Seznam abstraktů 2017: SEKCE A - NANOMATERIÁLY PRO ELEKTRONICKÉ, MAGNETICKÉ A OPTICKÉ APLIKACE. UHLÍKOVÉ NANOSTRUKTURY, KVANTOVÉ TEČKY

Graphene and other two-dimensional (2D) materials as hexagonal boron nitride (h-BN) attracted considerable interest over the last decade, featuring a wealth of intriguing properties. Especially heterostructures combining such atomically thin sheets open prospects to engineer nanomaterials [1]. On the other hand, self-assembly using (metal-)organic molecules is a well-established bottom-up process for the functionalization of surfaces and the fabrication of interfacial nanostructures [2].
We combine 2D materials with functional molecules to understand basic processes at the nanoscale and to achieve structures with distinct properties. To this end, graphene or h-BN is synthesized on metal single crystals [3] and applied as template for the adsorption of functional molecules [4]. The resulting model systems are comprehensively characterized under controlled ultra-high-vacuum (UHV) conditions, mainly employing low-temperature scanning probe microscopy.
Here, I will cover structural information of h-BN/Cu(111), including recent non-contact atomic force microscopy (nc-AFM) and X-ray standing wave (XSW) data. Furthermore, we will focus on the interaction of functional molecules with h-BN/Cu(111) and graphene/Ag(111), covering effects like site-selective adsorption, site-selective gating, tip-gated charging, intercalation, and edge functionalization [5]. These experiments provide access to (metallo-)supramolecular arrays and hybrid architectures with prospects for functionalities, e.g., in sensing, heterogeneous catalysis or molecular electronics.
REFERENCES: [1] A.K. Geim, I.V. Grigorieva, Nature 499, 419 (2013); [2] W. Auwärter et al., Nature Chem. 7, 105 (2015); [3] M. Garnica et al., Phys. Rev. B 94, 155431 (2016); [4] J.I. Urgel et al., J. Amer. Chem. Soc. 137, 2420 (2015); [5] Y. He et al., Nature Chem. 9, 33 (2017)

The development of new lightweight materials is crucial for numerous energy-conversion units or applications in automotive and aerospace industries. Low-cost low-density materials operating at higher temperatures ensure a lower fuel consumption or environmentally cleaner and more efficiently produced electricity. Fe-Al-based materials are well known for their outstanding corrosion resistance, good wear behaviour, low specific weight and relatively low material cost. But their limited ductility at ambient temperature and low creep strength above 600 C have resulted in a need of developing new ones. Quantum-mechanical calculations combined with scale-bridging models have recently emerged as powerful tools in modern materials design [1]. We exemplify this materials design concept by the development of new Fe-Al-based superalloy nano-composites employing also open-access databases with previous first-principles results.
REFERENCES: [1] M. Friák, D. Raabe, and J. Neugebauer, book chapter “Ab Initio Guided Design of Materials”, in “Structural Materials and Processes in Transportation”, eds. D. Lehmhus et al., pp. 481—495, Wiley-VCH Verlag GmbH & Co. KGaA (2013).

High performance functional materials, in particular nanostructured metal oxides, are regarded as highly promising for sophisticated applications in the field of ceramics, catalysis or electronics. To cover the increasing demand for these materials, advanced processes such as the nonaqueous synthesis are required that yield nanoparticles with defined sizes and morphologies and are suitable for large-scale production. In order to allow precise control of particle properties, one has to study the characteristics and kinetics of the chemical reactions that induce the particle formation process. Here, we present a study on the formation of zirconia and titania nanoparticles and unravel the underlying mechanisms that lead to nucleation, growth and agglomeration, showing the formation of a defined intermediate oligomer cluster species for the titania system [1]. We gained a deep understanding of the chemical as well as particle formation kinetics that govern the interdependence between process parameters and resulting properties and thus explain the occurrence of fractal morphologies and metastable polymorphs for the zirconia system [2]. Based on a derived kinetic model for the chemical reactions, we compute a theoretical monomer concentration which is assumed as the nucleation precursor species for crystallization. The monomer concentration was applied in a comprehensive population balance equation model to simulate the nanoparticle formation and is able to predict the final crystallite size and phase composition [3]. For the zirconia system, we simulate the tetragonal–to–monoclinic phase transition and thereby show how tetragonal crystals nucleate, grow and transit upon a certain size into the monoclinic phase. Furthermore, the population balance equation model for primary particle formation is extended to agglomeration and aggregation processes during the synthesis. Hence, we were able to distinguish between primary and secondary particle formation allowing us to develop a qualitative and quantitative understanding of the agglomeration behavior.

[1] M. Zimmermann, K. Ibrom, P. G. Jones, G. Garnweitner, ChemNanoMat 2016, 2, 1073-1076.
[2] P. Stolzenburg, A. Freytag, N. C. Bigall, G. Garnweitner, CrystEngComm 2016, 18, 8396-8405.
[3] P. Stolzenburg, G. Garnweitner, Reaction Chemistry & Engineering 2017, 2, 337-348.

Optical properties of Nb, Ta and Ti ultra-thin oxides are of high relevance due to their promising capabilities of nanocomposite formation enhancing photocatalytic activities in electrochemical energy production and/or storage applications. Even highly relevant current topics such as CO2 reduction or water splitting are in the end directly related to high photon absorption efficiencies. Variable angle spectroscopic ellipsometry (VASE) is used in the current work for optical properties mapping of ultra-thin anodic oxides grown on wide spread Nb-Ta and Nb-Ti thin film combinatorial libraries (prepared by co-sputtering). Such approach represents the first step toward identification of useful combination of oxides with tunable bandgaps. A simplified fitting model based on Tauc-Lorentz oscillators was possible by tuning the microstructure of the Nb-based par-ent metal alloys. The crystallographic mapping of both libraries allowed identification of relevant compositional thresholds where symmetry change occurs influencing the anodic oxide properties. Upon step-wise anodization up to 10 V the mixed oxides (with total thicknesses below 30 nm) showed absorption close to visible photon energies. Ad-ditionally, indications that an in-depth compositional gradient may be present were found. Individual bandgaps of Nb-based mixed oxides were compositionally mapped by performing VASE at various locations along the compositional gradient (VASE scan). A non-linear behavior was identified and was attributed to an in-depth compositional gradient of the mixed oxides. Surface enrichment of minority species in oxidized form triggered a depletion of that species at the metal/oxide interface shifting the metal alloys electronegativities in a non-linear manner. Compositional tuning of the parent metals revealed the possibility of mixed oxides bandgap tuning.

Bimetallic nanoparticles (NPs), which are composed of two different type of metals, are currently attracting much attention, because of their different catalytic, magnetic and conductive properties in comparison to monometallic NPs. The bimetallic NPs can be prepared by various methods and the conditions of NPs formation determine their structure and properties. Among the methods of synthesis of bimetallic nanoparticles, a galvanic replacement reaction (transmetalation method), which is based on the difference in reduction potentials of two metals, have been the most popular in the last years [1]. As the result of this reaction, particle structure between core-shell [1] and homogeneous alloy [2] depending on the reduction condition can be obtained.
Although, the methods of synthesis of bimetallic nanoparticles have been frequently proposed in recent years, the search for formation of low-cost, stable against aggregation and oxidation NPs, is still required. Therefore, the aim of our research was to obtain nickel-silver core-shell NPs, which are important from economic point of view because they can cut down the costs of production of various types of devices or sensors. In the formation of those NPs, the synthesis of inner part of it is important step. In our research, the Ni NPs were synthesized by the “wet” chemical method, i.e., by the reduction of metal ions by a proper reducing agent. Their properties (size, shape, degree of aggregation) were optimized by using various stabilizers as well as reducing agents. The structure of the Ni NPs was investigated by UV-VIS spectra, X-ray Photoelectron Spectroscopy (XPS) and SEM analysis.
ACKNOWLEDGEMENTS: The „Development of methodology of synthesis and stabilization of metal nanoparticles for conductive materials” project is carried out within the Homing programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund.
REFERENCES: [1] A. Pajor-Świerzy, Y. Farraj, A. Kamyshny, S. Magdassi (2017) Air stable copper-silver core-shell submicron particles: synthesis and conductive ink formulation, Colloids and Surf. A 521, 272-280.; [2] Y. Chen, H. Cao, W. Shi, H. Liu, Y. Huang (2013) Fe–Co bimetallic alloy nanoparticles as a highly active peroxidase mimetic and its application in biosensing, Chem. Commun. 49, 5013-5015.

