Seznam abstraktů 2021: SEKCE A - NANOMATERIÁLY PRO ELEKTRONICKÉ, MAGNETICKÉ A OPTICKÉ APLIKACE. UHLÍKOVÉ NANOSTRUKTURY, KVANTOVÉ TEČKY

This talk will inform on nanophotonic metasurfaces, both metallic and dielectric, which represent a new class of artificial materials that allow to manipulate the wavefront of passing light and thus provide unprecedented functionalities in optics and nanophotonics. In the first part we will inform on these functionalities, and in the second part on characterisation methods of their optical properties. In the latter case we will report on phase imaging of fields formed by metasurfaces using Coherence-controlled holographic microscopy (CCHM). CCHM is a real-time, wide-field, and quantitative light-microscopy technique enabling 3D imaging of electromagnetic fields, providing complete information about both their intensity and phase. We will demonstrate that CCHM is inherently suited to the task of characterization of optical fields formed by metasurfaces, including tunable ones. Finally, we report on a new strategy in incoherent holographic imaging of metasurfaces, in which unprecedented spatial resolution and light sensitivity are achieved [1].
ACKNOWLEDGEMENT: This work is supported by the EU Horizon 2020 Twinning project “SINNCE”.
REFERENCE: [1] P. Bouchal et al., “High-resolution quantitative phase imaging of plasmonic metasurfaces with sensitivity down to a single nanoantenna”, Nano Lett. 19, (2019), 1242.

We have performed a quantum-mechanical study of a series of stoichiometric and off-stoichiometric Ni2MnSn structures focusing on pressure-induced changes in their magnetic properties. Our study focused on the role of point defects, in particular Mn-Ni, Mn-Sn and Ni-Sn swaps in the stoichiometric Ni2MnSn as well as off-stoichiometric substituents. For most defect types we also compared states with both ferromagnetic (FM) and anti-ferromagnetic (AFM) coupling between (i) the swapped Mn atoms and (ii) those on the Mn sublattice. Our calculations show that the swapped Mn atoms can lead to magnetic moments nearly twice smaller than those in the defect-free Ni2MnSn. Further, the defect-containing states exhibit pressure-induced changes up to three times larger (but also smaller) than those in the defect-free Ni2MnSn. Importantly, we find both qualitative and quantitative differences in the pressure-induced changes of magnetic moments of individual atoms even for the same global magnetic state. Lastly, despite of the fact that the FM-coupled and AFM-coupled states have often very similar formation energies (the differences only amount to a few meV per atom), their structural and magnetic properties can be very different. For details see M. Friák et al., Materials 14 (2021) 523, https://doi.org/10.3390/ma14030523. We also show that some ferrimagnetic off-stoichiometric disordered atomic configurations, that represent excited states, exhibit an anomalous pressure dependence of the total magnetic moment that increases with increasing pressure.
ACKNOWLEDGMENTS: The authors acknowledge the Czech Science Foundation for the financial support received under the Project No. 20-16130S entitled “Multifunctional properties of powdered Ni-Mn-Sn Intermetallics”. Computational resources were made available by the Ministry of Education, Youth and Sports of the Czech Republic under the Project of the IT4Innovations National Supercomputer Center (project “e-Infrastructure CZ-LM2018140”) within the program Projects of Large Research, Development and Innovations Infrastructures and via the CESNET (Project No. LM2015042) and CERIT-Scientific Cloud (Project No. LM2015085).

Over the past 15 years, self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest due to their wide possible range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is usually carried out by electrochemical anodization of valve Ti metal sheets in various electrolytes. The advantage of anodic TiO2 nanotube layers compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal) are the tunability of dimensions, their directionality, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials [2].
The presentation will focus on the recent progress in the TiO2 nanotube layer synthesis. We will discuss a possible upscaling of the nanotube layers towards areas of dozens of cm2 [3], considering the control of the anodization parameters. Furthermore, we will discuss the use of bipolar electrochemistry in closed cells [4] as well as in open cells for the preparation of TiO2 nanotube layers on small Ti objects which cannot be connected to the potentiostat [5]. The selective etching of anodic TiO2 nanotube layers towards single-wall nanotube layers [6] and single nanotubes [7], where nanotubes are separated from one another into tube powders, will also be discussed.
REFERENCES: [1] J. M. Macak et al., Curr. Opin. Solid State Mater. Sci., 2007, 1-2, 3.; [2] K. Lee et al., Chem. Rev., 2014, 114, 9385.; [3] H. Sopha et al., Electrochem. Commun. 2018, 97, 91-95.; [4] H. Sopha et al., ChemElectroChem 2021, accepted. DOI: 10.1002/celc.202100799.; [5] H. Sopha et al., Electrochem. Commun. 2020, 111, 106669.; [6] M. Motola et al., Electrochem. Commun., 2018, 97, 1-5.; [7] D. Beketova et al., ACS Appl. Nano Mater. 2020, 3, 1553−1563.

