SESSION A - NANOMATERIALS FOR ELECTRONIC, MAGNETIC AND OPTIC APPLICATIONS. CARBON NANOSTRUCTURES, QUANTUM DOTS

The luminescent properties of nanoscale silicon were demonstrated in 1990 triggering the interest in Si nanostructures for optical emission. While the luminescence was quite strong even at room temperature, the micro-second long PL lifetimes revealed an inherited indirect bandgap from bulk Si. The luminescence mechanism was heavily debated whether quantum confinement really played a role or the emission would be due entirely from surface states. Many studies have confirmed the quantum confinement model but it has also been shown that the emission can be widely tuned by changing the surface passivation or by adding different ligands to the shell. The physics of the emission was however obscured by inhomogeneous line broadening due to the large size dispersion of the emitting entities in porous silicon or in matrices containing silicon nanocrystals. This called for single-dot spectroscopy studies as demonstrated for single molecules and later for nanocrystals of direct bandgap semiconductors.
In this talk I will review our work on PL emission and spectroscopy of individual Si quantum dots. These were initially fabricated using electron-beam lithography, plasma etching and oxidation resulting in micron spaced Si quantum dots that could be individually distinguished in an optical microscope. More recently we have also looked at more “randomly” spaced Si nanocrystals as well as colloidal nanocrystals fabricated from HSQ (hydrogen silsesquioxane). These studies have revealed many of the phenomena observed for the II-VI nanocrystals such as on/off intermittency (blinking), spectral diffusion and narrow linewidth. Indeed, the linewidth at low temperatures was found to be ~250 µeV, limited by system resolution while the room temperature homogenous linewidth was shown to depend on the surface passivation and ligand shell. Finally, recent data on the quantum yield of colloidal Si nanocrystals suggest that near 100 % internal quantum efficiency can be reached paving the way for many applications.

Absorption cross section (ACS) is a basic parameter of any absorbing material including semiconductor quantum dots / nanocrystals (NCs). It has a crucial importance for considering applications like solar cells or optically excited bio-labels. In our contribution we compare two experimental methods to determine ACS via (i) absorption spectra and morphology information (density of nanocrystals from TEM or dark-field scattering analysis) and (ii) luminescence spectroscopy under modulated excitation. The weak points of both approaches and experimental details are discussed. Our experimental results are compared to available literature data, including theoretical calculations. The results show that we can actually gain (about twice) absorption per Si volume by forming nanocrystals but the absorption per total nanocomposite (Si and oxide matrix) volume is lower than for bulk Si. Therefore, some tricks to increase ACS of Si NCs (e.g. using plasmonics) are needed.

InGaN/GaN multiple quantum well structures (QW) were prepared by metal-organic vapor phase epitaxy (MOVPE) and characterized them by fine X-ray diffraction measurements. We demonstrate their suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft X-ray source in extended dynamical and time scales. The photo-luminescence and radio-luminescence were measured: we have shown that the ratio of the intensity of QW exciton luminescence to the intensity of the yellow luminescence (YL) band IQW/IYL depends strongly on the type and intensity of excitation. Slower scintillation decay measured at YL band maximum confirmed the presence of several radiative recombination centers responsible for wide YL band, which also partially overlap with the QW peak.

Recent developments in nano science and technology has revealed the possibility of using Quantum dot fluorescence properties for medical imaging aided diagnostics.Quantum dots being one of the novel nano structure that exhibits wide range of quantum phenomena sprawling across optics, electronics and chemistry. This multi domain characterization makes the understanding and further development of any technology based on these devices quite a challenge that needs to be addressed through cross domain experimental and theoretical study.
We present a study of quantum fluorescence property of quantum dots. The emission and absorption rates and energy of the quantum dots are size and environment dependent due to the quantum confinement and discrete energy. We analyze quantum dot emission spectrum response to environmental and structural variations. We consider bruss energy relation and quantum statistical observations to model the quantum dot fluorescence activity. We demonstrate the model through simulation results.