Gas aggregation cluster sources (GAS) represent one of the most rapidly developing systems for synthesis of nanoparticles (NPs). Such sources were used for production of NPs from different materials ranging from metals or metal oxides to organic compounds. In recent years, the focus shifts to the production of heterogeneous NPs. In this work we have studied production of bimetallic NPs from copper and tungsten.
A composite W/Cu target was prepared from copper target with variable number of tungsten pellets inserted in the erosion track and mounted on a 3 inch DC magnetron. The sputtering took place in the water cooled aggregation chamber in argon atmosphere at pressures from 30 to 210 Pa, flow of Ar up to 15 sccm and magnetron current up to 500 mA. Aggregation chamber was ended with conical orifice 1.5 mm in diameter facing on substrate placed in the distance 10 cm in the deposition chamber with the background pressure below 1 Pa. The deposition process was monitored in-situ by means of optical emission spectroscopy and quartz crystal microbalance. Surface chemistry was determined by XPS and NPs morphology by SEM and HRTEM. Depending on the number of W pellets in the target and the deposition conditions (magnetron current, pressure and gas flow), nanoparticles with varying ratio between copper and tungsten were obtained.
ACKNOWLEDGEMENTS: This work was supported by the grant GACR 17-22016S from the Grant Agency of the Czech Republic.

The classical approach in particle physics is based on the fact, that the electron has some parameters like charge, mass, etc. but does not have a structure. The electron is calculated as point particle having magnetic and electric properties. Change in topology of structures can leads to quite different behavior of particles. Type of particle structure for Coulomb’s force between the proton and the electron for very small distances leads to quite opposite results (for point particles to infinity and for ring particles to zero). For larger distances are results the same. Vortex-ring theory VRT uses the electron as semi-fractal particle with a toroidal (ring) shape, which is formed by ring substructures connected to each other by vortex electromagnetic fields. The atomic nucleus can be built from the ring protons and neutrons. Knowledge of structure rules of the atomic nucleus and the properties of vortex electromagnetic field allow us to create relatively precisely the structures of individual atoms and molecules or nanostructures like graphene. It allows us to understand the fundamental physical and chemical reasons for the stability and topology of atoms and molecules. Theory VRT gives us a new tool that helps us create new nanostructures.

In this work we investigate the effect of nanoparticle size and shape on the properties of porous materials. Initial step of the porous material preparation is the synthesis of polymeric nanoparticles of various sizes and shapes. An emulsion polymerization of styrene in the presence of suitable surfactant was used to prepare spherical polystyrene nanoparticles (PS-NPs) with diameter ranking from 100 to 900 nm. In the case of polystyrene fiber-like nanoparticles, these were prepared by an anti-solvent precipitation of PS from the organic solvent in the highly viscose aqueous solution of glycerol. Once characterized, nanoparticles of both shapes were used as building blocks for synthesis of porous material using reactive gelation or chemical oxidative polymerization aniline (PANI) or pyrrole (PPY) in the presence of polystyrene nanoparticles (PS-NPs). Depending on the operating conditions, porous material in the form of microparticles or a monolith were successively prepared. Systematic investigation of the NPs properties on the morphology and properties of porous material (pore size distribution, porosity, mechanical strength etc.) was carried out to improve our understanding of the controlling mechanisms including interactions of PS NPs. Furthermore, in the case of conductive porous materials impact of process conditions on the conductivity was studied.
It was observed that both NP size and shape have strong impact on the porosity, pore size distribution as well as on strength of the prepared material, where larger particles lead to larger pores and incorporation of fibers improves mechanical properties as well as increases the porosity. Furthermore, it was demonstrated that a chemical oxidative polymerization aniline or pyrrole can be used to the tuning of the surface morphology of the porous material and it is strongly dependent on the ratio PANI or PPY / PS-NPs. In addition, it was found that for both conductive polymers the presence of PS NPs has positive effect on the morphology of conductive layer which cannot be obtained from conductive polymer alone. Over all it was found that porosities of up to 80% and surface areas between 10 to 20 m2/g, respectively, can be obtained by controlled assembly process of PS-NPs alone or in the presence of conductive polymer. Depending on the application, material can be further functionalized by suitable chemical groups (carboxyl, amine or other groups). In the case of conductive porous material we measured specific conductivities in the order of few mS/cm, comparable to the values measured for common semiconductors. Obtained results confirm possibility to tailor the final properties of porous material upon desired application.

We present the dielectric response for an ordered identical spherical Ag nanoparticles (NPs) system located on the surface of a uniaxial LiNbO3 crystal. The rectangular array of metallic NPs is characterized by a- and b-sizes, which represent the longitudinal (along C-axis) and transversal interparticle distances, respectively. Using the anisotropic behavior of the LiNbO_3 dielectric constants, we analyze the effective dielectric response in both the extraordinary and the ordinary directions of the crystal. For our simulation, we assume that the parallel dielectric response lies on the C-extraordinary direction of the lattice. The obtained results are discussed in terms of previous experimental findings as reported by Yraola et al. [1].
The widely known Maxwell-Garnett (M-G) model is used to account on the interaction between polarizable metallic spheres NPs in close relationship with the ordered composite systems. An extended continuum model performed by Monegotto et al. [2] and Persson et al. [3] is used to account on the effect of the LiNbO_3 anisotropy and their interaction with the two-dimensional array of Ag NPs. Both the parallel (épsilon_eff,||) and perpendicular (épsilon_eff,perp) values of the effective dielectric function are discussed in terms of NPs radii, the parallel and longitudinal interparticle distances and as a function of the NPs filling factor.
Our results reveal that, the interparticle distances, as the filling factor and particle sizes are key issues to tune the optical properties of NPs in the ordered systems under study. These results are compared with those previously reported in a three-dimensional random distribution of Ag NPs embedded in LiNbO3 matrix [4].
REFERENCES: [1] Yraola E, Molina P, Plaza J L, Ramírez M O and Bausá L E 2012 Adv. Mat. 25, 910.; [2] Monegotto and Horowitz F.2014. Appl. Optics 53, 2853.; [3] Persson B N J and Liebsch A. 1983, Phys. Rev. B 28, 4247; [4] de la Cruz R M, Kanyinda-Malu C and Muñoz Santiuste J E 2017 Mat. Res. Express 4, 025023.

Nano iron oxides have been intensively investigated due to their various potential biomedical applications. ε-Fe2O3 phase exerted internal coercivity value up to 20 kOe, high Curie temperature ( Tc=510 K), and magnetoelectric character. Accordingly, epsilon phase is recognized as a suitable material for medical spintronic biosensors production, that present important part for the lab-on-a-chip systems. Noteworthy, ε-Fe2O3 phase exerts peculiar magnetic behavior. To get better insight into the magnetism of this material, ε-Fe2O3/SiO2 sample was prepared by the combination of the sol-gel synthesis and microemulsion method (Tann=1050 °C, tann=4h). Afterwards, the sample was exposed to post-annealing treatment at 100 °C and 200 °C. Synthesized material was preliminary examined by XRD and SQUID techniques. Coercivity changes, induced by the post-annealing temperature oscillations, were monitored by hysteretic measurements. Sample annealed at 1050 °C for 4h, showed coercivity ~ 20 kOe. The same sample performed to the post-annealing treatment at 100 °C, exerted significantly decreased coercivity ( ~ 2100 Oe). Further rise of the post-annealing temperature (200 °C) resulted in the increased coercivity ~ 15 kOe. Obtained study showed that there is insufficient knowledge concerning the coercivity changes of the ε-Fe2O3 polymorph. The more detailed investigation will be conducted, in order to advance the control of the epsilon phase magnetic properties.