The A2B6 quantum dots (QDs) are perspective, tunable and photostable luminophors for optoelectronic devices, especially for those, where light conversion is needed. However, such applications require embedding QDs into solid state composites resistant to temperature changes and protected from oxygen. The most promising candidates for QDs incorporation are inorganic salts thanks to their matrix stability. Inorganic salt potassium dihydrogenphosphate (KDP) has unique non-linear optical properties that can be combined with properties of QDs.
Here we report on formation of single crystals of KDP doped by CdTe/CdS QDs, which were prepared by a slow evaporation technique from the mixture of saturated salt and colloidal solutions. The obtained crystals preserved optical properties of QDs and dramatically increased their chemo- and photostability.
We demonstrate application of such composites as infrared light conversion devices. The conversion is done via two-step process: from infrared light (1064 nm) to the second harmonic (532 nm), which is then transformed into the photoluminescence of QDs. We found that emission spectra of QDs, as well as their photoluminescence lifetime are practically identical both under UV and IR light excitations. Moreover these composites are made from cheap and abundant elements, the obtained samples have broad excitation and emission range, and fast response time.
Since the composites “salt:QDs” have wider working thermal range then colloidal solutions themselves, the luminescent thermometry can be proposed as another possible application. Thus, the temperature dependence of photoluminescence of KDP:CdTe/CdS composites is discussed, as well.

GaN-based nanostructures are used for many present semiconductor devices. The main topics are structures for blue LEDs and LDs, but there are also other interesting and important GaN devices namely for power electronics, scintillators and detectors as well as High Electron Mobility Transistors (HEMT). Several of our previous NANOCON contributions were devoted to the scintillator and detector structures [1]; one was a description of optimization of HEMT structures and their growth parameters [2].
The first part of this contribution is devoted to a general review of GaN power electronic devices, a comparison with other materials (mainly Si and SiC), a description of some fields of application and a future forecast.
The second part will describe our recent results - the influence of dislocation density on transport properties of HEMT structures is reported. Experimental results, obtained on HEMT structures prepared in the same growth run on templates with different dislocation densities, are compared. We show experimentally that lowering the dislocation density considerably increases the electron mobility in 2DEG. It is shown that the dislocation density has also a significant influence on the Fermi level position in GaN. Presented results suggest that reduction of the dislocation density can improve the performance of high frequency GaN HEMTs applications.
REFERENCES: [1] NANOCON 2019, SIMS studies of MOVPE GaN/InGaN scintillator nano-structures, E. Hulicius, at al., NANOCON 2017, Role of v-pits in the InGaN/GaN multiple quantum well structures, A. Hospodková, at al., NANOCON 2015, Nanostructures based on InGaN/GaN multiple quantum well for detector applications, A. Hospodková. , at al.; [2] NANOCON 2018, MOVPE GaN/AlGaN HEMT nano-structures, E. Hulicius, at al.

Kashiyama is a Japanese manufacturer of oil-free dry vacuum pumps committed to bring clean vacuum technology into your laboratory. Being the market leader in Japan, Kashiyama opened a new way for European customers with Japan Quality in 2018 in Munich, Germany.
When aiming for Ultra High Vacuum (UHV) for nanotechnology studies, a vacuum pump with a high H2 compression rate is essential. Our dry multi-stage roots pumps are designed for strict demands and performance, offering a low base pressure and high compression rates even for light gases. The roots of the pump rotate without mechanical contact inside so no particles such as PTFE tip seal dust are generated. NeoDry series is gap-sealed and requires no oil sealant, thus no oil vapor will contaminate UHV equipment. Your system stays free of hydrocarbons.
With over 10 years of market-proven reliability, this pump enables, on average, 6 years of maintenance-free operation handling high moisture content up to 600g/h. Being free of contamination and maintenance with a high-water vapor capacity, the NeoDry is the perfect backing pump for turbomolecular pumps and Ion Getter Pumps.
Furthermore, our pumps are compatible with various applications: Scanning Electron Microscopes, Transmission Electron Microscopes, Mass Spectrometers (w/ GC, LC, ICP, Ci, etc.), and analytic instruments, etc.

