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Nanostructures for Achieving Selective Properties of a Thermophotovoltaic Emitter
(MDPI, 2021-08-19) Šimonová, Lucie; Matějka, Milan; Knápek, Alexandr; Králík, Tomáš; Pokorná, Zuzana; Mika, Filip; Fořt, Tomáš; Man, Ondřej; Škarvada, Pavel; Otáhal, Alexandr; Čudek, Pavel
This paper focuses on the research and development of a suitable method for creating a selective emitter for the visible and near-infrared region to be able to work optimally together with silicon photovoltaic cells in a thermophotovoltaic system. The aim was to develop a new method to create very fine structures beyond the conventional standard (nanostructures), which will increase the emissivity of the base material for it to match the needs of a selective emitter for the VIS and NIR region. Available methods were used to create the nanostructures, from which we eliminated all unsuitable methods; for the selected method, we established the optimal procedure and parameters for their creation. The development of the emitter nanostructures included the necessary substrate pretreatments, where great emphasis was placed on material purity and surface roughness. Tungsten was purposely chosen as the main material for the formation of the nanostructures; we verified the effect of the formed structure on the resulting emissivity. This work presents a new method for the formation of nanostructures, which are not commonly formed in such fineness; by this, it opens the way to new possibilities for achieving the desired selectivity of the thermophotovoltaic emitter.
Water-Soluble Copper Ink for the Inkjet Fabrication of Flexible Electronic Components
(MDPI, 2021-04-26) Nabi, Shabanov; Rabadanov, Kamil; Suleimanov, Sagim; Amirov, Akhmed; Isaev, Abdulgalim; Sobola, Dinara; Murliev, Eldar; Asvarova, Gulnara
The aim of this work is preparation and investigation of copper conductive paths by printing with a different type of functional ink. The solutions based on copper-containing complex compounds were used as inks instead of dispersions of metal nanoparticles. Thermal characteristics of synthesized precursors were studied by thermogravimetry in an argon atmosphere. Based on the comparison of decomposition temperature, the dimethylamine complex of copper formate was found to be more suitable precursor for the formation of copper layers. Structure and performance of this compound was studied in detail by X-ray diffraction, test of wettability, printing on flexible substrate, and electrical measurements.
Effect of extrusion process and various elongation ratios on the structural and dielectric properties of PVDF-based copolymer containing micro and nano-sized crystallites
(TANGER Ltd., 2021-07-11) Mrlík, Miroslav; Cvek, Martin; Osička, Josef; Maslowski, Marcin; Tofel, Pavel
In this contribution, the effect of the extrusion process of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) with the subsequent elongation/poling on its structural and dielectric properties is presented. The extrusion can be understood as continuous processing of polymer melts in the large scale (in comparison to solvent casting), when the thickness of the final product can be varied depending on the final operation conditions. Herein, the PVDF-co-HFP sheets of 5 cm in width were extruded using a single screw extruder. The fabricated sheets were cooled down and then, they were cut to the stripes and subsequently stretched to various elongations (100, 200 and 500 %) using a universal tensile testing machine. Such samples were investigated using FTIR in order to determine the effect of the elongation process on the transformation of the alpha-phase to the beta-crystalline phase. The extend of the electro-active beta-phase was quantified and its impact on the dielectric properties was investigated. The results clearly demonstrated that the elongation has a crucial effect on the final dielectric properties of the PVDF-co-HFP.
Crack resistance of bismuth ferrite films obtained on a flexible substrate
(EDP Sciences, 2021-07-26) Ramazanov, Shikhgasan; Ţălu, Ştefan; Sobola, Dinara; Orudzhev, Farid; Ramazanov, Gusejn; Selimov, Daud; Kaspar, Pavel; Macků, Robert; Nazarov, Anton
Ultrathin BiOx and FeOx layers were obtained by Atomic Layer Deposition (ALD) on the surface of a flexible Kapton substrate (poly (4,4’-oxydiphenylene-pyromellitimide)) at a temperature of 250 °C. The layer thickness was 50 - 100 nm. Surface morphology, electrical polarization, and mechanical properties were investigated by Atomic Force Microscope, Piezoelectric Force Microscopy and Force Modulation Microscopy. Chemical analysis was performed by X-ray Photoelectron Spectroscopy, where the formation of Bi2O3 and Fe2O3 phases, as well as intermediate phases in the Bi-Fe-O system, was observed. With a small increase in the Bi content of the film, the BFO / Kapton structure becomes more crack resistant. Modification of the Kapton surface with bismuth and iron oxides showed that such a composition exhibits multiferroic behavior.
The effects of molecular and processing parameters on energy harvesting capability of PVDF-based nanogenerators
(TANGER LTD, 2021-10-18) Cvek, Martin; Osička, Josef; Srnec, Peter; Mrlík, Miroslav; Tofel, Pavel
In the research of the alternative vibration sensing systems, the major potential is attributed to piezoelectric materials that can generate the electrical output from the waste vibration sources of the industrial machines. Poly(vinylidene fluoride) (PVDF), mostly in the electroactive beta-phase, is a great option due to its excellent piezoelectric properties and good flexibility. The beta-phase PVDF can be obtained by simple stretching of the alpha-phase PVDF films, and the conditions of this process are well documented. Surprisingly, the implications of molecular parameters of the PVDF have not been addressed yet. This study investigates the effect of the molecular weight (Mw) of the PVDF on the beta-phase development and consequential vibration sensing capabilities after uniaxial stretching. The successful phase transformation was confirmed using FTIR and XRD. In the FTIR spectra, a typical alpha-phase peak at 762 cm(-1) diminished giving rise to the beta-phase peak at 840 cm(-1) after the stretching. The results also showed a remarkable impact of the Mw on d33 coefficient making Mw an important parameter that should not be overlooked in designing the PVDF-based sensing elements. The obtained data are highly important for the optimization of the PVDF-based vibration sensors applicable in the efficient structural and health monitoring nanosystems.

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