Pokročilé keramické materiály

Browse

Recent Submissions

Now showing 1 - 5 of 66
  • Thumbnail Image
    Item
    Optical Properties of Yttrium Ferrite Films Prepared by Pulse Laser Deposition
    (MDPI, 2024-11-18) Sobola, Dinara; Fawaeer, Saleh Hekmat Saleh; Kočková, Pavla; Schubert, Richard; Dallaev, Rashid; Trčka, Tomáš
    This study investigates the optical properties of yttrium ferrite thin films fabricated via pulse 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. Atomic force microscopy in contact mode revealed surface roughness variations up to 35 nm, indicating the films' ability to cover substrate defects. Reflectance measurements determined the optical band gap, which decreased from 3.17 eV for thinner films (44 nm) to 2.91 eV for thicker films (93 nm). Forbidden electronic transitions were also observed, attributed to heteroepitaxial growth and phonon interactions. These results demonstrate the effect of film thickness on morphology and optical properties, making YFeO3 films promising for a range of optoelectronic applications.
  • Thumbnail Image
    Item
    A Comparative Study of the Impact of La2O3 and La2Zr2O7 Dispersions on Molybdenum Microstructure, Mechanical Properties, and Fracture
    (SPRINGER, 2024-10-23) Tkachenko, Serhii; Slámečka, Karel; Bednaříková, Vendula; Remešová, Michaela; Gejdoš, Pavel; Ksenzova, Olha; Valášek, Daniel; Dvořák, Karel; Šulák, Ivo; Gálíková, Markéta; Baláž, Matej; Deák, Andréa; Cihlář, Jaroslav; Čelko, Ladislav
    We report, for the first time, the effect of lanthanum zirconate (La2Zr2O7) particles on the microstructure and mechanical behavior of an experimental molybdenum oxide dispersion-strengthened alloy. The focus was on the preparation of the novel Mo-La2Zr2O7 composite using high-energy ball milling and spark plasma sintering and on the comparison of its microstructural and mechanical properties with pure Mo and Mo-La2O3 ODS alloy counterparts. Mechanical properties were assessed using a Vickers hardness test at room temperature and a three-point flexural test in the temperature range from - 150 to 150 degrees C. The microstructure of the studied materials and their fracture behavior were evaluated using x-ray diffraction, energy-dispersive x-ray spectroscopy, and scanning electron and transmission electron microscopy. The strengthening effect of La2Zr2O7 particles was found to be lower than that of La2O3 particles, resulting in a 30-35% lower yield stress and flexural strength of the Mo-La2Zr2O7 alloy compared to the Mo-La2O3 alloy. The experimental Mo-La2Zr2O7 alloy exhibited low plasticity and no distinct ductile-to-brittle transition temperature (DBTT) in the tested temperature range, unlike pure Mo and the Mo-La2O3 alloy, which had the DBTT of 63 and 1 degrees C, respectively. Fracture occurred mainly in a brittle intergranular manner in the entire testing temperature range, while the counterpart materials showed localized plastic stretching at grain boundaries and within grains at and above the transition region. The observed behavior was primarily related to lower strengthening and brittleness as well as less effective grain boundary purification.
  • Thumbnail Image
    Item
    Spectroscopic study for the role of polymer binding agent in the quasi-harmonic field emission behavior of polymer graphite field emission cathodes
    (IOP Publishing Ltd, 2025-02-17) Allaham, Mohammad Mahmoud; Daradkeh, Samer Issa Abdel Razzaq; Košelová, Zuzana; Dallaev, Rashid; Sobola, Dinara; Knápek, Alexandr
    Graphite-based microcathodes have shown significant performance when operated as cold field emission electron sources. Specifically mentioned, cathodes that have been prepared from highly ordered pyrolytic graphite and polymer graphite pencil leads. Such cathodes are characterized by low operating voltages, a long lifetime, a cheap fabrication price, and a stable emission current. Recently, it was shown that polymer graphite cold field emission cathodes have a unique quasi-harmonic field emission behavior, where the process included emission of pulses of electrons with relatively higher emission current values. However, this behavior has not been reported for other graphite-based materials. In this paper, we study the effects of the polymer binding agent on the charge carriers' flow through the surface of polymer graphite using Raman-current spectroscopy. The results from polymer graphite were then compared to cathodes prepared from colloidal graphite conductive paint when deposited on a glass substrate. The results showed that the I(D)/I(G) ratio of polymer graphite had a fluctuating behavior, which was not the case for colloidal graphite, which had a more stable structure.
