Seznam abstraktů 2019: SEKCE A - NANOMATERIÁLY PRO ELEKTRONICKÉ, MAGNETICKÉ A OPTICKÉ APLIKACE. UHLÍKOVÉ NANOSTRUKTURY, KVANTOVÉ TEČKY

“Quantum dot (QD)” or, other name, “quantum box”, represents an ultimate case of size quantization in solids, where the motion of the charge carriers is restricted in all three dimensions (3D). The critical condition for the formation of truly atom-like density states is a high quality of interfaces surrounding such nano-objects. Defects at interfaces and the related scattering and nonradiative recombination effects drastically reduce or even eliminate advantages of the 3D nanoobjects. Consequently, heteroepitaxial overgrowth became necessary before all the advantages of zero-dimensional electron spectrum in QDs were implemented both in core-shell colloidal QDs and in epitaxially-grown QD heterostructures.

Lead sulfide (PbS) quantum dots (QDs) have been covalently attached to reduced graphene oxide (rGO). Thin films from a hybrid rGO-PbS nanomaterial have been formed by a Langmuir-Blodgett technique. We found that oleic acid on QDs surface induces self-organization of high-quality rGO-PbS films with a thickness of 1-2 monolayer. To utilize these films in optoelectronic devices, post-deposition ligand exchange procedures have been applied. We found both high conductivity and light-sensitivity in EDT- and TBAI-treated rGO-PbS films. We have applied rGO-PbS hybrid films to enhance the performance of a hybrid and heterojunction QD-based solar cells.

Following the isolation of graphene sheets by mechanical exfoliation of its parent crystal graphite, enormous effort has been directed towards two-dimensional (2D) crystals made of group-IV elements other than carbon. A particularly noteworthy example is silicene, the silicon equivalent of graphene with a natural compatibility with current semiconductor technology. Silicene is predicted to exist in a low-buckled honeycomb lattice, characterized by semimetallic electronic bands with graphenelike energy-momentum dispersions around the Fermi level (represented by touching Dirac cones). Unlike graphene, freestanding silicene has a large spin-orbit coupling, which would make it suitable for valley-spintronic applications, and an electrically, magnetically, or chemically tunable band gap, which would be crucial for engineering on-off current ratios and charge-carrier mobility in silicene field-effect transistors. Single layers of silicene are mostly synthesized by depositing silicon on top of silver, where, however, the different phases observed to date are so strongly hybridized with the substrate that not only the Dirac cones, but also the whole valence and conduction states of ideal silicene appear to be lost. Here, we provide evidence that at least part of this semimetallic behavior is preserved by the coexistence of more silicene phases, epitaxially grown on Ag(111). In particular, we combine electron energy loss spectroscopy and time-dependent density functional theory to characterize the low-energy plasmon of a multiphase-silicene/Ag(111) sample, prepared at controlled silicon coverage and growth temperature. We find that this mode survives the interaction with the substrate, being perfectly matched with the π-like plasmon of ideal silicene.

Laser surface processing is an established method to introduce surface functionalities on solid surfaces with the required throughputs for a commercial process. Fabrication of laser induced surface structures in an effective matter is done by laser interaction studies, which reveal the best processing parameters (laser wavelength, fluence, repetition, together with the processing speed and environment). Customized solutions are providing the best yields and they are being implemented faster than ever. However, the optics manufacturers are not being to keep up the pace with the new requirements, so they turn instead on older, but safer technology. In order to get a better understanding of optics capabilities, thorough testing is required. Common laser metallic mirrors, commercially available, are being rigorously tested using a nanosecond Yb:YAG laser and the results are compared with the vendor’s information.

Employing multi-scale in silico modeling we propose switching molecular diode based on endohedral fullerenes (fullerene-based switching diode, FSD), encapsulated with polar molecules of general type MX (M: metal, X: non-metal) to be used for data storage and processing. We demonstrate here for MX@C70 systems that the relative orientation of enclosed MX with respect to a set of electrodes connected to the system can be controlled by application of oriented external electric field(s). We suggest a four-terminal system of electrodes, in which the main electrodes help the current to pass through the device and help the switching between the conductive states of FSD via applied voltage. The gate electrodes then assist the switching by effectively lowering the energy barrier between local minima via stabilizing the transition state of switching process. Using non-equilibrium Green’s function combined with density functional theory (DFT-NEGF) computations, we further show that conductivity of the studied MX@C70 systems depends on the relative orientation of MX inside the cage with respect to the electrodes. Therefore, the orientation of the MX inside C70 can be both enforced (“written”) and retrieved by applied voltage. The studied systems thus behave like voltage-sensitive switching molecular diodes suitable for application in random access memories for short-term or memristors for long-term data storage. This depends on the energy barrier for the MX switching in the absence/presence of an external electric field, i.e. the lifetime of the states.