We present a combined experimental and theoretical study aimed at understanding the behavior of small organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate, hexane, and toluene) on the surface of graphite, graphene and its halogenated derivatives. We measured isosteric adsorption enthalpies and entropies by inverse gas chromatography for large interval of coverages. The strength of interaction between the surface and the organic molecules was estimated by various theoretical methods using both finite and periodic graphene models.[1] We also discussed in detail the role of high-energy sites in graphene and graphite.[2] In addition, interplay between ethanol adsorption to high-energy sites and ethanol clustering on graphene and graphite alters the measured isosteric adsorption enthalpies.[3] Finally, the graphene surface was compared to surfaces of halogenated graphenes. [4]
REFERENCES:
[1] Lazar P, Karlický F, Jurečka P, et al. J. Am. Chem. Soc., 135, 6372-6377, 2013
[2] Lazar P, Otyepková E, Banas P, et al. Carbon, 73, 448-453, 2014
[3] Karlický F, Otyepková E, Banáš P et al. J. Phys. Chem. C, DOI: 10.1021/acs.jpcc.5b06755, 2015.
[4] Lazar, P, Otyepková E, Karlický F et al. Carbon, 94, 804-809, 2015

Ionic liquids (IL) – by definition organic salts with melting points below 100°C – have widely been used as alternative solvents in the synthesis of a wide range of organic and inorganic products since the early 1990s and became popular as alternative “green” or “designer solvents”.
Major reasons for this development are the unique properties of ionic liquids that include high thermal stability over a wide temperature range, often a good solubility of many inorganic precursor salts as a consequence of the tunable polarity of ILs and their tenside like character, which allows the stabilization of e.g. metal, metal oxide [4,5] or carbon-based nanoparticles. In addition, these ILs have a negligible vapor pressure and are non-inflammable. This unique combination of properties makes ILs the media of choice for dispersing nanoparticles.
The use of ionic liquids as green solvents for the synthesis of nanoparticles and their impact on the size control of the produced nanoparticles will be highlighted in this contribution as well as their influence on the stabilization of metal-, metal oxide- and carbon-based nanoparticle dispersions will be discussed. Finally, results of the performed stability test via Photon Cross-correlation Spectroscopy (PCCS, Nanophox®) will be presented.

Creating or connecting together organic molecules, as polycyclic aromatic hydrocarbons (PAH), by chemical reactions readily on surfaces is the first step to a true advance in the field of molecular electronics. On-surface chemistry has become one of the most important strategies for bottom-up assembly of new nanostructures from their constituent molecular building blocks. Although diverse compounds have been formed in recent years using this methodology, a limited knowledge on the molecular machinery operating at the nanoscale has so far disallowed to control the reaction outcome.
We combined advanced in-situ surface techniques as STM, high-resolution XPS and NEXAFS with theoretical ab-initio (DFT) calculations to achieve a complete understanding of the self-assembling of organic molecules on metallic surfaces and to follow different coupling reactions between them. Thus, nanostructures of different dimensionality can be assembled “a la carte” just by choosing the adequate molecular precursor, temperature and the suitable surface termination.
Thus, in this talk, by merging information from these techniques and different single-crystal metal substrates, we report on the thermal controlled competitive intramolecular and intermolecular dehydrogenative processes respectively called cyclodehydrogenation and dehydrogenative polymerisation, which operate in the on-surface synthesis of N-doped fullerene, nanographene, polyaromatic network, single molecule polymers, membranes or graphene.

The real graphene samples contains defects. Their correct quantification is crucial for both fundamental science and practical applications. In addition for specific applications like sensors or for graphene functionalization a controllable defect formation is required. Here we used oxygen plasma to induce defects in graphene samples composed of monolayer, bilayer with Bernal stacked layers and bilayer with randomly stacked (turbostratic) layers. In this way, we were able to compare the effects of the same plasma treatment on monolayers and bilayers, either Bernal stacked or randomly stacked. We used isotopic labelling of graphene layers by 13C, which allowed us to address the Raman bands from the top and bottom graphene layers. Our results showed that the phonons of the AB stacked bottom graphene layer can be scattered by defects in the top graphene layer. Considering this effect we found that monolayer graphene on top layer of turbostratic bilayer contains similar number of defects, while the top graphene layer contains much less defects after a given time of oxygen plasma treatment. This result is reasonable because it confirms the behaviour of top layer of turbostratic graphene independent on the bottom layer, while the reactivity of the top layer in AB stacked graphene is significantly reduced by interactions with the bottom layer. Our findings have important consequences regarding graphene applications, showing that the presence of defects varies not only with the number of layers but also with the stacking order. Moreover, the number of defects estimation might not always be accurate, especially in co-dependent layers such as in Bernal stacked graphene.