Photonic crystal (PhC) slabs can be used for effective extraction of photoluminescence (PL) from bulk material via leaky modes. Moreover, the periodic structure forces light to radiate into air under defined angles. The emission into near-normal direction is of special interest from the application point of view. The effectivity of light extraction depends on various factors e.g. refractive index contrast, lattice type, or physical dimensions of PhC. Diamond PhCs are highly interesting because they may be used for enhanced extraction efficiency of PL from diamond waveguides, light emitting diodes or diamond color centers (NV, SiV).
In this study, we compare the optical properties, particularly the light extraction efficiency into near-normal direction, of nanocrystalline diamond PhC slabs with square lattice. The PhC structures with various physical properties (PhC lattice constant, layer thickness, column height) were designed by computer model (DiffractMod). However, the real structures differ in material (presence of nanocrystalline grains and grain boundaries) and structural (non-ideal shape) properties [ACS Nano 11 (2017) 2972]. These features depend on diamond deposition condition and fabrication technique.
In order to measure the performance of PhC, we compare the enhancement factor, which is the ratio between intensity of luminescence (originating from various defects and carbon phases in polycrystalline diamond) from photonic crystal and plain diamond layer. This is compared with structural and material properties of photonic crystals (analyzed by SEM, AFM, Raman). Our results show, that accurate shape of PhCs is not a critical factor for achieving high extraction enhancement (up to 14). Instead, the filling factor and thickness of diamond layer influence the performance greatly (difference up to 5). This finding can be helpful in designing future PhC for extraction of luminescence from various opto-electronic and sensor devices making use of diamond unique properties.
ACKNOWLEDGEMENTS: The work has been supported by 16-09692Y (GACR), SGS17/179/OHK4/3T/13 (CTU), and European Regional Development Fund project CZ.02.1.01/0.0/0.0/15 003/0000464.

Microfluidic devices present the basis of modern life sciences and chemical information processing.[1] To control the flow and to allow optical readout, a reliable sensor material that can be easily utilized for microfluidic systems is in demand. Here, we present a new optical readout system for pH sensing based on pH sensitive, photoluminescent glutathione capped cadmium telluride quantum dots that are covalently immobilized in a poly(acrylate) hydrogel. For an applicable pH sensing the generated hybrid material is integrated in a microfluidic sensor chip setup. The hybrid material not only allows in situ readout, but also possesses valve properties due to the swelling behavior of the poly(acrylate) hydrogel. In this work, the swelling property of the hybrid material is utilized in a microfluidic valve seat, where a valve opening process is demonstrated by a fluid flow change and in situ monitored by photoluminescence quenching. This discrete photoluminescence detection (ON/OFF) of the fluid flow change (OFF/ON) enables upcoming chemical information processing.[2]
In contrast to common fluid flow sensors, here the observation of a discrete flow rate change OFF/ON is realized by PL quenching ON/OFF and thus exhibiting an in situ optical fluid flow control. That fact offers future chemical information processing due to connecting the chemo-mechanical with chemo-optical characteristics.
REFERENCES: [1] G.M. Whitesides, Nature, 2006, 442, 368.; [2] G.M. Whitesides, Lab Chip, 2010, 10, 2317.

This presentation presents two unique writing modes developed by Raith to overcome known limits of traditional electron beam lithography.
Classical electron beam lithography tools work in step and write mode: First, in fixed sample position the electron beam scans over the resist-coated sample according to the CAD layout. To make larger devices the device area needs to be split in smaller sub-areas, very much like a chess board is made up of 64 individual fields. After a first write field is exposed, the sample will be moved in a second step to the adjacent field where the electron beam scan continues. This stitching together procedure (repeated as often as required to make a full device) requires however very precise sample stages (a laser interferometer stage) and there will be residual stitching errors.
In Raith’s “fixed beam moving stage” (FBMS) writing mode long lines are written in one continuous path without stopping in between. As there is no stop during the write there is no stitching and consequently no stitching error. Usage examples for FBMS, like Arrayed Waveguide Gratings (AWGs), are shown.
In Raith’s MBMS (“modulated beam moving stage”) mode both the beam and the stage are synchronously moved. This stich-less writing mode is mainly used for periodic elements where a basic structure needs to be repeated again and again. Usage examples are DFB laser gratings or Photonic Crystals.

Novel synthetic protocol for the synthesis of new zeolites and related materials is discussed here based on the experimental and theoretical considerations. ADOR mechanism (Assembly – Disassembly – Organization – reassembly) has been developed for the synthesis of novel feasible and “unfeasible” zeolites and related pillared materials having the same structure of the zeolitic layers but various connectivities. The principal step of the ADOR process is hydrolysis of parent germanosilicate zeolites providing layered precursors with the same structure as in the parent zeolite. Manipulation with layers provides pillared materials with organic or inorganic pillars or new zeolites, some of them with unprecedented energetic features. Syntheses and structures of new zeolites prepared from parent UTL and UOV zeolites will be discussed.


FIGURE Synthesis of ‘unfeasible’ zeolites. The ADOR process consists of (i) the selective disassembly of a germanosilicate with the UTL structure, to form a layered material (called IPC-1P) followed by (ii) the use of the choline cation (shown as a blue circle) as a structure directing agent to shift the layers with respect to each other (IPC-9P). The layers can then be reassembled in two ways, (iii) by calcination to form IPC-9 and (iv) calcination after intercalation of diethoxydimethylsilane to form IPC-10.

In-situ transmission electron microscopy (TEM) is a technique where a TEM tool is used to monitor a specific sample in real time. It provides kinetic information on a material under certain stimuli. The fast development in the microscopy instrumentation advances in-situ TEM into a fast-growing, increasingly important and fascinating technique in various fields ranging from materials science to chemistry, biology, etc. In this study, two in-situ experimental methodologies in the TEM were developed to investigate several nanomaterials for electronics applications. First, an in-situ approach was carried out to study the time-dependent dielectric breakdown (TDDB) failure mechanisms and degradation kinetics in on-chip Cu/Low-k interconnect stacks for 32 nm CMOS technologies. Following Moore’s Law, the Cu interconnect spacings are continuously decreasing; however, operation voltages have not scaled as fast and hence the electric fields have increased. For the first time, the movement of Cu nanoparticle have been investigated in situ. Furthermore, an in situ mechanical testing system was utilized to stretch patterned graphene nanoribbons (GNRs), aiming to investigate the mechanical strength of such GNRs. Focused ion beams and focused electron beams were used to directly pattern graphene into the ribbons. Focused electron beam techniques show a relatively slow patterning speed, but preserve much better the crystallinity of graphene. The mechanical response of the graphene ribbons is monitored in situ, and the low-loss electron energy loss spectrum (EELS) of the stretched ribbons under strain is recorded as an attempt to reveal a possible tuning of the bandgap.

Within this framework magnetic nanostructures consisting of two different metals are deposited within nanostructured silicon to control the magnetic switching behavior of the porous silicon/metal nanocomposite. Two different templates, porous silicon (PSi) and silicon nanotubes (SiNTs), are utilized to achieve such nanocomposites. The PSi templates are fabricated with a mesoporous morphology offering average pore diameters of 50 nm which are filled with a bi metal filling (Ni, Co). The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within SiNTs and the additional deposition of a Ni layer on the outer surface of the tubes. The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer (after the growth of Co particles inside the tubes) as a spacer before the Ni deposition. The magnetic properties of the systems strongly depend on the tunable size and shape of the deposited bi-metal nanostructures and also on the proximity of the Ni and Co structures to each other. If the distance is small enough magnetic exchange coupling between the two metal structures is present. Due to the size of the metal deposits and the coupling between them the switching behavior of the hysteresis can be tuned.