4K high-resolution microscope series VHX-7000 represents the new era of the 5th generation of digital microscopes, which allow more accurate images and easier operability than ever before. Thanks to a full-control system even first-time users can capture optimal images. High-resolution images draw out the finest details. Images can be observed and displayed in color.
VK-X series laser scanning microscope represents the latest contactless profilometer, able to measure fine, previously unmeasurable surface finishes. The main advantages are accurate surface analysis over a large area, measurement on all types of surfaces, resolution up to 0.5 nanometer and, last but not least, automated roughness measurement analysis.

In last two decades, GaN semiconductor became an important material for optical and electronic applications such as LEDs, laser diodes, RF and microwave devices and power switches. High-electron mobility transistors (HEMTs) based on group III-N heterostructures are considered to play an important role e.g. in 5G telecom networks as RF and microwave power devices. In particular, lattice-matched InxAl1-xN/GaN (x=0.18) heterostructure offers very high 2-dimensional electron gas (2DEG) density and excellent scalability allowing fabrication of HEMTs with record current gain cut-off frequency up to 400 GHz. Due to a high gate leakage current of Schottky-gated devices, metal-oxide-semiconductor (MOS) gate structure is often employed in InAlN/GaN HEMTs, improving their performance and stability. Yet, insertion of the oxide layer brings also challenges such as threshold voltage (Vth) instabilities. Moreover, there is still limited understanding on the oxide/III-N interface charge formation, being vital for the device’s Vth adjustment.
In this work, we will first review recent achievements in InAlN/GaN MOS-HEMT technology, followed by description of various defects observed in the MOS gate stack and suitable techniques for their characterization. Then, the oxide/III-N heterointerface electrostatics will be outlined and an effective method for oxide/barrier interface net charge density, Nint, extraction will be introduced. We will present possible technological approaches to manipulate Nint in order to process enhancement-mode InAlN/GaN MOS-HEMTs. Finally, we will discuss the origin of the charge compensating the III-N surface polarization charge.

Gallium nitride (GaN) and zinc oxide (ZnO) belong to the most investigated wide band gap semiconductors nowadays. ZnO is a direct band gap semiconductor with a large exciton binding energy and a broad range of potential applications in electronics and optoelectronics. The main drawback of ZnO is the lack of reliable p-type doping, which limits the applications to unipolar or heterojunction devices. The hetero-structures of ZnO and GaN have been broadly researched thanks to their identical crystal structure and similar lattice constants.
We show that when the n-ZnO/p-GaN heterojunction is realized in a nanostructured form using focused ion beam (FIB) to locally modify the p-GaN substrate, the electrical properties of the heterojunction can be significantly improved. To fabricate these heterojunctions, hexagonal periodic arrays of ZnO nanorods were grown by chemical bath deposition on FIB-modified GaN substrates. The periodic distribution of the nanorods guarantees uniformity of their physical properties and allows for the in-depth investigation of their growth mechanisms. The FIB treatment of the GaN surface, which results in the fabrication of shallow trenches, enables the nucleation to be uniform and spatially well-controlled. We attempt to explain how the nanorods nucleate and grow with respect to the parameters of the FIB treatment of the GaN substrate. For this purpose, site-specific lamellas were prepared by FIB to be further observed by transmission electron microscopy.

I present a project to design of the simplified model of thinking located in a little-explored field between neurobiology and psychology. While neurobiology in the incredibly complex microscopic system is dedicated with the structures and signals at the molecular level and the psychology is committed at the opposite extreme with highly complex, however, from the user’s point of view, they are very abstract and therefore difficult to grasp these wholes. There is a vast space between these two extremes, from the perspective of the inherent observers it is investigable without overcoming of the complexity of both points of interest.
The primary goal of this research is to construct a multi-layer nanoelectronic analog configuration space wherein the signals have the same properties (electrical, biochemical, physical and connections) as in the human brain.

