Seznam abstraktů 2023: SEKCE A - NANOMATERIÁLY PRO ELEKTRONICKÉ, MAGNETICKÉ A OPTICKÉ APLIKACE. UHLÍKOVÉ NANOSTRUKTURY, KVANTOVÉ TEČKY

The storage of solar energy in the form of chemical bonds through the synthesis of fuels and chemicals is a strategic approach to dispatch on-demand and continuous supply of clean energy carriers. Photo-active nanomaterials naturally transduce solar radiation in redox photo-potentials, thus enabling chemical transformations. In this contribution, I will discuss our most recent results showing how interface engineering and nanoscale assembly generate advanced nanomaterials with both improved optical and photocatalytic activity for various technologies, including colloidal photocatalysis, fuel cells, photoelectrochemical cells, and solar thermal processes.

Photo-active nanomaterials are receiving increasing attention due to their prospects for light-driven applications. However, exploiting the properties of photoactive materials and accessing their enhanced capabilities require a fine-tuning between their topology-dependent electronic structure and the ability to integrate them into photo-reactors or to deposit them on large surfaces. Subsequently, the synthetic approach, as well as post-synthesis manipulation could strongly affect the final photo-active nature of the materials and without developing a proper understanding of the electronic level changes of the material it is impossible to offer a genuine explanation for the observed physicochemical changes. By approaching this field from a computational material sciences angle, an integrated view (experiment+theory) allows researchers to develop a better understanding of the electronic behavior of the material and to connect with other possible application perspectives. The computational design of photo-active nanomaterial provides a valuable road map, outlining the common principles lying behind the diversity of materials rooted in their electronic structure, but also delimiting the imprecise border between the contrasting results and the most speculative studies. This comprehensive approach makes it ideal for the specialist but also for engineers, researchers, and students in related fields to provide individual contribution to combat the global energy crisis and offer a sustainable and a competitive business model that creates value for society.

2D semiconductors, particularly transition metal dichalcogenides (TMDs), and their alloys are intensively studied due to their wide range of applications. 2D TMDs exhibit new properties that differ from their bulk counterparts. In the present study, the electrical properties of monolayer and multilayer structures based on MoS0.5Se1.5 crystals were investigated. The samples were prepared using mechanical exfoliation and the dry transfer method [1,2]. To characterize the number of layers, Raman spectroscopy measurements were performed, which prove that single crystal layers were obtained. Specially prepared SiO2/Si substrates with 5 μm separated gold planar electrical contacts were used to fabricate the structures. Electrical investigations were carried out for the temperatures from 80 K to 450 K. As the temperature increased, the observed resistance decreased from 40 MΩ for T = 80 K to 630 kΩ for T = 450 K. In addition, we investigated the effect of illuminating the sample with LEDs of different wavelengths on the electrical properties of MoS0.5Se1.5 based structures. For T = 80 K there was a 44% increase in current when the LED was turned on, while for T = 450 K the current increased by much less, i.e. 6%. The results presented show that MoS0.5Se1.5 based devices can work as temperature or photo-detecting sensors. REFERENCES: [1] M. Tamulewicz et al. 2022 AIP Adv. 12 (2): 025328.; [2] A. Castellanos-Gomez et al. 2014 2D Mater. 1 011002.

Carbon fibers (CFs), carbon nanotubes, and carbon black are turbostratic allotropic forms of carbon [1]. Among carbon allotropes, CFs have attracted significant interest in recent years due to their immense thermal and electrical conductivity, superior thermal and chemical resistance, high specific surface area, and high mechanical characteristics [2], [3]. Polyacrylonitrile (PAN) is the most common precursor utilized in the production of CFs. The potential use of PAN-based CFs in sensors, supercapacitors, filtration systems, etc. has been identified [4]. Three steps are necessary for the synthesis of PAN-based CFs: i) synthesis of PAN fibers, ii) their stabilization and iii) finally carbonization. Among the available PAN fiber synthesis techniques, centrifugal spinning [5], [6] is one that produces CFs [7] on higher production compared to electrospinning.
Some materials such as TiO2, CdS, ZnO, etc. are effective photocatalysts [8] with a significant light harvesting property, and slow photogenerated charge carriers. TiO2 is the most widely used photocatalyst because it is very efficient when exposed to UV light, but also it is nontoxic, photostable and inexpensive.
The presentation will focus on the production of CFs and the decoration of TiO2 nanoparticles (NPs) on CFs using various concentrations of TiCl4 for the photocatalytic degradation of the methylene blue (MB) dye. REFENCES: [1] P. Toth. et al. Carbon N Y, vol. 178 ( 2021).; [2] R. S. Datta et al. RSC Adv, vol. 5 (2015).; [3] J. Miao. et al. J Nanosci Nanotechnol, vol. 10 (2010).; [4] C. Zhang. et al. J Nanomater, vol. 2015 (2015).; [5] M. Rihova et al., Nanoscale Adv, vol. 3 (2021).; [6] M. Rihova et al. J Appl Polym Sci, vol. 138 (2021).; [7] P.K. Chennam et al. J. Mater. Res. Tech., submitted.; [8] T. INOUE et al. Nature, vol. 277 (1979).

