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Imaging of carbon nanostructures by low energy STEM below 5 keV
Pokorná, Zuzana ; Knápek, Alexandr ; Jašek, O. ; Prášek, J. ; Majzlíková, P.
Our work deals with the imaging of nanostructures composed of light biogenic elements, such as carbon nanotubes, by low energy scanning transmission electron microscopy (STEM). Compared to imaging at the voltages commonly used for TEM and STEM, low energy electrons seem very promising in terms of specimen damage that is caused by a number of elastic andn inelastic collisions. In carbonaceous materials, the most problematic is probably the knock-on damage, where the structure can be impaired by carbon atom displacement. To avoid this problem with structures composed of light elements, a reduction in beam voltage going down to 5 keV has recently been proposed. The range below 5 keV has not been explored yet for this purpose, although electron scattering in matter is lower for these energies, which allows achieving a higher spatial resolution. We aim to demonstrate that additional reduction of incident electron energy may yield interesting contrast features.
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Synthesis of carbon nanotubes in mw plasma torch with different methods of catalyst layer preparation and their applications
Zajíčková, L. ; Jašek, O. ; Synek, P. ; Eliáš, M. ; Kudrle, V. ; Kadlečíková, M. ; Breza, J. ; Hanzlíková, Renáta
The microwave plasma torch (2 45 GHz) was used for the synthesis of carbon nanotubes from the mixture of CH4/H-2/Ar or C2H2/H-2/Ar on different substrates with iron catalyst Iron catalyst was prepared by vacuum evaporation of iron on Si, Si/SiOx or Si/AlxO(Y) substrates or by deposition of iron oxide nanoparticles on Si/SiOx substrate by decomposion of Fe(CO)(5) in gas feed Such prepared substrates were used for growth of carbon nanotubes. Recostruction of the iron catalyst layer into nanoparticles was also studied in dependence on substrate buffer layer, gas atmosphere and temperature Samples were studied by scanning and transmission electron microscopy and Raman spectroscopy. Synthesis resulted in rapid growth of MWNTs on all samples but the density, purity and nanotube diameter distribution varied Such prepared carbon nanotube layers were used for sensing applications.
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Důležitost vlivu nukleační fáze na vlastnosti nanokrystalických diamantových vrstev připraveným metodou PECVD
Zajíčková, L. ; Karásková, M. ; Jašek, O. ; Buršíková, V. ; Franta, D. ; Matějková, Jiřina ; Klapetek, P.
Microcrystalline diamond finds several applications due to its high hardness but also as electronic and optical devices. However, its roughness makes some applications like tribology, emission cathodes for flat panel displays, optical coatings and emerging Nano/Micro-Electro-Mechanical Systems (N/MEMS) difficult. A major advance was achieved in early 90ties when the crystalline size was decreased from down to nanometers. However, the processes leading to the deposition of small grain-sized diamond films are not yet properly understood and these films exhibit different properties and morphology depending on the method of preparation. Therefore, the nanocrystalline diamond (NCD) covers very different materials such as columnary grown films with the grain sizes usually quoted below 100 nm (but 30 nm are nowadays possible)and continuous dense coatings with grain sizes reaching 5-15 nm grown under high re-nucleation rates.
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Depozice a zpracování uhlíkových nanotrubek připravených metodou PECVD za atmosférického tlaku
Kučerová, Z. ; Zajíčková, L. ; Jašek, O. ; Eliáš, M. ; Synek, P. ; Matějková, Jiřina ; Rek, Antonín ; Buršík, Jiří
Carbon nanotubes (CNTs) were synthesized by plasma enhanced chemical vapor deposition from mixture of argon, methane and hydrogen using microwave plasma torch at atmospheric pressure. Nanotubes grew on a complex substrate system consisting of silicon wafer, buffer layer and thin catalytic iron film. As confirmed by scanning electron microscopy (SEM), this deposition technique produces bundles or ropes of nanotubes covered by crust composed of catalytic particles, amorphous carbon and other impurities such as fullerenes or other carbon nanoparticles. Because many scientific and technological applications, as well as characterization techniques require individual nanotubes a great attention has to be paid to the post-deposition processing of the deposit. The nanotube bundle could be separated by ultrasonication of the deposit in organic or inorganic liquid. Most commonly used liquids are water or ethanol.
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