Seznam abstraktů 2016: SEKCE A - NANOMATERIÁLY PRO ELEKTRONICKÉ, MAGNETICKÉ A OPTICKÉ APLIKACE. UHLÍKOVÉ NANOSTRUKTURY, KVANTOVÉ TEČKY

Because of their small size the properties of nanomaterials are often dominated by surface effects. The techniques developed in surface science, in particular Scanning Tunneling and Scanning Force Microscopy, can give direct insights into surface geometric and electronic structure, and into adsorption, diffusion, and reaction processes at the molecular scale. Our group is focusing such investigations on metal oxides, motivated by the wide use of these materials in technological applications. In the talk I will give selected examples of surface investigations of oxides including TiO2, In2O3, iron oxides, and selected perovskites.

We have investigated the synthesis and the magnetic properties of monodispersed iron oxide nanoparticles prepared by thermal decomposition of organometallic precursors in high-boiling solvents. Special focus was on the influence of the heating rate during the synthesis. Using TEM, TGA, XRD and SQUID measurements the size, number as well as magnetic and crystallographic properties of the particles were investigated.
By solely varying the heating rate from 1°C/min to 35°C/min, spherical particles with sizes ranging from 6-20nm were produced. The width of the size distribution is <10% for all particle sizes. Particle size increases with increasing heating rate. In case of smaller particles, we found a higher number of particles in the sample, compared to the larger particles. This suggests that during the nucleation process more nuclei are formed at lower heating rate.
Possible applications of such particles in the field of polymer processing are considered. For example, magnetic particles embedded in polymers can act as susceptors in external alternating magnetic fields to heat up the material, either for melting in case of a thermoplastic material or curing in case of resin material.

Photonic crystals are photonic structures with many possible applications in optics and photonics. For example, two-dimensional (2D) periodic structures prepared on dielectric materials can be used to control propagation of light on a nanometer scale. We fabricated 2D photonic crystals on polycrystalline diamond thin layers deposited on a silica substrate. Polycrystalline nature of the material causes that large number of various optically active defects (optical centers) is present inside the layer. Their luminescence spectrum covers whole visible range. Furthermore, depending on the growth conditions, SiV centers with narrow room-temperature luminescence peak can be incorporated into the diamond layers during their growth. Design and dimensions of the photonic crystals were chosen with a goal to enhance the extraction of light emitted by the optical centers. In case of the planar layer, most of light from the optical centers stays trapped inside the diamond layer due to total internal reflection on diamond-air interface. By structuring the surface of diamond into a well-designed periodic pattern, light emission from optical centers can be diffracted into air. We will show that this approach leads to more than 10 fold extraction enhancement of the centers luminescence and that the luminescence is extracted within a narrow solid angle. ACKNOWLEDGEMENTS: This work was supported by the GACR project No. 16-09692Y.

Nanodiamond particles (NDs) have risen recently in popularity owing to their unique and perspective properties. Merging NDs with organic molecules, such as polypyrrole (PPy), into hybrid organic-semiconductor functional systems gives rise to potential applications in photovoltaics (PV), which is supported by prior experimentally observed charge transfer between bulk diamond and PPy [1,2]. We have recently reported computed interaction of physisorbed and chemisorbed PPy on nanodiamond particle facets passivated by hydrogen, which indicated energetic level alignment promising for PV applications [3]. Oxidized nanodiamonds represent another interesting system as the surface dipole of oxygen on diamond is opposite and relatively stronger.
This work thus focuses on the most relevant (111) and (100) ND facets with different coverage of surface terminating oxygens in ether, epoxide, ketone, and peroxide positions [4,5]. We use density functional theory (DFT) computations employing B3LYP functional and 6-31G(d) basis set. Energetically the most favorable oxidized ND facets we further optimized with PPy in physisorbed configurations. Analyses of geometric parameters, binding energy, HOMO-LUMO gap, and charge transfer were done on the relaxed structures. For all of the structures, multiple hydrogen bonds between the amino groups of PPy and surface O atoms of ND form. The most energetically favorable and exothermic binding energy (Eb) of 2.76 eV is obtained for PPy on 1x1 reconstructed (111) ND facet that is 100% saturated with O atoms in peroxide positions (see Figure 1). At the same time, the highest charge transfer (Δq) in the dark of 0.26 e- from ND to PPy is calculated also for this structure. The HOMO-LUMO gaps of the initial ND facets are significantly lowered, by 2.2 eV on average. Moreover, HOMO and LUMO orbitals become mostly spatially separated. These features may be beneficial for photovoltaic applications of nanodiamond. REFERENCES: 1. B. Rezek, J. Čermák, A. Kromka, M. Ledinský, and J. Kočka, Diam. Relat. Mater. 18, 249 (2009).; 2. P. Galář, B. Dzurňák, P. Malỳ, J. Čermák, A. Kromka, M. Omastová, and B. Rezek, Int J Electrochem Sci 8, 57 (2013).; 3. P. Matunová, V. Jirásek, and B. Rezek, Phys. Status Solidi A (2016).; 4. X. M. Zheng and P. V. Smith, Surf. Sci. 262, 219 (1992).; 5. D. Petrini and K. Larsson, J. Phys. Chem. C 111, 795 (2007).

Properties of the resulting polymer nanofibres are often tailored by sonication technique applied prior or past an electrospinning process. The aim of this contribution is to evaluate morphology of nanofibrous mats formed by poly(ethylene oxide) with distributed magnetic nanoparticles (about 20 nm in diameter) in dependence on time of sonication of the used polymer solutions. The solutions were exposed to sonication (intensity 200W, frequency 24 kHz) for 10, 30, and 60 minutes. It was shown that rheological characteristics (viscosity, storage and loss moduli) strongly depend on time of sonication (particularly phase angle) in contrast to electric conductivity and surface tension. For analysis of homogeneous distribution of magnetic nanoparticles in polymer solution, the rheological measurements were carried out also in presence of external magnetic field and magnetorheological efficiency (a relation of corresponding viscosities) was determined for 80, 170, and 255 mT. Consequently, changed rheological characteristics participate significantly in the process of electrospinning and resulting quality of the obtained nanofibrous mats. Qualitative changes were described by means of scanning electron microscopy (variance of mean diameter of nanofibres), transmission electron microscopy (distribution of magnetic nanoparticles within nanofibrous mats). Static magnetic properties were determined by vibration sample magnetometer. It was shown that even distribution of magnetic nanoparticles in the mats can be achieved by mere sonication process without application of external magnetic field during the electrospinning process. However, time of sonication generates a degree of embedding of magnetic nanoparticles into individual nanofibres.

