Ústav fyzikálního inženýrství
Browse
Recent Submissions
- ItemElectrical properties of epoxy/graphite flakes microcomposite at the percolation threshold concentration(IOP Publishing Ltd, 2024-04-17) Alsoud, Ammar Awadallah Ahmad; Daradkeh, Samer; Shaheen, Adel A; Al-Hroub, Qasim Amjad; Knápek, Alexandr; Mousa, Marwan; Sobola, DinaraThe electrical properties and activation energy of epoxy/graphite flakes (GFs) micro-composite with different content of GFs (0.0625-1 wt%) were studied for electrical properties using Novocontrol Alpha Analyser (10-2 Hz-107 Hz). GFs sizes ranged from (100 nm to 10 mu m). The analysis was performed by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), visible spectrum reflectance spectra (VIS) spectra, and Fourier Transform Infrared spectra (FTIR) spectroscopy. Increasing GFs content caused multiple changes in electrical characteristics. At 0.0625 wt%, all electrical properties noticeably increased. But at 0.125 to 0.25 wt%, immobilized nanolayers were formed leading to decreased permittivity, dielectric loss (tan(delta)), quality factor (Q-factor), capacitance, conductivity, and figure of merit (F-factor). At 0.25 wt%, the epoxy microcomposite had lower permittivity, tan(delta), conductivity, and capacitance compared with unfilled epoxy. With 0.5 wt% of GFs, signified the percolation threshold, initiating a rise in permittivity, conductivity, capacitance, and tan(delta), accompanied by the closer proximity of grain boundaries, facilitating the formation of conductive channels. At a concentration of 1 wt% of GFs, the establishment of continuous interfacial conductive pathways resulted in a remarkable augmentation of all dielectric properties. The Cole-Cole analysis has been employed to investigate variations in epoxy/GFs microcomposites based on concentration levels.
- ItemClassification of diverse plastic samples by LIBS and Raman data fusion(Elsevier, 2024-04-15) Holub, Daniel; Palásti, Dávid Jenő; Fintor, Krisztian; Pořízka, Pavel; Galbács, Gábor; Kaiser, JozefThe plastic production and usage in the world is steadily increasing. This leads to increased amounts of plastic waste. Most of the waste could be potentially recycled, but only 14 % of plastic waste is recycled. In order to increase the share of recycling in plastic waste management, the recycling process should be completely automated. The problematic part of sorting is being solved by either manual (labor-intensive) or spectroscopy-based (still in development) methods. In this work, we propose the data fusion of Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy as a fast, robust, and reliable way to sort/classify any potential polymer material. The sample set of this work consists of several types of polymers in clear, colored, and even mixture versions. So far, no LIBS/Raman classification works involved all these categories in one experiment. Additionally, the low and medium level of data fusion is discussed, and the performance is compared. By using LIBS and Raman data fusion method and both linear and nonlinear chemometric techniques, increased accuracy reaching more than 98 % in the classification of investigated plastic samples was achieved, which was a significant improvement when compared with singular methods classification accuracy.
- ItemNear-field digital holography: a tool for plasmon phase imaging(Royal Society of Chemistry, 2018-12-07) Dvořák, Petr; Kvapil, Michal; Bouchal, Petr; Édes, Zoltán; Šamořil, Tomáš; Hrtoň, Martin; Ligmajer, Filip; Křápek, Vlastimil; Šikola, TomášThe knowledge of the phase distribution of near electromagnetic field has become very important for many applications. However, its experimental observation is still technologically very demanding task. In this work, we propose a novel method for the measurement of the phase distribution of near electric field based on the principles of phase-shifting digital holography. In contrast with previous methods the holographic interference occurs already in the near field and the phase distribution can be determined purely from the scanning near-field optical microscopy measurements without need of additional far-field interferometric methods. This opens a way towards onchip phase imaging. We demonstrate the capabilities of the proposed method by reconstruction of the phase difference between interfering surface plasmon waves and by imaging the phase of single surface plasmon wave. We also demonstrate a selectivity of the method towards individual components of the field.
- ItemSynthesis Dynamics of Graphite Oxide(Elsevier, 2018-05-10) Bannov, Alexander G.; Manakhov, Anton; Shibaev, Alexander A.; Ukhina, A.V.; Polčák, Josef; Maksimovskii, E. A.Graphite oxide synthesis dynamics were investigated using a sampling technique. The synthesis of graphite oxide was carried out by a modified Hummers’ method. Small samples of the solid phase (30–50 mg) were collected from the reaction mixture and analyzed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, energy dissipative X-ray spectroscopy, and X-ray photoelectron spectroscopy. The strongest oxidation was detected 10 min after the start of the synthesis, i.e., after the addition of KMnO4, when the formation of the graphite oxide phase with intercalated guest molecules begins. The intercalation of graphite started after 30 min of synthesis when the temperature was increased to 35°C. The addition of ice into the reaction mixture leads to the increase in the COOH group concentration, whereas the concentration of C=O groups slightly changes, and the concentration of the C–O and C=O groups remains almost constant. It was found that the degree of oxidation of graphite oxide exhibited complex change, and H2O2 plays a significant role not only in the removal of impurities but also in the increase in the GO oxidation degree that is reflected by a higher concentration of oxygen-containing functional groups. Differential scanning calorimetry and thermogravimetric analysis data confirmed that the additions of ice and H2O2 induce the stronger formation of surface functional groups instead of intercalated guest species.
- ItemPulsed laser deposition of Sb2S3 films for phase-change tunable nanophotonics(IOP Publishing Ltd, 2024-01-08) Kepič, Peter; Liška, Petr; Idesová, Beáta; Caha, Ondřej; Ligmajer, Filip; Šikola, TomášNon-volatile phase-change materials with large optical contrast are essential for future tunable nanophotonic applications. Antimony trisulfide (Sb2S3) has recently gained popularity in this field due to its low absorption in the visible spectral region. Although several Sb2S3 deposition techniques have been reported in the literature, none of them was optimized with respect to stoichiometry, lowest possible absorption, and large refractive index contrast (Delta n) upon the phase change. Here we present a comprehensive multi-parameter optimization of pulsed laser deposition of Sb2S3 towards this end. We correlate the specific deposition with the resulting compositional and optical properties and report parameters leading to films with extraordinary qualities (Delta n = 1.2 at 633 nm). Additionally, we suggest crystal orientations and vibrational modes associated with the largest change in the refractive index and propose them as useful large-scale indicators of the Sb2S3 switching contrast.