Národní úložiště šedé literatury Nalezeno 16 záznamů.  1 - 10další  přejít na záznam: Hledání trvalo 0.00 vteřin. 
Nanomechanical testing of an a-C:N nanolayer prepared by ion beam assisted deposition on Ti.sub.6./sub.Al.sub.4./sub.V alloy
Vlčák, P. ; Šepitka, J. ; Horaždovský, T. ; Jirka, Ivan ; Gregora, Ivan ; Němec, M.
We applied ion beam assisted deposition for preparing a-C:N nanolayers on Ti6Al4V alloy. A Hysitron TI 950 TriboIndenter (TM) nanomechanical test instrument was used to assess the depth profiles of the mechanical properties on modified titanium substrates. Two methods were employed : a) quasistatic partial unload, and b) dynamic Continuous Measurement of X (CMX). The average nanoindentation hardness increased from HIT similar to 5GPa for a reference sample to HIT similar to 8.6 GPa for a sample coated by an a-C nanolayer, and to HIT similar to 11.5 GPa for a sample coated by an a-C:N nanolayer. The average storage modulus of the sample coated by a-C:N increased from E' similar to 130 GPa (reference sample) to E' similar to 155 GPa. The storage modulus of the sample coated by the a-C nanolayer was less than the storage modulus of the titanium substrate.
Modeling of nanofibers interaction with the environment
Klicmanová, I. ; Sveshnikov, Alexey
Nanomaterials change our life. Every day they find applications in new branches of technology. At the same time, some branches of technology, like civil engineering, are rather conservative and do not accept new approaches lightly. Nanotextiles exhibit a number of qualities that make them a promising material for civil engineering applications. They can potentially play a role of filters, protective layers, armature and others. Properties of the nanotextiles can be significantly influenced by parameters of technological process. Pure experimental search of the optimal technological parameters to achieve the desired properties of the final material can be very tedious. Thus, a theoretical dependence of the properties of the nanotextile on parameters of the technological process must be established. Two independent tasks must be solved for this: the dependence of nanotextile structure on technological parameters, and determination of physical, chemical or biological properties of a nanotextile of a given structure. In this paper we discuss steps necessary for the solution of the second task.
Initial study of structure of nanofiber textiles and the creation of its model
Havrlík, M. ; Sveshnikov, Alexey
In this research, the structure of the fabrics was analyzed using an electron scanning microscope Tescan Maia 3. Two sets of the experiments have been carried out. In the first experiment the surface structure of the samples was studied. Photos created by SEM were analyzed using program Atlas and image editor GIMP. In this set of the experiments the initial parameters for the creation of a digital 2D model of a single layer have been determined (fiber size distribution, pore size and curvature of the fibers). In the second set of the experiments cross sections of nanofiber textiles were made in order to study the inner structure of the fabric. This information allows evaluation of the total number of 2D layers in the model and, thus, is very important for future creation of a 3D model of the fabric.
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.
Scanning thermal microscopy of thermoelectric pulsed laser deposited nanostructures
Vaniš, Jan ; Zelinka, Jiří ; Zeipl, Radek ; Jelínek, Miroslav ; Kocourek, Tomáš ; Remsa, Jan ; Navrátil, Jiří
New materials with high possible figure of merit ZT are of high interest as a promising candidates for thermoelectric applications such as energy harvesting. Miniaturization of such systems tends toward developing of the suitable characterization method with nanometer resolution ability. In our contribution, we present the development and experimental results of a simple scanning probe microscopy method for the relative thermal conductivity characterization. The possibility of the setup is demonstrated on the set of different thin thermoelectric layers grown from hot pressed targets by pulsed laser deposition on the reference Si substrate. All the measurements were performed on the commercial Veeco Multimode scanning AFM/STM microscope with home developed controller and by using PicoCal Inc. bolometer probes with tungsten resistive path. All the experiments were done in the air at the ambient condition. Additional sample treatment for the measurement will be also briefly described
Calculations of nanocrystalline diamond-covered waveguides based on amorphous silicon
Jirásek, Vít ; Prajzler, Václav ; Remeš, Zdeněk
Nanocrystalline diamond (NCD) coatings on planar waveguides (WG) in the IR region allow to design optical sensors sensitive to absorbers like proteins or other biomolecules. In this contribution, we present a 2D model of a multi-layer WG developed under FEM (finite element method) simulation software Comsol Multiphysics. The model is based on the modified wave equation solved in the frequency domain and includes optical absorption. It was found that for the single-mode WG working in the narrow region of 1550-2000 nm the silicon thickness must be 150-320 nm. It was found that in order to keep a reasonable signal attenuation, the NCD film must be prepared with the optical absorption coefficient lower than 10 cm-1, being a rather challenging task. Dependencies of the signal attenuation on the NCD film thickness, absorbing layer height, its absorption coefficient and exciting wavelengths are presented.\n
Growth of human adipose-derived stem cells on Ti-6Al-4V alloy with various surface modifications
Kročilová, Nikola ; Bačáková, Lucie ; Pařízek, Martin ; Havlíková, Jana ; Motarjemi, H. ; Molitor, M. ; Gabor, R. ; Marvan, J.