A convenient methodology has been established for fabrication of superhydrophobic/oleophilic composites based on highly fluorinated graphene oxide (HFGO) and nanocrystalline zeolite imidazole framework (ZIF-8). The structure directing properties of HFGO allow for selective nucleation of ZIF-8 nanoparticles over oxygen functionalities. Furthermore, the composite microstructure features pendant fluorine groups bonded at the graphene basal plane. A unique micro-mesoporous architecture is achieved, where the micropores originate from ZIF-8 nanocrystals, while the functionalized mesopores from randomly organized HFGO layers with ZIF-8 pillars. During my presentation I will highlight the exceptional superhydrophobic (water contact angle 162o) and superoleophilic (oil contact angle 0o) properties of the HFGO@ZIF-8 composites. In addition to that modified Sponge@HFGO@ZIF-8 composites are successfully utilized for oil-water separation.

Local control of strain and doping in graphene enables custom variation of the graphene electronic structure at submicron scale. For extremely strained graphene, giant magnetic pseudofields can be generated, which opens possibility to study Dirac fermions in extreme high magnetic field regimes. In order to reach control of spatial distribution of the strain and doping in graphene, we prepared graphene – nanoparticle heterostructures, constituted of isotopically labelled CVD-grown graphene monolayers transferred over substrates decorated with monodisperse nanoparticles acting as sources of the graphene corrugation. The strain and doping were inspected by Raman micro-spectroscopy. Typical fingerprint of the delaminated fraction of the graphene is identified as substantial contribution to the principal Raman active modes of the graphene (G and G’). Correlation analysis of the Raman shift of the G and G’ modes clearly resolved the graphene in contact and delaminated from the substrate, respectively. Intensity of the Raman features of the delaminated graphene increases linearly with the amount of wrinkles, determined by advanced processing of atomic force microscopy data. The study thus demonstrates possibility of tailoring the electronic structure of the graphene by implementation of the nanoparticles through the spatially modulated charge-strain distribution. Finally, the magnitude and symmetry of strain related to the magnetic pseudo-fields in graphene is critically examined.

Diamond and carbon thin films due to their variability and superior mechanical, optical, electrical, and biocompatible properties, become widely used over the world in multi-disciplinary fields such as material engineering, optoelectronics, biochemistry, life science or even microbiology (anti-adhesive and antibacterial coatings). However, their intrinsic properties have to be tailored to specific requirements (like surface morphology, electrical conductivity, transparency, etc.).
In this contribution we point out the key technological aspects in fabrication of micro- and nano-sized carbon-based structures. The diamond nanorods were fabricated by employing plasma-assisted thermal annealing of thin metal layers (Au and Ni) followed by reactive ion etching of planar diamond films (the top-down strategy). We found that the diameter of diamond nanorods can be controlled in a broad range from 10 to 200 nm by the masking material and its initial thickness. The self-assembled templates (periodical arrays) of polystyrene (PS) microspheres (500 or 1000 nm in diameter) were fabricated by their spin-coating on silicon and diamond substrates. Except to spin-coating process parameters, the concentration of PS microspheres dispersed in DI/ethanol was a crucial technological parameter to assemble them into monolayer. We will discuss application of PS microspheres in fabrication of periodical diamond arrays. The self-standing diamond membranes were fabricated by selective area deposition employing optical lithography and wet etching (bottom-up strategy). The initial diamond growth from the seeding layer, etching of carbon phases by oxygen containing gas species and parasitical diamond growth were the main competitive processes resulting in successful fabrication of self-standing diamond membranes in mesh- or interdigital-like geometry.
ACKNOWLEDGEMENTS:
This work was supported by the GACR project 15-01687S.

The transfer of chemical vapor deposited (CVD) graphene from metal catalyst to target substrate is an important step in preparing desirable nanoscale structures in various fields of science, and thus searching for fast, cheap and clean method attracts great interest. Investigation of mechanical properties of graphene, which are crucial for applications in flexible electronics, performed on bendable synthetic materials, requires a transfer technique using polymers soluble in aliphatic solvents harmless for target polymer substrates. In this study we explore a dry technique using polydimethylsiloxane (PDMS) as stamping polymer and polyisobutylene (PIB) layer as graphene-support polymer. After the transfer PDMS is peeled off and PIB is dissolved in hexane, hence this method fullfils the above mentioned prerequisite. The effectiveness of this transfer was examined by scanning electron microscopy, optical microscopy and Raman microspectroscopy including micro-mapping, and finally by X-ray photoelectron spectroscopy. With all methods carried out, it was found that this sort of stamp-technique is suitable for a high precision transfer of CVD graphene onto polymer substrates with large yields and similar purity compared to PMMA-based transfer methods. However, it introduces substantial quantity of surface discontinuities, and therefore this is not a proper method for large scale aplications.
ACKNOWLEDGEMENTS:
This work is supported by Czech Science Foundation (project nr. 14-15357S).

