Carbon- or nitrogen-containing nanostructured thin films

Resume : Plasma polymer deposition enables the controlled modification of material’s surfaces such as e.g. polymers (including textiles and fibers) at the nanoscale. Industrial applications based on plasma polymer deposition require reliable processes that can be transferred to production-scale reactors. For this purpose, both gas phase and surface processes should be well controlled during plasma polymerization. While gas phase processes are governed by the energy invested per particle (plasma chemistry), surface processes also depend on the energy flux and on the momentum transfer during film growth (plasma physics). For the deposition of a-C:H:N plasma polymers gaseous mixtures of NH3/C2H4 as well as N2/H2/C2H4 are examined using RF discharges both in a batch reactor and in a pilot plant (at low pressure). The gas composition and energy input are found to determine the incorporation of nitrogen into the hydrocarbon network, while ion bombardment during film growth supports the formation of nucleation sites, surface diffusion, chemical bond opening and cross-linking. The amine-functional group density thus depends both on gas phase and surface processes. Moderate energetic conditions favor the formation of voids during film growth due to steric hindrance of incorporated amino groups resulting in a nanoporous film structure. Such a-C:H:N films are used for the attachment of molecules (e.g. thermoresponsive PEGs enabling controlled drug release through membranes) as well as for improved adhesion (e.g. light-weight fiber-reinforced composites). Plasma polymers containing more than 2 at% of amino groups, however, undergo hydrolysis and show leaching of polyamines in aqueous environments which has to be considered for biomedical applications (e.g. tissue engineering). The remnant films (after washing the leachable products) are found to be very stable enabling for example superhydrophilic surfaces due to the remaining nanostructure.

Resume : Plasma polymerization of sulfur-based molecules such as propanethiol is a promising approach to grow thiol (-SH) supporting surfaces that can serve as nucleation centers for gold nanoparticles or for the immobilization of DNA molecules. However, despite the potential of such a kind of thin films, it is still necessary to get a deeper understanding of the plasma polymerization of sulfur-based precursors. In this work, propanethiol plasma polymers (Pr-PPF) were synthesized varying the mean power (

) dissipated in the discharge in pulsed and continuous modes. The –SH density ([SH]) is measured by means of XPS combined with a recently developed derivatization method. As a function of

, nearly constant values of [SH] of the Pr-PPF are observed. This peculiar behavior is explained considering (i) mass spectrometry data revealing a similar relative concentration of condensable SH-bearing species in the plasma and (ii) similar energetic conditions at the growing film/plasma interface. On the other hand, it has been observed that the low

synthesized Pr-PPF are not chemically stable in aqueous solutions likely due to the release of trapped sulfur-based species supported by mass spectrometry measurements. In addition, DFT calculations have been employed to assist the interpretation of the experimental data. The whole set of our data allows drawing a clear picture of the growth mechanism of Pr-PPF which is essential in view of the optimization of the layers properties.

Resume : Polycrystalline TiN and related transition-metal nitride (TMN) thin films are typically deposited by reactive magnetron sputter deposition and employed as diffusion barriers in microelectronics as well as hard, wear-, and corrosion-resistant coatings in mechanical and optical applications. We use a combination of HR-XRD, TEM, HR-XTEM, AFM, and STM analyses to characterize micro- and nanostructures. We will review the fundamental film growth processes - nucleation, coalescence, competitive growth, and recrystallization - and their role in thin film microstructure evolution as a function of substrate temperature. Special attention will paid to in-situ substrate treatment by ion-irradiation and its effect on film microstructure and adhesion. Using spontaneous natural patterning processes, we show that self-organized nanostructures consisting of commensurate nanolamellae, nanocolumns, nanospheres, and nanopipes can be synthesized to further extend the range of achievable properties. All of these structures are a result of kinetic limitations and require low growth temperatures combined with low-energy (less than the lattice atom displacement potential), very high flux, ion irradiation during deposition. Quantitative information of adatom transport and surface site energies required for the models are obtained from in-situ high-temperature STM and LEEM analyses. In addition, we use classical molecular dynamics and the modified embedded atom method formalism to investigate the dynamics of atomic-scale transport and film growth on a low-index model compound surface, TiN(001). This approach allows us to gain insight in kinetics of the pathways of Ti, N, and TiNx (x = 1 – 3) adspecies on terraces and single-atom-high TiN(001) in the picosecond regime which are not accessible by state of the art atomistic experimental techniques or by static DFT calculations. We will also review recent advances in the selective use of metal ions during HIPIMS co-sputtering to extend the attainable structures and properties in metastable TMN with examples of Ti(1-x)AlxN, Ti(1-x)SixN, ad Ti(1-x)TaxN.