This presentation is about Raith’s ionLINE (a FIB centric tool), which comprises special features. Applications making use of these features and the advantages of a focused ion beam are presented.
For write field calibration, stitching and beam on sample drift correction ionLINE uses a built-in laser interferometer stage. In this set-up the in-plane sample position is controlled with a double laser interferometer. The interferometer laser source defines a natural calibration standard for the nano pattering process. Beyond calibration this type of sample stage enables flawless fabrication of elongated devices which do not fit in one write field, e.g. photonic crystal waveguides with a length of millimetres.
In true nano patterning with critical dimensions below 100 nm the currents used are in the pA range. Current stability at low currents is important to make high quality devices. Moreover the positional drift during processes which may take many hours must be addressed. The make of plasmonic structures or x-ray zone plates are presented as examples.
The standard of FIB tools is the Gallium based liquid metal ion source (LMIS). ionLINE however operates alternatively also with focused gold or silicon ion beams. Using this alternative species the drawbacks of unwanted Gallium contamination can be overcome and new techniques like functionalization of substrates by implantation become available. One example is the selective growth of graphene nano ribbons on SiC substrates.

Silicon (Si) quantum dots (QDs) have been a subject of intensive research for many years as a nanoscale luminescence material. In particular, the research on colloidal Si-QDs are growing rapidly in recent years, because of the versatility in many kinds of applications. Recently, we have developed a new type of all-inorganic Si-QDs that can be dispersed in alcohol and water almost perfectly without any surface functionalization processes. The unique property arises from the core-shell structure. The shell is very heavily boron (B) and phosphorus (P) doped Si, which induces negative potential on the surface and prevents the agglomeration in polar solvents. The B and P codoped Si-QDs have characteristic properties not being observed in conventional Si-QDs. Among them, an important feature is the insensitiveness of the luminescence property to environment and to chemical treatment of the surface. Because of the insensitiveness, the codoped Si-QDs are a very suitable material for the production of a variety of Si-QD-based nanocomposites. In this work, we first discuss structural and optical properties of B and P codoped colloidal Si-QDs. We then show the formation of a variety of composite structures composed of Si-QDs and metal nanostructures by using electrostatic attraction, chemical bonding and DNA hybridization. We demonstrate the enhancement of the absorption cross-section and the radiative decay rate by tuning the surface plasmon resonance energies to the excitation and luminescence energy, respectively. We also demonstrate strong modification of the luminescence spectral shape by the coupling with surface plasmons.

Integration of semiconductor quantum dots (QDs) with integrated photonic elements would be a useful platform for integrated quantum photonics, aimed at producing, processing and detecting quantum states of light (e.g., single photons) on chip. Implementation of such integrated structures is highly challenging, requiring both position and spectral control of the QD systems involved. Here we describe recent progress in the fabrication of such structures, based on the integration of site-controlled pyramidal QDs [1] with photonic crystal (PhC) membrane cavities and waveguides. The use of high-precision electron beam lithography and advanced alignment techniques for fixing both the inverted-pyramid nucleation sites for the QDs and the PhC holes yield relative alignment precision of better than 20nm. The relatively small inhomogeneous broadening of the QDs (<5meV for the exciton lines) permits reproducible detuning of the QD transitions with the resonances of the PhC structures investigated. Using this approach, we demonstrate coupling of the transitions of one or several QDs to selected modes of PhC Ln cavities of different sizes [2], coupling of QD pairs to PhC molecules [3], and coupling of several QD single photon emitters to PhC waveguides in the mode-guiding regime [4]. Possible designs of more complex integrated structures such as fast/slow light waveguides and PhC cavity networks will be discussed. REFERENCES: [1] A. Mohan et al., Small 6, 1268 (2010); [2] A. Lyasota et al., Jour. Cryst. Growth 414, 192 (2015).; [3] B. Rigal et al., APL 107, 141103 (2015).; [4] B. Rigal et al., META’16 Conf., 25-28.7.16, Malaga, Spain.

Photo- and electro-luminescence quantum yield (QY) is a crucial parameter for any material to be used in light-emitting devices, fluorescent probes, wavelength converters etc. In case of materials composed of ensembles of nanocrystals (NCs) in a solid matrix or liquid medium we distinguish external and internal QY (EQY and IQY). EQY is defined as the total number of emitted photons divided by number of absorbed photons for the whole sample, while IQY concerns only the luminescing subensemble of NCs. In most of NC ensembles there is significant number of “dark” NCs that can absorb but not emit photons due to presence of non-radiative recombination centres (defects). EQY is conveniently measured using an integrating sphere [1, 2] but IQY is not easily measurable. The most feasible way to obtain IQY is variation of local density of optical states which affects radiative but not non-radiative lifetime, so enabling to decouple these two components and calculate IQY. We study both EQY and IQY of Si nanocrystals (SiNCs) using either special samples with variable distance between NCs and a high-n substrate or by approaching such substrates to a layer of NCs. We show that large number of SiNCs are dark and discuss the mechanisms limiting PL QY in ensembles of SiNCs. REFERENCES: [1] J. Valenta, Nanoscience Methods 3 (2014) 11-27 (OA).; [2] J. Valenta et al., Appl. Phys. Lett. 105 (2014) 243107.

The nonequilibrium quantum transport theory is used to develop formula for irreversible transfer of electronic excited state (exciton), or of an electron, between two quasi-zero-dimensional nanostructures. The interaction of the electronic subsystems with the vibrations of the atomic lattices is included in a non-perturbative way. The formula should be suitable for the analysis of the light-conversion measured data and in systems with electronic charge transfer processes like the electrically conductive polymers. The properties of the formula are shown with using numerical calculations performed for two interacting quantum dots. We acknowledge the project LD14011 (HINT COST Action MP1202), the CSF project 16-10429J and the CAS project KONNECT-007.

