Sdílená laboratoř RP1

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Porous-anodic-alumina-templated Ta-Nb-alloy oxide coatings via the magnetron-sputtering anodizing as novel 3D nanostructured electrodes for energy-storage applications
(Elsevier, 2024-06-26) Mozalev, Alexander; Bendová, Mária; Gispert-Guirado, Francesc; Llobet, Eduard; Habazaki, Hiroki
The Ta-Nb thin alloy films were magnetron sputter-deposited over a low-aspect-ratio nanoporous anodic-alumina template formed in 0.05 M tartaric acid solution at 250 V and modified by the pore-widening technique to enlarge the pores up to 500 nm. The alloy coated the pores evenly, thus forming a 3D continuous conducting nanofilm on the template. Partially anodizing the templated alloy in a borate buffer solution of pH 7.5 generated a compact amorphous mixed-oxide anodic film thickening proportionally to the applied voltage. An unusual two-layered structure with a sharp electrical interface revealed in the 3D oxide films anodized to 30–130 V, comprising a low-resistivity layer superimposed on the high-resistivity layer, is explained by an immobile negative space charge in the outer film part. The air-annealing at moderate temperatures releases the space charge and transforms the two layers into a high-resistivity single layer having substantially improved dielectric properties and thermostable (up to 250 deg) capacitance of 1.2 F cm2 achieved for the film anodized to practical 50 V. The 3D films having up to 4.5 times enlarged effective surface area can be utilized as novel metal/oxide nanostructured electrodes for electrolytic microcapacitors suitable for classical electronic circuits and energy-storage applications.
XPS characterization of metal-oxide nanocolumn arrays via anodizing Al/Nb/Mo metal layers
(TANGER LTD, 2024-01-01) Bendová, Mária; Prášek, Jan; Mozalev, Alexander
Molybdenum oxides exhibit numerous electronic properties thanks to the ability of Mo to possess various oxidation states and coordinations. Molybdenum oxides are thus attractive for applications in energy storage, conversion, electrochromic, gas sensing, or superconducting devices. The nanostructuring of molybdenum oxides, controlled through the preparation conditions, is advantageous for enhancing the material's properties. The so-called porous-anodic-alumina (PAA)-assisted anodizing, based on the anodic oxidation of a metal layer through a PAA overlayer, may also be a way to grow molybdenum-oxide nanocolumn arrays if their stability in water-containing electrolytes can be secured. To take on the challenge, we envisioned mixing MoOx with the oxide of a different metal (Nb), by placing a thin interlayer of Nb between the Al and Mo in the precursor thin-film stack. The arrays were prepared from the magnetron-sputtered Al/Nb/Mo trilayers by anodizing at 46 V, then re-anodizing to 180 V, followed by selective dissolution of the PAA overlayer. Detailed XPS characterization confirmed that various Mo species were present in the column material, with a total amount of Mo reaching 16 at.% (Mo+Nb = 100%). The fitting of the narrow-scan Nb 3d and Mo 3d spectra showed that Mo6+, Mo5+, and Mo4+, in various ratios, were present at the column surface material, whereas Nb2O5 was almost entirely stoichiometric. Further investigation is underway to understand the formation-structure-morphology relationship and explore the functional properties of the novel nanoarrays.
Energy gap measurements based on enhanced absorption coefficient calculation from transmittance and reflectance raw data
(Elsevier, 2024-01-18) Allaham, Mohammad Mahmoud; Dallaev, Rashid; Burda, Daniel; Sobola, Dinara; Nebojsa, Alois; Knápek, Alexandr; Mousa, Marwan; Kolařík, Vladimír
The absorption coefficient plays an important role in studying and characterizing semiconducting materials. It is an important parameter to study the mechanism of photons absorption within the structure of the studied material. Thus, it helps to study the several types of charge carrier transport along with the energy band structure and its defects. In literature, a formula was reported to precisely calculate the absorption coefficient from raw data of transmittance and reflectance of electromagnetic radiation. However, the reported formula has several issues limiting its validity in the literature. In this paper, we provide a more mathematically accurate form of this equation to precisely obtain the absorption coefficient from the raw data, by considering the total internal reflection at the different interfaces. Moreover, the equation is tested by simulated data and is applied to study the optical characteristics of a single-component epoxy resin from its transmittance and reflectance raw data.
Near-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, Tomáš
The 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.
Synthesis 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.

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