Тонкі плівки оксиду диспрозію, утворені при швидкому термічному відпалі на пористих підкладках SiC

In this paper, we consider the effect of rapid thermal annealing (RTA) on the properties of Dy2O3 film formed on the surface of a substrate with a por-SiC/SiC structure. The atomic composition of the films under study was analyzed as a function of the RTA time. It is shown that the RTA method makes it possible to obtain thin Dy oxide films with a composition close to the stoichiometric one. In this case, an increase in the RTA time leads to improving the quality of film-substrate interface and increasing the optical transmission of Dy2O3/por-SiC/SiC structureУ цій роботі розглянуто вплив швидкого термічного відпалу (ШТВ) на властивості плівки Dy2O3, що утворюється на поверхні підкладки зі структурою por-SiC/SiC. Атомний склад досліджуваних плівок аналізували як функцію часу ШТВ. Показано, що метод ШТВ дозволяє отримувати тонкі плівки оксиду диспрозію зі складом, близьким до стехіометричного. У цьому випадку збільшення часу ШТВ призводить до поліпшення якості межі поділу плівка-підкладка і до збільшення оптичного пропускання структури Dy2O3/por-SiC/SiC

Luminescent properties of fine-dispersed ZnS:Cu prepared using self-propagating high-temperature synthesis

Fine-dispersed ZnS doped with Cu was prepared using self-propagating hightemperature synthesis. In the photoluminescence excitation spectra, the blue shift of the host lattice excitation peak is observed for powder ZnS:Cu that contains nano- and mesosized (submicron) particles. The obtained spectra indicate that radiative recombination in meso-sized particles is significantly reduced as compared to micro-sized particles, which can be caused by the increase of non-radiative relaxation processes in surface states

Influence of the presence of a fluxing agent and its composition on the spectral characteristics of ZnS(Cu) obtained by self-propagating high-temperature synthesis

Investigated in this work were the photoluminescence spectra and luminescence excitation spectra of powered ZnS:Cu, obtained using the method of selfpropagating high-temperature synthesis (SHS) with addition of NaCl and MgCl₂ as a fluxing agent into the charge and without them. It was shown that increasing the amount of fraction with the particle sizes ≤5 nm in powdered ZnS:Cu-SHS, where fluxing agents are present in the charge, is caused by the decrease in temperature inside the reactor in the course of the synthesis reaction. Besides, related increasing the intensity of the PL blue band with λmax ~ 450…465 nm in powdered ZnS:Cu-SHS/MgCl₂, which is associated with redistribution of the copper impurity in the bulk of microcrystals, probably, occurring as a result of increasing the partial pressure of Cl during synthesis

Electroluminescence powdered ZnS:Cu obtained by one-stage synthesis

Photo- and electroluminescence properties of ZnS obtained using selfpropagating high-temperature synthesis and doped with Cu were studied in this work. It has been shown that high-temperature one-stage synthesis enables to obtain two-phase system ZnS-Cu₂₋xS with the maximum radiation 515 nm for photo- and electroluminescence. Since the synthesis process is non-equilibrium, impurities distribute nonuniformly in the bulk of microcrystals. Additional annealing and introducing the Ga coactivator lead to more non-uniform distribution of impurities in the bulk of microcrystals. It causes the increase in the intensity of the blue band in photoluminescence spectra and shift of the maximum of electroluminescence toward longer wavelengths. It is probable that this increase in the intensity of the blue band in photoluminescence spectra is caused by formation of the radiative centers Cui₋CuZn

Interface features of SiO₂/SiC heterostructures according to methods for producing the SiO₂ thin films

In this work, we studied comparative characteristics of the SiO₂/SiC heterostructures. The following two techniques were used for SiO₂ formation: thermal oxidation in water vapor (i) and oxidation in solution (ii). According to experimental results obtained from optical absorption and photoluminescence spectra as well as from measurements of internal mechanical stresses, one can conclude that the thin SiO₂ films prepared using the technique (ii) possess SiO₂/SiC interface with a less number of defective states than that for SiO₂ films prepared using the technique (i)

Effect of heating rate on oxidation process of fine-dispersed ZnS:Mn obtained by SHS