Diamond exhibits a unique combination of physical, mechanical, (bio)chemical, and electrical properties tailorable on demand. Besides that, high optical transparency in the infrared (IR) region, high refractive index and the possibility to host a variety of optically-active colour centres open the way to implement single-crystal plate or polycrystalline diamond (PCD) films also in optical elements. Optically tailored PCD films were fabricated by two complementary microwave (MW) plasma chemical vapor deposition reactors: i) focused MW plasma with ellipsoidal cavity resonator and ii) pulsed MW plasma with linear antenna arrangement. We will present our recent developments in the fabrication of diamond-based optical elements for IR spectroscopy and photonic structures (PhC) for visible and IR regions. Firstly, we show that Au mirrors coated with nanostructured PCD films enhance the detection limit of adsorbed molecules or proteins 1. Similarly, the PCD film is perspective as a functional and protective layer of Si and Ge prisms used in ATR-FTIR spectroscopy 2. Secondly, the PCD-based 2D PhC with subwavelength lattice constants fabricated by electron beam or microsphere lithography, and by employing reactive ion etching processing reveal enhanced light emission. For fabrication of diamond PhCs, we have developed 3 different approaches : i) top-down by the dry etching of continuous diamond film 3, ii) bottom-up by the diamond growth on periodically structured quartz substrates 4 and iii) combined dry&wet top-down etching for fabrication of suspended PhCs 5. Finally, ways for incorporation of colour centres in diamond by ion implantation (Er and Yb for IR region 6) or by CVD process (Si for visible region 7) will be also highlighted more in details.
ACKNOWLEDGEMENTS: Supported by the MoRePro project No. 19MRP0010 and GAČR project No. 19-14523S.
REFERENCES: [1] Kozak, H. et al., Langmuir 30, 2054-2060 (2014).; [2] Babchenko, O. et al., Vib. Spectrosc. 84, 67-73 (2016).; [3] Fait, J. et al., Nanophotonics 8, 1041-1050 (2019).; [4] Ondič, L. et al., ACS Nano 11, 2972-2981 (2017).; [5] Ondič, L. et al., Nanoscale 12, 13055-13063 (2020).; [6] Cajzl, J. et al., Phys. Chem. Chem. Phys. 19, 6233-6245 (2017).; [7] Stehlik, S. et al., ACS Appl. Mater. Interfaces 9, 38842-38853 (2017).

Non-fullerene acceptors (NFA) in the form of small molecules or inorganic nanoparticles made a break-through in OPV efficiency in the past decade due to their optical properties, electronic tunability as well as high thermal, photochemical and structural stability. In this work, we study nanoscale composites of detonation nanodiamonds (DND) and polypyrrole (PPy) and their use for energy generation [Sci. Rep. 11 (2021) 590]. We developed a technology for the composite layer-by-layer synthesis that is suitable for solar cell fabrication. The formation, pronounced material interaction and photovoltaic properties of DND-PPy composites are characterized down to nanoscale by atomic force microscopy, infrared spectroscopy, Kelvin probe, and electronic transport measurements. The data show that DNDs with different surface terminations (hydrogenated, oxidized, poly-functional) assemble PPy oligomers in different ways. This leads to composites with different optoelectronic properties, where combination of both oxygen and hydrogen functional groups on the nanodiamonds appears to be the most favorable. Tight material interaction results in significantly enhanced photovoltage and broadband (1 - 3.5 eV) optical absorption in DND/PPy composites. Theoretical DFT calculations corroborate the experimental data and confirm that nanodiamonds can act as inorganic electron acceptors. Prototype solar cells demonstrate functionality of the concept. ACKNOWLEDGEMENTS: The work has been supported by the Centre of Advanced Photovoltaics (CZ.02.1.01/0.0/0.0/15_003/0000464) and Czech Science Foundation.