Term and concept of a new branch of science and technology, namely, “nanoionics”, were formulated in IMT RAS (1991-1992). It was the article "A step towards nanoionics". New area R&D devotes to nanoscale fundamentals of fast ionic transport (FIT) in solid-state materials, as well as to methods for design of FIT-nanomaterials, for description of local FIT-space-temporal processes, for creation of devices with FIT on a nanoscale ("nanoionic devices"), etc. Main achievements of IMT RAS in nanoionics are: (1) new optically-active nano-physical-chemical systems Ag(Cu)Hal -M, created in high vacuum (M are rare-earth/transition metals); (2) new classification of solid-state ionic conductors (it distinguishes for the first time a new class of solid state conductors - “advanced superionic conductors“, i.e., materials whose crystal structures are closely to optimum for FIT); (3) new scientific direction "nanoionics of advanced superionic conductors"; (4) a crystal-engineering of heteroboundaries in FIT-materials and an invention of supercapacitors with coherent polarized heterojunction and record-high frequency-capacitance characteristics ("nanoionic supercapacitors"); (5) substantiation about possibility of using of nanoionic supercapacitors in deep-sub-voltage nanoelectronics; (6) definition of ways for heterointegration in supercapacitors of advanced superionic conductors and carbon nanostructures with a high quantum capacitance; (7) theory of a dynamic response of layered nanostructures with ionic hopping transport in a non-uniform potential landscape ("structure-dynamic approach of nanoionics"); (8) new fundamentals of electrostatics related to materials with FIT; (9) proposition of a non-linear non-local dynamics for FIT-materials. Future nanoionic researches are analyzed in terms of the dynamic theory of information.

The effective thermal designs of package systems have been required because high operating temperature is problem of performance and reliability of micro-electronics. We investigated the thermal conductivity and mechanical reliability of MWCNT-containing EMC and Ag decorated multi-walled CNT (Ag-MWCNT) composite Ag pastes for fan-out wafer level package. The MWCNT have suitable thermal, electrical and mechanical properties for application in microelectronic devices. The MWCNT composite material was designed for thermal interface material of fan-out package. Thermal conductivity of composite material with various MWCNT load was measured by hot disk thermal constant analyzer. The temperature of fan-out LED component with MWCNT-containing EMC and Ag-MWCNT composite pastes was measured by IR camera. And temperature gradient of the fan-out LED component was simulated by using the finite element method (FEM) analysis. The mechanical reliability of fan-out LED component was evaluated by thermal shock test in compliance with JESD22-A104D. Thermal conductivity of MWCNT-containing EMC increased with increasing the content of MWCNTs. However, thermal conductivity of Ag-MWCNT composite paste increased by about 6 % compared to Ag paste without Ag-MWCNT. The peak temperature of fan-out FCLED component decreased 5 °C when component was fabricated with Ag-MWCNT composite pastes. The thermal cycles of fan-out component with Ag-MWCNT-containing composite paste was 5 times higher than that with Ag paste. The thermal conductivity was increased due to increasing thermal path by MWCNT. Furthermore, mechanical reliability Ag-MWCNT composite paste was improved due to crack blunting effect because of network structure of Ag-MWCNT.

First-principles spin-polarized density functional theory investigations are reported to understand the effect of functionalization (vanadium and titanium) on tunneling magnetoresistance (TMR) and spin-polarized transport of black phosphorene (BP ) nanosheet based magnetic tunnel junction (MTJ) with CrO2 as electrodes. The results show, vanadium adsorbed black phosphorene based structure exhibits better spin filtration and high TMR, as compared to titanium adsorbed black phosphorene and pristine black phosphorene based structures. In addition, vanadium adsorbed black phosphorene nanosheet exhibits ferromagnetic behavior with a magnetic moment of 2.6388 µB. The magnetic moment for pristine black phosphorene and titanium adsorbed black phosphorene nanosheets are reported to be 0.000007144µB and 2.2 µB, respectively. Higher TMR, better spin filtration and ferromagnetic behavior for vanadium adsorbed black phosphorene based structure open up its possibility as spin filter (injector) in MTJs and other spin-based devices.

