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Fracture behavior of FeAlSi intermetallics
Čech, J.; Haušild, P.; Karlík, M.; Nová, K.; Průša, F.; Novák, P.; Kopeček, Jaromír
2020 - English
The study is devoted to the intermetallic alloy FeAl20Si20 (wt.%) with the potential applications in high temperature aggressive environments. The samples of the same chemical composition were prepared by spark plasma sintering from the different mechanically alloyed powders (pure elements and pre-alloyed powders).
Keywords:
FeAlSi; fracture toughness; nanoindentation; SPS
Available at various institutes of the ASCR
Fracture behavior of FeAlSi intermetallics
The study is devoted to the intermetallic alloy FeAl20Si20 (wt.%) with the potential applications in high temperature aggressive environments. The samples of the same chemical composition were ...
Mathematical method for submolecular resolution of helicene-based macrocycles by atomic force microscopy in air
Ukraintsev, Egor; Houska, Václav; Vacek, Jaroslav; Starý, Ivo; Stará, Irena G.; Rezek, B.
2020 - English
We introduce a straightforward mathematical method for improving the AFM image resolution, applied to image analysis of helicene-based macrocycles adsorbed on HOPG. The method reveals structural details from insufficiently resolved AFM images and attributes them to internal structure and ordering of the macrocycles. Our findings are also corroborated by molecular mechanics simulations, validating that the structure provided by the method has lower potential energy compared to other tested macrocycle arrangements.
Keywords:
atomic force microscope; mathematical modeling; submolecular resolution; macrocycles; molecular mechanics simulations
Available at various institutes of the ASCR
Mathematical method for submolecular resolution of helicene-based macrocycles by atomic force microscopy in air
We introduce a straightforward mathematical method for improving the AFM image resolution, applied to image analysis of helicene-based macrocycles adsorbed on HOPG. The method reveals structural ...
Comparison of microbial interactions of zinc oxide nanomaterials in various size and shape
Rutherford, D.; Jíra, J.; Mičová, J.; Remeš, Zdeněk; Hsu, H.S.; Rezek, B.
2020 - English
Zinc oxide nanoparticles (ZnO NP) have shown great potential as a novel antibacterial material at a time when resistance towards conventional antibiotics is becoming more prevalent. We report bacteria inactivation by ZnO NP with novel hedgehog-like morphology using model gram-negative (E. coli) and gram-positive (S. aureus) bacteria. E. coli exposed to the novel ZnO hedgehog NP during growth resulted in 4 orders of magnitude reduction in viable cell concentration after 24 h, which is more than 2 orders higher reduction compared to commercially available ZnO NPs with nominal sizes from 50 nm to 20 um. There was a positive correlation between hedgehog NP concentration and bacteria cell concentration reduction within the range tested 0.1 – 1.0 mg/mL. S. aureus was less sensitive to ZnO NP exposure and inactivation effect of various ZnO NP, was comparable. The effect can be thus attributed to direct mechanical damage of the bacterial mebrane that is the most effective for the novel hedgehog ZnO NP. This conclusion was corroborated also by disk diffusion assays.\n
Keywords:
nanotechnology; microbiology; zinc oxide
Available at various institutes of the ASCR
Comparison of microbial interactions of zinc oxide nanomaterials in various size and shape
Zinc oxide nanoparticles (ZnO NP) have shown great potential as a novel antibacterial material at a time when resistance towards conventional antibiotics is becoming more prevalent. We report bacteria ...
Why monitor acoustic emissions during nanomechanical tests?
Čtvrtlík, Radim; Václavek, L.; Tomáštík, J.
2020 - English
Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and nanotribological testing. Local mechanical properties of surfaces or micro object are routinely explored using nanoindentation, scratch test or dynamic impact tests that are evaluated based on analysis of depth-load-time records or microscopic observation of residual indents, scratch grooves or impact craters, respectively. Although these approaches have been proven to be sufficient in most cases for a variety of materials, there are many situations where they do not provide sufficient information for a complex understanding of the deformation response. On the other hand, analysis of AE signals generated during these tests may provide valuable complementary information and provide some insight into the dynamics of phenomena like cracking, phase transitions, plastic instabilities, etc.\n
Keywords:
acoustic emission; indentation; scratch test; thin films
Available at various institutes of the ASCR
Why monitor acoustic emissions during nanomechanical tests?
Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and ...
Role of Urbach Energy in Photovoltaics
Vlk, Aleš; Abelová, Lucie; Hájková, Zdeňka; Remeš, Zdeněk; Holovský, Jakub; Ledinský, Martin
2020 - English
Organic-inorganic halide perovskites provide new opportunities for improvement of optoelectronic device performance, especially the efficiency of solar cells. To evaluate the quality of a new material many parameters has to be taken into account. Here, we discuss one of the often overlooked semiconductor’s parameters, Urbach energy, which is an easily accessible measure of material disorder. Moreover, we present its importance on the example of organic-inorganic halide perovskites.
Keywords:
organic-inorganic halide perovskites; photoluminescence; Urbach energy
Available at various institutes of the ASCR
Role of Urbach Energy in Photovoltaics
Organic-inorganic halide perovskites provide new opportunities for improvement of optoelectronic device performance, especially the efficiency of solar cells. To evaluate the quality of a new material ...
