Кафедра фізико-математичних наук

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    Elucidation of conditions for excitation of surface polaritons in Mg0.2Zn0.8O ceramics using the disturbed total internal reflection method
    (2022) Melnichuk, Olexandr; Korsunska, Nadiia; Melnichuk, Lyudmyla; Khomenkova, Larysa; Venger, Yevgen
    Conditions for the excitation of surface polaritons in Mg0.2Zn0.8O ceramics have been theoretically analyzed for the first time, and the surface of the disturbed total internal reflection І(ν) / І0(ν) has been plotted, which is a three-dimensional representation of the transmission coefficient in the IR spectral interval. Its dependence on the frequency and incidence angle of radiation is determined. The external reflection IR spectra are measured to calculate the required optical and electrophysical parameters of ceramics using the method of dispersion analysis. The possibility of researching the resonant interaction between optical phonons and plasmons has been demonstrated. The obtained results are in good agreement with the literature data.
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    Comprehensive investigation of Er2O3 thin films grown with different ALD approaches
    (2022) Khomenkova, Larysa; Merabet, H.; Chauvat, M.-P.; Frilay, C.; Portier, Xavier; Labbe, C.; Marie, P.; Cardin, J.; Boudin, S.; Rueff, J.-M.; Gourbilleau, F.
    The effect of Er precursor nature (Er(CpMe)3 or Er(tmhd)3) and annealing treatment at 500–1100 ◦C on the structural and optical properties of Er2O3 films grown on Si substrates by thermal or O2-plasma-assisted atomic layer deposition was studied by means of spectroscopic ellipsometry, Fourier-transform infrared spectroscopy, Xray diffraction, transmission electron microscopy coupled with energy dispersive X-ray spectroscopy as well as photoluminescence method. An annealing at 500–800 ◦C resulted in the film crystallization mainly. Thermal treatment at high temperatures caused the formation of Er silicate phase due to the diffusion of Si atoms from the substrate in the films depth. This phase was found to be Er2SiO5 being crystallized at 1100 ◦C. Light emitting properties of the films are determined by Er2O3 native defects (like oxygen vacancies) and intra-4f shell transition in Er3+ ions. The latter dominated in the films annealed at 1000–1100 ◦C. The most intense Er3+ emission, observed in the films grown with O2-plasma-assisted approach, was explained by a lower contribution of oxygen vacancies as well as by pronounced crystallization of Er silicate phase. In this latter, the effect of concentration quenching of Er3+ luminescence was lower due to a larger distance between Er3+ neighbor ions.
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    Enhancement of radiation-induced EPR signal in bioapatites
    (2022) Nosenko, Valentyna; Vorona, Igor; Lemishko, Serhii; Golovina, Iryna; Yukhymchuk, Volodymyr; Okulov, Serhii; Neimash, Volodymyr; Povarchuk, Vasyl; Solopan, Serhii; Belous, Anatolii
    Amplification of a dosimetric EPR signal in mineralized biological materials available in limited quantities has been demonstrated in this paper. Powders of irradiated enamel, dentin, and bone tissue were placed into silica ampoules with the outer diameter close to 1.4 mm. To amplify the signal, the dielectric insert in the form of cylinder with the outer radius 2.85 mm, the inner radius 0.75 mm, and the height 1.85 mm made of a high-κ and low-loss ceramic material BaTi4O9 + 8.5% ZnO has been used. It has been shown that maximum signal amplification (about an order of magnitude) has been achieved when the sample is completely inserted into this dielectric. It has been found that the line shape of the dosimetric signal is not distorted, if using the dielectric insert. Decomposition of the amplified EPR spectra allowed us to determine the relative contribution of two types of CO2– radicals to the dosimetric signal, which coincides with the literature data.
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    Size- and position-controlled Ge nanocrystals separated by high-k dielectrics
    (2022) Lehninger, D.; Honeit, F.; Rafaja, D.; Klemm, V.; Röder, C.; Khomenkova, Larysa; Schneider, F.; Borany, J. von; Heitmann, J.
    Germanium nanocrystals embedded in high-k dielectric matrices are of main interest for infrared sensing application, as a role model for Ge-based nanoelectronics passivation or for nonvolatile memory devices. The capability of the size control of those nanocrystals via rapid thermal processing of superlattice structures is shown for the [Ge–TaZrOx/TaZrOx]n, [Ge–TaZrOx/SiO2/TaZrOx]6, and [ TaZrOx/Ge–SiO2]n superlattice systems. All superlattices were deposited by radiofrequency magnetron sputtering. Transmission electron microscopy (TEM) imaging confirms the formation of spherically shaped nanocrystals. Raman scattering proved the crystallization of Ge above 700°C. The TaZrOx crystallizes above 770°C, associated with a phase separation of Ta2O5 and ZrO2 as confirmed by x-ray diffraction. For the composite layers having 3 nm and 6 nm thickness, the size of the Ge nanocrystals correlates with the deposited layer thickness. Thicker composite layers (above 9 nm) form two fractions of nanocrystals with different sizes. An additional SiO2 layer in the [Ge– TaZrOx/SiO2/TaZrOx]6 superlattice stacks facilitates the formation of larger and better separated Ge nanocrystals. The deposition of Ge-SiO2 composite layers separated by pure TaZrOx illustrates the barrier effect of TaZrOx against Ge diffusion. All three material systems allow the controlled formation of Ge nanocrystals in amorphous matrices at temperatures above 700 and below 770°C.
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    Особливостi процесiв збудження фотолюмiнесценцiї у керамiцi оксиду цинку, легованої елементами I групи
    (2022) Корсунська, Надія; Маркевич, І.; Стара, Т.; Козоріз, К.; Мельничук, Людмила; Мельничук, О.; Хоменкова, Лариса
    Дослiджено спектри домiшкової фотолюмiнесценцiї, спектри її збудження i спектри поглинання керамiки ZnO, легованої лiтiєм, мiддю i срiблом, а також нелегованої керамiки, спеченої в рiзних атмосферах. Показано, що легування керамiки акцепторами приводить до появи смуг люмiнесценцiї у видимому дiапазонi спектра, iнтенсивнiсть яких суттєво перевищує iнтенсивнiсть видимого випромiнювання нелегованих зразкiв. Виявлено, що в спектрах збудження цих смуг домiнує селективний максимум в областi 390–400 нм, зазвичай вiдсутнiй у спектрах збудження самоактивованих смуг люмiнесценцiї в нелегованих зразках. Запропоновано пояснення, що його поява зумовлена взаємодiєю мiж центрами випромiнювання i дефектами, якi виникають в околi домiшок, а оже-процес є найбiльш iмовiрним механiзмом передачi енергiї вiд цих дефектiв до центрiв випромiнювання. За допомогою синтезу керамiки у присутностi вуглецю показано, що поява такого максимуму в спектрах збудження люмiнесценцiї в нелегованих зразках зумовлена видаленням кисню з керамiки. Зроблено висновок щодо природи центрiв збудження домiшкової люмiнесценцiї.