We combine theoretical and experimental tools to study elastic and magnetic properties of Fe-Al-based superalloys. Focusing on samples with chemical composition Fe71Al22Ti7, we use transmission electron microscopy to detect their two-phase superalloy nano-structure (consisting of Fe-Al-Ti cuboids embedded into an Fe-Al matrix). The chemical composition of both phases was determined from an Energy-Dispersive X-ray Spectroscopy analysis. Quantum-mechanical calculations were employed to obtain an insight into thermodynamic, magnetic and elastic properties of the two phases. Three distributions of chemical species with different level of (dis-)order were simulated for each of the phases. The most ordered phases are predicted the most stable. Next, the elastic tensors of all phases were calculated. The maximum Young's modulus is found to increase with increasing chemical order. Further we simulated an anti-phase boundary (APB) in the cuboid phase and observed an elastic softening (as another effect of the APB, we also predict a significant increase of the total magnetic moment by 140% when compared with the APB-free material). Finally, to validate these predicted trends, a nano-scale dynamical mechanical analysis (nanoDMA) was used to probe elasticity of phases. Consistent with the prediction, the cuboids were found stiffer (for details see Friák et al., Crystals 9 (2019), 299; https://doi.org/10.3390/cryst9060299).

The high-entropy alloys Al$_{x}$CrFeCoNi exist over a broad range of Al concentrations (0 < x < 2). With increasing Al content their structure is changed from the fcc to bcc phase. We investigate the effect of such structural changes on transport properties including the residual resistivity and the anomalous Hall resistivity. We have performed a detailed comparison of the first-principles simulations with available experimental data. We show that the calculated residual resistivities for all studied alloy compositions are in a fair agreement with available experimental data as concerns both the resistivity values and concentration trends. We emphasize that a good agreement with experiment was obtained also for the anomalous Hall resistivity. We have completed study by estimation of the anisotropic magnetoresistance, spin-disorder resistivity, and Gilbert damping. The obtained results prove that the main scattering mechanism is due to the intrinsic chemical disorder whereas the effect of spin polarization on the residual resistivity is appreciably weaker.

Liquid metals become superior materials for soft electronic circuits due to their high electrical conductivity and infinite mechanical failure strain. Stiffness of electric circuits slows down their implementation in applications where motion is crucial. The liquid based metal alloys can form excellent conductors and enable to fabricate deformable metallic materials. These alloys can be shaped for various devices such as skin contact sensors. Electromigration is one of the long term reliability issues in electrical circuits. After analyzing the electron flux induced atomic displacement in Al-Cu alloys, Ga-based libraries were screened for improved electromigration resistance. A combinatorial approach was used to fabricate Cu-Ga and Al-Ga thin film alloys by thermal evaporation for developing 2D wires for electromigration testing. The surface of Ga reacts with oxygen rapidly and causes a thin oxide layer (about 1-3 nm), however the oxide layer is so thin that it does not have a significant effect on electrical measurements. Testing on Ga-based thin film alloys wires was performed using a modified 4-point technique for excluding unwanted effects of contact resistance on the measurements. The microstructure changes of Cu-Ga and Al-Ga alloys along the compositional gradient in the thin film library were studied in details. SEM imaging was used for observing the current flux induced damage areas in Ga-based alloys 2D test wires. Power density calculations based on the measurements showed 20% increase on Cu-Ga thin film alloys as compared to Al-Cu alloys, therefore these materials are promising for future flexible electronic devices.

This study addresses the effects of atmospheric-pressure plasma on the properties of methylammonium lead halide perovskite thin films. Plasma-treated films then were used to fabricate an inverted p-i-n perovskite solar cell. The plasma treatment employed a large-area plasma of extremely high-volume power density, up to 100 W/cm3, capable of generating diffuse, homogeneous and cool plasma (<70 °C) in ambient air, as well as in other technical-grade gases including nitrogen, argon, methane, hydrogen, carbon dioxide and pure water vapour. Although the temperature of the plasma remained very low, the population of energetic states proved sufficient to induce both physical and chemical changes on the surfaces of perovskite films. The results demonstrate that plasma treatment leads to perovskite films with homogeneous surfaces. Photoluminescence measurement revealed that plasma treatment enhanced the intensity of peaks, a property that may be attributed to improved crystallinity. Most importantly, plasma treatment of perovskite films improved the performance of the perovskite solar cells.