The hyperfine interaction between electron and nuclear spins is traditionally regarded only as one of effects contributing to the electron spin relaxation in solids. Under certain circumstances, however, the spin of electrons is effectively transferred to nuclei by the interaction (effect known as dynamic nuclear polarization). The polarized nuclei can act with strong hyperfine fields back on the electron spin system. This opens physics with interesting possibilities which will be illustrated on the example of an all electrical electro-nuclear transistor. The device is a hybrid ferromagnetic metal/semiconductor micro-structure (based on Fe/n-GaAs epitaxial layer system) which utilizes dynamically polarized nuclear spins to control electron spins in an n-GaAs channel. The operation principle of the device consists of two steps. In the first step a weak signal out-of-plane electron spin polarization is generated by the Spin Hall effect which is used for the dynamic polarization of GaAs nuclei. In the second step the non-local spin Hanle experiment is performed. Electrons are injected from an Fe injector with in-plane spin polarization and the non-local spin signal is detected on an adjacent Fe detector as function of external out-of-plane field. The precession of in-plane spins is controlled by the nuclear spin polarization via hyperfine interaction. The subtle signal out-of-plane nuclear spin polarization (0.01-0.1%) controls precession of the strong in-plane spin polarization (1-10%) of injected electrons. Hence, the device performs amplification of the original spin signal used for the polarization of nuclei. The device allows for a convenient electrical detection of very weak spin polarization.

The research on graphene has attracted much attention since its first successful preparation in 2004. It possesses many unique properties, such as an extreme stiffness and strength, high electron mobility, ballistic transport even at room temperature, superior thermal conductivity and many others. The affection for graphene was followed swiftly by a keen interest in other two dimensional materials like transition metal dichalcogenides. As has been predicted and in part proven experimentally, the electronic properties of these materials can be modified by various means. The most common ones include covalent or non-covalent chemistry, electrochemical, gate or atomic doping, or quantum confinement. None of these methods has proven universal enough in terms of the devices’ characteristics or scalability. However, another approach is known - mechanical strain/stress, but experiments in that direction are scarce, in spite of their high promises.
The primary challenge consists in the understanding of the mechanical properties of 2D materials, as we have recently presented for the case of graphene [1]. Afterwards, several techniques can be used to deform the specimens and thus to induce changes in their electronic structure, out of which the uniaxial in-plane [2] and out-of-plane [3] stress, and substrate modification will be shortly reviewed.
ACKNOWLEDGEMENTS:
This work is supported by Czech Science Foundation (project nr. 14-15357S).
REFERENCES:
[1] GALIOTIS et al. Annu. Rev. Chem. Biomol. Eng., 2015, vol. 6, DOI: 10.1146/annurev-chembioeng-061114-123216.
[2] FRANK et al. Nano Lett., 2012, vol. 12, p. 687.
[3] PEÑA-ÁLVAREZ et al. Nano Lett., 2015, vol. 15, p. 3139.

In the past decade, it has been found that nanomaterials play an important role in many analytical applications such as nanomaterial-based sensors or biosensors [1]. Among others iron oxide nanoparticles exhibit great chemical stability, biocompability, low toxity which make them suitable for biomedical applications including drug delivery, immunoassay etc [2, 3]. It has been also shown, that iron oxide nanoparticles have some specific electrical advantages such as a high specific capacitance or narrow bandgap. On account of these properties, iron oxide nanoparticles appear as a promising candidate for electronic devices [4, 5].
In this work two different applications will be presented. A new simple electrochemical sensor for the detection of antibiotics chloramphenicol has been developed. The amplification strategy of this sensor is based on application of nanocomposite consists of magnetite nanoparticles stabilized with carboxymethyl cellulose (Fe3O4-CMC) and decorated with nanometer-sized gold nanoparticles (Fe3O4-CMC@Au). The second part is devoted to the application of iron oxide nanoparticles (gamma-Fe2O3, Fe3O4) in electrochemical sensing of paraquat herbicide.
REFERENCES
[1] R.J. Mortimer, Electrochromic materials, Chem. Soc. Rev., 26 (1997) 147-156.
[2] Z.L. Cheng, A. Al Zaki, J.Z. Hui, V.R. Muzykantov, A. Tsourkas, Multifunctional Nanoparticles: Cost Versus Benefit of Adding Targeting and Imaging Capabilities, Science, 338 (2012) 903-910.
[3] S. Laurent, D. Forge, M. Port, A. Roch, C. Robic, L.V. Elst, R.N. Muller, Magnetic iron oxide nanoparticles: Synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications, Chem. Rev., 108 (2008) 2064-2110.
[4] B. Sarma, A.L. Jurovitzki, R.S. Ray, Y.R. Smith, S.K. Mohanty, M. Misra, Electrochemical capacitance of iron oxide nanotube (Fe-NT): effect of annealing atmospheres, Nanotechnology, 26 (2015) 11.
[5] M.S. Wu, R.H. Lee, Electrochemical Growth of Iron Oxide Thin Films with Nanorods and Nanosheets for Capacitors, J. Electrochem. Soc., 156 (2009) A737-A743.