Doped semiconductor nanocrystals (NCs) is a new material for tunable plasmonics. NCs of copper deficient copper chalcogenides possess a localized surface plasmon resonance (LSPR) which can be tuned thorough the near-infrared (NIR) spectral region. The opportunity to couple LSPR in doped semiconductor NCs with NIR emitting quantum dots (QDs) is of great importance for the development of nanoscale devices for NIR-light detection and light harvesting.
In the present work we coupled oleylamine-capped Cu2-xSe nanocrystals with LSPR in the NIR region with lead sulfide (PbS) QDs. An emission spectrum of PbS QDs can be tuned through the entire NIR region by varying QD size and can be easily coupled with LSPR frequency. We analyzed an influence of adding of Cu2-xSe to PbS QDs prepared in colloidal solution, in organic matrices and on glass substrates. We found that photoluminescence (PL) signal from QDs is considerably affected by Cu2-xSe NCs, which results in slowdown of PL decay and change of PL intensity. The behavior of PL signal drastically depends on the surrounding matrix and QD-NC separation distance. Despite Cu2-xSe NCs provide an enhancement of PbS QDs PL, they also caused and acceleration of QD degradation when QDs and NCs interact. This process was analyzed in details for colloidal QD solution.

Colloidal nanoparticles are of great interest for the last decades. They are perspective nanoscale materials for different applications in fundamental research, nanophotonics, sensors, photovoltaics, biology and medicine.
In this work we discuss our last achievements of the colloidal synthesis and applications of different nanoparticles, among which are semiconductor, metal and metal oxide materials. These nanoparticles have been obtained employing stabilizers which provide compatibility with a wide variety of media from nonpolar organics to water. Thanks to their versatile solubility, the nanomaterials obtained have the ability of spontaneous multiphase transfer. They have been shown to permeate through cell membranes without endocytosis which makes them interesting for bio-applications. We also report on the influence of the chirality of semiconductor nanocrystals on the efficiency of their uptake by living carcinoma cells.

This talk will focus on state-of-the-art nanocrystalline soft magnetic materials, with an emphasis on their optimization for various energy conversion systems and magnetic sensors. Strategies for improved material performance include new alloy and compound development, nanoscale structure control, novel geometries, and improved processing methods. A special attention will be devoted to nanocrystalline alloys in the form of bilayer ribbons prepared by a double-nozzle planar flow casting technique, which offers the possibility of simultaneous formation of two mechanically solid connected homogeneous layers with different composition and uniform thickness of tenths of microns along the ribbon length. This technique makes possible combining unlike alloys with selected properties and unique overall behavior. The resulting bilayer ribbons are interesting for their intrinsically graded properties, which can lead to specific sensor or actuator principles. We also show that the thermal processing under the presence of external magnetic field, called also „magnetic annealing“ is a very powerful tool to produce the controllable anisotropy and domain structure in series of nanocrystalline magnetic alloys. Examples of our recent work on the tuning of soft magnetic properties in Fe-based nanocrystalline materials for energy harvesting and sensor applications will be briefly highlighted.

DC reactive magnetron sputtering of metallic target in oxide atmosphere is a simple method of depositing the nominally undoped (intrinsic) polycrystalline layers of metal oxides. We have optimized the deposition of ZnO thin films on fused silica substrates and investigated the localized defect states below the optical absorption edge using photothermal deflection spectroscopy (PDS) that allows to measure the optical absorption down to 0,01% in a broad spectral range from UV to near IR. We have shown that the defect density and thus the electrical resistivity as well as the optical transparency can be significantly increased by annealing in air at 400C and reduced by the hydrogen plasma. We acknowledge the CSF project 16-10429J and the CAS project KONNECT-007.

Thanks to their wide transparency in the infrared range, low phonon energy, photosensitivity and high linear and nonlinear refractive index, chalcogenide glasses are prospective materials for photonics devices. Radio-frequency sputtering is widely used for film fabrication due to its relative simplicity, easy control, and often stoichiometric material transfer from target to substrate. Amorphous Ge–Sb–Se thin films were fabricated by rf-magnetron co-sputtering technique employing three cathodes. Three targets of following compositions: GeSe2, Sb2Se3 and Ge28Sb12Se60 were used to obtain films of various compositions. The influence of the composition determined by energy-dispersive X-ray spectroscopy on the optical properties was studied. Optical bandgap energy E_g^opt was determined using variable angle spectroscopic ellipsometry and UV-Vis-NIR spectrophotometry. The morphology and topography of the selenide sputtered films was studied by scanning electron microscopy and atomic force microscopy. The films structure was determined using Raman scattering spectroscopy. The aim of the present work is to study the photostructural changes of fabricated films maintained under an inert atmosphere to prevent photo-oxidation of exposed films.

Flexible strain sensor based on MWCNTs/epoxy nanocomposite coated on a Polyimide (Kapton HN) substrate are often referred due to their outstanding properties. Nevertheless, polyimide has a poor adhesion with different classes of material, such as ceramic, polymers and metals, caused by its hydrophobic nature and low specific surface energy. Generally, the physicochemical properties at the substrate interface are decisive for the performance of strain sensors. To enhance the adhesion to substrate, oxygen plasma cleaning is proposed as an adhesion improvement technique. For this different exposure times were investigated, such as 2 min, 4 min, 5 min and 10 min. The PI surface wettability was investigated by static contact-angle measurements using two different liquids water and n-hexane. The contact angle of water decreased with increasing the oxygen plasma treated time to reach a completly hydrophilic surface with a contact angle of 12,6° after 4 min. The effect of plasma treatment on thin film nanocomposite performance was evaluated using DC measurements. To understand the phenomena behind the increased conductivity by plasma cleaning, the chemical groups introduced by the treatment were examined using Raman spectroscopy measurements. The results show the formation of more carbonyl groups with the elimination of hydrocarbon impurities after 4 min of exposure to plasma that increase the electrical resistance.