Nanoalloys composed by transition metals currently attract much attention, since the combination of properties belonging to their components provides smart solutions in various fields. The traditional synthesis of such materials relies on two main alternatives: mechanical alloying by ball milling using high-temperature and pressure treatments, or the chemical reduction of metal salts using hazardous ammonium compounds or borohydrides. In any case, the combination of hardly-miscible elements requires extreme reaction conditions, which is the main limitation of the traditional methods. In the current contribution, we propose the laser-mediated reduction of precursor salt solutions to produce Fe-Cu nanoalloys. These two elements exhibit a very low miscibility (ca. 3%) under the normal conditions.
For this purpose, the water-based solution of CuCl2∙2H2O and FeCl2∙4H2O was irradiated by a nanosecond pulsed laser source. The laser peak intensity was set to 3∙1012 W/cm2. The incoming energy dissociated the H2O molecule and the solvated electrons and hydrogen radicals that arise from the H2O dissociation reduced the metal salts, which later formed the Fe-Cu nanoalloys by mixed coalescence. The produced nanoparticles were homogeneously composed by 41.8wt.% Cu, 37.3wt.% Fe and 20.5wt.% O, exhibited a size of 5±2nm and a saturation magnetization of 13.60emu∙g-1.
The results suggest that the laser-based methodology can be exploited for the synthesis of nanoalloys composed by hardly-miscible elements. In contrast to the conventional methodologies, while no special conditions or hazardous reducing agents are required.

Niobium carbide (NbC) because of high melting point (~3610 °C) is one of the key components for ultra-high temperature ceramics (UHTCs) for space industry. It exhibits good physical properties such as high hardness, high toughness and Young's modulus; good chemical properties such as corrosion resistance; excellent electrical conductivity. Niobium water solution was prepared by dissolving of niobium pentoxide powder in a 48 % aqueous solution of hydrofluoric acid with a 10 % excess of a stoichiometric ratio. The resulting suspension was stirred at a temperature of 65 ℃ until the powder was completely dissolved. Then the solution was cooled down to room temperature, after which a 20 % ammonium hydroxide was added to it in small portions, which resulted in the neutralization of an excess of hydrofluoric acid and precipitation of niobium hydroxide. The precipitate was separated from mother liquor on a vacuum filter and washed with distilled water till pH≈7. Next, the precipitate was mixed with water solution of citric acid with different excess of citric acid of up to 2 times from stoichiometric ratio and stirred at room temperature until a clear solution of niobium citrate was formed. The solution was then dried at 80 °C. The resulting mixture of niobium citrate with citric acid was subjected to decomposition in a vacuum furnace at a temperature of 1200 °C and holding time for 1 hour. Resulting product represented by nanosized NbC with crystallite size less than 10 nm and amorphous carbon. Some samples contain small amounts of carbon graphite-like ordered structures. ACKNOWLEDGEMENTS: The work is supported by RSCF grant 19-73-20012.

In the last few years, new generation of portable electronics devices have been enriching our professional and recreational lives to an extent that they have become indispensable for almost everyone. Flexible and stretchable devices can be used in a wide range of consumer applications, ranging from wearable electronics, to mobile healthcare, to Internet of Things (IoT) technology [1].
Development of flexible energy photovoltaic generation and storage devices is crucial in this context and imposes stringent limits in terms of choice of materials constituting the stack and device architectures, because the most common flexible substrates, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), or paper are not compatible with high temperature treatments, which are usually employed for sintering some of the layers in highly efficient devices [2]. In this presentation two different type of flexible devices, perovskite solar cells (PSCs) and supercapacitors, realized with printing technique on flexible substrates will be shown highlighting the role of the technological process conditions for obtaining good performances and scalable devices.
In particular, for the case of PSCs it will be shown how it is possible to pass from a small area flexible devices with a maximum efficiency of 14% to a small module with a promising efficiency of 9 %. In case of supercapacitors, we report on the fabrication of devices with different dimensions on paper with a specific capacitance of 1 mF∙cm-2 and a power density of 20µW∙cm-2. REFERENCES: [1]S.Pan et al.Adv. Energy Mater.2016,6,1501867; [2]V. Zardetto et al.Polym.Sci.B Polym. Phys., vol.49,2011,pp. 638-648.