Porous silicon (PSi) in the nanoporous regime with pore diameters of 2 – 5 nm is known to emit light in the visible. The aim of this work is to combine luminescent PSi with a ferromagnetic metal (Ni) to influence on the one hand the photoluminescence by the presence of metal deposits and on the other hand the optical properties by an external magnetic field. First the optical properties of the fabricated luminescent PSi are investigated, second Ni is electrochemically deposited in the porous silicon samples and subsequently the nanocomposite specimens are characterized optically and magnetically. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm and the luminescence intensity is increased. Concerning the magnetic properties of the nanocomposite the embedded Ni structures can be superparamagnetic from the size of the pore diameters but due to the branched morphology the achieved deposits tend to be interconnected and thus do not offer necessarily a superparamagnetic behavior. Field dependent magnetization measurements with the magnetic field applied perpendicular and parallel to the surface show a clear film-like magnetic anisotropy due to the interconnected Ni structures. Temperature dependent magnetization measurements give no hint for a superparamagnetic behavior.
The optical characterization of luminescent PSi with respect to photoluminescence intensity and decay times compared with Ni filled samples is discussed in detail as well as the corresponding magnetic properties of the nanocomposites.

Core-shell nanomaterials are a class of nanostructured materials that have recently established growing attention due to their interesting properties as well as a broad range of applications in catalysis, material chemistry and sensors. Notably, core-shell nanomaterials for catalysis can now be designed and prepared with need for specific catalytic applications via more benign pathways with unique structure, morphology and composition. Some of the as-prepared core-shell nanomaterials can be further embedded with magnetic active nanoparticles or other metallic and metal oxides nanoparticles with well-defined sizes, shapes and properties. This, in turn, allows tuning the properties of the materials in a number of useful ways. Our recent activity in this area including some catalytic and electrocatalytic applications will be highlighted.
REFERENCES: Gawande et al. Account of Chemical Research 2014, 47, 1338−1348; Chemical Society Reviews 2015, 21, 7540-7590; ACS Applied Material and Interfaces 2017, 9, 2815−2824; Chem. Eur. J. 2016, 22, 1577-1581; RSC Advances 2013, 3, 1050-1054.

Graphene, a single two-dimensional sheet of carbon atoms arranged in hexagons with sp2 bonding, has captured an eminent interest of the scientific community since its isolation in 2004. Besides its extraordinarily high electrical conductivity and surface area, graphene shows a long spin lifetime and limited hyperfine interactions, which favors its potential exploitation in spintronic and biomedical applications, respectively, provided it can be made magnetic. However, pristine graphene is diamagnetic in nature due to solely sp2 hybridization. Thus, various attempts have been proposed to imprint magnetic features into graphene. Following recent theoretical and experimental studies, it is believed that magnetic moments in graphene evolve only upon introduction of defects into the crystal lattice of graphene. The defects include local topology perturbations, vacancies, non-carbon atoms in the graphene lattice, adatoms, mixed sp2-sp3 hybridization, and edges. The defect-induced magnetic moments must communicate with each other if a magnetic ordering is supposed to be established. However, there are doubts if the mediators of the magnetic interactions are sufficiently powerful to maintain the communication pathway and, hence, ensure self-sustainable magnetic ordering over the graphene lattice at relatively high temperatures.
In the present contribution, strategies involving doping of graphene lattice with non-carbon atoms and functionalization of graphene surface will be discussed with respect to the recent theoretical and experimental advancement in the quest for “magnetic” graphene. In particular, the issue of doping of graphene lattice with sulfur and nitrogen will be addressed in details highlighting the effect of the chemical nature and electronic character of the doping element, doping concentration, and doping-induced magnetic configurations on the magnetic properties of graphene.1,2 A new magnetically active derivative of graphene, hydroxofluorographene, will be introduced as an example of the organic graphene-based magnets with a magnetic ordering self-sustainable up to room temperature due to proper sp3 functionalization.3 The potential applications of graphene-based magnets will be also covered. REFERENCES: [1] Tucek, J.; Blonski, P.; Sofer, Z.; Simek, P.; Petr, M.; Pumera, M.; Otyepka, M.; Zboril, R. Sulfur Doping Induces Strong Ferromagnetic Ordering in Graphene: Effect of Concentration and Substitution Mechanism. Adv. Mater. 2016, 28, 5045-5053. DOI: 10.1002/adma.201600939; [2] Blonski, P.; Tuček, J.; Sofer, Z.; Mazánek, V.; Petr, M.; Pumera, M.; Otyepka, M.; Zbořil, R. Doping with Graphitic Nitrogen Triggers Ferromagnetism in Graphene. J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.6b12934.; [3] Tuček, J.; Holá, K.; Bourlinos, A. B.; Błoński, P.; Bakandritsos, A.; Ugolotti, J.; Dubecký, M.; Karlický, F.; Ranc, V.; Čépe, K.; Otyepka, M.; Zbořil, R. Room temperature organic magnets derived from sp3 functionalized graphene. Nat. Commun. 2017, 8, 14525, DOI: 10.1038/ncomms14525.

The concept of graphene-enhanced Raman scattering (GERS) was proposed and experimentally demonstrated in 2010. It was observed that molecules in very low concentrations exhibit a significant Raman signal in vicinity of graphene layer. In addition, the photoluminescence of molecules placed on graphene is quenched. A theoretical work by Barros et al. brought more insight by suggesting conditions for GERS enhancement.
In our work we used functionalized graphene to experimentally probe the theoretical GERS conditions with Rhodamine 6G (R6G) molecules by assuming the change of the Fermi level of graphene due to its functionalization. We showed that the photoluminescence of R6G was quenched also with functionalized graphene. By comparing multiple R6G Raman modes on differently functionalized graphene layers we were able to qualitatively validate the theoretical GERS conditions. Furthermore, we studied how the degree of functionalization, specifically fluorination, affects the GERS effect by inducing sp3 defects in graphene. We found that high fluorination degree leads to loss of the GERS effect, however it can be restored upon fluorine removal.
REFERENCE: [1] V. Valeš, P. Kovaříček, X. Ji, X. Ling, J. Kong, M. S. Dresselhaus, and M. Kalbáč, “Quenching of photoluminescence of Rhodamine 6G molecules on functionalized graphene,” Phys. status solidi B 253, 2347–2350 (2016).; [2] V. Valeš, P. Kovaříček, M. Fridrichová, X. Ji, X. Ling, J. Kong, M. S. Dresselhaus, and M. Kalbáč, “Enhanced Raman scattering on functionalized graphene substrates,” 2D Mater. 4, 25087 (2017).; [3] V. Valeš, Z. Melníková, T. Verhagen, J. Vejpravová, and M. Kalbáč, “Reversibility of Graphene-Enhanced Raman Scattering with Fluorinated Graphene,” Phys. status solidi B, 1700177 (2017).

Methods for covalent derivatization of graphene enable tuning of graphene’s surface and electronic properties, thus expanding its application potential.[1] However, existing approaches based on chemistry of graphene and graphene oxide achieve only limited level of functionalization due to chemical inertness of the surface[2] and non-selective simultaneous attachment of different functional groups,[3] respectively.
Here we present a conceptually different route towards graphene derivatives based on fluorographene (FG) which is a stoichiometric and well-defined graphene derivative introduced in 2010.[3,4] It is a very hydrophobic material with a large band gap and it was considered rather unreactive as a counterpart of Teflon.[5] However, numerous recent studies have shown that FG is susceptible to reductive defluorination and nucleophilic attack.[5-8] The reactions result in homogeneously and selectively functionalized graphenes, with unprecedented functionalization degrees. Importantly, during functionalization, FG is defluorinated back to graphene, without affecting the already installed functional groups, unlike GO. Defluorination is triggered by the nucleophiles, which simultaneously initiate substitution and reductive defluorination.Typical examples are the carbon-carbon bond formation reactions on FG with Grignard reagents[7] or with the pseudohalide of -CN and its subsequent hydrolysis to “graphene-acid”.[8] These findings demonstrate that FG is a very robust and reactive substrate towards the preparation of valuable graphene derivatives.
REFERENCES: [1] V. Georgakilas etal. Chem. Rev., 2012, 112 , 6156.; [2] Jaehyeung Park and Mingdi Yan Acc. Chem. Res., 2013, 46 , 181.; [3] A. Y. Eng, etal. Nanoscale, 2015,7, 20256.; [4] R. R. Nair etal. Small 2010, 6, 2877.; [5] R. Zbořil etal. Small 2010, 6, 2885.; [6] J. Tuček etal. Nat Commun. 2017, 8, 14525.; [7] D.D. Chronopoulos, et.al. Chem. Mater. 2017, 29, 926.; [8] A. Bakandritsos etal. ACS Nano 2017, 11, 2982.