Nanocrystalline holmium-doped yttrium titanates, which crystallize in a pyrochlore structure with general formula (HoxY1-x)2Ti2O7), have been recently investigated for their interesting luminescence properties. Holmium ions provides an intensive emission around 2 um. This spectral region is a part of so called “eye safe” wavelength region. The presence of yttrium ions in the pyrochlore structure prevents the non-radiative interactions between Ho3+ ions thus it enormously improves the luminescence properties. These advantages make (HoxY1-x)2Ti2O7 promising materials for the construction of novel optical amplifiers and high power fiber-lasers.
We present a generic sol-gel synthesis of nanocrystalline (HoxY1-x)2Ti2O7 powders and thin films. The effect of the composition and nanocrystalline structure of prepared nanomaterials on their optical properties have been investigated. The optimized nanocrystals were incorporated into an optical fiber and the prepared fiber was tested as an active medium in a fiber-laser ring set-up.
The presented approach led to the formation of nanocrystalline (HoxY1-x)2Ti2O7 powders and thin films with tailored grain sizes ranging from 15 nm to 100 nm. It was found that the Ho3+ and Y3+ ions were regularly distributed inside the crystal lattice. Optimal concentration of Ho3+ ions in the structure was around x=0.05 providing the most effective luminescence properties.
The results brings fundamental information about the effect of the size of the nanocrystals to their luminescence properties. The promising application of prepared nanocrystals in the field of fiber-lasers and planar optical amplifiers is widely discussed in the contribution. ACKNOWLEDGEMENTS: This work was supported by the Czech Science Foundation, contract No 14-35256S.

The major advantage of investigations on combinatorial libraries is the possibility to simultaneously generate a multitude of different compositions within one single production process on one sample. Thus, the influence of the composition on the oxidation behaviour for instance can be easily evaluated without the necessity of handling several samples.
Combinatorial manganese/silicon thin films on iron substrate (99.6 at.-% purity) were deposited using a self-made state of the art vacuum chamber in order to investigate their properties. The concentration of manganese was set from 30 to 70 at.-%, and the amount of silicon from 70 to 30 at.-%, along the 76 mm y-axis of the sample. Subsequently, they were annealed at atmospheric pressure at 900 °C, for annealing times of 120 s and 600 s in atmospheres containing 10 % H2 in N2 at defined dew points. The oxygen partial pressure was chosen to be only oxidative for the elements in the combinatorial library, but not for the Fe substrate material.
On the one hand the surface structure of the annealed samples strongly depends on the composition of the deposited thin film. On the Mn-rich side of the substrate the sample shows a regularly arrayed surface, whereas the Si-rich side provides rather disordered amorphous surface structures. On the other hand the oxygen partial pressure represented by the dew point during annealing must be taken into account, as it represents the oxidative force according to Ellingham diagrams. With increasing dew point more oxide structures could be found at the surface.

The ability to control the rates of chemical or biochemical reactions at length-scales comparable to those of single-cell organisms or their sub-cellular compartments would be desirable in a number of situations, ranging from fundamental studies of transfer phenomena to applications such as controlled delivery of actives from functional materials in the pharmaceutical, food, personal care or crop protection products. Strategies for the control of biochemical reactions have been applied to autonomous micro-scale systems called “chemical robots”. A chemical robot is an internally structured microparticle consisting of a semi-permeable membrane that regulates molecular transport between the interior and the surroundings, a system of stimuli-responsive internal compartments that store and release reactants, immobilised enzymes or catalysts for facilitating chemical reactions, and magnetic nanoparticles that act as susceptors and enable receiving radiofrequency signals.
The talk will present an implementation of chemical robots based on soft hydrogel bodies produced by drop-on-demand inkjet printing and microfluidic methods, with internal storage reservoirs formed by phospholipid vesicles (liposomes) and immobilised enzyme (laccase) as a bio-catalyst. Super-paramagnetic iron oxide nanoparticles that dissipate heat when exposed to alternating magnetic field in the radiofrequency range are used as susceptors that facilitate the control of local temperature, which in turn controls the diffusion rate of reactants from liposomes and thus the local reaction rate. The talk will cover fabrication methods for the bottom-up assembly of chemical robots, their structural and functional characterisation. Several scenarios will be presented, including simple one-off release of a pre-synthesised chemical payload, repeated on/off release, and finally repeated starting, stopping and restarting of a local chemical reaction that produces a chemically unstable but physiologically active product. The flow and deposition of chemical robots in porous media observed by MRI in the context of spatially specific delivery of actives will be discussed. Examples of the interaction between chemical robots and living cells or their colonies will be shown.

Two-state electric field-driven molecular switch based on a dipolar molecule enclosed inside a non-spherical fullerene was studied, see Figure. The operation and functionality of the switch will be shown here on a series of endohedral MX@C70-C6H10 (MX=LiF, LiCl, NaF, NaCl) molecules and their response to the electric field by means of density fucntional calculations. We show, that two possible low-energy minimum orientations of the molecular dipole inside the cavity along the longest axis of the fullerene provide distinguishable molecular states of the system separated by energy barrier connecting these minima. Switching of the molecular states is realized by application of external electric field, which forces reorientation of the enclosed dipole while removing the energy barrier connecting the minimum states.

Accurate non-destructive method for thickness control is essential for the successful integration of a wide range of ultrathin films in an equally wide variety of electronic devices. Our profilometry method is based on attenuation of the substrate Raman signal by absorption in the overlaying thin film. We exploit this phenomenon to develop a contactless thickness profiling method for thin films even on rough substrates. We demonstrate this technique by measuring profiles of thin amorphous silicon stripes deposited on rough silicon surfaces, which is a structure exploited in high-efficiency silicon heterojunction solar cells [1]. Our spatially resolved Raman measurements enable the thickness mapping of amorphous silicon over the whole active area of test solar cells (several cm2) with very high precision. The thickness detection limit is well below 1 nm in this case and the spatial resolution is down to 500 nm, limited only by the optical resolution of used detection set-up.
Above that, we discuss the wider applicability of this technique for single-layer counting of multilayer 2D materials such as graphene, MoS2 and WS2. These materials absorb visible light, total absorption is given by number of layers. Since Raman spectroscopy is standard characterization tool for almost all 2D materials, this additional information is easy to obtain. Moreover for more than three layer graphene stack the number of layers is hard to determine based on shape of the Raman spectra. The first results show that our method works very well for multi layered graphene. REFERENCES: [1] K. Masuko, M. Shigematsu, T. Hashiguchi, D. Fujishima, M. Kai, N. Yoshimura, T. Yamaguchi, Y. Ichihashi, T. Mishima, N. Matsubara, T. Yamanishi, T. Takahama, M. Taguchi, E. Maruyama, and S. Okamoto, "Achievement of More Than 25% Conversion Efficiency With Crystalline Silicon Heterojunction Solar Cell", IEEE Journal of Photovoltaics, 4, 2014, 1433-1435.