Metal-halide perovskite nanomaterials are gaining significant attention due to their structure, size and shape versatility; facile synthesis and easy processing from solutions. In addition, they possess outstanding optical properties, such as emitting light within a narrow bandwidth of the visible spectrum and high photoluminescence quantum yields. Thus, perovskite nanoparticles have proven to be applicable for optoelectronic devices, such as OLEDs, photodetectors and lasers [1].
The present work is focused on the synthesis of methylammonium lead bromide (MAPbBr3) perovskite nanoparticles which are stabilized by bio-originated capping agents. Proteinogenic amino acids L-Lysine and L-Arginine were chosen alongside with various surfactants not only for the stabilization but also for the surface modification. It was observed that spherical perovskite nanoparticles were obtained with below 10 nm sizes and exhibiting photoluminescence quantum yields close to 100 % [2].
As far as amino acids have been incorporated into the perovskite structure by their side chains, oligopeptides containing L-Lysine or L-Arginine can be used for nanoparticles stabilization [3]. It is supposed that aforesaid approach can broaden the applicability of perovskite nanoparticles, because oligopeptides on the surface can enhance the affinity to desired surfaces, therefore self-assembly properties and sensing abilities.
ACKNOWLEDGEMENTS: The work was supported by the Czech Science Foundation, grant No. 19-23718S.
REFERENCES: [1] K. Hong et al. J. Mater. Chem. C, 2018, 6, 2189-2209.; [2] A. Jancik Prochazkova et al. ACS Appl. Nano Mater. 2019.; [3] A. Jancik Prochazkova et al. Scientific Reports, under review.;

Prevailing modes of the manufacture of modern energy-harvesting systems and other electronics based on silicon fail to meet the requirements of the steps involved in low-cost fabrication. Rapid and low-cost roll-to-roll manufacture - the future of commercialization for flexible and printed electronics - requires flexible and low-cost substrates such as polyethylene terephthalate, polyethylene naphthalate and, more recently, green materials such as nano-paper. The temperature at every single fabrication stage is crucial with such materials and cannot exceed a certain threshold, generally 150 °C or less. Low-temperature plasma, therefore can provide an excellent way forward for future manufacturing methods.
This contribution presents a proprietary, large-area plasma of extremely high-volume power density, up to 100 W/cm3, capable of generating diffuse, homogeneous and cold plasma (<70 °C) in the open air, as well as in technical-grade gases including nitrogen, argon, methane, hydrogen, carbon dioxide and pure water vapour. Although the temperature of the plasma is very low, the population of energetic states is sufficient to induce physical/chemical changes on the surfaces of a range of nanostructured materials and semiconductors, such as graphene oxide, titanium dioxide, perovskites, and others, resulting in various changes to crystallinity, optoelectronic, and wettability properties depending on the gas employed for plasma generation. The low temperature of the plasma and rapid treatment times, in the order of 1-10s, enables the integration of plasma processing into roll-to-roll manufacture, a significant step forward in commercial viability within the emerging field of flexible and printed electronics. This study provides an example of rapid (<1 min) low-temperature plasma processing of indium-tin-oxide electrodes as a replacement for time-consuming chemical treatment before deposition of PEDOT:PSS in a p-i-n perovskite solar cell.

Materials based on polycrystalline tetragonal zirconia are widely used as structural and functional ceramics with excellent physical and chemical properties. These materials are used as fuel cells and other electro physical devices.
The characteristics of the initial powders and various additives have a significant influence on the process of the structure formation and properties of zirconia powders in the compacted state. The segregation of impurities, both technological and special, at the grain boundaries of zirconia grains leads to a change in the mechanical and electro physical properties of the compacted material. Thus, it is very important to investigate the process of purposeful formation of the structure of a ceramic composite material during the densification process, when diffusion redistribution of impurities occurs in the structure of the material. At the same time, the competition between the processes of densification and grain growth with the diffusion of impurities can lead to the formation of different structures in the material with different properties. Therefore, in this study the comparative analysis of densification processes of nanopowders obtaining by various methods (synthesis process and dopant addition method) and analysis the relationships between nanopowders characteristics with the parameters of the densification mechanisms were done.

Advanced superionic conductors (AdSICs) have the best ion-transport properties. These properties are determined by the AdSIC crystal structure that is close to optimal for fast ionic transport (FIT). The structure represents a close-packed cubic lattice of motionless ions penetrated by a 3D-network of uniform FIT-tunnels in which mobile ions move by hopping mechanism. The descriptors, based on a symmetry group of an immobile rigid sublattice and a local symmetry interconnected interstitial sites through which mobile ions move, are revealed. A new geometry and packing of FIT-tunnels inside the unit cell are presented. Some unusual properties of AdSICs are discussed. It is shown that the specific crystal structure of AdSICs may serve as a basis for searching and 3-D designing new solid ionic materials with high ion-transport properties.