The aim of our work is to study the formation of graphene via a Ni-catalyzed transformation of diamond surface layers. Nanocrystalline diamond (NCD) films grown on Si or Si/SiO2 substrates were covered with 20 nm and 500 nm Ni films and heated at temperatures between 800 and 900 °C. Afterwards, the specimens were analyzed by scanning and transmission electron microscopy and Raman spectroscopy. In general, NCD graphitization through a catalytic reaction with Ni involves diffusion of C along Ni surfaces, but the exact mechanism still remains unclear. If the SiO2 layer is too thin, the Ni penetrates through the NCD and reacts with Si to form NiSi2. The thick Ni film was found to form NiSi2 columns covered with graphite layers. In addition, the Si reacts with the NCD forming SiC. The NCD film was significantly consumed by the catalytic reactions. In the case of thin Ni films, heating causes dewetting of the Ni film and isolated Ni nanoparticles are formed. The Ni particles dissolve carbon atoms by etching grooves in the NCDs. Subsequently, the C atoms are segregated forming graphite on the NCD surface. Interestingly, in some cases, the graphitic layers grow upright from the NCD grains. Electronic transport properties are strongly correlated with the structural features in the NCD specimens. The conduction mechanism depends on the thickness and crystallinity of graphitic layers and can be explained by different portions of intrinsic conduction in graphite combined with charge tunneling through potential barriers

Inexpensive, unobtrusive, and safe renewable energy sources are nowadays increasing in importance. Diamond nanoparticles (NDs) possess numerous beneficial properties for a wide range of applications. However, their potential in photovoltaics, supported e.g. by measured transfer of photo-generated charge between bulk diamond and polypyrrole (PPy) [Diam. Relat. Mater. 18 (2009) 249], remains mostly unexplored. Here we compare interactions of PPy with hydrogen (H), oxygen (O), and amorphous carbon (a-C:H, a-C:O) terminations of NDs by DFT computations on the atomic scale. In particular, the inclusion of amorphous carbon brings the theoretical computations close to real nanodiamonds. Different physisorbed and chemisorbed (covalently bonded) configurations of PPy on NDs are calculated in the ground state.
Binding energies reveal that physisorbed structures on oxidized NDs are energetically more favorable compared hydrogenated NDs and all chemisorbed structures owing to hydrogen bonds between PPy and oxygen surface atoms. For the majority of the oxidized NDs with or without the inclusion of a-C and with both physisorbed and chemisorbed PPy we observe spatially separated HOMO and LUMO and considerable charge transfer (up to 0.36 e- from PPy to ND). However, for H- and OH- terminated NDs these effects are limited to only chemisorbed or physisorbed PPy on (100) facet of H-NDs regardless amorphous carbon presence. The HOMO-LUMO spatial separation can promote dissociation of excitons and thereby generation of free charge carriers under illumination. The computed results thus provide guidance for the synthesis of real ND-PPy composites suitable for photovoltaic applications.

Nanodiamond (ND) is being extensively investigated due to inexpensive synthesis, rich surface chemistry and non-toxicity. Although diamond is a wide band gap semiconductor, NDs may absorb visible light and exhibit photoluminescence due to surface chemistry, sp2 carbon reconstruction and defects on the surface. This indicates the possibility of using NDs as energy conversion material. Surface photovoltages (SPV) measured by KPFM on as-received detonation nanodiamonds with multiple surface groups including C-H (poly-DND) and oxidized DND (O-DND) have been recently reported [MRS Advances 1 (2016), 971]. In our work, we present new SPV data taken from 25 measurements on three types of particles: poly-DND (as-received), O-DND (annealing at 450 0C for 30 min in O2) and H-DND (annealing at 600 0C for 6h in H2). We used macroscopic Kelvin probe technique, which is drift- and stray capacitance-free compared to KPFM. As a light source, 100 W halogen lamp was used. Chemical composition of the particles was characterized by FTIR and Raman spectroscopies. DNDs were deposited on doped Si substrates as dense monolayers consisting of single particles with few agglomerates. The morphology of the layers was investigated by SEM and AFM. SPV was calculated as the difference of surface potentials under illumination and in dark: 6 ± 7 mV on H-DND, 28 ± 10 mV on O-DND, 55 ± 10 mV on poly-DND. The reasons for different SPV on H-DND, O-DND and poly-DND are discussed in the work. Minimum SPV on H-DND correlates with low amount of surface states and surface conductivity of H-DND as previously reported for monocrystalline hydrogenated diamond as well for hydrogenated HPHT NDs [MRS Advances 1 (2016), 1105]. Oxidation of DNDs removes most of amorphous carbon and terminates the surface by carbonyl, hydroxyl, carboxylic and lactone groups, thereby removing surface conductivity, creating surface states and consequently increasing the SPV of O-DND compared to SPV of H-DND. Maximum SPV on poly-DND is supposed to be due to non-diamond carbon phase on not-annealed poly-DNDs which provides additional energetic levels in DND band gap [Galar et al., Journal of Applied Physics, 2014] beneficial for SPV creation.

Carbon nanodots (CDs) are the new type of carbon-based semiconductor with high luminescent efficiency. Focusing on the main problems in this field, the author proposed a method of controlling the bandgap emissions of CDs through nitrogen rich assembles and achieved efficient green, orange, red and near infrared emissive CDs and realized optical pumped green laser from CDs. Based on “supra-CDs” systems, water-jet luminescent printing and effective NIR photothermal conversion up to 54% were also achieved.

Sensing with continuous measurement of physiological parameters is an effective way to monitor personal health. Wearable and flexible health monitoring devices, such as smart bracelets, wrist-bands and smart watches, are becoming a new popular fashion. For human friendly comfortable health monitoring systems, sensor integrated or mounted wearable systems are required. In addition, wearable and flexible sensors which are able to be integrated into clothes should be comfortable and do not affect people’s everyday life and activities.
For the physical sensing, normal pressure and lateral strain are two main elements. Normal pressure sensing can help to realize the grasp control, object manipulation, and orientation determination, while tensile strain monitoring can facilitate the enhancement of proprioception at the joint positions.
In this talk, flexible and wearable physical sensors (pressure and strain) based on rGO (Reduced Graphene Oxide)-SWCNT composite coated fabrics for electronic gloves are introduced. Sensing performance and reliability at different points such as fingertip, finger joint and wrist, are presented. The signal has good reproducibility in response to pressing, bending and stretching. Water tolerance of fabric-based sensors are also evaluated. This sensor can be applicable for personalized physiological monitoring and prosthetic hand.