Nanocomposites with exceptional properties are promising materials that gain a market share during the current years. Multi-walls Carbon nanotubes (MWCNT) can be used as a filler for polymeric matrix; however, their attractive forces lead to their agglomeration and affect the properties of the final nanocomposite. Therefore, the surface of the MWCNT is functionalized in this work using carboxylic and amino functional groups. The functionalized MWCNT are added at different weight fractions to an epoxy matrix to manufacture nanocomposite plates and coupons of the nanocomposite are tested in tension to evaluate the tensile moduli and strengths. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) were used to evaluate the topological and the surface properties of the nanocomposites. Results indicate an initial increase in the mechanical properties of the nanocomposites at low proportions of the f-MWCNT followed by a decrease at higher proportions.

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Recent developments indicate that magnetic nanoparticles could help to improve clinical practice in the treatment of cancer, most probably in synergy with other conventional treatments [1]. There already exist methods to obtain magnetic nanoparticles with the appropriate properties to be used in diagnosis and therapy but these properties need to be optimized to avoid its alteration after intravenous injection, via interaction between the nanoparticles and the blood components, aggregation in lysosomes inside cells or accumulation in tissues [2].
In this work we will describe a number of proven synthesis routes for magnetic nanoparticles intended for their use in biomedical applications [3]. We will show the effect of different characteristics of the magnetic colloids, such as particle size and size distribution, colloidal properties of the aqueous suspensions, such as hydrodynamic size and surface modification, and magnetic properties on their MRI relaxivity and heating capacity. Finally, it will be shown that magnetic nanoparticles biodistribution following systemic administration and its transformation over time can be tracked by AC magnetic susceptibility measurements, which allow identifying and quantifying magnetic nanoparticles in tissues, differentiating them from other endogenous species such as the ferritin iron cores [4].
ACKNOWLEDGEMENTS:
This work was partially supported by projects from the Spanish Ministry of Economy and Competitiveness (MAT2011-23641), EU-FP7 MULTIFUN project (246479), EU-FP7 NANOMAG (604448), and AXA Research Fund (L.G.).
REFERENCES:
[1] M. Colombo, et al, Chem. Soc. Rev., 41, 4306, 2012.
[2] Y. Luengo, et al, Nanoscale, 5, 11428, 2013; A. Ruiz, et al, Nanoscale, 5, 11400, 2013.
[3] L. Gutiérrez, et al, Dalton Transactions 2015 (in press).
[4] R. Mejías, et al, Journal of Controlled Release 171, 225, 2013; L. Gutiérrez, et al, Phys. Chem. Chem. Phys., 16, 4456-4464, 2014;

Sustainable nanomaterials have recently attracted great attention as highly functionalized nanocatalysts in diverse catalytic areas including solid-supported nanocatalysts, graphene materials, core-shell catalysts and other types of nanostructures. Rapid technology development over recent decades has allowed a series of advances in the development of increasingly sustainable heterogeneous catalysts. In particular, catalytic materials can now be prepared with greater precision via nanotech-enabled processes. Metal supported nanoparticles which often serve as active catalytic components can be synthesized in a more environmentally friendly manner with well-defined sizes, shapes, crystal facets, structure, and composition. An overview of our recent activity developing activity developing novel methodologies based on the use of nanomaterials, will be highlighted including supported metal and metal oxides and related nanostructures.
REFERENCES:
Gawande et al. Account of Chemical Research 2014, 47, 1338−1348; Chemical Society Reviews 2013, 42, 3371-3393; Green Chemistry 2013, 15, 1895-1899, ChemCatChem 2014, 2014, 6, 12, 3312–3313; Chemical Society Reviews 2015, DOI: 10.1039/c5cs00343a.

