Constantly developing nanotechnology provides the possibility of manufacturing nanostructured composites with a polymer matrix doped with ceramic nanoparticles, including ZnO. A specific feature of polymers, i.e. ceramic composite materials, is an amelioration in physical properties for polymer matrix and reinforcement. The aim of the paper was to produce thin fibrous composite mats, reinforced with ZnO nanoparticles and a polyvinylpyrrolidone (PVP) matrix obtained by means of the electrospinning process and then examining the influence of the strength of the reinforcement on the morphology and optical properties of the composite nanofibers. The morphology and structure of the fibrous mats was examined by a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) and Fourier-transform infrared spectroscopy (FTIR). UV –Vis spectroscopy allowed to examine the impact of zinc oxide on the optical properties of PVP/ZnO nanofibers and to investigate the width of the energy gap.
The paper presents the results of investigations concerning the application of zinc oxide - a wideband gap semiconductor in optical planar waveguide structures. ZnO is a promising semiconducting material thanks to its attractive optical properties. The investigations were focused on the determination of the technology of depositions and the annealing of ZnO layers concerning their optical properties. Special attention was paid to the determination of characteristics of the refractive index of ZnO layers and their coefficients of spectral transmission within the UV-VIS-NIR range. Besides that, also the mode characteristics and the attenuation coefficients of light in the obtained waveguide structures have been investigated. In the case of planar waveguides, in which the ZnO layers have not been annealed after their deposition, the values of the attenuation coefficient of light modes amount to a~ 30 dB/cm. The ZnO layers deposited on the heated substrate and annealed by rapid thermal annealing in an N2 and O2 atmosphere, are characterized by much lower values of the attenuation coefficients: a~ 3 dB/cm (TE0 and TM0 modes). The ZnO optical waveguides obtained according to our technology are characterized by the lowest values of the attenuation coefficients a encountered in world literature concerning the problem of optical waveguides based on ZnO. Studies have shown that ZnO layers elaborated by us can be used in integrated optic systems, waveguides, optical modulators and light sources.
A series of copper oxide thin films were synthesized through direct current magnetron sputtering on glass and silicon substrates with various process parameters. Initially, optical microscopy images and their histograms were analyzed to determine the optical quality of the obtained layers and then histograms were created using Image Histogram Generator software. Next, the morphology, and cross-section and layer composition of the samples were evaluated. Finally, the transmission spectra of the thin films were recorded. Transmittance and reflection spectra of the UV–vis analysis were utilized to calculate the optical band gap, the extinction coefficient, and the absorption coefficient of the oxidized layers. Samples showed low transmittance (up to 40%) in the region of 400 to 1000 nm. The mean absorption coefficient varied from ~3 · 105 to ~6 · 105 1/cm and from ~2 · 105 to ~4 · 105 1/cm in the region of 2 eV to 3.5 eV. The extinction coefficient ranged from 0 to 0.11 in the region from 300 to 3000 nm. Reflectance of the samples was ~20% in the region of 1000 to 2500 nm and ranged from 20%-50% in the region of 1000 to 3000 nm. We verified the process parameters of the Cu2O structure to improve the quality as a buffer layer. On the basis of this preliminary analysis, we propose the most promising and future-oriented solutions in photovoltaic applications.
This work summarizes efficiency measurement results of a full bridge, 3 phase inverter composed of state-of-the-art Si IGBT transistors and Si or SiC diodes. Different (symmetrical and discontinuous) space vector modulation strategies were chosen in order to examine their influence (together with modulation frequency) on inverter losses. Induction machine was used as load, different load points were examined. Results clearly show, that proper modulation strategy, minimizing the switching losses of semiconductor switches, can increase the overall output efficiency at about 1% in case of both silicon and hybrid constructions. The drawback of DPWM approach is connected with the decreased quality of inverter output current. Hybrid technology can also improve the output efficiency at about 1% when compared to traditional constructions, but only in case of elevated switching frequencies. At low frequencies (below 10 kHz) modern semiconductor offer comparable results at much lower device costs.
Among the various thin film coating techniques, atomic layer deposition (ALD) has features of good controllability of the thickness, excellent step-coverage in 3-dimensional object even in the sub-nm thickness range at the relatively low deposition temperature. In this study, SnO2 thin films were grown by ALD in the variation of substrate temperatures from 150 to 250°C. Even such a low temperature may influence on the growth kinetics of the ALD reaction and thus the physical characteristics of thin films, such as crystallinity, film density and optical band gap, etc. We observed the decrease of the growth rate with increasing substrate temperature, at the same time, the density of the film was decreased with increasing temperature. Steric hindrance effect of the precursor molecule was attributed to the inverse relationship of the growth temperature and growth rate as well as the film density. Optical indirect band gap energy (~3.6 eV) of the ALD-grown amorphous SnO2 films grown at 150°C was similar with that of the literature value, while slightly lower band gap energy (~3.4 eV) was acquired at the films grown at higher temperature.