Carbon-encapsulated iron nanoparticles (CEINs) are the core-shell nanomaterial, which comprises of the magnetic core covered by curved graphene layers [1]. This carbon nanostructure attracts a great deal of attention because of its encouraging wide-range of possible applications [2]. This broad scope of applications is directly associated with the interesting physicochemical properties of CEINs. Nevertheless, all the pristine carbon-based nanomaterials need to be functionalized before synthesis of more complex structures because of the lack of functional groups on their surface.
In the presented work, a new grinding-induced method for the functionalization of carbon-encapsulated iron nanoparticles, will be presented. Firstly, the CEINs surface has been decorated with various type of organic moieties via the 1,3-cycloaddition reaction, which employs the nitrile oxides bearing unprotected carboxyl or hydroxyl moieties, as well as a metalorganic or a sugar unit [3]. The mechanochemical amidation-type reactions with the selected CEINs derivatives, have been also developed. All the herein developed eco-friendly routes are fast, versatile and result in high coverage degrees. Possible application of the obtained materials will be also presented.
All the obtained nanoconjugates were characterized by a variety of techniques, including spectroscopic methods, materials characterization techniques and electrochemical assays.
REFERENCES: [1] J. Borysiuk, A. Grabias, J. Szczytko, M. Bystrzejewski, A. Twardowski and H. Lange, Carbon, 2008, 46, 1693-1701.; [2] J. K. Park, J. Jung, P. Subramanian, B. P. Shah, C. Kim, J. K. Lee, J.-H. Cho, C. Lee and K.-B. Lee, Small, 2011, 7, 1647-1652; [3] A. Kasprzak, M. Bystrzejewski, M. Koszytkowska-Stawinska and M. Poplawska, Green Chem., 2017, DOI: 10.1039/C7GC00282C.
ACKNOWLEDGEMENTS: This work was financially supported by the National Science Center (Poland) through the grant PRELUDIUM (No. 2016/21/N/ST5/00864).

Carbon encapsulated magnetic nanoparticles (CEMNPs) are core-shell structures and consist of the ferromagnetic nanocrystal surrounded by well graphitized carbon coating. The CEMNPs obviously have relatively high hydrophobicity, which is similar to other carbon nanomaterials [1, 2]. The hydrophobic nature of CEMNPs is a drawback which makes difficulties in obtaining stable aqueous dispersions.
In this work various stabilizing agents were tested to obtain stable dispersions of CEMNPs. Several anionic (e.g. CMC-Na), cationic (e.g. CTAB-Na) and nonionic (e.g. PVA, PVP) surfactants were studied. The typical procedure involved ball milling of the mixture of CEMNPs and the stabilizer (9 wt. % of CEMNPs) for 24 h. The as-obtained mixtures could be easily dispersed in a medium without the use of ultrasounds. The stability of the dispersions was investigated by turbidimetric measurements. Three media were studied: (i) distilled water, (ii) 10% FBS in DMEM and (iii) PBS. Additionally, the obtained suspension were analyzed with DLS to evaluate the hydrodynamic diameter distribution of the suspended particles. The highest stability was found for CMC-Na and PVP stabilizers. In this case more than 75% of initially dispersed particles were still present in the suspension. It has been also found that the hydrodynamic diameter slightly decreases after 12 h.
ACKNOWLEDGEMENTS: This work was financially supported partially by the GEMNS project granted in the European Union’s Seventh Framework Program under the ERA-NET EuroNanoMed II.
REFERENCES: [1] BYSTRZEJEWSKI M., PYRZYŃSKA K., Kinetics of copper ions sorption onto activated carbon, carbon nanotubes and carbon-encapsulated magnetic nanoparticles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011, vol. 377, pp. 402-408.; [2] GRUDZIŃSKI I.P., BYSTRZEJEWSKI M., et. al., Comparative cytotoxicity studies of carbon-encapsulated iron nanoparticles in murine glioma cells. Colloids and Surfaces B: Biointerfaces, 2014, vol. 117, pp. 135-143.

Reaching the ultimate potential of graphene in multitude of fields requires means of on-demand tuning of its properties. Covalent chemical functionalization of the graphene monolayer provides merely unlimited space for targeted attachment of various moieties and thus manipulation of intrinsic parameters of the material. The approach, however, is facing three crucial challenges on the way towards its goal: inducing chemical reaction, properly characterizing its product, and application of the chemical functional group in extending functionality of the material.
The long-known graphene grafting with diazonium-derived radicals has been recently complemented by nucleophilic and electrophilic substitution methods on fluorinated and hydrogenated graphene, respectively, thus proving alternative for chemically incompatible species. The issue of characterization, conventionally dominated by Raman spectroscopy and XPS, was elaborated in detail by application of surface-specific and surface-enhanced versions of mass spectrometry, thermal programmed desorption, Raman spectroscopy and others. These methods provided unambiguous experimental evidence for particular chemical moieties being grafted to the monolayer regardless the reaction employed by reporting on the mass and spectroscopic fingerprints of these species.
The modified surface was studied for chemoselective heterostructure formation. For instance, sulfonate-functionalized photolithographically patterned graphene was used to selectively promote oxidative polymerization of PEDOT and to stabilize the product. The reaction provided thin (<5 nm) hybrid material with down to micrometer scale resolution of the semiconducting polymer, extremely difficult to produce by other means, while preserving the differentiated hole/electron charge carrier mobilities and electrochromism.
REFERENCES: [1] Matulková, I.; Kovaříček, P.; Šlouf, M.; Němec, I.; Kalbáč, M. Carbon.; [2] Valeš, V.; Kovaříček, P.; Fridrichová, M.; Ji, X.; Ling, X.; Kong, J.; Dresselhaus, M. S.; Kalbáč, M. 2D Mater. 2017, 4 (2), 025087.; [3] Drogowska, K.; Kovaříček, P.; Kalbáč, M. Chem. Eur. J. 2017, 23 (17), 4073–4078.; [4] Kovaříček, P.; Vrkoslav, V.; Plšek, J.; Bastl, Z.; Fridrichová, M.; Drogowska, K.; Kalbáč, M. Carbon 2017, 118, 200–207.; [5] Plšek, J.; Kovaříček, P.; Valeš, V.; Kalbáč, M. Chem. Eur. J. 2017, 23 (8), 1839–1845.; [6] Valeš, V.; Kovaříček, P.; Ji, X.; Ling, X.; Kong, J.; Dresselhaus, M. S.; Kalbáč, M. Phys. Status Solidi B 2016, 253 (12), 2347–2350.; [7] Kovaříček, P.; Drogowska, K.; Melníková Komínková, Z.; Blechta, V.; Bastl, Z.; Gromadzki, D.; Fridrichová, M.; Kalbáč, M. Carbon 2017, 113, 33–39.; [8] Kovaříček, P.; Bastl, Z.; Valeš, V.; Kalbáč, M. Chem. Eur. J. 2016, 22 (15), 5404–5408.

Magnetic nanoparticles have unique properties, e.g. they may exhibit superparamagnetic performance [1-2]. The small size of magnetic nanoparticles diminishes their stability, because they are susceptible to corrosion, oxidation and agglomeration. These drawbacks forces the use of various stabilizing agents which properly protect and preserve the properties of magnetic nanoparticles. Carbon coatings can be used for this purpose. The carbon coating which covers the magnetic nanoparticle is believed to be a perfect agentwhich stabilizes the magnetic nanoparticles and make them resistant against unwanted processes [3].
The aim of this work was to determine the corrosion stability of carbon-encapsulated iron nanoparticles (CEINs) in solutions of nitric, sulfuric, acetic and hydrochloric acids. The studies were carried out in the room temperature and the boiling point. The amount of iron released from CEINs was determined via thermogravimetry. Moreover, the changes of morphological features and magneticparameters were tracked by electron microscopy and magnetic measurements.
The studies draws a conclusion that the carbon shell is a perfect barrier which protects the magnetic core, because the loss of the magnetic phase was on a low level (less than 5 %) in most cases. The higher corrosion rates were observed for nitric acid only. As it was expected, the loss of encapsulated Fe resulted in the decrease of the magnetic performance of CEINs.
REFERENCES: [1] ARRUEBO M., FERNANDEX-PACHECO R., IBARRA M.R. SANTAMARIA J. Magnetic nanoparticles for drug delivery. Nano Today, 2007, vol. 2, no. 3 pp. 22-32.; [2] HUBER D.L Synthesis, Properties and Applications of Iron Nanoparticles. Small, 2005, no. 5 pp. 482-501.; [3] BYSTRZEJEWSKI M., ŁABĘDŹ O., KASZUWARA W., HUCZKO A., LANGE H., Controlling the diameter and magnetic properties of carbon-encapsulated iron nanoparticles produced by carbon arc discharge. Powder Technology, 2013, vol. 246 pp. 7-15.