In the rapidly evolving landscape of materials science, two-dimensional (2D) materials have emerged as remarkable candidates for a wide range of technological applications [1-3]. Among these, monoelement germanane, a novel member of the 2D material family[4], has garnered substantial attention due to its unique properties that enable diverse applications in the domain of fluorometric sensing [5]. This abstract sheds light on the potential of methyl-functionalized germanane (CH3Ge) as a versatile platform for the development of fluorometric sensors.
Recently, we developed an innovative fluorescence-based sensing platform utilizing CH3Ge. This platform has proven effective for gas detection, pH measurement, and anti-counterfeiting purposes. Notably, when gas molecules are introduced into the interlayer space of CH3Ge, the material emits a luminescent red-orange light. This luminescence signal diminishes upon the removal of the gas molecules. This unique property enables us to directly detect gas absorption by analyzing the fluorescence emitted by CH3Ge. To showcase the practicality of this method for real-time, on-the-spot testing, we accurately quantified absorbed gas molecules like humidity and ammonia using a smartphone camera equipped with a color intensity processing application (APP). Moreover, we integrated CH3Ge films into actual food packaging (such as fish and milk containers) to monitor the freshness of perishable goods. Using density functional theory calculations, we investigated the changes in CH3Ge's band gap and optical response caused by various gas molecules. Additionally, we extended the application of CH3Ge-based materials to rewritable paper, demonstrating its potential for covert communication through rapid coloration induced by water jet printing. The color changes are easily reversible through water evaporation, enabling practical and secretive communication scenarios. REFERENCES: [1] Vaghasiya, J. V.; Mayorga-Martinez, C. C.; Vyskočil, J.; Pumera, M., Nat. Commun. 2023, 14 (1), 2.; [2] Reza Rezapour, M.; et al., ACS Appl. Mater. Interfaces 2017, 9, 24393.; [3] Lemme, M. C.; Akinwande, D.; Huyghebaert, C.; Stampfer, C., Nat. Communi. 2022, 13, 1392.; [4] Ng, S.; Pumera, M., Adv. Mater. 2023, 35, 2207196.; [5] Asel, T. J.; et al. Chem. Mater. 2020, 32, 1537.

One of the most important part of supercapacitors is represented by the electrode since it controls the overall performances, including capacitance, charge-discharge efficiency, power/energy density, as well as electrochemical/mechanical stability. The synergistic combination of polymers characterized by flexibility, low density and facile processing with the outstanding attributes of carbon nanotubes (CNTs) enabled the design of various versatile CNT-polymer nanocomposites with overall improved physical properties as compared to the pristine polymer, extending their field of application. In order to obtain flexible electrodes with high capacitance and large volumetric energy density, versatile materials with improved performances in terms of cyclability, potential window, material fabrication capability, and cost considerations were developed [1,2].
To enlarge the library of materials for energy storage applications, MWCNTs nanocomposite films have been obtained by MWCNTs-assisted polycondensation reaction leading to a polymer with functional groups able to develop interfacial interactions with the inorganic filler. Thus, nanocomposite flexible films incorporating different amounts of MWCNTs were obtained and investigated with regard to their morphology, mechanical behavior, thermal stability, electrical and electrochemical characteristics. The highest loading of MWCNTs led to the flexible electrode with the best electrical storage capacity. This was further tested in a flexible device configuration which provided satisfactory performance.
ACKNOWLEDGEMENTS: This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project no. PN-III-P4-PCE-2021-1728 (contract no. 46/2022), within PNCDI III. REFERENCES: [1] T. An, W.L. Cheng, Recent progress on stretchable supercapacitors, J. Mater. Chem. 6 (2018) 15478-15494.; [2] K.Y. Yasoda, S. Kumar, M.S. Kumar, K. Ghosh, S.K. Batabyal, Fabrication of MnS/GO/PANI nanocomposites on a highly conducting graphite electrode for supercapacitor application, Mater. Today Chem. 19 (2021) 100394.

