Equipment

OD-EPR spectrometer based on «Radiopan SE/X-2243»	X-band EPR spectrometer «RadiopanSE/X-2244»

X-band EPR spectrometer «RadiopanSE/X-2547»	ENDOR spectrometer «ЭЯ-1301»

Achievements

Structural and optical properties of ZnS:Mn synthesized with different Zn/S ratio in the charge

Manganese is an important impurity for zinc sulfide, which creates bright orange lights during photo- and electrical excitation. The structural and optical properties have been studiedfor manganese-doped zinc sulfide, which was obtained by high-temperature self-propagating synthesis (SPS) with different ratio Zn/S in the charge: ZnS:Mn - stoichiometric ratio, ZnS(S):Mn - with sulfur excess and ZnS(Zn):Mn - with zinc excess.

TEM image of ZnS(S):Mn, ZnS:Mn and ZnS(Zn):Mn powders.

Normalized EPR and photoluminescence spectra of ZnS(S):Mn, ZnS:Mn and ZnS(Zn):Mn powders.

It has been found for ZnS: Mn powders synthesized by the SPS method, that the Zn / S ratio in the charge affects the size of ZnS crystallites, the 2H/3C ratio of polytypes, and the luminescent properties. The most uniform size distribution of crystallites is observed at the stoichiometric ratio of Zn/S in the charge, while excess sulfur led to the appearance of a large number of small size crystallites. The crystallites of all investigated powders had a hexagonal 2H structure with small inclusions of the 3C-ZnS polytype, the number of which increased with increasing sulfur in the charge. The maximum amount of Mn_Zn²⁺ is found for ZnS:Mn powder.

BaTiO₃ Thin Films from Atomic Layer Deposition: A Superlattice Approach

The growth of BaTiO₃ thin films has been used as an example to demonstrate that an approach that splits the deposition process into extensive binary subcycles of Ba−O and Ti−O results in the growth of superlattice (SL) thin films enabling superior uniformity and compositional control. The solid state reaction between binary oxide layers to form ternary BaTiO₃ upon annealing is investigated by in situ X-ray diffraction, transmission electron microscopy, and Raman scattering spectroscopy.

It is demonstrated that partially crystalline Ba(OH)₂ layers and amorphous TiO₂ layers react to polycrystalline BaTiO₃ above 500 °C, releasing H₂O. This solid-state reaction is accompanied by an abrupt decrease in film thickness. The presence of hexagonal BaTiO₃ in addition to the perovskite phase in the annealed films are revealed. The electrical properties transition from the initially highly insulating dielectric semiamorphous SL into a polycrystalline, polymorph BaTiO₃ thin film with a dielectric constant of 117 and a dielectric loss of 0.001 at 1 MHz after annealing at 600 °C in air, which, together with the suppression of ferroelectricity at room temperature, are very appealing properties for voltage tunable devices.

M. Falmbigl, I.S. Golovina, A.V. Plokhikh et al. BaTiO₃ Thin Films from Atomic Layer Deposition: A Superlattice Approach. Journal of Physical Chemistry 121, 16911–16920 (2017).

Effect of annealing conditions on the electrical properties of ALD-grown polycrystalline BiFeO₃ films

To analyze the influence of annealing conditions on the carrier transport, leakage current and dielectric properties of ALD-grown amorphous Bi–Fe–O thin films after their crystallization into BiFeO₃ the films have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS) techniques after each annealing process.

It is established that the interface-limited Schottky emission is dominant in 70 nm thick Fe-rich films after relatively short annealing, whereas a space-charge-limited conduction is dominant in stoichiometric films with a thickness of 215 nm independent of the annealing conditions. Analysis of changes in dielectric properties, on one hand, and the film composition, microstructure and morphology, on the other hand, reveal the key role of grain boundary interfaces for the conductivity of the polycrystalline ALD-grown BiFeO₃ thin films. Extended annealing in oxygen results in 2–3 orders-of-magnitude reduction in leakage current accompanied by decreases in dielectric loss, highlighting the importance of optimizing annealing conditions for any applications of BiFeO₃ thin films.

І.S. Golovina, M. Falmbigl, A.V. Plokhikh et al. Effect of annealing conditions on the electrical properties of ALD-grown polycrystalline BiFeO₃ films. Journal of Materials Chemistry C6, 5462-5472 (2018).

Developments

Development of new generation polymer composites

Aromatic polyamides such as Phenylon C-2 (PhC-2) belong to the class of "superplastics" and are the basis for the creation of heat-resistant and high-strength materials for a wide range of purposes. The purpose of creating the latest PhC-2 composites with nanostructured fillers was to significantly improve the actual characteristics of these materials. Magnetic resonance imaging helps to determine the properties of the electronic states of polymer matrices and fillers, the mechanisms of their interaction and the impact on the actual tribological characteristics. They also allow to give an expert assessment of the possibility of using composite structures as elements of electromagnetic shielding

The work was carried out in cooperation with the laboratory of polymer composites of DTU MES of Ukraine (Kamyanske). Polymer composites based on aromatic phenylon polyamide have been developed and put into practice, which combine relatively low cost with the best physical and mechanical characteristics. New technological schemes for the production of nanocomposites with given thermophysical, mechanical and magnetic properties have been developed. Hybrid composites of the second and third generation have been created, which are significantly superior to well-known domestic and foreign analogues. The results of developments are summarized in the monograph: Burya O.I., Eremina K.A., Lysenko O.B., Konchyts A.A., Morozov O.F. "Polymer composites based on thermoplastic binders", Dnipro, 2019. The developed composites have found wide practical application in many fields of technology, including the defense industry. The results are further multimillion economic effect, of which more than three million were obtained with the direct participation of Konchits A.A.