Various nanofillers belonging to the ceramic and carbon group were successfully used in modification the polymer matrix, and have become applicable in the medical field. New nanocomposite materials are characterized by properties better than pure polymers or conventional composite materials. The nanofillers should have high specific surface area with exposed, chemically active groups, which in turn can interact with the polymer chain. The form and chemical structure of silicate and carbonous nanofillers are similar. The silicate flake-shaped form structurally corresponds with graphite oxide: both of them are characterized by the presence of various oxygen groups located at the flakes edges (for silicate; Si-O-Si, Si-OH, for carbons: C=O, C-OH, COOH).
In the present study, both types of flake-shaped forms, i.e. silicate (MMT-montmorillonite) and carbon (GO-graphite oxide) were used for modification of biopolymer matrices: chitosan (CS) and sodium alginate (NA). Nanocomposite scaffolds were obtained by the freeze-drying method. The microscopic observations showed both types of the nanofiller had affected microstructure of the scaffolds. MMT present in both biopolymer matrices guaranteed similar shape and size of pores, while GO created larger and much disordered pores in the scaffolds. These effects of the nanofillers were confirmed during a compression test. Chitosan-based scaffolds with GO were weaker than scaffolds with MMT nanofillers, but the CS/GO nanocomposite was more rigid and survived the test. FT-Raman spectra showed that MMT interacted with the polymer chain strongly than GO. This effect was also visible in biological properties of the nanocomposites because only CS/MMT showed bioactivity and water uptake.

Nanocrystalline rare-earth doped yttrium titanates, which crystallize in a pyrochlore structure with general formula RE2Ti2O7 or (RExY1-x)2Ti2O7 (RE=rare-earth element), have been investigated for their interesting luminescence and magnetic properties. However, their physico-chemical properties limit the preparation of microstructures and integrated structures.
In this contribution we present the laser-assisted preparation of nanocrystalline Eu2Ti2O7 and (Eu0,5Y0,5)2Ti2O7 thin films and the laser processing of microstructures inside the films.
Highly transparent amorphous thin films of the thickness about 500 nm were prepared by the sol-gel method. Prepared films were irradiated by CO2 laser or thermally treated up to 1200 °C to prepare nanocrystalline material. Alternatively, the oriented microstructures such as ribbons and pillars were written by the laser beam into the thin films. Formation of nanocrystals was observed by the structural methods and by the steady-state luminescence measurement.
The presented approaches led to the formation of homogenous nanocrystalline Eu2Ti2O7 and (Eu0,5Y0,5)2Ti2O7 thin films with tailored grain sizes ranging from 20 nm to 120 nm. It was found that the laser beam induced the nucleation process, however it didn’t significantly contribute to the crystal growth and to the recrystallization of formed nanocrystals. Selective laser writing allowed to prepare oriented microstructures such as ribbons and pillars.
The results bring information about the laser processing of nanocrystalline rare-earth titanates thin films. The promising applications of prepared nanocrystals and prepared microstructures in the field of planar optical amplifiers are widely discussed.
ACKNOWLEDGEMENTS:
This work was supported by the Czech Science Foundation, contract No 102/13/37368P.

TiO2 has high dielectric constant (30-100) and refractive index (2.5<n<2.9 at 593nm) combined with high transparency in visible. Therefore, it is a good candidate for the development of high density capacitors in planar integrated device and for designing optical integrated waveguides or optical devices. However, some engineering is still necessary to overcome TiO2 intrinsic limitations. Columnar morphology is generally observed in TiO2 thin films prepared by vapor deposition techniques. It leads to increased optical losses and degradation of electrical insulating properties. In addition, its rather low band gap (~3.2eV) imposes also a limitation for reaching low leakage current. In the present work we study plasma enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD) of Ti(1-x)SixO2 materials that can overcome some of the limitations given by TiO2 material. PECVD of Ti(1-x)SixO2 thin films was carried out in inductively coupled plasma using titanium tetraisopropoxide Ti(OC3H7)4 (TTIP) and hexamethyldisiloxane SiO2(CH3)6 (HMDSO) vapors mixed with oxygen. Different Ti/Si ratio in the films was achieved by varying the flow rates of TTIP and HMDSO. Addition of Si precursor led to the suppression of film columnar structure and XRD amorphous Ti(1-x)SixO2 material but still the question about mixing TiO2 and SiO2 materials remains. Characterization techniques suggest that there are a few nanometers domains of TiO2 and SiO2. Ti(1-x)SixO2 films were also obtained by ALD combining cycles with tetrakis(dimethylamido)titanium and tris(dimethylamino)silane for Ti and Si monolayers, respectively, with oxidizing step. The process was enhanced by plasma and the substrate temperature was 250oC.

Synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications.
It is the nanotubular TiO2 that has received the highest attention after porous Al2O3, motivated by its range of applications, including photo-catalysis, solar cells and biomedical uses. However, the TiO2 nanotube potential for a range of advanced devices, in particular when considering all possible shapes and geometries, has not at all been exploited. One of the major issues to extend the functional range of nanotubes is to coat homogenously tube interiors by a secondary material, potentially until the complete tube filling. Efforts based on electrochemical deposition, chemical deposition and spin-coating led only to limited success with a narrow range of materials.
The presentation will therefore focus in detail on the coating of secondary materials inside the nanotubes by means of ALD. The deposited materials influence strongly optical, electrical and mechanical properties of nanotubes. Experimental details and some very recent results will be presented and discussed.

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that outperforms current Li-ion batteries in terms of energy density, power density, safety, material sustainability, long-term stability, and cost. Two major directions are being investigated: improved intercalation materials (e.g., multi electron and high voltage materials) and new concepts for anodes (e.g., based on conversion reaction or alloying) and cathodes (e.g., Li-O2, Li-S). The jury is still out on which of the various investigated routes that promise taking energy storage beyond current Li-ion batteries will become eventually a success. Decisive will be how they satisfy the overriding factor of improved energy storage metrics under the constraint of material sustainability and cost. All these new battery chemistries have their particular problems but they have one challenge in common: massive requirements onto the electrolyte and electron conductors that cannot be satisfyingly met by current materials.
We will discuss recent results on two our major research directions: metal-O2 cathodes and electron/ion conducting materials for alloying, conversion and high-voltage materials.
Concerning metal-O2 batteries recent results on electrolyte and cathode stability and the reaction mechanism will be discussed. By this understanding, it has been possible to demonstrate that sustained reversible Li2O2 formation/decomposition can be achieved, essential if the Li-O2 battery is ever to succeed. The insulating nature of Li2O2 presents a particular problem at the cathode; detailed investigation of charge transport in Li2O2 and approaches to mitigate the problem will also be discussed.
Understanding the properties of the solid electrolyte interface (SEI) at the anode and the surface layer (SL) at the cathode in alkaline-ion batteries is important for improving SEI/SL related phenomena including irreversible capacity, interfacial resistance, cycle life and safety. Alloying, conversion and high-voltage materials impose even more severe demands on the interface layers than current graphite anodes or 4 V class cathodes. A resilient SEI/SL permeable to lithium or sodium ions but impeding electron transfer is vital for the long-term performance of a cell. Despite its vital role in the cell there has hardly been work on fundamental understanding of Li+ or Na+ transport in the SEI. We will discuss recent progress towards interfaces with improvements in (i) resilience towards surface strains to avoid cracking upon expansion/contraction of electrode materials (ii) Li+ or Na+ conductivity and electronic insulation, (iii) high voltage oxidation stability, (iv) insolubility in the electrolyte.

Nanocrystalline diamond (NCD) thin films are suitable biointerfaces having excellent stability due to their hardness and chemical inertness. Combining NCD layers with waveguides (WG) in the IR region allow to design optical WG sensors sensitive to absorbers like proteins or other biomolecules. In this contribution, we present a 2D model of a multi-layer WG developed under FEM simulation software Comsol Multiphysics. The model is based on the modified wave equation solved in the frequency domain and includes optical absorption. Prior to these simulations, analytical calculations of optical modes were performed in order to design a suitable single-mode planar optical WG with the NCD/Si/glass heterostructure. It was found that for the single-mode WG working in the narrow region of 1600-2000 nm the silicon thickness must be 150-250 nm. Shorter wavelengths are excluded due to the optical absorption of both amorphous silicon and diamond. It was found that in order to keep a reasonable signal attenuation, the NCD film must be prepared with the optical absorption coefficient lower than 5 cm^-1, being a rather challenging task. Dependencies of the signal attenuation on the NCD film thickness, absorbing layer height, its absorption coefficient and exciting wavelengths are presented.
ACKNOWLEDGEMENTS:
This work was supported by the Czech Science Foundation, project No. GA14-05053S.