The ever-increasing energy demands of modern society together with the commitment of limiting global warming by lowering the greenhouse gas emissions and by use of renewable sources lead to significant transformation of the energy and transportation sector. In this regard, the concept of the so-called Hydrogen Economy proves to be very promising. For its successful implementation, the efficiently working proton exchange membrane water electrolyzers (PEM-WEs) are essential. PEM-WEs use electrical power to drive electrochemical water splitting into hydrogen and oxygen. One of the top research priorities in this field is a significant reduction of noble metal dependence, predominantly on anode, through systematic studies of new materials. This talk will cover different approaches on how to improve the performance and durability of PEM-WE not only by employing new catalysts but also by modifying the membrane/catalyst interface. We will be focusing on magnetron sputtering as it is a very dependable, cost-effective, and industrially scalable method for depositing thin-film multielement catalysts and is also capable of enlarging the surface of PEM by so-called sputter-etching process. Finally, we will introduce several recent methods for operando analysis of membrane electrode assemblies within PEM-WE single cells which have potential to shed more light on complicated activity-stability relationship of novel catalytic materials.

Anodic oxides of valve metals have shown remarkable performances as memristive elements. The switching between a high and a low resistance state depends on the selection of electrodes and active layers. This impacts the conductive pathways formation, which is mediated by oxygen vacancies and/or cations, and their field-activated movement inside the oxide. The synthesis of such oxide layers is commonly done by atomic layer deposition or sputtering, but the electrochemical anodization process should not be neglected. This is a faster, less complex and inexpensive method, with precise composition and oxide thickness. The current work is focused on the behavior of anodic memristors based on ultra-thin Hf superimposed on Ta films. The control of resistive filaments is based on the particularities of the anodization process, when the interface between both oxides is dynamically changing. Anodization of superimposed metals leads to nanoscale oxide columns formation, when a metal producing a more resistive oxide is superimposed on a metal producing a less resistive one. This phenomenon results from the ionic current preferring the less resistive paths, enhancing the growth of the correspondent oxide. Anodization of Hf/Ta system leads to this effect since HfO2 is the more resistive oxide. The boundary between Hf and Ta oxides may influence the conductive pathways required for the memristive effect, thus being most relevant for fabrication of highly stable and forming-free memristors. Additionally, the use of superimposed films with gradient but complementary thicknesses allows investigating the ideal Hf/Ta ratios for which the best memristive behavior is obtained.

Due to their unique physicochemical properties, transition metal oxides (TMOs) have become literally irreplaceable materials in a wide range of modern technologies, such as (photo)catalysis, bio- or gas-sensing, energy harvesting/storage, or biomedical applications. In many cases, the performance of TMOs may be enhanced by their nanostructuring that not only increases the specific surface and facilitates interfacial phenomena but allows for the precise tuning of their functional properties to comply with the particular application. Because of this, various strategies are recently developing to enable the controlled synthesis of TMOs nanostructures. The aim of this study is to introduce and investigate an original two-step approach that utilizes magnetron-based gas aggregation sources of metallic nanoparticles that are subsequently thermally annealed to induce their transformation to oxides. As shown on the examples of selected transition metals from groups IV, V and VI, namely Ti, V, Nb and W, this strategy allows for the solvent-free and time-effective fabrication of highly porous micrometre-thick films composed of TMOs nanoparticles whose oxidative state and porosity may be furthermore tailored by employed annealing procedure. This paves the way for the reliable production and advanced design of novel TMOs-based nanocoatings with desired functionalities (e.g., photocatalytic activity, thermochromic behaviour or sensing capability) that will be briefly discussed. ACKNOWLEDGEMENTS: This work was supported by the grant GAČR 21-05030K from the Grant Agency of the Czech Republic.

