National Repository of Grey Literature 61 records found  1 - 10nextend  jump to record: Search took 0.02 seconds. 
Histology and micro-CT study of diamond-coated metal bone implants
Potocký, Štěpán ; Ižák, Tibor ; Dragounová, Kateřina ; Kromka, Alexander ; Rezek, Bohuslav ; Mandys, V. ; Bartoš, M. ; Bačáková, Lucie ; Sedmera, David
A conformal coating of a thin diamond layer on three-dimensional metal bone implants was shown directly on stainless steel and TiAl6V4 cortical screw implant using ultrasonic and composite polymer pretreatment method. The best conformation coverage was achieved in the case of the WO3 interlayer for both stainless steel and TiAl6V4 screws. The process of osteointegration of the screw implants into rabbit femurs is evidenced by the formation of a bone edge via desmogenous ossification around the screws in less than six months after implantation. A detailed evaluation of the tissue reaction around the implanted screws shows good biocompatibility of diamond-coated metal bone implants.
Optimization of device for measurement field emission from GaN nanocrystals surface
Horák, Stanislav ; Kromka, Alexander (referee) ; Mach, Jindřich (advisor)
This diploma thesis deals with the design and optimization of the device for measurement of field emission from gallium nitride (GaN) nanocrystals surface. The first part of the thesis is the topic review, which contains the introduction to the problematics of field emissio focused on GaN. Then there were designed, constructed and optimized two versions of the device for the measurement of field emission. Through the optimization phase, the first successful test has been performed with zinc oxide (ZnO) nanowires. Simultaneously GaN nanocrystals were fabricated on the silicon substrate Si(111) with 2 nm of silicon dioxide SiO2 and also on the copper foil covered by graphene by molecular beam epitaxy (MBE). In the last chapter, there are presented the results of the measurement for emission of GaN nanocrystals. Finally, this study is comparing results with the current research in the area of field emission, which displays the improved characteristics for field emission of GaN nanocrystals on the copper foil covered by graphene.
Controlled structuring of self-assembled polystyrene microsphere arrays by two different plasma systems
Domonkos, Mária ; Ižák, Tibor ; Stolcova, L. ; Proška, J. ; Kromka, Alexander
In this study we present a successful manipulation of microspheres by reactive ion etching (RIE). A self-assembled monolayer close-packed array of monodisperse polystyrene microspheres (PM) with diameter of 471 nm was used as the primary template. The PM templates were processed in two different RIE systems: (i) capacitively coupled radiofrequency plasma (CCP) and (ii) dual plasma system which combines CCP and pulsed linear-antenna microwave plasma (PLAMWP). The influence of process conditions on the PM geometry was systematically studied by scanning electron microscopy (SEM). It was found out that choosing optimal parameters results in a tunable diameter of PM with various shapes (from spheres to pyramid-like structures) while keeping their periodic hexagonal ordering.
Influence of dispersed particles on utility properties od polyvinyl alcohol-based nanotextiles: macromechanical properties
Rácová, Z. ; Nežerka, V. ; Ryparová, Pavla ; Kromka, Alexander ; Tesárek, Pavel
The paper deals with the influence of different dispersed particles on utility properties of polyvinyl-alcohol (PVA) based nanofiber textiles. The purpose of the dispersed particles was to produce textiles of antibacterial character, and these were added into water-polymer solution, which was used for electrospinning in two various ways: in form of copper and silver ions, or in form of diamond nanoparticles. In order to assess the strength of textiles, macromechanical testing of modified PVA-based nanofiber textiles was carried out on samples with variable weight per area in range between 0.5 and 5 g/m(2). The obtained results were compared with the results of measurements on plain reference samples. The study revealed that the addition of silver ions causes the strength and stiffness reduction, the addition of copper ions has an opposite effect, while the diamond nanoparticles did not have any significant influence on the mechanical properties.\n
Wettability enhancement of polymeric and glass micro fiber reinforcement by plasma treatment
Trejbal, J. ; Šmilauer, V. ; Kromka, Alexander ; Potocký, Štěpán ; Kopecký, L.
Plasma treatments were used to modify surface properties of polyethylene terephthalate (PET) and glass micro fibers, to improve their wettability. PET fibers, having diameter of 400 μm, and glass fibers (14 μm) were exposed to low pressure oxygen plasma. A direct horizontal optical method was used for contact angle measurements on fiber surfaces submerged into distilled water. Surface morphology changes before and after treatment were characterized by scanning electron microscopy. Finally, cement paste specimens reinforced with PET and lime-based mortars reinforced with glass fibers were made and after 28 days of mixture curing tested by four-point bending tests. After oxygen plasma treatment contact angles decreased by 60 % on PET fibers and by 25 % on glass fibers in comparison with untreated fibers. Next, SEM images revealed the significant surface damages of PET fibers and minor damages of glass fibers. Both four-point tested samples reinforced with treated fibers exhibited the maximum bending strength loss about to 10 to 20 percent compared to samples with untreated reinforcement.
Comparative study on functionalization of NCD films with amine groups
Artemenko, Anna ; Kozak, Halyna ; Stuchlík, Jiří ; Biederman, H. ; Kromka, Alexander
Two plasma-based processes for functionalization of oxygen or hydrogen terminated NCD surfaces with amino groups were compared. The first process was based on deposition of thin (8 nm) amine containing plasma polymer by RF magnetron sputtering of Nylon target in Ar/N-2 working gas mixture. RF plasma treatment in NH3 for 10 minutes was used in the second process. The properties of NCD films before and after amination were characterized by scanning electron microscopy (SEM), wettability measurements, spectral ellipsometry, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and current-voltage (I-V) measurements. The presence of nitrogen (and thus amino groups) on the surface was confirmed by XPS measurements in both cases. The obtained results indicated that NCD surface functionalization from amine containing plasma polymer by RF magnetron sputtering is an alternative technological solution for successful functionalization of diamond surfaces for biosensor applications.