The influence of annealing at 350 °C in air atmosphere on the luminescent characteristics of powdered ZnS: Mn obtained by self-propagating high-temperature synthesis has been studied. It was shown that variation in material heating rate due to changes in the annealing temperature results in different behavior of oxidative processes. It has been ascertained that the slow heating of powdered ZnS:Mn, compared with the rapid one in the presence of oxygen, promotes active oxidation of ZnS and formation of Frenkel pairs, increases mileage of defects acting as sensitizers, and their localization near Mn²⁺. The model which explains the observed changes in the luminescence and PLE spectra has been presented

Comparison of properties inherent to thin titanium oxide films formed by rapid thermal annealing on SiC and porous SiC substrates

The comparative analysis of optical characteristics inherent to TiO2/SiC and TiO2/por-SiC/SiC structures has been performed. It has been shown that, in these structures regardless of the substrate structure, formation of TiO2 layers with approximately the same width 60 nm takes place. In this case the TiO2 film composition is close to the stoichiometric one. At the same time, the presence of an additional porous layer in the TiO2/por-SiC/SiC structure leads to blurring the oxide film – substrate interface but promotes an increase in the intensity of the Raman scattering signal from the oxide film

The factors influencing luminescent properties of ZnS:Mn obtained by the method of one-stage synthesis

Considered in this paper is the model that combines appearance of defects responsible for self-activated (SA) emission in ZnS with its piezoelectric properties. Being based on analysis of the luminescence spectrum, the authors demonstrate the influence of mechanical destruction, impact of ultrasound, microwave radiation and pulsed magnetic field on the emission efficiency for centers of luminescence connected with intrinsic defects in ZnS:Mn prepared using the method of self-propagating hightemperature synthesis (SHS). It has been shown that downsizing the ZnS:Mn crystals prepared according to the above method as well as more discrete differentiation of phases present in this material due to development and growth of inner boundaries and surface under external actions leads to quenched SA-photoluminescence with λ ~ 400–525 n

Relationship between oxidation, stresses, morphology, local resistivity, and optical properties of TiO2, Gd2O3, Er2O3, SiO2 thin films on SiC

The relationship between internal mechanical stresses, surface morphology, nanoscale electrical properties, and optical characteristics in TiO2, Gd2O3, Er2O3, and SiO2 thin films on SiC substrates was investigated. The oxide films were synthesized using the rapid thermal annealing and analyzed through scanning spreading resistance microscopy, photoluminescence, and absorption spectroscopy. Tensile stresses were found in the films, they are attributed to thermal and lattice mismatch, oxidation, and grain boundaries. These stresses influence on surface morphology, resistivity variations, and photoluminescence intensity. Surface roughness and grain structure were found to correlate with variations in resistivity, which were attributed to conductive pathways along grain boundaries and possible metallic phases. Photoluminescence intensity was also observed to correlate with estimated lattice mismatch strain. Gd2O3/SiC exhibited the fewest defects, while Er2O3 and TiO2 showed more, with Er2O3 being the most mismatched and roughest. The results indicate that internal strains in oxide thin films on SiC substrates can influence on surface morphology, leading to formation of defects and spatial inhomogeneity. These fluctuations in local conductivity and luminescence center density have significant implications for dielectric and optical applications. The study provides insights for future processing refinements to mitigate internal strains and enhance the performance of oxide thin films in semiconductor and optical technologies

CdSe nanoparticles grown with different chelates

Modified reverse micelles method allowing fabrication of CdSe nanoparticles in toluene solution in series of sizes with average diameter from 1.2 to 3.2 nm and size distribution ∼ 12-30 % is presented. Simple empirical relation between the CdSe nanoparticle diameter and exciton absorption wavelength is proposed, which allows to do prompt and effective monitoring the particles size and size distribution during the synthesis. Optical absorption and photoluminescence measurements as well as EDX demonstrated good quality of obtained nanocrystallites. Besides, study of nanoparticles produced using two complexing agents (SNTA and Trilon B) revealed similar stoichiometric and optical properties. Trilon B is suitable for CdSe nanoparticles growth instead of SNTA. Because of higher stability of the chelate complex of Trilon B and Cd²⁺ ions, it is possible to use higher temperature for growth which allows preparation of large size nanocrystals