Benefits of use of acoustic emission in scratch testing
Václavek, L.; Tomáštík, Jan; Chmelíčková, H.; Čtvrtlík, R.
2020 - English
Scratch test is regularly used for assessment of cohesive and adhesive strength of thin films and coatings. By default, its evaluation is based on analysis of depth-load-time record and microscopic observation of residual scratch groove. The visual analysis of the residual groove provides the most detailed description of the final damage of the surface (crack patterns, extent of plastic deformation, delamination, etc.), but it may be a time demanding approach. Although the continuous recording of indenter penetration depth and applied load offers instantaneous information about the performance of the tested material, it may not provide sufficient description of the sample’s deformation behaviour. Therefore, other complementary techniques for description of the deformation response to scratch loading are desirable.
Keywords:
acoustic emission; laser cladding; scratch test; thin films
Available at various institutes of the ASCR
Benefits of use of acoustic emission in scratch testing
Scratch test is regularly used for assessment of cohesive and adhesive strength of thin films and coatings. By default, its evaluation is based on analysis of depth-load-time record and microscopic ...
Adhesion improvement between bitumen and mineral aggregate:theoretical principles and their impact on pavement structure lifetime
Trejbal, J.; Demo, Pavel; Nežerka, V.; Sveshnikov, Alexey; Valentová, T.; Valentin, J.
2019 - English
Influence of nanomaterial-based adhesion promoters on maximizing of intermolecular interactions between bitumen and aggregate surfaces was studied. Topological and physico-chemical properties were described and it is shown that presence of promoters increases adhesion about 18%.
Keywords:
adhesion promoters; interface interactions
Available at various institutes of the ASCR
Adhesion improvement between bitumen and mineral aggregate:theoretical principles and their impact on pavement structure lifetime
Influence of nanomaterial-based adhesion promoters on maximizing of intermolecular interactions between bitumen and aggregate surfaces was studied. Topological and physico-chemical properties were ...
Inactivation of aspergillus niger on paints containing ZnO
Rácová, Z.; Baudys, M.; Krýsa, J.; Tichá, P.; Demo, Pavel
2019 - English
Antifungal capability of ZnO against bacteriae A. niger (including its photocatalytic activity) was analyzed. The optimal conditions for mould mycelium growth was estimated from evolution growth models. It was shown that prepared protective coating exhibits antifugal effect.
Keywords:
self-cleaning; ZnO; photocatalysis; niger
Available at various institutes of the ASCR
Inactivation of aspergillus niger on paints containing ZnO
Antifungal capability of ZnO against bacteriae A. niger (including its photocatalytic activity) was analyzed. The optimal conditions for mould mycelium growth was estimated from evolution growth ...
MOVPE GaN/AlGaN HEMT nano-structures
Hulicius, Eduard; Kuldová, Karla; Hospodková, Alice; Pangrác, Jiří; Dominec, Filip; Humlíček, J.; Pelant, Ivan; Cibulka, Ondřej; Herynková, Kateřina
2019 - English
GaN/AlGaN-based high electron mobility transistors (HEMTs) attain better performance than their state-of-the-art full silicon-based counterparts do, offering higher power, higher frequency as well as higher temperature of operation and stability, although their voltage and current limits are somewhat lower than for the SiC-based HEMTs. GaN/AlGaN-based HEMTs are a potential choice for electric-powered vehicles, for which they are approved not only for their power parameters, but also for their good temperature stability, lifetime and reliability. It is important to optimize HEMT structures and their growth parameters to reach the optimum function for the real-world applications. HEMT structures were grown by MOVPE technology in AIXTRON apparatus on (111)-oriented single-surface polished Si substrates. Structural, optical and transport properties of the structures were measured by X-ray diffraction, optical reflectivity, time-resolved photoluminescence and micro-Raman spectroscopy.\n
Keywords:
GaN; MOVPE; HEMT
Available at various institutes of the ASCR
MOVPE GaN/AlGaN HEMT nano-structures
GaN/AlGaN-based high electron mobility transistors (HEMTs) attain better performance than their state-of-the-art full silicon-based counterparts do, offering higher power, higher frequency as well as ...
New binary refractory metal-Fe intermetallic compounds for hard magnet applications
Tchaplianka, Maxim; Shick, Alexander
2019 - English
We investigate theoretically the electronic and magnetic structure of Fe2Hf. The density functional theory is used to calculate the magnetic moments on individual atoms, the total and projected densities of states, and the magnetic anisotropy energy. The Fe2Hf is found to be metallic and ferrimagnetic, with the magnetic moments of Fe and Hf atoms pointing in the opposite directions. The negative magnetic anisotropy, and the “in-plane” preferential direction of the magnetization are found as a result of theoretical calculations. Our study suggests that the chemical control of the magnetic anisotropy has to be investigated in order to evaluate the potential of Fe2Hf for the permanent magnet applications.\n
Keywords:
electronic structure; magnetic anisotropy; permanent magnets
Available at various institutes of the ASCR
New binary refractory metal-Fe intermetallic compounds for hard magnet applications
We investigate theoretically the electronic and magnetic structure of Fe2Hf. The density functional theory is used to calculate the magnetic moments on individual atoms, the total and projected ...
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