Understanding to material properties down to few nanometers in size is important, yet often challenging task. In diamond, the size of 3 nm represent a critical threshold below which quantum-sized effects as well as transformation of the nanodiamond (ND) structure have been theoretically predicted. Preparation and/or isolation of sub-3 nm NDs from commercially available detonation nanodiamonds (DNDs) and high-pressure high-temperature (HPHT) NDs is possible but volumetrically dominant sub-2 nm fractions are difficult to obtain [1]. Recently, accurate size control in the sub-3 nm region has been achieved by using halogenated adamantanes as a precursors in bottom-up HPHT synthesis (b-uHPHT) [2]. This provides great opportunity to investigate size-related phenomena in Raman spectra of extremely small NDs.
Here we show that the Raman spectra of the 1.2 - 8 nm b-uHPHT NDs exhibit some unique features compared to conventional DNDs and HPHT NDs. The most striking is nearly complete absence of sp2-C related features in most of the investigated samples. Since the samples are in form of solid micron-sized pieces consisting of tightly bound individual b-uHPHT NDs the effect of deaggregation needs to be investigated.
In addition to the Raman diamond peak (≈1330 cm-1), we observed bands at 1150 cm-1, 1340 cm-1, 1450 cm-1, and 2800-3000 cm-1 whose intensity increased with decreasing ND size. These were identified as surface-originated C-Hx bonds and it indicates that the as-synthesized b-uHPHT NDs are hydrogen-terminated. The size-dependent evolution of diamond peak parameters (position and full width at half maximum) was investigated by multi-wavelength (442, 532, and 633 nm) Raman spectroscopy to possibly identify and avoid any heating effect of the excitation laser on the diamond line position. Use of multiple wavelengths also enabled to study dispersion of Raman active bands. We show that down to 2.6 nm the diamond Raman line shift is only minor (2-3 cm-1) which do not corroborate with current phonon confinement models commonly used in NDs. Only when the size decreases below 2 nm, larger shifts are observed (8-9 cm-1 for 1.4 nm sample). Finally, we provide analysis of the low-frequency (“breathing”-like) acoustic modes and show that these features can be used for size analysis of sub-4 nm NDs as we evidenced a good match with the size values obtained from XRD data (Scherrer’s formula).
REFERENCES: [1] S. Stehlik, M. Mermoux, B. Schummer, O. Vanek, K. Kolarova, P. Stenclova, A. Vlk, M. Ledinsky, R. Pfeifer, O. Romanyuk, I. Gordeev, F. Roussel-Dherbey, Z. Nemeckova, J. Henych, P. Bezdicka, A. Kromka, B. Rezek, Size Effects on Surface Chemistry and Raman Spectra of Sub-5 nm Oxidized High-Pressure High-Temperature and Detonation Nanodiamonds, J. Phys. Chem. C. 125 (2021) 5647-5669.; [2] E.A. Ekimov, S.G. Lyapin, Yu.V. Grigoriev, I.P. Zibrov, K.M. Kondrina, Size-controllable synthesis of ultrasmall diamonds from halogenated adamantanes at high static pressure, Carbon. 150 (2019) 436-438.

MXenes have drawn considerable attention in the past decade, thanks to their attractive properties such as metallic conductivity and surface hydrophilicity. In recent years, these two-dimensional (2D) materials have been explored in a wide range of applications such as supercapacitors, batteries, non-volatile resistive memory devices, field effect transistors and as electrode materials in photovoltaic devices. For effective utilization of two-dimensional materials in device applications, a systematic investigation of the film formation process is required. While many studies of MXenes as suspensions in different solvents exist, most of the evaluations have been done with water as a solvent. While MXenes form highly stable dispersions in water, it can act as a limitation for certain applications such as photoactive layer in photovoltaic devices.
In this work, delaminated MXenes aqueous solution type Ti3C2 was prepared first, and then we have used a solvent-exchange technique and prepared suspensions of MXenes in 3 polar aprotic solvents namely, DMSO, DMF and NMP. Upon spin-coating under the same conditions, each solvent variation yields a different thin film morphology - in terms of particle size and surface coverage, as evidenced from AFM investigations. While the MXenes in DMSO yielded large aggregated particles with μm-sized islands in the film, MXenes in DMF and NMP were found to form films with well-dispersed MXene sheets in the size range 250 nm-50 nm and 80 nm-10 nm, respectively. This study also provides additional insights into the microstructure, opto-electronic properties and surface photovoltage effects of each of the MXene thin films using correlative Raman, Photoluminescence and Kelvin probe microscopy.
The information obtained by this study about the variations in the properties depending on the solvent used to process and spin-cast the films from, are key precursors for evaluating MXenes in thin film device applications such as novel electrode materials, or as templates for controlling the photoactive layer grain sizes in photovoltaic devices.