Bismuth oxyiodide (BiOI) is the promising bismuth-based material which has been applied as photocatalyst and absorber in photovoltaic devices. Some efforts have been attempted to prepare BiOI films via hydrothermal method, successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) which involved the solvent usage. Here we reported the BiOI film preparation via direct annealing of BiI3 and studied the deposition time of BiI3 on the BiOI characters. First, the material deposition onto glass substrate could be fixed easily by the vapor deposition of BiI3 in a different time. Then, direct annealing at 350 oC was introduced to all of deposited BiI3 films and it resulted in the BiOI transformation. X-Ray diffraction (XRD) analysis showed that all films in our work were BiOI without any residue of BiI3. The BiOI character was proven by the existence of (001); (002); (102); and (110) crystal planes at 2θ around 9.7; 19.5; 29.7; and 31.8o in the annealed films, respectively. We noticed that the deposition time was not only have the effect on the film thickness of BiOI films but also in the appearance of (002) and (110) crystal planes which rose after 90 minutes deposition. By the difference in the crystal planes composition, those BiOI films will have different optical property which should affect its activity in photocatalytic and photovoltaic applications.

Graphene and carbon nanotubes are potentially sustainable materials able to replace metals, avoiding hazardous wastes linked to metal mining and disposal.
Dispersing carbon nanotubes without sonication nor high shearing, in order to preserve their length seemed like an impossible task up to now. This is in fact possible by individualizing carbon nanotubes through (true) dissolution of a nanotubide alkali metal salt in an organic solvent and then transfer to water,[1] in a somewhat similar way to the obtention of graphene water.[2] Under the right conditions, adsorption of hydroxide ions stabilize the nanotube dispersions. Photoluminescence, typical of individualized single-walled carbon nanotubes, is observed and superior conducting films compared with surfactant based dispersions can be made.
Starting from food waste, a nanocarbon originating from biomethane can be obtained that form tiny, defect free carbon nanopucks that have been used to prepare nanocarbon/metal nanoparticle electrocatalysts for fuel cell technology,[3,4]
Both works open practical perspectives in cleaner technologies.
REFERENCES: [1] Hydroxide Ions Stabilize Open Carbon Nanotubes in Degassed Water, G. Bepete et al. , ACS Nano 2018, 12, 8606−8615.; [2] Surfactant Free Single Layer Graphene in Water, G. Bepete et al. Nature Chemistry, 9, 347-352 (2017).; [3] Graphenide solutions: A chemical platform for nanoparticle nanocarbon composites, Ferdinand Hof & Alain Pénicaud, Chemistry, a European Journal 2018, 24, 16246 - 16250.; [4] Size Control of Nanographene Supported Iron Oxide Nanoparticles Enhances Their Electrocatalytic Performance for the Oxygen Reduction and Oxygen Evolution Reactions, F.Hof et al., J. Phys. Chem. C, 2019, DOI: 10.1021/acs.jpcc.9b05843.

In the quest of large scale storage of renewable energy, we suggest an approach to convert carbon dioxide (CO2) to value-added fuels (CO2 recycling). This can be achieved by multi-electron reduction of CO2 using electrocatalysis, bio-catalysis as well as photocatalysis. Among several catalytic systems, using biological catalysts, enzymes, offers advantages in selectivity toward a desired product and mild reaction condition (at neutral pH under ambient pressure and temperature). However, in such enzymatic reactions, the need of a sacrificial cofactor (for example, reduced nicotinamide adenine dinucleotide, NAD) as a proton and electron source is of great obstacle due to the instability and cost issues. We have examined an alternative pathway for supplying protons and electrons by direct electron injection from the electrode to the catalytic site of the enzymes (bio-electro-catalysis). In this work, different dehydrogenases including formate, formaldehyde and alcohol dehydrogenases, were immobilized covalently onto the surface of graphene acid through the amide bond resulting enzyme-functionalized graphenes. Results show that in such hybrid bio-catalytic graphene system, the enzymatic activity is preserved. We demonstrate electrocatalytic systems based on single-enzyme and three-enzyme functionalized graphenes for the chemical and electrochemical reduction of acetaldehyde to ethanol and the three-cascade reduction of CO2 to methanol, respectively.