As manufacturer of both techniques we recently integrated a monochromated microfocus XPS system with a Raman spectrometer. The focal points are aligned such that data can be acquired from the same point simultaneously, and that the sizes of the analysis areas are comparable in size. This combined approach is particularly powerful when analyzing carbon nanomaterials. Chemical modifications of the material can be easily determined and quantified with XPS, and Raman offers a fast way of determining the quality and conformity of the material. The greater depth of field of the Raman spectrometer also offers bulk information to complement the surface sensitive XPS data. The maximum benefit of this in-situ combination is drawn if the XPS is equipped with a combined monatomic and gas cluster ion source enabling state-of-the-art depth profiling. In this presentation we will discuss the strengths of this combined, in-situ approach to surface analysis, illustrated by Graphene.

In the present research work transition element substituted strontium ferrite SrFe12-xMexO19 (Me = Al, Mg, Co, Vd and Zn) were prepared by chemical co precipitation method. As it is synthesised power was calcined at a temperature of 9000C for 4hrs. Strontium hexaferrite nanocrystals with magnetoplumbite structure were confirmed through X-ray diffraction and transmission electron microscopy analysis. The prepared ferrite particles were exposed to dielectric analysis including dielectric constant (ϵ’), dielectric loss (ϵ″) and loss tangent (tanδ).They were examined for different transition elemental substitution of same concentration. On the basis of the result analysis their application for high frequency are explored.

Graphene is a two–dimensional one-atom-thick carbon sheet built by fusing an infinite number of benzene rings. When an infinite graphene sheet is cut into nanofragments, a variety of graphene nanostructures having different sizes and geometries are created. Here their electronic structures depend crucially on the edge geometry. Indeed, armchair-edged nanostructure is subjected to the formation of standing wave (aromatic stability) together with the opening of energy gap, whereas nonbonding edge state, which is the origin of electronic, magnetic and chemical activities, is created in the vicinity of the edges in zigzag-edged nanostructures. In addition, the electronic structures depend on how the edge carbon atoms are bonded to foreign chemical species. Accordingly the interplay between edge geometry and chemistry gives rise to a huge variety of electronic structures.
We investigated the electronic structures of graphene nanostructures, such as linear edges, defects with one and two missing carbon atoms, and corner edges, with edge carbon atoms terminated with hydrogen or oxygen atoms, using microprobe (STM/STS, AFM) experiments together with DFT calculations. A monohydrogenated zigzag edge shows the presence of edge states, while replacing mono-hydrogenated sites with dihydrogenated sites in every three edge carbon site in a zigzag edge creates a standing wave of √3×√3 superstructure at the expense of edge state. The edge state in a ketonated zigzag edge penetrates into the oxygen atoms and also into the interior of graphene with a long decay length due to charge transfer from graphene to the oxygen atoms. A defect having one missing carbon atom has a variety of electronic structures with or without edge state depending on how the edge carbon atoms are terminated with hydrogen atoms. In defects having two missing carbon atoms with edge carbon atoms being oxidized, we observed an interesting switching phenomenon between edge state and standing wave, induced by the mechanical force of an AFM tip. The corner between two linear zigzag edges with a mutual angle of 60 ˚ has no edge state, when one additional carbon atom is incorporated at the corner.
REFERENCES
[1] T. Enoki, Phys. Scr. T146, 014008 (2012) (Nobel Symposium on Graphene and Quantum Matter); [2] S. Fujii and T. Enoki, Acc. Chem. Res. 46, 220 (2013); [3] S. Fujii, M. Ziatdinov, M. Ohtsuka, K. Kusakabe, M. Kiguchi and T. Enoki, Faraday Discussions, 173, 173 (2014).

Single-layer graphene film shows potential for use as a transparent, conductive, flexible electrode, an alternative for conductive metal oxides like indium tin oxide or aluminium-doped zinc oxide. Moreover, graphene layer can be transferred on semiconducting materials, such as silicon, for forming Schottky junction devices. Graphene-based Schottky junction solar cells have been intensively investigated in last several years because of their simple and low cost fabrication and the potential to achieve high power conversion efficiencies. However, the combination of graphene with inexpensive materials used in microelectronics and photovoltaics, namely hydrogenated amorphous and microcrystalline (μc-Si:H) silicon thin films, was neglected up to now.
In this study, Schottky barrier-based solar cells composed of chemical vapour deposited graphene transferred onto μc-Si:H film were investigated for the first time. We demonstrated sample with an open-circuit voltage of 445 mV, a remarkable value for undoped graphene-based solar cell. Furthermore, photovoltaic properties of graphene/silicon junctions were characterised by current-voltage (I-V) curves obtained locally by conductive atomic force microscopy (C-AFM) and also macroscopically by standard I-V measurement using AM1.5G solar simulator. A very good correlation between both independent measurements proved the C-AFM as a highly useful tool for local photovoltaic characterization of 2D material/semiconductor junctions at the nano- and microscale.

We study formation and properties of graphene grown on diamond films with a prospect for large area deposition and devices of graphene. Nanocrystalline diamond thin films (grain size ~ 200 nm) are coated with a thin Ni layer (nominal thickness ~ 20 nm) and heated to 900°C in a forming gas atmosphere (H2/Ar) to initiate a thermally driven catalytic transformation of the diamond surface into graphene by a reaction of Ni with carbon. The samples are cleaned from residual Ni after the catalytic transformation. We employ scanning electron microscopy, Raman micro-spectroscopy, and Kelvin probe force microscopy showing how diamond and grain boundaries influence the graphene growth as well as graphene material, structural, and electronic properties.