A new group of two dimensional (2D) nanomaterials called MXenes, which offers attractive structural diversity and metallic conductivity was first time reported in 2011 [1] and despite their short history has already shown great potential in various applications such as supercapacitors, batteries, water purification, catalysis, antibacterial films, transparent conductive electrodes, sensors and others. [2] The most studied nanomaterial from the MXene family is Ti3C2Tx. One of the most highlighted properties of Ti3C2Tx and other MXenes compared to the other nanomaterials is their hydrophilicity, which is exhibited by MXenes due to the presence of polar surface functional groups Tx. The most common method to determine the hydrophobicity or hydrophilicity of the material is a contact angle measurement. However, the measurement of the static contact angles using a sessile drop method has been criticized in numerous articles due to a huge effect of randomness and the reproduction of these experimental static contact angles becomes a challenge for the other laboratories.
In this work, we investigated Ti3C2Tx−water interactions for Ti3C2Tx 1, 2 and 3 layers on substrates of different chemical composition using advancing and receding contact angle measurements, which are the only reproducible contact angles. An effect of the substrate chemical composition to the contact angle hysteresis on Ti3C2Tx layer will be discussed.
ACKNOWLEDGEMENT: This work was supported by the Slovak Research and Development Agency under the contract No. APVV-19-0465 and APVV-SK-BY-RD-19-0011 and by project VEGA 02/0010/18.
REFERENCES: [1] Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals: Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2 (Adv. Mater. 37/2011). Adv. Mater. 2011, 23 (37), 4207-4207. https://doi.org/10.1002/adma.201190147.; [2] Gajdošová V., Lorencová L. Procházka M., Mičušík M., Omastová M., Procházková S., Kvetoň F., Jerigová M., Velič D., Kasák P., Tkáč J. Microchimica Acta, 187, art. no. 52, 2020.

Engineering nanocomposites with a rational design is an ongoing challenge to access materials with predictable properties that can be optimized using structure-texture-morphology-activity relationships. Among the proposed inorganic materials, silica and titania promise unparalleled opportunities due to their synthetic versatility, chemical inertness, controlled size and porosity, processability, and the possibility to create ordered mesostructures. These advantages render these materials ideal for building new composites with defined properties that can find applications as sorbents and catalysts. The inorganic mesostructure serves as a scaffold for homogeneously dispersing active phases in the form of highly reactive small and ultrasmall (< 3 nm) nanoparticles: its regular and ideal pore size renders the active phase easily accessible from a numerous species, whereas the mesochannels walls hamper possible sintering phenomena making the material regenerable. Playing with the nature (amorphous or crystalline) and composition (SiO2 or TiO2) of the inorganic mesostructure, it is possible to produce different nanophases providing a general way for designing an appealing class of materials for a wide range of applications including sorption and catalysis. Here, we intend to present a brief overview of our most recent activities on SiO2[1-6] and TiO2-based[4] mesostructured sorbents (for gaseous H2S or ionic arsenate removal [6] and catalysts (for dimethyl ether production). In particular, coupling ultrasmall active nanoparticles with mesostructured inorganic supports was proved to be extremely effective for designing highly active and regenerable materials. Furthermore, the possibility to replace commercial silicon precursors with industrial waste [5] opens new perspectives for its use on a large scale.
References: [1] Cannas C.*et al. J. Mater. Chem. A, 2014, 2, 19396.; [2] Cannas C. *et al. J. Mater. Chem. A, 2017, 5, 21688.; [3] Cannas C. *et al. J. Phys. Chem. C, 2018, 122, 23, 12231.; [4] Cannas C.* et al. Micr. Mes. Materials, 2020, 298, 110062.; [5] Cannas C.* et al. ACS Sustainable Chem. Eng. 2020, 8, 38, 14286.; [6] Cannas C.* et al. Nanoscale Adv., 2021, DOI: 10.1039/D1NA00487E.