The paper describes the preparation and identification of hybrid compounds based on graphene oxide, graphene oxide - fullerene C60, graphene oxide CFx, graphene oxide-biochar and graphene oxide-MWCNT. Chemical modification procedures of the foils and its compounds with nanoparticles of metals (oxides) are further described. In conclusion, alternative applications of hybrid foils and synthesized compounds are proposed.

Polyacrylonitrile (PAN) is commonly used as a raw material for making carbon fibers. This work is about dissolving waste acrylic fibers in suitable solvent to make thick acrylic solution. This solution is coated onto glass fiber mats. Acrylic coated glass mats are irradiated with CO2 laser and possibility of carbonizing acrylic is studied. These coated samples are preheated at different temperatures from 300 °C to 500 °C to stabilize Polyacrylonitrile before converting it to carbon structure. It is found that stabilization at 300°C works well in order to stabilize acrylonitrile prior to laser irradiation. Heat treated and non-preheated samples were irradiated by laser for studying possibility of carbonization of PAN polymer. It is found that laser treatment of PAN coated glass fiber mats produces electrically conductive lines on the surface of the material. Moreover the conductivity is increased when the material is preheated to 300°C before laser irradiation. It is also found that conventional heat treatment is not suitable for carbonizing PAN coated surface.

Already in 2004, it was experimentally demonstrated that 1% epitaxial strain can induce ferroelectric order in thin films of SrTiO3 near room temperature.[1] Lowest-frequency polar phonon is highly sensitive on external electric field and therefore permittivity is well tunable by electric field in microwave and THz region.[2] Unfortunately, high microwave dielectric loss does not allow any application of this tunability.
We demonstrated that 1% tensile strain induces ferroelectric phase transition also in incipient ferroelectric Srn+1TinO3n+1 (n=1-6) crystallizing in Ruddlesden-Popper structure.[3] TC increases with n and reaches 180 K in Sr7Ti6O19 film. Simultaneously, the n=6 film exhibits high tunability and exceptionally low dielectric loss at 300 K that rivals all known tunable microwave dielectrics.[3] In this contribution, I will explain the origin of the low loss and high tunability.
In 2010, we have demonstrated that biaxial strain can induce the ferroelectric and ferromagnetic state in epitaxial thin films of EuTiO3,[4] a material that is paraelectric and antiferromagnetic in the bulk form. We found that 1% tensile strain in EuTiO3/DyScO3 induces ferroelectricity at 250 K and ferromagnetism at 4.2 K. Strained EuTiO3 should exhibit strong magnetoelectric coupling, but temperature range, where it works, is too low for practical applications. Higher critical ferroelectric and ferromagnetic temperatures were predicted from first principles in strained EuO [5] thin films. Epitaxial thin films of EuO were prepared using molecular epitaxy on various substrates inducing strain from 0 to 6.4%. Optical soft mode gradually softens with the strain indicating emergent lattice instability, but no soft mode anomaly typical for a ferroelectric phase transition was observed in samples with the strain below 5.5%. Only superlattice of (EuO)2(BaO)2 grown with 6.4% strain on LSAT substrate exhibits soft mode anomaly near 100 K confirming ferroelectric phase transition. Unfortunately, the ferromagnetic phase transition temperature reduces from 69 K (for EuO) to 25 K in (EuO)2(BaO)2 superlattice due to dilution of Eu spins. Other perspectives of strain engineering will be outlined.
REFERENCES: [1] J. H. Haeni et al. Nature 430, 758 (2004).; [2] C. Kadlec et al. Phys. Rev. B 80, 174116 (2009).; [3] C. H. Lee et al. Nature 502, 532 (2013).; [4] J.H. Lee et al. Nature, 466, 954-959 (2010).; [5] E. Bousquet, N.A. Spaldin et al., Phys. Rev. Lett. 104, 037601 (2010).

Au-Fe thin films with 30 at. % and 15 at. % of Fe have been obtained by RF sputtering co-deposition from Au and Fe targets. Fe nanoclusters of similar size but with different organizations have been obtained in specific deposition conditions, e.g. with either self-organization (in the case of the sample with higher Fe concentration) or randomly dispersed Fe nanoparticles. The effect of the self-organized as compared to dispersed system has been studied also theoretically by micromagnetic simulations performed with OOMMF (Object oriented Micromagnetic Software), open source software developed at National Institute of Standards and Technology. Simulations have been performed considering a quasi 2D rectangular geometry with magnetic moments arranged in lamellar configurations, described by inter and intra-lamellar distances. Using OOMMF plug-ins for finite temperature simulations, it has been shown that the system of nanoparticles has a coherent, ferromagnetic behavior only if the intra-lamellar distances are small enough so that the exchange interactions to play an important role. In the case of dispersed system (assimilated to higher inter and intra lamellar distances) the nanoparticles will behave in a super-paramagnetic manner and the total magnetic moment of the system will drop to 0 in less than nanosecond time.

Hematite, α-Fe2O3, is considered as one of the most promising materials for sustainable hydrogen production via photoelectrochemical water splitting with a theoretical solar-to-hydrogen efficiency of 17%. However, the poor electrical conductivity and short diffusion length of photogenerated holes are substantial limitations reducing hematite’s efficiency in real experimental conditions. We report on addressing these two drawbacks by deposition of very thin nanocrystalline hematite films (~ 30 nm) by advanced plasma deposition method known as high-impulse magnetron sputtering (HiPIMS). Despite of computing models suggesting that the electrical conductivity is extremely anisotropic, revealing up to four orders of magnitude higher electron transport with conduction along the (110) hematite crystal plane, synthetic approaches allowing the sole growth in that direction have not been reported yet. We present a new strategy based on HiPIMS for tuning the crystal orientation of 2D thin hematite films by carefully controlling the energy of particles bombarding the substrate during the plasma assisted deposition procedure. The fabricated hematite films showed isolated texture along the desired (110) plane and consequently significantly enhanced photoelectrochemical (PEC) activity. The PEC activity can be even boosted when commonly used fluorine doped tin oxide (FTO) conductive substrate is substituted by platinized substrate. Oriented platinum substrate can induce crystalline defects in hematite film during its growth under very high energy bombardment, which are thermodynamically difficult to obtain. Such anomalies further considerably increase final PEC activity of hematite photoanodes. The effect of HiPIMS deposition modes on the properties of hematite photoanodes were monitored by XRD, conversion electron Mössbauer spectroscopy, XPS, SEM, AFM, PEC water splitting, IPCE, transient photocurrent measurements, and Mott-Schottky analysis.

Amorphous phases rich in dopant ions, in amounts below the detection limit of X-ray diffraction methods, were observed by electron paramagnetic resonance (EPR) in nanostructured II-VI semiconductors doped with Mn2+, i.e. nanostructured ZnO films and nanocrystalline ZnO and ZnS powders [1]. Even small amounts of such phases can be responsible for collective magnetism and also affect the optical and electrical properties. As shown in our previous work [2], the magnetic properties observed in nanocrystalline Mn2+ doped ZnS powders are associated with the formation of Mn2+ clusters in the amorphous phase localized in the intergrain region and the presence of intrinsic surface defects, which both play an important role in the photoluminescence properties as well.
Considering the importance of this amorphous phase in understanding and controlling the magnetic and optical properties of the II-VI semiconductor nanostructures, we have investigated its chemical composition, origin and thermal stability by correlated analytical transmission electron microscopy, multifrequency EPR and FTIR spectroscopy. Our results point to the possibility to modulate the properties of the semiconductor nanostructures not only by varying synthesis conditions such as precursors, solution pH, synthesis temperatures but also by post-synthesis thermo-chemical treatments.
ACKNOWLEDGEMENTS: Financial support from CNCS-UEFISCDI, Project PN-II-RU-TE-2014-4-0939 is gratefully acknowledged.
REFERENCES: [1] M. Stefan, L.C. Nistor, I.D. Vlaicu, D. Ghica, S.V. Nistor, Appl. Surf. Sci. 462 (2017) 342 and cited references.; [2] S.V. Nistor, M. Stefan, L.C. Nistor, V. Kuncser, D. Ghica, .I. D. Vlaicu, J. Phys. Chem. C 120 (2016) 14454 and cited references.