Correlated microscopy of electronic and material properties of graphene grown on diamond thin films
Rezek, Bohuslav ; Čermák, Jan ; Varga, Marián ; Tulic, S. ; Skákalová, V. ; Waitz, T. ; Kromka, Alexander
In this work we compare growth of graphene on diamond thin films that enable large area processing. We use films with different crystal size and surface roughness to obtain deeper insight into formation and properties of GoD. The diamond films are coated by a nm thin sputtered Ni layer and heated to 900°C in a forming gas atmosphere (H2/Ar) to initiate catalytic thermal CVD process. The samples are cleaned from residual Ni after the growth process. We employ scanning electron microscopy, Raman micro-spectroscopy and Kelvin probe force microscopy to correlate material, structural, and electronic properties of graphene on diamond. We show how grain size and grain boundaries influence graphene growth and material and electronic properties. For instance we show that the grain boundaries (with non-diamond carbon phases) in diamond films have an important role. They influence the electronic properties and they are beneficial for forming graphene on diamond higher quality.
Vascular and osseous cells in polymer structures for tissue engineering
Filová, Elena ; Bačáková, Lucie (advisor) ; Maxová, Hana (referee) ; Motlík, Jan (referee) ; Kromka, Alexander (referee)
Artificial vascular and bone prostheses are engineered as bioinert, not allowing cell attachment and growth. Our aim was to prepare materials based on natural and synthetic polymers that could modify the surface or create the bulk material of prostheses, and test their bioactivity in vitro. We prepared fibrin assemblies of various thicknesses and evaluated the adhesion, growth and differentiation of endothelial cells (EC) on these layers. We observed increased cell spreading on twodimensional fibrin assemblies and improved cell growth and maturation on thick fibrin gels. Fibrin coated with collagen I, or fibronectin, increased the adhesion area and the proliferation activity of vascular smooth muscle cells (VSMC). Synthetic polymers were based on an inert block copolymer of poly(DL-lactide) and polyethylene oxide (PDLLA-b-PEO) in which 5% or 20% of the PEO chains were grafted with Gly-Arg-Gly-Asp-Ser-Gly oligopeptide, a ligand for cell adhesion receptors. Grafting oligopeptide peptide to the cell non-adhesive copolymer restored adhesion and growth of VSMC, even in a serum-free medium. Synthetic polymers could therefore serve as artificial extracellular matrix analogues for vascular tissue repair and regeneration. Our study with human osteoblast-like MG 63 cells cultured in poly(lactic-co-glycolic acid)...
Polymeric nanofibrous scaffolds reinforced with diamond and ceramic nanoparticles for bone tissue engineering
Bačáková, Lucie ; Pařízek, Martin ; Staňková, Ľubica ; Novotná, Katarína ; Douglas, T.E.L. ; Brady, M. A. ; Kromka, Alexander ; Potocký, Štěpán ; Stránská, D.
Three types of nanofibrous scaffolds were prepared by electrospining: (1) poly(lactide-co-glycoside) (PLGA) scaffolds reinforced with 23 wt.% of diamond nanoparticles (DNPs), (2) poly(L-lactide) (PLLA) scaffolds with DNPs in concentration ranging from from 0.4 wt.% to 12.3 wt.%, and (3) PLLA scaffolds with 5 wt.% or 15 wt.% of hydroxyapatite (HAp) nanoparticles. The diameter of the nanofibers ranged between 160 and 729 nm. The nanofibers with nanoparticles were thicker and the void spaces among them were smaller. Mechanical properties of the nanoparticle-loaded scaffolds were better, as demonstrated by a rupture test in scaffolds with DNPs and by a creep behavior test in scaffolds with HAp. On PLGA scaffolds with DNPs, the human osteoblast-like MG-63 cells adhered in similar numbers and grew with similar kinetics as on pure PLGA scaffolds. Human bone marrow mesenchymal stem cells grew faster and reached higher population densities on PLGA-DNP scaffolds. However, on PLLA-based scaffolds, the activity of mitochondrial enzymes and concentration of osteocalcin in MG-63 cells decreased with increasing DNP concentration. On the other hand, the metabolic activity of MG-63 cells and content of osteocalcin in these cells were positively correlated with the HAp concentration in PLLA scaffolds. Thus, PLGA nanofibers with 23 wt% of DNPs and PLLA nanofibers with 5 and particularly 15 wt.% of HAp seem to be promising for bone tissue engineering.
Diamond coated AlGaN/GaN high electron mobility transistors - effect of deposition process on gate electrode
Vanko, G. ; Ižák, Tibor ; Babchenko, O. ; Kromka, Alexander
We studied the influence of the diamond deposition on the degradation of Schottky gate electrodes (i.e. Ir or IrO2) and on the electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs). In present study, the diamond films were selectively deposited on the AlGaN/GaN circular HEMT by focused (ellispoidal cavity reactor) and linear antenna (surface wave) microwave plasma at different temperatures from 400°C to 1100°C. The preliminary results on electrical measurements on the diamond-coated c-HEMTs showed degraded electrical properties comparing to c-HEMTs before deposition process, which was attributed to degradation of the Ir gate electrodes even at temperatures as low as 400°C. On the other hand, metal oxide gate electrode layer (IrO2) can withstand diamond CVD process even at high temperatures (~900°C) which make it suitable for fabrication of all-in-diamond c-HEMT devices for high-power applications.

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