Functionalization of graphene can mitigate its tendency for restacking and boost interactions with target chemical species. Fucntionalization must be selective and dense if high performance is required, combined with stability in challenging environments. Such properties are pre-requisites for sustainalbe sorbents and electrode materials for energy storage and catalysis.
By leveraging the susceptibility of fluorographene to nucleophiles, advanced and tailored graphene derivatives can be obtained for targeted applications. Graphene acid (GA), cyanographene (G-CN), superdoped graphene are indicative examples. GA bears carboxyls which are strong metal-coordination sites. Therefore, GA exhibits high proclivity for sorption and sensing of Cd2+ and Pb2+, as well as for the valorisation of waste Pt for developing electrocatalysts for the oxygen reduction reaction. The all-covalent and spacer-free C-COOH bonds render GA bullet-proof in highly acidic media, enabling metal recovery and full sorbent regeneration.[4] As Li-ion battery anode, GA reveals i) high redox capacity stemming from its carboxyl groups, ii) high conductivity, boosting the rate capability, and iii) extra charge storage due to the co-presence of high content in sp2 moieties serving as Li intercalation sites. The nitrile groups of G-CN display the required coordination strength and electronic communication with the aromatic skeleton of graphene for preparing undercoordinated and mixed valence catalysts, enabling the effective production of pharmaceutical synthons via cooperative mixed valence single atom catalysts.
Such graphene derivatives lay the ground for the development of the next generation materials for energy storage, catalysis, sorption and environmental monitoring.

Two dimensional (2D) materials have drawn attention in many scientific areas due to their extraordinary electronic, mechanical and optical properties, which originate from their 2D morphology connected with very low thickness. The best-known 2D material is graphene. MXene is one of the many alternatives of 2D structures. The general formula for MXenes is Mn+1XnTx (n = 1-3), where M represents transition metals (Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and others), X is carbon and/or nitrogen and Tx refer to various functional groups on the surface (e.g. OH, O, F, etc.). The combination of 2D materials such as MXene and 1D fillers such as carbon nanotubes and consequent implementation into the polymeric matrix enables to prepare polymer composites with a high electroconductivity and electromagnetic interference (EMI) shielding capacity.
At first, we prepared and characterized MXene 2D nanoparticles, which were used as active filler in the polymer composites. For the final application it is always important to know the detailed structure of MAX phase used for MXene preparation1.
One of the main drawbacks of MXene application is the relatively low stability on air. In our study we used XPS and TEM in multiple modes (bright field imaging, energy-dispersive analysis of X-rays, and selected-area electron diffraction) in order to study the chemical and morphological changes in 2D MXene exposed to air for several months. We have observed the progressive development of Ti4+ state accompanied by the development of TiO2 formation, which led to a slow disintegration of 2D MXene nanosheets, although their overall morphology and crystalline structure persisted for several months
ACKNOWLEDGEMENTS: This work was supported by the Slovak Research and Development Agency under the project APVV-SK-BY-RD-19-0011 and Belarusian Republican Foundation for Fundamental Research under grant № Х20СЛКГ-004 and from agency VEGA 02/0010/18 (Slovakia).
REFERENCE: [1] Ivanovskaya, Maria - Ovodok, Evgeni - Kotsikau, Dzmitry - Azarko, Igor - Mičušík, Matej - Omastová, Mária - Golovanov, Vyacheslav. Structural transformation and nature of defects in titanium carbide treated in different redox atmospheres. In RSC Advances, 2020, vol. 10, no. 43, p. 25602-25608. https://doi.org/10.1039/d0ra02959a.

Microwave plasma-based gas-phase synthesis of graphene and its derivates represents simple, environmentally friendly, and easily scalable production method enabling large-scale deployment of such material in the emerging energy storage, sensor, and flexible electronic devices applications. Microwave plasma decomposition of organic precursors, hydrocarbons, and alcohols, forms a high-temperature environment, where the process of catalyst-free dehydrogenation and consequent formation C atoms and C2 molecules leads to the nucleation and growth of high-quality few-layer graphene nanosheets. In this work we show how the spatial and temporal distribution of heat field formed by microwave plasma environment influences the reaction pathway of atomic and molecular species and leads to a high yield synthesis, over 50 % of available carbon is converted into the graphene and enables synthesis of structure with controlled functional properties. Prepared material was analyzed by SEM, TEM, Raman and X-ray photoelectron spectroscopy and thermogravimetry. Information about plasma processes was obtained by optical emission spectroscopy, high speed and ICCD camera imaging, FTIR spectroscopy and mass spectrometry. Comparison of electrical conductivity, high temperature oxidation resistance and mechanical properties of gas-phase synthesized graphene and liquid exfoliated graphene will be presented.

