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Depozice funkčních oxidových tenkých vrstev ke zlepšení vlastností elektronových zdrojů
(Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, ) Košelová, Zuzana; Fohlerová, Zdenka; Krysztof, Michal; Albuquerque de Assis, Thiago
Působením elektrického pole o velmi vysoké intenzitě na povrchu kovu nastává elektronová emise, a to i bez nutnosti jeho zahřívání. Tento jev se označuje jako studená vlastní emise, neboli autoemise elektronů a vzniká v důsledku zúžení potenciálové bariéry a formování Schottkyho-Nordheimovy bariéry. Po dostatečném snížení a tedy zúžení bariéry mohou začít tunelovat elektrony s energetickými stavy blízkými Fermiho hladině. Takto získaný proud volných elektronů se uplatňuje v elektronové mikroskopii, elektronové litografii či například jako zdroj elektronů v rentgenkách. V posledních letech byly zkoumány vlastnosti řady žáruvzdorných kovů, polovodičů i uhlíkových nanotrubiček. Pro mnohé aplikace, typickým příkladem je elektronová mikroskopie, však nadále zůstává první volbou wolframový hrot o průměru 100 až 200 nm. Jeho hlavními přednostmi jsou trvanlivost a nízký poměr rozprašování. Nanesení tenké vrstvy na wolfram může výrazně ovlivnit emisní vlastnosti. Povlak dokáže snížit relativně vysokou výstupní práci, snížit prahové napětí, prodloužit životnost, zvýšit jas emisního obrazu a zlepšit kondenzaci elektronového svazku. Ochranná vrstva zároveň brání uvolňování atomů wolframu vlivem nárazu vysokoenergetických pozitivních iontů a snižuje tak jeho reaktivitu. V některých případech může působit i jako filtr pro tunelující elektrony, nebo naopak vytvářet rezonančně zesílené tunelování, které zvyšuje pravděpodobnost emise. Klíčové je ovšem správně zvolit tloušťku a materiál povlaku, aby byla zajištěna stabilita a dosaženy požadované vlastnosti. Téma práce se zaměřuje na výrobu a následnou depozici tenké oxidové vrstvy na wolframových katodách a na hloubkovou analýzu jejich autoemise buzené polem. Jako oxidační techniky byly použity termická oxidace a anodizace. K analýze byla využita Murphyho-Goodova metodika. Hlavním nástrojem pro hodnocení katod je autoemisní elektronový mikroskop pracující ve vakuovém rozsahu UHV, který umožňuje detailní studium emise pole. Doplňkově lze využít elektronový mikroskop, který poskytuje cenné informace o tvaru a morfologii vyrobených elektrod.
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Comparative analysis of machinability and microstructure in LPBF and conventionally processed M300 maraging steel
(2025-12-01) Kolomý, Štěpán; Slaný, Martin; Doubrava, Marek; Sedlák, Josef; Zouhar, Jan; Řehořek, Lukáš
The heat treatment and machining can be considered as necessary post process operations to create functional components manufactured by means of laser powder bed fusion. Therefore, complex investigation of influence of microstructure on the machinability of maraging steel (MS) M300 parts produced by laser powder bed fusion (LPBF) and rolling was performed. The main evaluation was carried out in regard to hardness, milling forces, surface morphology, surface roughness, chip formation, and subsurface hardness and microstructure. The findings revealed that LPBF MS M300 after direct aging heat treatment, containing martensite with dispersed precipitates and reversed austenite, generated highest milling forces. Surface roughness of this material showed a lower surface roughness in comparison to as-built sample Due to the higher hardness, which caused a lower lateral plastic flow and most severe tool wear. The subsurface hardness under the milled area of direct aged samples increased by 24% (900 HV) in comparison to the bulk value, while in case of conventionally manufactured rolled sample the increase was only by 9%. More pronounced increase in subsurface hardness was measured on samples milled utilizing highest cutting speed (60 m.min-1). Furthermore, milling induced strain hardening affecting the subsurface area up to approximately 40 m in depth.