As the first isolated two-dimensional (2D) material, graphene leads an unprecedented boom in interdisciplinary research in the past decade. It shows tremendous potential applications. One of them is in the area of the novel electronic devices due to the superior charge carrier mobility and very high thermal conductivity. However, it seems that the application of graphene in transistors as a planar channel material is unlikely to happen within the next decade because of the absence of a bandgap. Bandgap engineering and increasing the on/off ratio are very essential for its application in transistors. One of the approaches to tune the bandgap of graphene is strain engineering. On the other hand, potential applications of graphene in electronic devices and sensors inevitably involve sophisticated structure fabrications (patterning). Considerable challenges exist in the patterning of graphene due to its single layer characteristic and the sensitivity of its intrinsic properties to the geometry, residue, and the damage from the patterning.
In this study, focused ion beam and focused electron beam are used to directly pattern graphene into ribbons. Focused electron beam shows relatively slow patterning speed, but preserves much better crystallinity of graphene. An in-situ experimental methodology in the transmission electron microscope (TEM) is demonstrated to stretch the patterned ribbons. 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 the tuning of bandgap. The correlation from simulations are provided as well.

Graphene, its derivates and inorganic analogues are most intensively studied materials in the last decade. This enormous attraction originates from several unique properties of this broad family of layered materials. The unique properties of graphene and other 2D materials can be further modified and tuned by various types of chemical modifications using covalent and also non-covalent interactions. The electronic structure of graphene as well its inorganic analogues is highly sensitive towards interaction with surrounding environment including non-covalent interactions. For the chemical modification of graphene several procedures well known from organic chemistry can be applied and new materials like fluorographene and graphane can be synthesized. Compared to graphene, the electronic structure of its inorganic analogues can be changed even by reducing the number of layers within the materials. These outstanding properties give a huge application potential to this new group of materials. The main field of research is currently focused on applications in nanoelectronics and optoelectronics. Here the materials prepared by “bottom-up” methods like CVD deposition are mainly applied. The individual single and few layer materials can be prepared in the form of a homogeneous layer covering large area on various substrates. For the energy related applications in electrocatalysis, batteries and supercapacitors these materials are typically prepared by “top-down” procedures based on mechanical or chemical exfoliation of bulk forms and by following chemical modifications.

Graphene covalent derivatization represents a vivid approach to module its properties, e.g., electronic structure, water dispersability etc., and enhances its application potential. However, a direct derivatization of graphene is impractical due to low reactivity of graphene. Fluorographene is a stoichiometric and well-defined graphene derivative. Being perfluorinated hydrocarbon, fluorographene was considered unreactive. On a couple of examples we show that fluorographene can be converted to graphene derivatives at rather mild conditions. For instance, we show that as prepared thiofluorographene exhibits suitable electrochemical sensing properties. Covalent functionalization of graphene significantly modulates its physical chemical properties and broadens its application potential.1,2 In 2010, the stoichiometric derivative of graphene named fluorographene was prepared.3-5 Fluorographene electronic properties considerably differ from graphene, because it has a wide band-gap (~8 eV)6-8 and is considered the thinnest insulator.4 It can be prepared by fluorination of graphene, mechanical or chemical exfoliation of graphite fluoride, which is industrially used lubricant. The preparation of flurographene dispersions can easily up-scaled, e.g., following the procedures suggested for graphene by Coleman and coworkers.9 Flurographene (CF)n is a perfluorinated hydrocarbon and therefore it was considered unreactive.4 It is also thermally stable material up to ~300 °C.4 The low reactivity of fluorographene was questioned by early experiments, which shown that at higher temperature (180 °C) it could react with KI and produced low quality graphene.5 This reaction was, however, considered a curiosity. Very recently it was shown that fluorographene reacts at very mild conditions as electrophile with many nucleophiles.10-13 Namely the reaction with NaSH leading to preparation of thiofluorographene should be highlighted, because thiofluorographene can be effectively used to electrochemical sensing applications.13 These results indicate that fluorographene is a very promising material for large-scale preparation of dispersions of various graphene derivatives with designed properties. Further prospects and very recent advances in fluorographene derivations will also be discussed. ACKNOWLEDGEMENTS: Support from grants ERC (683024) by EU; LO1305 by MEYS of CZ and Neuron fund are gratefully acknowledged. REFERENCES: [1] Georgakilas V, Otyepka M, Bourlinos AB, Chandra V, Kim N, Kemp KC, Hobza P, Zbořil R, Kim KS: Chem. Rev., 112 (2012), 6156.; [2] Criado A, Melchionna M, Marchesan S, Prato M: Angew. Chem., Int. Ed. 54 (2015) 10734.; [3] Robinson …: Chem. Rev., 112 (2012), 6156.; [3] Nair RR, Ren W, Jalil R, Riaz I, Kravets VG, Britnell L, Blake P, Schedin F, Mayorov AS, Yuan S, Katsnelson MI, Cheng HM, Strupinski W, Bulusheva LG, Okotrub AV, Grigorieva IV, Grigorenko AN, Novoselov KS, Geim AK: Small 6 (2010) 2877.; [4] Zbořil R, Karlický F, Bourlinos AB, Steriotis TA, Stubos AK, Georgakilas V, Šafářová K, Jančík D, Trapalis C, Otyepka M: Small, 6 (2010) 2885.; [5] Karlický F, Otyepka M: J. Chem. Theory Comput. 9 (2013) 4155.; [6] Leenaerts O, Peelaers H, Hernández-Nieves AD, Partoens B, Peeters FM: Phys. Rev. B 82 (2010) 195436; [7] Karlický F, Otyepka M: Ann. Phys. 526 (2014) 408.; [8] Paton KR, Varrla E, Backes C, Smith RJ, Khan U, O’Neill A, Boland C, Lotya M, Istrate OM, King P, Higgins T, Barwich S, May P, Puczkarski P, Ahmed I, Moebius M, Pettersson H, Long E, Coelho J, O’Brien SE, McGuire EK, Sanchez BM, Duesberg GS, McEvoy N, Pennycook TJ, Downing C, Crossley A, Nicolosi A, Coleman JN: Nat. Mater. 13 (2014) 624.; [9] Dubecký M, Otyepková E, Lazar P, Karlický F, Petr M, Čépe K, Banáš P, Zbořil R, Otyepka M: J. Phys. Chem. Letters, 6 (1015), 1430.; [10] Whitener KE, Stine R, Robinson JT, Sheehan PE: J. Phys. Chem. C 119 (2015), 10507.; [11] Lazar P, Chua CK, Holá K, Zbořil R, Otyepka M, Pumera M: Small, 11 (2015), 3790.; [12] Urbanová V, Holá K, Bourlinos AB, Čépe K, Ambrosi A, Loo AH, Pumera M, Karlický F, Otyepka M, Zbořil R: Adv. Mater. 27 (2015), 2305.; [13] Pykal M, Zbořil R, Otyepka M: Chem. Listy 110 (2016) 335.