2D semiconductor transition metal dichalcogenides have attracted considerable attention due to their layered structure, suitable band gap, electrochemically active unsaturated edges and relatively good stability against photocorrosion. These properties result promising for different applications including, Li-ion batteries, photocatalysis and hydrogen evolution reaction (HER). Apart from the widely studied 2D MoS2, 2D selenide and telluride equivalents, MoSe2 and MoTe2, have gained considerable interest due to their higher electrical conductivity, wider inter-layer distance and narrower bandgap as compared to MoS2, high surface area and close to zero Gibbs free energy edges for hydrogen adsorption. Unlike sulfide dichalcogenides, the lack of Se and Te precursors have prevented the synthesis of selenide and telluride dichalcogenides by ALD. In order to surpass such impediment, we present a set of novel in-house synthesized Se and Te compounds combined with commercial Mo precursor to synthesize MoSe2 and MoTe2 [1-5]. The as-deposited ALD MoSe2 and MoTe2 were extensively characterized by different techniques, which confirmed the chemical composition and the growth of 2D flaky nano-crystalline MoSe2 and MoTe2. In parallel, MoSe2 and MoTe2@TiO2 nanotube layers (TNTs) heterostructures were fabricated in a simple and fast fashion to explore and exploit the MoSe2 and MoTe2 photo- and electrocatalytic properties. TNTs act as excellent photoactive supporting material providing a high surface area, unique directionality for charge separation, and highly effective charge collection.
The presentation will describe the synthesis of the 2D Mo dichalcogenide family, the corresponding physical and electrochemical characterization and results obtained in HER [4,5], photocatalysis [4-6] and Li-ion batteries [7].
REFERENCES: [1] R. Zazpe et al, FlatChem (2020) 21 100166.; [2] J. Charvot et al, Chempluschem (2020) 85 576.; [3] J. Charvot et al, RSC Adv. 2021, revision submitted.; [4] R. Zazpe et al, ACS Appl. Nano Mater. 2021, 3, 12, 12034.; [5] R. Zazpe et al, Appl. Mater. Today 2021, in revision.; [6] M. Motola et al, Nanoscale 11 (2019) 23126.; [7] H. Sopha et al FlatChem 17 (2019) 100130.

Valve metals and their oxidized forms have been widely used as switching materials in the next generation of non-volatile electronics. Memristive devices based on high-κ dielectric materials, such as Hf and Ta, can be excellent candidates concerning the development of redox-based resistive switching memories (ReRAMs) or artificial neural networks. The memristive effect was recognized for metal-insulator- metal architectures in which the switching mechanism is based on the CFs formation inside of the oxide layer placed between two metallic electrodes.
In this study, memristive devices containing pure Hf, Ta or their alloys as bottom electrodes, their oxides as insulating layers and Pt as top electrodes, were investigated. Metallic electrodes were fabricated by sputtering, while oxides were grown via electrochemical anodization. Hence, the memory materials were produced by an inexpensive, simple and fast method. Electrochemical parameters were tuned and optimized during the anodization of pure Hf and Ta and consequently applied for the fabrication of the oxides grown on Hf-Ta alloys. A thin film combinatorial library had the total compositional spread ranging from 5 to 92 at.% Hf. Memristive behavior was screened over Hf-Ta library with 1 at.% resolution which showed specific memory characteristics defining three different compositional zones. The switching mechanisms differed, suggesting that CFs varied in size and shape or location in the oxide for each zone containing a high number of produced memristors. This was confirmed by depth profile investigation during XPS and imaging of CFs by HRTEM. Finally, such approach may lead towards formation of defect engineered memristors.