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How different aspects of plasma treated liquids (PTLs) influence their antimicrobial properties
(2025-09-29) Trebulová, Kristína; Klementová, Kamila; Bednaříková, Svatava; Dofková, Daniela; Krčma, František; Paličková, Ivana; Barančeková, Miroslava; Čížek, Alois; Kozáková, Zdenka
This work studies the decontamination efficacy of different plasma treated liquids (PTLs) on bacteria from the genera Staphylococcus and Pseudomonas, both commonly associated with various infections. Clinical isolates and reference strains were used, to ensure the relevance to real-life applications. Bacterial suspensions were exposed to studied PTLs and to different comparative solutions that help dissect the mechanisms behind the observed antimicrobial effects. These comparative solutions comprised standard solutions of major reactive species (hydrogen peroxide, nitrites, nitrates) typically found in PTLs, solutions simulating the chemical composition of PTLs, and solutions adjusted to different pH levels to isolate the role of acidity in bacterial inactivation. The antimicrobial effects of studied solutions were examined at various contact times from 10 min up to 24 h. This allowed for a comprehensive understanding of both immediate antimicrobial effects and the persistence of PTL´s activity over time. The findings of this research demonstrate a superior antimicrobial efficacy of plasma treated liquids compared to the other studied solutions. Neither the individual standard solutions of reactive species, the solutions simulating the chemical composition of PTLs, nor pH-adjusted solutions were able to match the antimicrobial efficacy of the tested PTLs. Although it has been found that for some bacterial species, pH of the PTL may play a key role in the decontamination efficacy. The study also shows that different PTLs vary in their antimicrobial efficacy, depending on the specific formulation and the type of targeted microbial species. These differences in bacterial response may be influenced by factors such as cell wall structure, antioxidant capacity, and pH tolerance. In conclusion, this work supports the potential of indirect cold plasma treatment (via PTLs) for antimicrobial purposes. It highlights the complex interplay of factors involved in microbial inactivation and offers deeper insight into the differing responses of gram-negative and grampositive bacterial species to various PTLs. Furthermore, the study provides an overview of the antimicrobial effects of individual components present in PTLs across a wide range of concentrations and pH conditions. This may help other researchers compare the efficacy of different antimicrobial agents and explore potential mechanisms of inhibition.
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Damping enhancement in YIG at millikelvin temperatures due to GGG substrate
(2025-03-01) Serha, Rostyslav O.; Voronov, Andrey; Schmoll, David; Klingbeil, Rebecca; Knauer, Sebastian; Koraltan, Sabri; Pribytova, Ekaterina; Lindner, Morris; Reimann, Timmy; Dubs, Carsten; Claas, Abert; Verba, Roman; Urbánek, Michal; Suess, Dieter; Chumak, Andrii V.
Quantum magnonics aims to exploit the quantum mechanical properties of magnons for nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), which offers the longest magnon lifetimes, is a key material typically grown on gadolinium gallium garnet (GGG) substrates for structural compatibility. However, the increased magnetic damping in YIG/GGG systems below 50 K poses a challenge for quantum applications. Here, we study the damping in a 97 nm-thick YIG film on a -thick GGG substrate at temperatures down to 30 mK using ferromagnetic resonance (FMR) spectroscopy. We show that the dominant physical mechanism for the observed tenfold increase in FMR linewidth at millikelvin temperatures is the non-uniform bias magnetic field generated by the partially magnetized paramagnetic GGG substrate. Numerical simulations and analytical theory show that the GGG-driven linewidth enhancement can reach up to 6.7 times. In addition, at low temperatures and frequencies above 18 GHz and temperatures below 2 K and frequencies above 10 GHz, the FMR linewidth deviates from the viscous Gilbert-damping model. These results allow the partial elimination of the damping mechanisms attributed to GGG, which is necessary for the advancement of solid-state quantum technologies.
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General solutions of weakly delayed discrete systems in 3D
(2025-10-24) Diblík, Josef; Boháčková, Hana; Růžičková, Miroslava; Šafařík, Jan
Discrete systems x ( k + 1 ) = A x ( k ) + B x ( k - m ) x\left(k+1)=Ax\left(k)+Bx\left(k-m) , k = 0 , 1 , & mldr; k=0,1,\ldots \hspace{0.33em} are analyzed, where m m is a fixed positive integer, A A , B B are constant 3 by 3 matrices and x : { - m , - m + 1 , & mldr; } -> R 3 x:\left\{-m,-m+1,\ldots \right\}\to {{\mathbb{R}}}{3} . Assuming that the system is weakly delayed, its general solution is constructed for every case of the Jordan form of the matrix A A . It is shown that, for k >= 3 m k\ge 3m or for k >= 2 m k\ge 2m , these formulas reduce to simple forms depending on only the three independent parameters generated by the initial values. Formulas connecting these parameters with the initial ones are found. The results are illustrated by examples. Open problems for future research are discussed, and comparisons are given with the previous results.