We present a combined experimental and theoretical study of surface-related magnetic states in TiO2. Our experiments performed on nano-sized thin films of pure TiO2 have suggested that the observed room-temperature magnetism originates from defects, particularly from the surface of thin films as well as from point defects, such as vacancies located mainly at the surface. To clarify this phenomenon, we performed quantum-mechanical density functional theory (DFT) calculations. Our fixed-spin-moment calculations identified both the bulk and the bulk-like TiO2-terminated vacancy-free (001) surfaces as non-magnetic. In contrast, oxygen vacancies in the TiO-terminated and TiO0.75-terminated (001) surfaces led to ferromagnetic and rather complex ferrimagnetic states, respectively. The spin-polarized atoms are the Ti atoms (due to the d-states) located in the surface and sub-surface atomic planes. Finally, the O-terminated surfaces are also magnetic due to the surface and sub-surface oxygen atoms and sub-surface Ti atoms (however, their surface energy is high). For further details, see Friák et al., Journal of Applied Physics 134, 013902 (2023), DOI: 10.1063/5.0155282. ACKNOWLEDGEMENTS: The authors acknowledge the financial support from the Czech Science Foundation (Project No. 22-21547S) and Masaryk University (Project No. MUNI/A/1298/2022; for covering "NANOCON" participation expenses (K.G.).

Molybdenum oxides exhibit numerous electronic properties thanks to the ability of Mo to possess various oxidation states and coordinations. Molybdenum oxides are thus attractive for applications in energy storage, conversion, electrochromic, gas sensing, or superconducting devices. Nanostructuring molybdenum oxides, controlled through the preparation conditions, is advantageous for enhancing the material's properties. The so-called porous-anodic-alumina (PAA) assisted anodizing, based on the anodic oxidation of a metal layer through a PAA overlayer, may also be a way to grow molybdenum-oxide nanocolumn arrays if their stability in water-containing electrolytes could be improved. To take on the challenge, we envisioned mixing MoOx with the oxide of a different metal (Nb), by placing a thin interlayer of Nb between the Al and Mo in the precursor thin-film stack.
The arrays were prepared from the magnetron-sputtered Al/Nb/Mo trilayers by anodizing at 50 V, then re-anodizing to 180 V, followed by selective dissolution of the PAA overlayer. Detailed XPS characterization confirmed that various Mo species were present in the column material with a total amount of Mo reaching 16 at.% (Mo+Nb = 100%). The fitting of narrow-scan Nb 3d and Mo 3d spectra, complicated by Nb loss features, showed that Mo6+, Mo5+, and Mo4+, in various ratios, were present in the column surface material, whereas Nb2O5 was almost entirely stoichiometric. Further investigation is underway to understand the formation-structure-morphology relationship and explore the functional properties of the novel nanoarrays. ACKNOWLEDGEMENTS: This research is supported by GACR grant no. 23-07848S.

We have performed a theoretical study of three different allotropes of Pb-supersaturated Sn-rich Pb-Sn alloys with the α-Sn, β-Sn and a simple hexagonal γ-Sn structure employing quantum-mechanical calculations. Structure-property relations were analyzed in the case of the lattice parameters, thermodynamic stability, elastic properties and mechanical stability as well as electronic-structure density of states. Compositional trends in structural, thermodynamic and electronic-structure properties were found nearly linear. Our theoretical study sheds new light on a decades-long controversy related to the γ-phase of supersaturated Sn-rich Pb-Sn alloys. We suggest that the experimental difficulties in synthesizing the γ-phase solid solutions are due to the high formation energy of this phase. ACKNOWLEDGEMENTS: Financial support received under the Project No. 22-05801S from the Czech Science Foundation is gratefully acknowledged. Computational resources were provided by the e-INFRA CZ project (ID:90254), supported by the Ministry of Education, Youth and Sports of the Czech Republic. These resources were utilized through IT4Innovations National Supercomputing Center, MetaCentrum as well as CERIT Scientific Cloud.

Tungsten-based compounds are widely used in various fields such as sintering metallurgy, microelectronics, aerospace, biomedical applications, etc. Typically, nanoparticles of tungsten itself, its oxides (usually WO3) or various bimetallic composites are used. Although there exist numerous strategies for the production of such nanoparticles that are based on chemical synthesis, in this work we consider the possibility of obtaining bimetallic W/Cu nanoparticles by means of a magnetron-based gas aggregation source (GAS) of nanoparticles, i.e., by purely physical process. For this, a GAS of original construction was equipped with a segmental target consisting of two metals: tungsten and copper. The properties of prepared bimetallic W/Cu nanoparticles, namely their morphology, chemical structure, optical properties and antibacterial action, are subsequently compared with single metal tungsten nanoparticles deposited by the same GAS deposition system, but using only a tungsten target. In addition, the changes in the properties of synthesised induced by their thermal treatment in air were studied as well.
This work was supported by the Grant Agency of Charles University in the frame of the grant GAUK 375921.