Graphene, a two-dimensional (2D) material has attracted a lot of attention especially due to its remarkable electrical, optical and mechanical properties. Despite these aforementioned extraordinary properties, pristine graphene poses some limitations, such as chemical inertness, structural defects as well as zero bandgap. Nevertheless, it has been shown that doping the sp2 carbon lattice with radicals or halogens, such as fluorine, can transform a hybrid state of graphene to sp3, which significantly changes its electronic properties. Such a change enables to open a bandgap through the removal of bands near the Fermi level.
Here, we present an electrochemical sensor for detection of bio-relative compounds such as amino acids or proteins based on glassy carbon electrode (GCE) modified with fluorographene. The modified GCEs were characterized by different electrochemical techniques including cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry.

Graphene oxide (G.O.) is considered as a highly applicable graphene derivative due to the ease of production and its processability. It can be prepared in high yields from bulk graphite and is well dispersible in water. Therefore, G.O. dispersions can be used for development of films and various functional composites. G.O. is an insulator and in order to regain part of the lost conductivity of pristine graphene, reduction methods are applied. Nevertheless, G.O. reduction results in dramatic suppression of its dispersibility and amount of functionalities. Unequivocally, a major challenge in the field would be the production of a graphene adduct, with well-defined and homogeneous functionalities, high yield and water dispersibility, whilst retaining the conductive character of graphene.
Herein, we report on the production of oxidized and conductive graphene, with high water dispersibility. Elaborate characterization provided clear evidence for its successful preparation. The sharply identified carbonyl bands in the FT-IR spectra are freely accessible and can be easily derivatized to other adducts. The high yield of functionalization is further confirmed by XPS, Raman and chemical mapping with high-resolution TEM. Finally, the excellent dispersibility in water further highlights its facile chemical processability, which implies its smooth integration in interfaces and composite devices.

Oxidation process of graphite leads to exfoliation of graphene oxide (GO) single layers turning to electrical insulator. In order to restore the graphene properties, oxide groups must be removed. At the process of reduction, the atomic structure degrades together with material properties expected for graphene. In this work we study kinetics of the oxidation process of graphite in order to find the lowest oxidation stage when the exfoliation of graphite to single layers is possible. The goal is to minimize the degradation of the atomic structure and, consequently, of the graphene electronic properties. We study evolution of intercalation of oxygen between graphitic layers correlating the content of oxygen with the inter-layer distance in graphite crystal, using XPS and XRD analyses along different steps of oxidation process. Atomic structure of the exfoliated GO layers is further characterized by STEM down to atomic level. Removal of the oxide groups from GO was achieved by heating and the reduction process was recorded by DSC and TGA. The effect of reduction temperature on electronic transport, optical absorption and Raman spectra will be also presented.

Graphene decorated with metal-nanoparticles (MNPs) is envisaged to be an ideal nano-compound that can be used in several applications, from nanomedicine to optoelectronics, due to the combination of graphene and MNPs electronic characteristics. Traditionally, the synthesis of such nano-assembly has been promoted by in-situ reduction of metal salts in the presence of graphene derivatives or by the separated fabrication of MNPs and subsequent decoration of graphene derivatives. These methodologies either don´t avoid the creation of byproducts leading to cross-chemical effects or don´t allow the production of small MNPs without requiring the presence of any chemical stabilizer leading to the decrement of MNPs surface activity. In this communication, we present the creation of Gold NPs and its direct immobilization on graphene-oxide (GO) sheets without the use of any stabilizer through and in-situ methodology, Pulsed Laser Ablation in Liquids (PLAL), fabricating NPs in a liquid environment composed by a mixture of Water (18MΩ) and GO at different concentration ratios. In all the experiments, the presence of GO in PLAL promoted the creation of particles with sizes from 2 to 6nm that are directly immobilized on GO´s surface. The results suggest that no matter the ratio concentration in the liquid mixture, PLAL promotes the minimum creation of byproducts and the lack of stabilizers ensures the maximum surface activity on MNPs, obtaining in all the cases the same particle size range. The methodology presented constitutes an improvement over traditional synthesis approaches of GO and small MNPs nano-assamblies which may inspire future developments.

