Příprava a charakterizace nanostruktur
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- 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.
- ItemW18O49 Nanowhiskers Decorating SiO2 Nanofibers: Lessons from In Situ SEM/TEM Growth to Large Scale Synthesis and Fundamental Structural Understanding(AMER CHEMICAL SOC, 2023-12-05) Kundrát, Vojtěch; Bukvišová, Kristýna; Novák, Libor; Průcha, Lukáš; Houben, Lothar; Zálešák, Jakub; Vukusic, Antonio; Holec, David; Tenne, Reshef; Pinkas, JiříTungsten suboxide W18O49 nanowhiskers are a material of great interest due to their potential high-end applications in electronics, near-infrared light shielding, catalysis, and gas sensing. The present study introduces three main approaches for the fundamental understanding of W18O49 nanowhisker growth and structure. First, W18O49 nanowhiskers were grown from gamma-WO3/a-SiO2 nanofibers in situ in a scanning electron microscope (SEM) utilizing a specially designed microreactor (mu Reactor). It was found that irradiation by the electron beam slows the growth kinetics of the W18O49 nanowhisker, markedly. Following this, an in situ TEM study led to some new fundamental understanding of the growth mode of the crystal shear planes in the W18O49 nanowhisker and the formation of a domain (bundle) structure. High-resolution scanning transmission electron microscopy analysis of a cross-sectioned W18O49 nanowhisker revealed the well-documented pentagonal Magn & eacute;li columns and hexagonal channel characteristics for this phase. Furthermore, a highly crystalline and oriented domain structure and previously unreported mixed structural arrangement of tungsten oxide polyhedrons were analyzed. The tungsten oxide phases found in the cross section of the W18O49 nanowhisker were analyzed by nanodiffraction and electron energy loss spectroscopy (EELS), which were discussed and compared in light of theoretical calculations based on the density functional theory method. Finally, the knowledge gained from the in situ SEM and TEM experiments was valorized in developing a multigram synthesis of W18O49/a-SiO2 urchin-like nanofibers in a flow reactor.
- ItemBismuth, by high-sensitivity low energy ion scattering(AIP Publishing, 2023-12-01) Vaníčková, Elena; Průša, Stanislav; Šikola, TomášLow energy ion scattering is an analytical technique with extreme surface sensitivity. It enables qualitative and quantitative elemental analy-sis of the outermost atomic layer. Straightforward quantification is possible by using well-defined reference samples, as the measured signal is related to known surface atomic concentration. Bi, like Pb, exhibits strong oscillatory behavior of backscattered ion yield when primary ion beam energy is varied. Here, we present the spectra of bismuth obtained by scattering of 4He+ ions in a wide range of energies (0.5-6.0 keV). These should cover a regularly used range of energies for He analysis and serve as standards or reference spectra for analysis of bismuth if the scattering angle is 145 degrees or similar. For this purpose, high-purity foil cleaned by ion sputtering was used. The sensitivity of the instrument in use (high-sensitivity low energy ion scattering spectrometer) is defined by the 3 keV4He+ spectrum of copper. The related atomic sensitivity and relative sensitivity factors are determined.