práce)
Tato bakalářská práce se zabývá problematikou bezdrátových sítí. Vysvětluje základní pojmy a dělení bezdrátových sítí. Dále popisuje mezinárodní standard IEEE 802.11 a jeho rozšíření. Detailně se věnuje zabezpečení bezdrátových sítí včetně bezpečnostních doporučení pro jednotlivé skupiny sítí.
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Design of a Non-Resonant General Purpose Sample Holder for Terahertz Electron Paramagnetic Resonance Spectroscopy
Martínek, Tomáš ; Sojka, Zbigniew (oponent) ; Neugebauer, Petr (vedoucí práce)
The aim of this diploma thesis is to design dedicated sample holders for a high-frequency electron paramagnetic resonance spectroscopy. The main task deals with the development of a user-friendly and fast locking system for connection between microwave waveguide and a sample holder. Two types of sample holders are designed one for loading multiple samples and one for single crystal rotation. Thanks to loading up to 6 samples the overall measurement time is estimated to be reduced more than twice. In the case of the single crystal rotator based on the precise piezoelectric rotator with resistive encoder a milliradian, precision is provided. Both sample holders are designed in such a way that the full automatization can be applied in the measurement.
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Optical setup for torque detected electron spin resonance spectroscopy
Kern, Michal ; Vetushka, Aliaksei (oponent) ; Neugebauer, Petr (vedoucí práce)
This thesis has been devoted to the improvement of a Torque Detected Electron Spin Resonance (TDESR) spectrometer by replacing the current capacitive detection of cantilever bending with optical methods. The thesis covers the basics of Electron Spin Resonance (ESR) spectrometry with the focus on TDESR and the field of single molecule magnetism. Laser beam deflection and interferometric detection methods are explained. The design of the TDESR spectrometer and its performance is shown on successfully obtained high quality TDESR spectra of an Fe4 single molecule magnet single crystal. Obtained results prove the feasibility of implemented detection method and its superiority with respect to the previously used capacitive method in terms of quality, resolution and speed. To further improve the TDESR setup, we have designed and assembled a system which uses an interferometer for detection of cantilever bending.
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Design of the far-infrared spectrometer coupling to a superconductive magnet and magneto-optical measurements in the far-infrared region
Dubnická Midlíková, Jana ; Slageren, Joris van (oponent) ; Neugebauer, Petr (vedoucí práce)
The thesis deals with the development of the far-infrared (FIR) spectroscopy in the high magnetic field. The combination of the FIR spectroscopy and high magnetic field is a very important tool in the characterization of materials such as Single-Molecule Magnets (SMMs). It also presents an ideal experimental technique that can probe and elucidate properties of novel 2D materials. The FIR spectroscopy in the magnetic field also allows studying Electron Paramagnetic Resonance (EPR) of SMMs with very large zero-field splitting, mainly based on transition metal complexes or lanthanides, in which commonly used EPR systems do not provide experimental access to the magnetic resonance transitions. In the thesis, two setups of the FIR spectrometers coupled to the superconductive magnets are described in detail. The first described setup, located at the University of Stuttgart, is already assembled and its performance is discussed. The magneto-optical measurements of SMMs performed on this setup are presented. The second magneto-optical setup draws on the experiences gained in the first setup and is designed for CEITEC.
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Frequency-swept rapid-scan EPR on organic radicals
Tuček, Marek ; Marko, Andriy (oponent) ; Neugebauer, Petr (vedoucí práce)
This thesis describes a historically first multi-frequency rapid-scan EPR. While introducing microwave radiation at 200 GHz range with subsequent sinusoidal modulation, the frequency sweep rates up to 61 500 THz/s were achieved and the rapid passage distortion known as ”wiggles” was observed in the spectra of both studied organic radicals samples – BDPA in a polystyrene matrix and LiPc. This thesis presents a flexible method of conducting rapid-scan EPR experiments, using a voltage controlled oscillator (VCO) and zero-bias detector (ZBD) as a source and detector, respectively, and thus opening the possibility to advance further into high field / high frequency range. Furthermore, the method of extracting the steady-state absorption spectra from the rapid-scan results, known as Fourier deconvolution, is described and subsequently, the spin dephasing times of the samples are determined from the comparison of the spectra with the results of numerically solved Bloch equations. The resulting values are 50 ns for BDPA and 12 ns for LiPc.