Exotic condensed matter physics, represented by strong electron correlations, large spin-orbit coupling, and complex topology of electronic states is usually a privilege of systems with heavy electrons. Unconventional states including Mott insulating regime, unconventional superconductivity, pseudoLandau levels and excitonic Bose - Einstein condensate, can be achieved in hexagonal two dimensional (h2D) crystals via controlled interactions with environment. The solely unique properties of h2D crystals is the Berry curvature, which is imprinted in all degrees of freedom of Bloch electrons, including charge, spin, and valley degeneracy and enables addressing the quasiparticles like excitons with chiral selectivity. In my talk I will discuss our recent achievements in experimental realization of exotic regimes in h2D lattices such as phase coexistence of van Hove singularities and pseudoLandau levels and excitonic Bose-Einstein condensate. I will also introduce the power of cryomagnetic optical spectroscopies for investigation of exotic regimes in h2D crystals and other strongly correlated electron systems.

Nanodiamonds (NDs) bring the extraordinary properties of diamond to the nanoscale. NDs gain increasing interest in spintronics, quantum computing and biomedicine due to broad possibilities of their surface chemistry modifications, availability in large quantities, biocompatibility, and photoluminescence properties. Here we present the study of zeta potential of hydrogenated high-pressure high-temperature nanodiamonds (HPHT NDs) and detonation nanodiamonds (DNDs) with varying non-diamond surface sp2 carbon content. The sp2 carbon content is controlled by ND annealing in the air via variations of temperature and time of the annealing. The HPHT NDs were annealed at 450°C for 0, 10, 30 and 300 min while the DNDs were annealed at 410°C, 30 min, 450°C, 30 min and 520°C, 50 min. Increase of the annealing temperature and/or longer annealing time resulted in a significant reduction of the sp2 carbon content as shown by Raman spectroscopy. Such processed NDs were further hydrogenated by annealing in a hydrogen atmosphere at 700°C for 6 hours at atmospheric pressure of hydrogen gas. In all the ND samples the hydrogenation process reduced original surface C-O and C=O groups and introduced surface C-Hx groups as confirmed by Fourier-transform infrared spectroscopy (FTIR), yet significantly spectral differences were found between hydrogenated HPTH NDs and DNDs. The resulting hydrogenated ND powders were then dispersed in water for zeta potential measurements. We found out that while zeta potential value of hydrogenated HPHT NDs decreased with the reduction of surface sp2 carbon below 30 mV, i.e. to colloidal instability region, the zeta potential of hydrogenated DNDs did not decrease below 30 mV and the DNDs with lowest sp2 C content remained colloidal stable. This behaviour is explained by different sp2 surface structure revealed by analysis of Raman G-band of hydrogenated HPHT NDs and DNDs which in case of HPHT NDs consists predominantly of graphitic sp2 C patches while sp2 C chains or isolated defects were found in DNDs.

Owing to the exceptional properties of graphene and the crucial role of the substrate on the performance of electrochemical biosensors, several graphene-based hybrid structures have recently emerged, yielding improved selectivity and sensitivity. To date, most of the reported biosensors utilize solution-driven graphene flakes with drawbacks of low conductivity (due to high inter-junction contact resistant) and structural fragility. Herein, we present a conductive three-dimensional CeO2 semiconductor nanoparticles/graphene nanocomposite, as a platform for sensitive detection of hydrogen peroxide, an important molecule in fundamental biological processes. The 3D conductive graphene architecture is fabricated by chemical vapor deposition on nickel foam. The fabricated biosensor displays high sensitivity (60 μA.mM−1) at a low negative potential of −0.25 V, a low detection limit (<1.0 μM at S/N = 3), and a fast response (<5 s) in the range of 2.8 to 160 μM. Furthermore, density functional theory simulations show that improved detection is not only related to the catalytic effect of ceria nanoparticles, but also to more efficient charge transfer from nanoparticles to the 3D graphene network. Moreover, it is established that the amperometric response of the biosensor is insensitive to interfere molecules such as glucose, sucrose, and potassium chloride, indicating its potential for practical applications.

Single-atom-catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Exploiting fluorographene’s chemistry, a two-dimensional ligand was developed as a metal atom trap. Specifically, graphene functionalized with nitrile groups (cyanographene) was employed for the robust coordination of Cu(II) ions, which were partially reduced to Cu(I) due to graphene-induced charge-transfer. Inspired by nature’s selection of Cu(I) in enzymes for oxygen activation, this two-dimensional mixed-valence SAC was evaluated performing flawlessly in an O2-mediated reaction involving the oxidative coupling of amines towards high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability were attained with very low metal loadings in the reaction. The synergistic effect/cooperation of Cu(II) and Cu(I) was identified an essential part in the reaction mechanism. The developed strategy opens the door for a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.