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. 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 for controlling the crystal orientation of very thin hematite films during advanced pulsed reactive magnetron sputtering technique. Another way to significantly enhance the photoeficiency is a passivation of surface states acting as traps by isocrystalline overlayers. Highly active hematite films fabricated by plasma deposition were thus in the next stage covered by ultra-thin (< 2 nm) alumina films using the atomic layer deposition (ALD) method. The effect of plasma deposition modes, hematite texture, and the alumina passivating films 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.

Recently, a new family of 2D materials with exceptional optoelectronic properties has stormed into the scene of nanotechnology, the transition metal dichalcogenides (e.g., MoS2). In contrast with graphene, which is a zero band gap semiconductor, many of the single layered materials from this family show a direct band-gap in the visible range. This band-gap can be tuned by several factors, including the thickness of the sample; the transition from a direct to indirect semiconductor state takes place in MoS2 when increasing the number of layers from 1 towards the bulk. Applying strain/stress has been revealed as another tool for promoting changes in the electronic structure of these materials; however, only a few experimental works exist for MoS2. In this work we present a comparative study of single layered and bulk MoS2 subjected to direct out-of-plane compression, using high pressure anvil cells and monitoring with resonant and non-resonant Raman spectroscopy; accompanying the results with theoretical DFT studies [1]. In the case of monolayer MoS2 we observe transitions from direct to indirect band-gap semiconductor and to semimetal, analogous to the transitions observed under hydrostatic pressure, but promoted at more accessible pressure ranges (~25 times lower pressure). For bulk MoS2, both regimes, hydrostatic and uniaxial, lead to the semimetalization at similar pressure values, around 30 GPa. Our calculations reveal different driving forces for the metallization in bulk and monolayer samples.
ACKNOWLEDGEMENTS:
This work is supported by Czech Science Foundation (project nr. 14-15357S).
REFERENCES:
[1] PEÑA-ÁLVAREZ et al. Nano Lett., 2015, vol. 15, p. 3139.

Zinc oxide is a versatile material with many applications. Doped nanosized zinc oxide is capable of exhibiting fluorescence. The emission colour of such doped nanoparticles is dependent on the selected dopant, ratio of dopant to zinc oxide, and size of the nanocrystal or aggregate. In this work, we present zinc oxide colloids with different emission colours and a method of evaluation of the obtained colours. First step is the preparation of the precursor which is done according to Spanhel’s and Anderson’s sol-gel method [1]. Second step is the condensation process of the precursor with lithium hydroxide to form the ZnO colloid. The set of colloids studied in this work uses for condensation various concentrations of LiOH to which the precursor solution was added. In all cases the precursor solution’s concentration was 25 mM. The optical properties were studied using UV-VIS spectrophotometry and fluorescence measurements. From the spectral characterisation of fluorescence in the visible region one cannot determine the actual colour of emission directly from the shape of spectral band. Therefore, the relative spectral intensities of emission were recalculated into CIELAB or CIExyY colorimetric model from which it is easy to determine the colour of fluorescence.
REFERENCES:
[1] Spanhel, L. and M.A. Anderson, Semiconductor clusters in the sol-gel process: quantized aggregation, gelation, and crystal growth in concentrated zinc oxide colloids. Journal of the American Chemical Society, 1991. 113(8): p. 2826-2833.

In this work was studied the processing of aluminum alloys (silumins) by ligatures containing various carbon modifications (in the form of microcrystalline graphite, nanocarbon additives in the form of fullerenes, fullerene soot, fullerene niello) when casting-deformation technology of the manufacturing of products. In work were studied the elemental and phase composition, structural state and mechanical and tribological properties of the initial components of the charge in the Al-C and Al-Si-C after its mechanical activation alloys after severe plastic deformation (extrusion) of the charge and cast aluminum workpieces after processing by ligatures. Gradually studied the processes of structure formation of alloys in the system Al-C and Al-Si-C when they are received and thermomechanical loading. This of particular interest is the formation of superhard carbon phases in ligatures, where instead of microcrystalline graphite was used nanocarbon additives. Using spectroscopy of combined light scattering was revealed that these amorphous phase, similar to glassy carbon. In ligatures identified also carbides of aluminum Al4C3 and/or silicon SiC (during annealing (800º C, 30 minutes) to 10-12% carbides). Such structural state of alloys obtained when the activation of the charge (mechanical activation in dispersive devices and at intensive plastic deformation) determines the prospects of their use as additives providing not only dispersed hardening, but also the modification of the alloy when creating composites characterized by high anti-friction, plastic and strength properties.