Neuromorphic engineering is rapidly developing branch of science that aims to implement the unique attributes of biological neural networks in artificial devices. Most neuromorphic devices are based on resistive switching effect, which involves changing the device’s conductivity in response to external electric field. For instance, percolating nanoparticle (NP) networks produced by gas aggregation sources (GAS) show collective spiking behavior in conductivity reminiscent of brain-like dynamics. Nevertheless, the problem of dynamic spatial reconfiguration in solid-state neuromorphic systems remains unsolved. Herein, novel nanofluids with resistive switching properties are proposed as neuromorphic media. They are produced by depositing silver NPs from GAS into vacuum-compatible liquids (paraffin, silicon oil, and PEG) without use of surfactants or other chemicals. When electric field is applied between two electrodes, the migration of NPs toward biased electrode is pointed out in all liquids. The electrophoretic nature of NPs movement was proved by means of ζ-potential measurements. The limited colloidal stability of nanofluids was beneficial, leading to the self-assembling of NPs in conductive paths connecting the electrodes and, as a result, to resistive switching. The electrical response strongly depended on the dielectric constant of the base liquid. The Ag-PEG nanofluid demonstrated the best switching performance reproducible during several tens of current-voltage cycles. The growth of flexible and reconfigurable conductive filaments in nanofluids makes them appropriate media for potential realization of 3D neural-like networks. ACKNOWLEDGEMENTS: The work was supported via grant GACR 23-06925S from Czech Science Foundation and via Czech-German Mobility grant 8J23DE016 from Ministry of Education, Youth, and Sports.

We find that for MOVPE grown GaN, reducing the dislocation density (DD) greatly increases the electron mobility in the 2DEG. In structures with a low DD, parallel currents were observed through the deeper parts of the heterostructure. A properly designed AlGaN backbarriers help prevent this phenomenon. Si and Ge doping of GaN can cause a huge increase in yellow band luminescence (the unwanted slow defect part of the spectrum). Highly Si-doped GaN grows in 3D columns, while Ge-doped remains smooth. Light extraction for PL is affected by the change in morphology. InGaN:Ge layer growth: decreasing the GeH4 flux resulted in a higher In content in this layers. Incorporation of Ge into intentionally undoped InGaN layers was detected. GeH4 diluted in H2 is not detrimental to the growth of InGaN with an In content of around 8 %. The optimal growth conditions for achieving high electron mobility were 950 °C, TEGa, lower growth rate, nitrogen atmosphere, and 150 mbar. The improved channel technology increased the electron mobility in the channel by 30 % to 1896 cm2/vs. HEMT mobility is lower in structures with high DD due to scattering at point defects or trapping of carriers in dislocation-decorating traps is likely to be the main factor controlling mobility in the channel. An atomically flat AlGaN/GaN interface is not necessary to achieve high electron mobility of the 2DEG in the HEMT structure. The formation of V-pits at the AlGaN/GaN interface can be beneficial for HEMT structures containing thread dislocations and lead to increased electron mobility.

Using the ring model of atoms and molecules, was revealed that there must be two types (type A and type B) of atoms that differ in the direction of rotation of individual rings (for type B, all rings rotate opposite to the directions of rotation for type A). The rotations of protons and neutrons in atoms are given by a system that resembles a "cogwheel" in gear box. Both types A and B have the same structure. Solution to this problem was found in the design of the TiO2 model, which has a total of 22 protons, 22 electrons and 26 neutrons in titanium atom (Ti). Each oxygen atom has 8 protons, 8 electrons and 8 neutrons. The TiO2 model therefore consists of 118 rings (protons, neutrons and electrons). Two types of electrons are distinguished in the model (valence electrons are colored light blue and inner electrons are colored dark blue). The direction of rotation of the proton determines the direction of the magnetic moment that exits the atom. For an external view of the proton, it has (for clockwise rotation of the proton) the proton has a magnetic moment that exits the proton (yellow arrow). For counterclockwise rotation of the proton) the proton has a magnetic moment that enters the proton (green arrow). For example, in the case of an oxygen molecule O2, oxygen atoms of type A and type B are joined. The magnetic moments in the binding of two protons must follow the same direction. Only the magnetic moment with the yellow arrow can be combined with the magnetic moment with the green arrow.