Pokročilé keramické materiály

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    Optical and electrical performance of translucent BaTiO3-BaSnO3 ceramics
    (ELSEVIER SCI LTD, 2024-08-15) Bijalwan, Vijay; Kaštyl, Jaroslav; Erhart, Jiří; Prajzler, Vladimír; Tofel, Pavel; Sobola, Dinara; Velazquez, Jose J.; Galusek, Dušan; Maca, Karel
    Lead-free piezoceramic with the composition of 0.89BaTiO(3)-0.11BaSnO(3) (BT-11BS) was prepared by solid-state reaction followed by conventional sintering achieving nearly full density. The influence of sintering temperature on electrical properties were thoroughly investigated, implying a significant role in achieving best properties, which were obtained between 1420 and 1440 degrees C. The addition of SnO2 in BaTiO3 solid solution promoted grain growth, eventually resulting in the grain sizes between 145 and 216 mu m. An ultra-high dielectric permittivity >5.0 x 10(4) and related dielectric loss of 3.1 % at similar to 40 degrees C was achieved. A high value of quasi-static piezoelectric constant (d(33)) of 693 pC/N and the converse piezoelectric constant (denoted as d(33)*) reached a value of up to 831 pm/V in the frequency range between 10 and 110 Hz. The transmittance of similar to 25 % in the visible region and similar to 40 % in the infrared region together with good electromechanical properties showcasing a unique combination for this material.
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    Comprehensive analysis of charge carriers dynamics through the honeycomb structure of graphite thin films and polymer graphite with applications in cold field emission and scanning tunneling microscopy
    (ELSEVIER, 2024-09-13) Allaham, Mohammad Mahmoud; Daradkeh, Samer; Al-Braikat, Hatem; Dallaev, Rashid; Burda, Daniel; Košelová, Zuzana; Al-Akhras, M-Ali; Jaber, Ahmad; Mousa, Marwan; Sobola, Dinara; Kolařík, Vladimír; Knápek, Alexandr
    Polymer graphite electron sources have performed satisfactorily as field emission emitters and scanning tunneling microscopy probes in the past few years. However, the emission process was characterized by limited total emission currents. This paper introduces the elemental, vibrational, electronic structure, and optical analysis of polymer graphite and glass-graphite composite field emission cathodes to study these limitations. Moreover, the field emission characteristics are studied including the changes in the potential energy barrier of the used materials and structures. Among the studied structures, the cathodes prepared from graphite thin films deposited on a micropointed glass substrate (film-GMF) showed superior performance as random field emission arrays. This includes obtaining much higher emission current values 20 times) and lower threshold voltages 1/2) compared to the results obtained from polymer graphite samples. The enhancement factor in such emitters is believed to be the three-dimensional honeycomb structure of graphite. Moreover, the study includes applying graphite coatings to tungsten nano-field emission cathodes and scanning tunneling microscopy probes, which improves the performance of such cathodes/probes in both microscopic techniques.
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    Optical Properties of YttriumOrthoferrite Films Prepared by PlasmaLaser Deposition
    (Preprints.org, 2024-08-08) Sobola, Dinara; Fawaeer, Saleh Hekmat Saleh; Kočková, Pavla; Schubert, Richard; Dallaev, Rashid; Trčka, Tomáš
    This study investigates the optical properties of Yttrium Orthoferrite thin films fabricated via plasma laser deposition. Yttrium Orthoferrite, a ferrimagnetic material known for its potential applications in spintronics and photonics, was deposited on single-crystal substrates under controlled conditions to analyze its optical characteristics. The influence of deposition time, on the film quality and optical properties was examined.
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    Comprehensive Analysis of E478 Single-Component Epoxy Resin and Tungsten-E478 Interface for Metallic-Polymer Composite Electron Source Applications
    (American Chemical Society, 2024-06-29) Allaham, Mohammad Mahmoud
    This study provides comprehensive elemental, optical, and energy gap characteristics of the E478 single-component epoxy resin. This type of epoxy resin has imperative applications in medium voltage insulation and cold field emission of electrons. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and hydrogen nuclear magnetic resonance (1H-NMR) were used to study the elemental and structural analyses, ultraviolet photoelectron spectroscopy (UPS) was used to obtain the local work function and the ionization potential energies, and ultraviolet/visible light spectroscopy (UV/VIS) was used to report the optical and energy gap characteristics of the epoxy resin being studied. Moreover, the UPS and UV/VIS analyses were merged to obtain the electron affinity of the E478 epoxy resin and to study the epoxy's energy band diagram and the tungsten-epoxy interface band structure. The results showed that the E478 epoxy resin is considered an n-type semiconductor of energy gap similar to 3.94 eV, local work function similar to 3.42 eV, ionization potential similar to 6.10 eV, electron affinity similar to 2.16 eV, and tungsten-epoxy Schottky contact barrier height similar to 2.50 eV.
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    Field Ion Microscopy of Tungsten Nano-Tips Coated with Thin Layer of the EpoxyResin
    (Preprints.org, 2024-07-30) Sobola, Dinara; AL Soud, Ammar; Knápek, Alexandr; Mousa, Marwan; Schubert, Richard; Kočková, Pavla; Škarvada, Pavel
    This paper reports results of analysis of field ion emission mechanism from tungstenepoxy composite emitters that are compared to tungsten nanofield emitters. In this context, the mechanism of emission from this type of emitters is described based on a theory of induced conductive channels. The tungsten emitters were prepared using the electrochemical polishing technique and coated with a layer of the epoxy resin. Field ion microscope (FIM) analyses are reported including the study of the emissionion density distributions from both the uncoated and coated emitters. Two forms of emission patterns have been observed in the ion emission microscopy technique describing the differences in the emission mechanism of both types of emitters. The observed results show: (a) the expected crystalline surface atomic distribution images of the field ion microscopy in the case of uncoated tungsten tips, and (b) randomly distributed emission spots that describe the locations of the induced conductive channels inside the resin coating layer.