Energy storage is a dominant factor in the development of the economy through the widespread introduction of electricity and refined chemical fuels such as petrol, kerosene and others.
Supercapacitors (SCs), as one of most promising emerging energy storage devices, are of great interest owing to their high power density with great mechanical compliance, making them very suitable as power back-ups for future stretchable electronics. Two-dimensional (2D) nanomaterials, including the quasi-2D graphene and inorganic graphene-like materials have been greatly explored to providing huge potential for the development of new types of SCs with higher electrochemical performance.
The hybrid consisting of carbon-based materials, transition metal oxides or hydroxides, and conductive polymers can improve capacity, due to the Faradaic reaction and separation of charge between the electrode-electrolyte interfaces. Several conductive polymers have been studied for application in SCs as polypyrrole or polyaniline (PANI).
In our work the improvement of cyclic stability of PANI through a combination of reduced graphene oxide (rGO) and copper-metal-organic framework (MOF) was achieved. Crystalline porous MOFs as organic units that link metal ions to clusters are characterized by a large surface area, high stability, large pore volume, and organic functionality and these properties predetermine them for the preparation of the electrode in supercapacitors [1]. Compared to pure graphite, GO is more reactive due to the oxygen functional groups on its surface and edges, but it is also less conductive. However, this can be remedied by reducing it and decreasing the oxygen content. The properties of the prepared electrode materials were examined by ATR-FTIR spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). In the next step new type of 2D materials, MXenes were used for hybrid electrode preparation. The first results showed promising results for application as electrodes in SCs.
ACKNOWLEDGEMENTS: This work was supported by the M-era.Net 2019 call project "LiBASED Li-ion BAttery-SupErcapacitor Hybrid Device" grant No. M-ERA.NET 2/2019/966/LiBASED from Slovak Academy of Sciences and International mobility of TBU researchers in Zlín, grant No. CZ.02.2.69/0.0/0.0/16_027/0008464.
REFERENCE: [1] L.Q. Bao et al., Electrochimica Acta 367 (2021) 137563.

The organic-inorganic hybrid perovskites seem to be strong competitor for conventional silicon based electronic devices. Hybrid perovskite-based materials are promising materials for the development of solar cells, solid-state lasers, light emitting diodes (LEDs), photodetectors, etc. Hybrid perovskite-based materials can easily be deposited from their precursor solutions into a thin film by solution-based processes [1]. Nevertheless, the prepared films possess defects which cause non-radiative recombination, current-voltage hysteresis and rapid degradation due to the low stability of the resulting devices [1]. On the other hand, efficiency of the functional devices decreases dramatically when amorphous materials are implemented instead of highly crystalline ones. Therefore, it is challenging to optimize and up-scale the production of large-sized single crystals of perovskite materials. Here, we describe a novel and original approach to MAPbBr3, FAPbBr3, MAPbI2 and FAPbI2 lead halide perovskite single crystals preparation which consists in applying microwave radiation during the crystallization [1]. The facile microwave assisted method of preparation is highly reproducible, fully automated and in addition, it can be applied for various different perovskite structures. Simultaneously, this eco-friendly method is expected to be easily up-scalable because of its versatility and low energy consumption. We believe that this method will make preparation of single crystals, nanosystems, 2D systems and the final functional devices fabrication (like solar cells, LEDs, photodetectors, i. e.) more convenient and efficient.
ACKNOWLEDGEMENTS: The work was supported by the FCH-S-21-7553 and GACR project 20-29499Y funded by Czech Science Foundation.
REFERENCE: [1] Jan Jancik, Anna Jancik Prochazkova, Markus Clark Scharber, Alexander Kovalenko, Jiří Másilko, Niyazi Serdar Sariciftci, Martin Weiter, and Jozef Krajcovic, Crystal Growth & Design 2020 20 (3), 1388-1393, DOI: 10.1021/acs.cgd.9b01670.

Valence engineering has been proved an effective approach to modify the electronic property of a catalyst and boost its oxygen evolution reaction (OER) activity, while the limited number of elements restricts the structural diversity and the active sites. Also, the catalyst performance and stability are greatly limited by cationic dissolution, ripening, or crystal migration in a catalytic system. Here we employed a widely used technique to fabricate heteroepitaxial pyrite selenide through dual-cation substitution and a boron dopant to achieve better activity and stability. The overpotential of Ni-pyrite selenide catalyst is decreased from 543 mV to 279.8 mV at 10 mA cm-2 with a Tafel slope from 161 to 59.5 mV dec-1. Our theoretical calculations suggest both cation and boron doping can effectively optimize adsorption energy of OER intermediates, promote the charge transfer among the heteroatoms, and improve their OER property.

Sea balls (pillae marinae) were impregnated with diammonium hydrogen phosphate (DAHP), carbonized, and activated using carbon dioxide or steam. Thus, activated carbon fibers (ACFs) with unique morphology and specific surfaces of 243 m2 g-1 were produced. These ACFs were studied as electrode materials for supercapacitors that achieved specific capacities of 38 F g-1 in an organic electrolyte, resulting in specific energy for the supercapacitor of 9.7 W h kg-1.