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Preparation and Characterization of Graphene Based Hybrid Materials
Hrubý, Jakub ; Novák, Jiří (oponent) ; Neugebauer, Petr (vedoucí práce)
Graphene with metal complexes could provide novel approaches in graphene-based hybrid materials and molecular magnetism. Both topics are highly innovative as such, however, there is a little research into possibilities of mixing them. Samples were prepared by a liquid-phase sonication of graphite which resulted in the exfoliation of graphene. Subsequently, various metal complexes were deposited onto a graphene-covered substrate by modiied Langmuir–Schaefer method. An essential step was to determine the material’s properties. Consequently, properties of new hybrid materials were characterised by high frequency electron paramagnetic resonance (HFEPR), scanning electron microscopy (SEM), Raman spectroscopy and four-point probe resistance measurements. Herein, the results conirmed our presumption that it is possible to mix exfoliated graphene with potential molecular magnets in order to gain novel magnetic and electronic properties which could be possibly utilised in the next generation of detectors and electronics.
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Design of mobile vacuum chamber for loading samples into high-frequency electron paramagnetic resonance spectrometer
Láznička, Tomáš ; Slageren, Joris van (oponent) ; Neugebauer, Petr (vedoucí práce)
In order to be able to characterize atmosphere sensitive samples in high-frequency electron paramagnetic resonance spectrometer (HF-EPR), a system of vacuum transportation is needed. The scope of this thesis is to design and develop a vacuum transport system which will allow this transportation. The vacuum system, which consists of a mobile vacuum suitcase, palette holder and airlock, was designed, assembled and tested. The pressure of 4.3 10^{-10} mbar was achieved, which will ensure inert condition for sample transportation. The transport of the sample from an ultra-high vacuum (UHV) cluster to the HF-EPR spectrometer was performed. The contamination of the test samples was characterized using x-ray photoelectron spectroscopy. It was found that there is no detectable contamination if the sample is in the vacuum system for less than 16 hours. The extension for transportation of the samples from a glove box and sample palette for graphene were proposed, but their production has not been performed yet. The developed vacuum system is fully functional and provides the alternative to commercially available products, thus it will be further used in the investigation of an atmosphere sensitive samples in CEITEC Nano laboratories.
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Development of Fourier Transform InfraRed Spectroscopy in High Magnetic Fields
Dubnická Midlíková, Jana ; Marsik, Přemysl (oponent) ; Schnegg, Alexander (oponent) ; Neugebauer, Petr (vedoucí práce)
Fourier-transform infrared (FTIR) spectroscopy in high magnetic fields, concisely FTIR magneto-spectroscopy, is a powerful spectroscopic technique used to investigate many important effects in materials, e.g., electron paramagnetic resonance, cyclotron resonance, and transitions between Landau levels. Despite their enormous potential in solid-state physics, infrared magneto-spectrometers are still relatively rare and custom-made since such systems generally require complex infrastructure. This doctoral thesis describes in detail the design and implementation of a versatile FTIR magneto-spectroscopic setup operating in the range of 50 – 10 000 cm-1, high magnetic field up to 16 T and temperatures between 2 – 320 K located at the Central European Institute of Technology of Brno University of Technology. This setup allows us to perform a variety of magneto-optical measurements spanning the range from THz/far-infrared (FIR) to near-infrared (NIR). It consists of a commercial FTIR spectrometer coupled to a 16 T cryogen-free superconductive magnet by the custom-designed optical coupling and transmission probes designed for experiments with multiple detectors and samples in Faraday geometry. The novelty of the setup lies in the usage of a cryogen-free superconducting magnet. We have optimized and tested the performance of the FTIR magneto-spectroscopic setup for various configurations and determined a workable setup range. The functionality of the FTIR magneto-spectroscopic setup was demonstrated by the magneto-optical measurements of the zero-field splitting in cobalt(II)-based single ion magnet in the FIR region, indirect inter-band transitions between Landau levels (LLs) in germanium in the NIR region, and inter-band transitions between LLs in graphene in the FIR region. Moreover, we measured the I-V characteristics of graphene bolometer devices.
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