Adipose-derived stem cells (ASCs) are of a great importance for bone tissue engineering. We compared ASCs obtained by liposuction under two pressures (-200 mmHg and -700 mmHg). The number and proliferation activity of cells isolated under -700 mmHg (ASC-H) were higher than in cells isolated under -200 mmHg (ASC-L). However, the ASC-L was more active in osteogenic differentiation, as manifested by a higher intensity of fluorescence of alkaline phosphatase and osteocalcin in these cells. The adhesion and growth of ASCs were then studied on Ti-6Al-4V samples either unmodified (K, roughness parameter R-a = 280 nm) or modified by shot blasting and tarnishing A, R-a = 200 nm), vibratory finishing (B, R-a = 100 nm) and vibratory finishing, shot blasting and polishing (C, R-a = 80 nm). All modified samples were more wettable than the K samples. On day 1 after seeding, the size of cell spreading area on some modified samples was lower than on K samples, namely on B samples in ASC-L, on B and C in ASC-H and on A in control MG-63 cells. On day 3, the cell number on some modified samples became higher than on K samples, namely on C samples (ASC-L), on B (ASC-H) and on B and C s (MG-63 cells). On day 7, the numbers of ASC-H and MG-63 cells on all modified samples evened out and became significantly higher than on K samples. On ASC-L samples, the highest cell numbers were obtained on A samples. Thus, all studied modifications of Ti-6Al-4V enhanced growth of ASCs and human osteoblast-like MG-63 cells.
Growth and differentiation of human osteoblast-like cells on TI-6AL-4V alloy modified with anodization
Doubková, Martina ; Bačáková, Lucie ; Pařízek, Martin ; Vandrovcová, Marta ; Musílková, Jana ; Lisá, Věra ; Gabor, R. ; Marvan, J.
Titanium and its alloys are widely used as hard tissue implants for their high biocompatibility and suitable physical properties. Along with other surface treatment methods, anodization technique is known to enhance osseointegration. The aim of this study is to evaluate the adhesion, growth and osteogenic differentiation of human osteoblast-like SAOS-2 cells on Ti-6Al-4V samples anodized in electrolytes composed of a stable volume of KOH (336.48 g/l) and variable volumes of liquid glass (124.47 g/l, 84,12 g/l and 37.38 g/l; samples s5, s6 and s7, respectively). Non-anodized Ti-6Al-4V samples, cell culture polystyrene (PS) and microscopic glass coverslips served as control materials. On days 2 and 4 after seeding, the cell number did not differ significantly among the tested samples. However, on day 7, the cell number on s6 samples reached the lowest values, which could be attributed to a non-homogeneous TiO2 film on s6 samples formed during anodization. Nevertheless, the osteogenic differentiation, estimated by the intensity of fluorescence of collagen I in cells grown in a differentiation medium, was the highest on s6 samples. On s5 samples, coated with homogeneous TiO2 films, both cell numbers and intensity of fluorescence of collagen I was relatively high. The bone matrix mineralization, evaluated by Alizarin Red staining, was the highest on s5 samples in standard culture medium, and similar on all tested samples in differentiation medium. Thus, the surface modification of s5 samples could be considered the most suitable for application in bone implants.
Experimental and Theoretical Comparative Study of Monolayer and Bulk MoS2 under Compression
del Corro, Elena ; Morales-García, A. ; Peňa-Alvarez, M. ; Kavan, Ladislav ; Kalbáč, Martin ; Frank, Otakar
Recently, a new family of 2D materials with exceptional optoelectronic properties has stormed into the scene of nanotechnology, the transition metal dichalcogenides (e.g., MoS2). In contrast with graphene, which is a zero band gap semiconductor, many of the single layered materials from this family show a direct band-gap in the visible range. This band-gap can be tuned by several factors, including the thickness of the sample; the transition from a direct to indirect semiconductor state takes place in MoS2 when increasing the number of layers from 1 towards the bulk. Applying strain/stress has been revealed as another tool for promoting changes in the electronic structure of these materials; however, only a few experimental works exist for MoS2. In this work we present a comparative study of single layered and bulk MoS2 subjected to direct out-of-plane compression, using high pressure anvil cells and monitoring with non-resonant Raman spectroscopy; accompanying the results with theoretical DFT studies. In the case of monolayer MoS2 we observe transitions from direct to indirect band-gap semiconductor and to semimetal, analogous to the transitions observed under hydrostatic pressure, but promoted at more accessible pressure ranges (similar to 25 times lower pressure). For bulk MoS2, both regimes, hydrostatic and uniaxial, lead to the semimetallization at similar pressure values, around 30 GPa. Our calculations reveal different driving forces for the metallization in bulk and monolayer samples.
Bouša, Milan ; Kalbáč, Martin ; Jirka, Ivan ; Kavan, Ladislav ; Frank, Otakar
The transfer of graphene prepared by Chemical Vapor Deposition (CVD) from metal catalyst to target substrate is an important step in preparing desirable nanoscale structures in various fields of science, and thus searching for fast, cheap and clean method attracts great interest. Investigation of mechanical properties of graphene, which are crucial for applications in flexible electronics, performed on bendable synthetic materials, requires a transfer technique using polymers soluble in aliphatic solvents harmless for target polymer substrates. In this study we explore a dry technique using polydimethylsiloxane (PDMS) as stamping polymer and polyisobutylene (PIB) layer as graphene-support polymer. After the transfer PDMS is peeled off and PIB is dissolved in hexane, hence this method fulfils the above mentioned prerequisite. The effectiveness of this transfer was examined by scanning electron microscopy, optical microscopy and Raman microspectroscopy including micro-mapping, and finally by X-ray photoelectron spectroscopy. With all methods carried out, it was found that this sort of stamp-technique is suitable for a high precision transfer of small grains of CVD graphene onto polymer substrates with large yields and similar purity compared to poly(methylmethacrylate) (PMMA)based transfer methods. However, it introduces substantial quantity of surface discontinuities, and therefore this is not a proper method for large scale applications.

Národní úložiště šedé literatury : Nalezeno 16 záznamů.   1 - 10další  přejít na záznam:
Chcete být upozorněni, pokud se objeví nové záznamy odpovídající tomuto dotazu?
Přihlásit se k odběru RSS.