Magneto-Optická a THz Spektroskopie


Recent Submissions

Now showing 1 - 5 of 38
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    Implementation of Broadband Electrically Detected Magnetic Resonance in a Sub-THz FraScan Spectrometer
    (2023-06-20) Solodovnyk, Artur; Savchenko, Dariya; Laguta, Oleksii; Neugebauer, Petr
    Electrically detected magnetic resonance (EDMR) is an effective spectroscopic method used for characterizing semiconductive solid-state materials. High spin sensitivity and the capability to explore spin-dependent transport mechanisms, which are crucial for the development of semiconductor devices, define it from other methods based on magnetic resonance. High frequency and high magnetic field EDMR implementation was motivated by the necessity to obtain access to more precise, high-resolution data to enhance the method's research potential. We present an EDMR system based on a unique THz FraScan spectrometer, which performs frequency sweeps ranging from 80 GHz to 1.1 THz, and the magnetic field sweeps up to 16 T. The study addresses the instrumentation, detection scheme, and 85-328.84-GHz EDMR results on highly nitrogen-doped 15R SiC monocrystals. Furthermore, the results demonstrate a subjective advantage of frequency-domain EDMR (FD EDMR) over conventional magnetic field domain measurements in terms of substantially greater signal-to-noise ratio (SNR) and the ability to record an EDMR frequency-field map (EDMR FFM).
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    Pyrolysis of Colombian spent coffee grounds (SCGs), characterization of bio-oil, and study of its antioxidant properties
    (TAYLOR & FRANCIS LTD, 2023-12-14) Malagón-Romero, Dionisio; Torres-Velasquez, Andres C.; Tinoco Navarro, Lizeth Katherine; Arrubla-Velez, Juan P.
    Coffee is the second most consumed beverage in the world. Spent coffee grounds (SCGs) are promising raw material for pyrolysis. The Kissinger-Akahira-Sunose model (KAS) and Ozawa-Flynn Wall (OFW), determined the pyrolysis activation energy to be 142.40 and 66.08 kJ/mol, respectively. The pyrolysis products were bio-oil with a 22.5% yield and a calorific power of 28.91 MJ/kg. The bio-oil composition was 50.86% fatty acids, 31.65% linear hydrocarbons, and 11.31% aromatics, as determined by GC-MS. The total phenolic content (TPC) was 362 & PLUSMN; 44 mg GA g(-1), with DPPH activity of 24.8 & PLUSMN; 2% inhibition and antioxidant activity of 108.5 & PLUSMN; 13.6 mg L-1 of Trolox equivalents. The results showed that bio-oil could be used as a biofuel and a source of chemical compounds.
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    High harmonic generation in monolayer MoS2 controlled by resonant and near-resonant pulses on ultrashort time scales
    (AIP Publishing, 2023-08-01) Peterka, Pavel; Slobodeniuk, Artur; Novotný, Tomáš; Suthar, Pawan; Bartoš, Miroslav; Trojánek, František; Malý, Petr; Kozák, Martin
    We report on experimental investigation of nonperturbative high harmonic generation (HHG) in monolayer MoS2 in the ultraviolet spectral region driven by mid-infrared light. We study how the HHG is influenced by pre-excitation of the monolayer using resonant and near-resonant pulses in a pump-probe-like scheme. The resonant light creates high density exciton population. Due to ultrafast dephasing caused by electron-electron scattering, the HHG is suppressed in the presence of pre-excited carriers. In the case of near-resonant excitation with photon energy below the exciton transition, the dynamics of the observed suppression of the HHG yield contains a fast component, which is a consequence of momentum scattering at carriers, which are excited by two-photon transition when the two pulses temporally overlap in the sample. This interpretation is supported by comparing the experimental data with theoretical calculations of the two-photon absorption spectrum of the MoS2 monolayer. This work demonstrates a possibility to control HHG in low-dimensional materials on ultrashort timescales by combining the driving strong-field pulse with a weak near-resonant light.
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    Variation of Spin-Transition Temperature in the Iron(III) Complex Induced by Different Compositions of the Crystallization Solvent
    (American Chemical Society, 2023-03-01) Nemec, Ivan; Kotásková, Lucie; Herchel, Radovan
    We crystallized the Schiff-base iron(III) spin-crossover complex [Fe(3,5Cl-L5)(NCSe)] from different two-component solvent mixtures containing methanol and chloroform (phi = V(CH3OH)/V(solvent) = 0.05, 0.25, 0.50, 0.83, and 1.00). The obtained crystalline products were characterized by X-ray diffraction, and it was confirmed that they are all composed of the same crystalline phase, and they do not contain any crystal solvent. However, significant differences in magnetic properties were observed, and thermal hysteresis changed from (in K) 121T down arrow and 134T up arrow for phi = 0.05 and 0.25, down to 72T down arrow and 96T up arrow for phi = 1.00. The crystal structures of the low-spin and high-spin phases were studied theoretically and experimentally.
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    Transparent LiOH-doped magnesium aluminate spinel produced by spark plasma sintering: Effects of heating rate and dopant concentration
    (Elsevier, 2023-07-01) Pouchlý, Václav; Talimian, Ali; Kaštyl, Jaroslav; Chvíla, Martin; Ščasnovič, Erik; Beltran, Ana Maria; Lozano , Juan Gabriel; Galusek, Dušan
    The effects of LiOH doping of magnesium aluminate spinel powders and various Spark Plasma Sintering (SPS) schedules on densification behavior and final transparency of polycrystalline magnesium aluminate spinel were studied. Two commercial magnesium aluminate spinel powders, with different specific surface areas, were doped with up to 0.6 wt% of LiOH and consolidated using SPS with slow (2.75 degrees C/min) and fast (100 degrees C/min) heating rates. The slow heating rate was optimal for undoped magnesium aluminate spinel (LiOH-free) with the best real in-line transmittance (RIT) of 84.8% (measured at 633 nm on a disc 0.8 mm thick). For the magnesium aluminate spinel doped with 0.3 wt% of LiOH, the fast heating rate was beneficial, and an RIT of 76.5% was achieved. mu-Raman analysis confirmed that the addition of LiOH suppressed carbon contamination.