Graphene's two dimensional nature, highly sensitive unique electrical properties and low intrinsic noise characteristics make it a prime candidate for the creation of a new generation of molecular electronic sensors. The long standing target of molecular electronic sensors is to achieve single-molecule sensitivity and the ability of selective determination of the detected molecules. Although graphene electronic sensors have been demonstrated to be extremely sensitive in vacuum, their sensitivity in air or liquids is still very far off from the desired single-molecule sensitivity. The limited selectivity to different molecules also remains a major problem for their practical use.
Here we present our recent experiments using graphene field-effect transistors (GFETs) to detect different physisorbed molecules on their surface via conductance changes as a function of gate voltage. We demonstrate that bare GFETs have a potential to measure distinct, coverage dependent, conductance signatures upon adsorption of small organic molecules in vacuum [1,2]. This method allowed electronic discrimination of individual DNA nucleobases on GFETs [1], providing a first step towards label-free graphene based electronic DNA sequencing. We compare DNA detection on GFETs in vacuum, air and liquids and present various strategies for the label-free electrical detection of DNA molecules, as well using controlled chemical functionalization, to attain high sensitivity and selectivity. To get a deeper insight into the origin of the sensing mechanism and molecular recognition in GFET measurements we also performed ab initio electronic structure calculations using density functional theory (DFT) [3]. The molecular recognition mechanism was found to be closely linked with specific noncovalent molecular interactions with graphene. These effects open up a range of new opportunities for molecular recognition and enhancement of molecular sensitivity of graphene-based electronic sensors.
REFERENCES:
[1] N. Dontschuk, A. Stacey, A. Tadich, K. J. Rietwyk, A. Schenk, M. T. Edmonds, O. Shimoni, C. I. Pakes, S. Prawer, and J. Cervenka, Nature Communications 6, 6563 (2015).
[2] J. Cervenka, A. Budi, N. Dontschuk, A. Stacey, A. Tadich, K. J. Rietwyk, A. Schenk, M. T. Edmonds, Y. Yin, N. Medhekar, M. Kalbac, C. I. Pakes, Nanoscale 7, 1471 – 1478 (2015).
[3] Y. Yin, J. Cervenka and N. V. Medhekar, J. Phys. Chem. C, 119 (33), 19526–19534, (2015).

The outstanding properties and potential of single layer graphene are widely recognized in the scientific community. The tuning of the properties of graphene is envisaged to further extend the range of the potential applications of this novel material. Covalent grafting of substituents to graphene is a promising way to answer this urgent need. However, most of the approaches to functionalize graphene are based on reaction in liquid phase, which is not compatible with industrial requirements and also with the application in the nanoelectronics. Here we perform the reaction on the chemical vapor deposition grown graphene, which can be prepared on large scale and it is also suitable for fabrication of nanoelectronic devices. We demonstrate that it is possible to realize covalent reactions on pristine graphene under mild ambient conditions exclusively by gas-phase methods. Our study also demonstrate that the reactivity of graphene can be further tuned by the substrate and by defects in graphene.

In this contribution we describe efficient methods to grow high-quality epitaxial graphene on silicon carbide (SIC) in the Ar atmosphere or UHV and we introduce ways to achieve high-quality n- and p-doping of graphene by single-atom dopants. The clean and doped graphene is investigated using the scanning tunnelling microscope (STM), photoemission spectroscopy (XPS) and near-edge x-ray absorption spectroscopy (NEXAFS).
Nitrogen as the n-type dopant is introduced into the graphene/SiC(0001) by ion implantation and subsequent thermal stabilisation. We observe single or double nitrogen dopants, all located exclusively at substitutional positions in the graphene lattice [1]. Boron as the p-type dopant is deposited onto the SiC(0001) prior to graphene growth and then gradually annealed in the UHV until graphene is formed. The doping process and the chemical state of boron have been monitored by means of STM, XPS and NEXAFS [2]. The results are supported by extensive DFT calculations and STM simulations. [1,2,3].
Annealing of SiC(0001) substrate in UHV is known to produce a surface with a variety of coexisting reconstructions: buffer layer, single- and bilayer graphene, etc. [4]. On the other hand, the growth of very homogeneous single- and bilayer graphene has been achieved in Ar atmosphere, however at substantially higher temperatures (>1600C) [5]. To avoid using costly RF equipment we developed a relatively simple reactor that produces homogeneous samples with micrometer-size terraces of the single-layer graphene. REFERENCES: [1] ACS Nano, 8 (7), 7318 – 7324, 2014; [2] Phys. Rev. B, 93, 041302(R); [3] ACS Nano, 9 (9), 9180 – 9187, 2015; [4] Materials Science Forum, 615 – 617, 219 – 222, 2009; [5] Nature Materials 8, 203 – 207, 2009.

Standard methodics of transfering graphene to semiconductor surfaces use acetone to dissolve a layer of polymethakrylate (PMMA) from the surface of the graphene layer at the end of the so-called wet transfer. During this procedure, however, adhering of nano-sized impurities takes place, which subsequently have a negative impact on the use of graphene in the field of optometrics. To optimize the wet transfer graphene using PMMA as a carrying polymer, a comparison of final contamination of several different solvents has been done. Among the selected solvents there was acetone, chlorophorm, dimethylsucinate (DMG) and n-ethyl pyrolidone (NEP). The lowest contamination was studied by atomic microscopy (AFM) when using the NEP solvent.

Recent publications have shown that carbon nanotubes (CNT) reinforced aluminum composite may be used in wide range of structures due to it high mechanical properties. Behavior of CNT during joining process of such composites is of practical interest. Multi-walled carbon nanotubes were added in to gap between two aluminum sheets which were welded with tungsten inert gas arc welding (TIG). Longitudinal sections of welded joint fracture were investigated with scanning electron microscopy. Evidences of CNT survival during arc welding process were found.

Recycling of atmospheric CO2, the ultimate by-product of all processes involving oxidation of carbon compounds, for use as fuel is one of the most promising alternatives to combat global warming and energy crisis. Photoelectrocatalytic method can efficiently convert CO2 into light molecule organic substances using photocatalysts at anode. Among photocatalysts, visible light responsive materials are of major interest as it could use solar irradiation as light source. In the present paper, we report the preparation of reduced graphene oxide (rGO) modified CuFe2O4 nanoparticles and their activity towards photoelectrochemical reduction of CO2 in aqueous phase under visible light irradiation. The rGO was prepared by exfoliation of graphite using potassium permanganate followed by reduction with ascorbic acid and CuFe2O4 nanoparticles were prepared by sol-gel method. The modified rGO- CuFe2O4 was prepared by ultrasound assisted precipitation. Transmission electron micrograph (TEM) revealed the production of ~5-10nm CuFe2O4 nanoparticles over rGO. Modification by rGO dramatically increased the CO2 reduction to products (mainly methanol and methane) by a factor of 3. The increase in activity was due to the drastic reduction of e-/h+ recombination rate in the photoelectrochemical method. Mott-Schottky analysis revealed increased donor electron density in rGO- CuFe2O4 compared to CuFe2O4.