  • Thumbnail Image
    Item
    Comparative analysis of surface layer functionality in STM and AFM probes: Effects of coating on emission characteristics
    (SLOVAK UNIV TECHNOLOGY, 2024-08-01) Knápek, Alexandr; Allaham, Mohammad Mahmoud; Košelová, Zuzana; Burda, Daniel; Podstránský, Jáchym; Mousa, Marwan S. Mousa; Sobola, Dinara
    This study compares different types of scanning probe microscopy (SPM) probes according to the function of the surface layer at the tip apex. Three main types of SPM probes were analyzed: scanning tunneling microscopy (STM) tungsten probes, conductive atomic force microscopy (AFM) probes, and non-conductive AFM probes. The tungsten STM probes were coated with a graphite layer to simulate the effects of carbonization. The tested AFM probes were specifically NenoProbe conductive AFM probes (platinum-coated tip) and Akiyama non-conductive AFM probes coated with gold. The gold coating is intended to improve surface conductivity and help achieve a homogeneous, oxidation-resistant surface. The three samples were measured in a field emission microscope to study their current-voltage characteristics. The obtained current-voltage characteristics were tested and analyzed by the Forbes field emission orthodoxy test, providing the field emission parameters that correlate with the state of the scanning probe tip. In this study, the most important parameter is the formal emission area parameter, which indicates the formal tunneling current density through the probe tip-sample nanogap. For an STM tip, this reflects the size and shape of the region from which electrons tunnel to the sample surface. If this area is larger than expected or desired, it may indicate problems with tip function or tip wear. This information is critical for evaluating the performance and accuracy of the STM tip and can help diagnose problems and optimize its function.
  • Thumbnail Image
    Item
    Porous silica-doped calcium phosphate scaffolds prepared via in-situ foaming method
    (ELSEVIER SCI LTD, 2024-11-01) Šiška Virágová, Eliška; Novotná, Lenka; Chlup, Zdeněk; Šťastný, Přemysl; Šárfy, Pavlína; Cihlář, Jaroslav; Kučírek, Martin; Benák, Leoš; Streit, Libor; Kocanda, Jan; Sklenský, Jan; Filipovič, Milan; Repko, Martin; Hampl, Aleš; Koutná, Irena; Částková, Klára
    The effect of silica (SiO2) addition (0 wt%-20 wt%) on the microstructural and mechanical properties, as well as the in vitro response of calcium phosphate scaffolds for potential application in bone tissue engineering (BTE) was investigated in this research. Scaffolds characterized by high porosity (77%-88 %) and interconnected spherical pores with a broad range of pore sizes (5-600 mu m) were fabricated using in-situ foaming method. Incorporated silica affected the phase transformation of hydroxyapatite (HA) to beta-tricalcium phosphate (beta-TCP) and led to the development of new crystalline silica-rich phases like silicocarnotite and wollastonite. The reinforcement of silica became apparent during the tests of mechanical properties. Scaffolds with 5 wt% of SiO2 exhibited compressive strength (1.13 MPa) higher than pure HA scaffolds (0.93 MPa). Bone bonding potential of the materials was tested in simulated body fluid (SBF), demonstrating this potential in silica-doped samples. Additionally, degradation experiments showed gradual material degradation, making it suitable for BTE applications. Furthermore, cell culture studies using human mesenchymal stromal cells (MSC) confirmed the scaffold's non- toxicity and provided insights into how the silica content influences cell viability, morphology, and osteogenic potential. The findings of this study offer valuable insights into the design and development of advanced scaffolds with tailored properties for effective BTE applications.