Hafnium oxide (HfO2) is a high-temperature ceramic with excellent electrical, dielectric and optical properties, which may be substantially enhanced in the nanostructured material. Here, for the first time, we have developed self-organized arrays of hafnium oxide nanorods and examined their properties by electrochemical impedance spectroscopy (EIS). For sample preparation, Al/Hf layers are magnetron sputtered onto SiO2/Si substrates, anodized at 140 V and then re-anodized up to 400 V. This results in the growth of a porous alumina film, followed by pore-assisted oxidation of the hafnium underlayer. The films consist of discrete hafnium-oxide protrusions, penetrating the alumina pores and anchored to a uniform oxide layer that forms under the pores. Post-anodizing treatments include annealing at 600°C in air or vacuum and selective dissolution of the alumina overlayer.
The electrical/dielectric behavior of the hafnium oxide nanorod arrays, embedded in or free from alumina, was EIS-investigated in a borate buffer solution. It was revealed that, in the as-reanodized (not annealed) state the bottom oxide layer behaves as a good dielectric whereas, surprisingly, the nanorods themselves are semiconducting in nature. This situation does not change substantially by the annealing in air, still resulting in a dielectric bottom layer and semiconducting nanorods. However, after the annealing in vacuum, both the bottom oxide and nanorods behave as an n-type semiconductor. Further investigation is in progress to understand the formation-structure-morphology relationship, aiming at exploring the functional properties of the films.

Boron doped diamond (BDD) films have become popular as electrode material because of combination of attractive electrochemical, physical, and mechanical properties [1]. Among other organic analytes, they outperformed other sp2 carbon-based materials in detection of neurotransmitters including dopamine serving as one of oxidizable redox probes. Nevertheless, only limited possibilities to enhance BDD specific surface area exist, although it is advantagouse in a number of applications, including electroanalysis [2,3].
The aim of this contribution is to report on electrochemical and spectral properties of conventional planar nano-crystalline BDD thin films [1] and BDD deposited on a porous template composed of SiO2 nanofibres prepared by spin coating [3]. Silicon subsrate microwave plasma enhanced chemical vapour deposition (MW PECVD) with variable B/C ratio in the gas phase 500 to 8000 ppm was used in both cases. Beside that nano-crystalline BDD layers deposited in a microwave PECVD system with linear antenna delivery (MW-LA-PECVD) with reduced electrical conductivity and possibly problematic boron incorporation due to necessary addition of oxygen species [4] were investigated. All deposited BDD layers were characterized using Raman spectroscopy, SEM, AFM, and voltammetric techniques. The Raman spectra revealed almost no graphitic or amorphous carbon impurities in planar samples and metallic character of conductivity for B/C ratios 2000 ppm and higher. For porous BDD thin film, high levels of non-diamond carbon in some areas measured were observed. Cyclic voltammetry with the outer- and inner sphere redox markers [Ru(NH3)6]3+/2+ and [Fe(CN)6]3−/4− and dopamine confirmed fast electron transfer kinetics for all as-deposited samples with higher current densities and proclivity to adsorption in the porous material. Further, electrochemical properties including potential window in commonly used buffers and stability of the BDD layers on the silicon substrate towards anodic, cathodic and mechanical type of pretreatment will be assessed.
ACKNOWLEDGEMENTS: This research was carried out within the framework of Specific University Research (SVV 260440). The research was financially supported by the Czech Science Foundation (projects 17-15319S).
REFERENCES: [1] Peckova K., Musilova J., Barek J., Crit. Rev. Anal. Chem. 39, 148-172 (2009).; [2] Ruffinatto S., Girard H. A., Becher F., Amault J. C., Tromson D., Bergonzo P.: Diam. Relat. Mater. 55, 123-130 (2015).; [3] Petrak V., Zivcova Z. V., Krysova H., Frank O., Zukal A., Klimsa L., Kopecek J., Taylor A., Kavan L., Mortet V.: Carbon 114, 457-464 (2017).; [4] Taylor A., Ashcheulov P., Cada M., Fekete L., Hubik P., Klimsa L., Olejnicek J., Remes Z., Jirka O., Janicek P., Bedel-Pereira E., Kopecek J., Mistrik J., Mortet V., Phys. Status Solidi A 212, 2418-2423 (2015).

The optical absorptance and photoluminescence studies has been applied on the hydrogen and oxygen plasma treated, nominally undoped (intrinsic) ZnO thin films and aligned nanocolumns grown on the nucleated glass substrate by the hydrothermal process in an oil bath containing a flask with ZnO nutrient solution. The localized defect states at 2.3 eV below the optical absorption edge were detected by photothermal deflection spectroscopy (PDS) in a broad spectral range from near UV to near IR. The optical absorptance spectroscopy shows that hydrogen doping increases free electron concentration changing ZnO to be electrically conductive (hydrogen doping). The high Dc current flow degrades the optical and electronic properties. Photoluminescence spectroscopy shows that after plasma hydrogenation, the exciton related emission band centered near the optical absorption edge at the wavelength 375 nm (3.3 eV) is partly deteriorated but fully recovers after the subsequent plasma oxidation. Therefore, the exciton related photoluminescence is influenced significantly by the plasma treatment and it correlates with free electron concentration. This work was supported by the Ministry of Science and Technology of the Republic of China, Taiwan, under Contract No. MOST 104-2112-M-153 -002 -MY3, MOST 105-2911-I-153 -501, CSF project 16-10429J and the MEYS project LTC17029 INTER-COST Action MP1406. This work was carried out in the frame of the LNSM infrastructure

Development of the scientific instrumentation and analytical methods was in the last decade significantly influenced by the integration of different techniques into the compact instrumentation. The scanning electron microscopy (SEM)) and scanning probe microscopy (SPM) are commonly used imaging techniques in the Material Sciences, Nanotechnology and Life Sciences. Integration of LiteScope SPM produced by NenoVision into the SEM extend the instrument capabilities and offer several benefits like 3D characterization, measurements of electrical and magnetic properties and others. On the top of that we present new measurement techniques for the true correlative imaging which enable direct comparison of the images from SEM and SPM. Unique measurement technique Correlative Probe and Electron Microscopy (CPEM) for correlative imaging has been developed by the SPM manufacturer NenoVision and tested in the SEM instruments for various applications.
Correlative Probe and Electron Microscopy (CPEM) is based on the different principle than traditional approach of correlative microscopy of the SEM and SPM techniques. In the past both techniques were already integrated but used separately. Therefore, the comparison of obtained images was very difficult and misleading due to different scanning systems, image distortions, resolutions etc. Using CPEM technology electron beam is focused close (100 nm) to the SPM tip, where scanning is made by piezo scanner with the sample. During the measurements distance between the tip and electron beam is constant. Simultaneous collection of SPM and SEM signals enables simultaneous imaging of the slightly shifted areas by SEM and SPM. The shift is simply eliminated during the post-processing. Obtained images can be correlated very easily due to their identical scanning system and coordinates. Images can be directly correlated without any further data processing, where each pixel is represented by the X, Y, Z coordinates given by SPM and color (mask) corresponding to the one or more signal from SEM detectors. CPEM can accommodate several more signals from different detectors or related techniques like EBIC or CL. Each signal is then represented by the unique mask and can be used for the further image analyses.