Magneto-Optická a THz Spektroskopie

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Raman scattering excitation in monolayers of semiconducting transition metal dichalcogenides
(NATURE PORTFOLIO, 2024-01-10) Bartoš, Miroslav; Zinkiewitz, Malgorzata; Grzeszczyk, Magdalena; Kazimierczuk, Tomasz; Nogajewski, Karol; Pacuski, Wojciech; Watanabe, Kenji; Taniguchi, Takashi; Wysmołek, Andrzej; Kossacki, Piotr; Potemski, Marek; Babinski, Adam; Molas, Maciej
Raman scattering excitation (RSE) is an experimental technique in which the spectrum is made up by sweeping the excitation energy when the detection energy is fixed. We study the low-temperature (T = 5 K) RSE spectra measured on four high quality monolayers (ML) of semiconducting transition metal dichalcogenides (S-TMDs), i.e. MoS2, MoSe2, WS2, and WSe2, encapsulated in hexagonal BN. The outgoing resonant conditions of Raman scattering reveal an extraordinary intensity enhancement of the phonon modes, which results in extremely rich RSE spectra. The obtained spectra are composed not only of Raman-active peaks, i.e. in-plane E ' and out-of-plane A(1)', but the appearance of 1st, 2nd, and higher-order phonon modes is recognized. The intensity profiles of the A(1)' modes in the investigated MLs resemble the emissions due to neutral excitons measured in the corresponding PL spectra for the outgoing type of resonant Raman scattering conditions. Furthermore, for the WSe2 ML, the A(1)' mode was observed when the incoming light was in resonance with the neutral exciton line. The strength of the exciton-phonon coupling (EPC) in S-TMD MLs strongly depends on the type of their ground excitonic state, i.e. bright or dark, resulting in different shapes of the RSE spectra. Our results demonstrate that RSE spectroscopy is a powerful technique for studying EPC in S-TMD MLs.
Novel Trinuclear Copper(II) Complex: Crystal Structure at 100 K and Magnetic Properties of (R, S)-di[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolato]-tetra(2-hydroxybenzoato)-diaqua-tricopper dihydrate, [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]2(H2O)
(SPRINGER/PLENUM PUBLISHERS, 2024-06-01) Valach, Fedor; Pavlik, Ján; Šalitroš, Ivan; Melník, Milan; Kožíšek, Jozef
The crystal structure of [Cu-3(C7H5O3)(4)(C20H20NO5)(2)(H2O)(2)]2(H2O) (1) and analysis of temperature and field dependence of magnetic susceptibility is reported in this work. The structure of 1 is composed of trinuclear complex units and water molecules. The middle copper atom occupies the center of symmetry. N, O-bonded (6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolato ligands, 2-hydroxybenzoates with bridging carboxylic groups, and oxo-bridged water molecules connect the middle Cu(II) atom with the terminal copper atoms. Two 2-hydroxybenzoates coordinate the terminal copper atoms via one carboxylic oxygen and an O atom of the hydroxyl group. The analysis of copper coordination by bond-valence sum approach and relevant structural correlation is consistent with hexacoordinated Cu(II) centers. CuCu separation is 3.0269(3) & Aring;. The magnetism of 1 shows a strong ferromagnetic interaction between the neighboring metallic centers accompanied by very weak antiferromagnetic intermolecular interactions. The complex units are mutually held by pipi stack interactions of 2-hydroxybenzoates and hydrogen bonds.
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).
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.
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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