Resume : Since the pioneering materials selection concept of Holleck [1] to design multi-component hard coatings, efforts have been made to synthesize new ternary or multinary transition metal nitride (TMN)-based alloys, which offer the possibility of fine tuning the mechanical and physical properties by an appropriate choice of metal or non-metal alloying elements and by optimizing deposition process parameters. Recent ab initio calculations by Sangiovanni et al. [2] have shown that Mo and W alloying into TiN decisively induced a ductile behaviour, which corresponds to a shear modulus to bulk modulus (G/B) ratio lower than 0.5, while retaining high hardness. However, there exists little experimental evidence of such improved ductility, as the elastic properties of such metastable compounds are scarcely studied. In an effort to address this issue, we have carried out a thorough investigation of the elastic properties of various ternary TMN systems, by combining thin film growth experiments and computational modeling. Three systems will be comparatively reviewed, TiZrN, TiTaN and TaZrN, for which the valence electron concentration spans the region of interest from 9 to 10 and which corresponds as well as to iso- and non-isostructural cases. All ternary films were obtained by reactive magnetron co-sputtering in Ar+N2 atmosphere, with the composition covering the whole range from binary counterparts. The transverse and longitudinal sound velocities were determined by Brillouin Light scattering (BLS) and picoseconds acoustics (PA), while the hardness was measured by nanoindentation. The evolution with composition of polycrystalline (effective) elastic constants , deduced from BLS and PA, will be compared to that of single-crystal elastic constants cij derived from ab initio calculations (on ordered and disordered alloys with cubic structure). The influence of phase composition, crystal structure, preferred orientation and film morphology on the elastic and mechanical properties will be discussed. Rather complex variations of and elastic constants with alloy composition are reported for both TiTaN and TaZrN systems. First, the evolution of and does not reflect in a direct way the evolution of sound velocities due to the large increase in mass density as TaN fraction increases. Another important contribution arises from the change in texture and phase composition observed for TaN-rich films. Interestingly, for TaN atomic fractions ranging from 0.5 to 0.8, the formation of a nanocomposite structure, with cubic and hexagonal grains, results in enhanced hardness (>30 GPa). [1] H. Holleck, J. Vac. Sci. Technol. A 4, 2661 (1986) [2] D. G. Sangiovanni, L. Hultman, V. Chirita, Acta Mater. 59, 2121 (2011)

Resume : Carbon-based materials, including diamond-like carbon (DLC), have been suggested as promising materials for solar energy harvesting. The properties of DLC may be tuned by the incorporation of transition metal atoms, either dispersed or forming nanoparticles. In a recent work [1], we studied DLC/metal nanocomposites, with metal atoms (Ag, Cu) dispersed in the matrix at substitutional sites. We used 64-atom computational cells and density functional theory (DFT) calculations. We found that metal inclusions enhance the optical absorption in the visible, but lower the sp3 fraction and thus the strength and hardness of the DLC matrix. Here, we extend these studies to the nanoparticle case. We start with metal atoms inserted in the DLC matrix interstitially, which eventually grow into larger nanocrystals. We use larger cells of 512 atoms. The initial DLC networks are generated with tight-binding calculations. The final structures with metals are relaxed with DFT and then properties are calculated. The first results indicate that the reduction of sp3 fraction is less drastic than in the dispersed case, which is beneficial for the mechanical properties. Also, the optical absorption is enhanced. By decomposing the absorption coefficient into site contributions, we aim to identify the strong absorbing atoms in the system, especially in the metal nanocrystals. [1] G. Tritsaris, C. Mathioudakis, P. C. Kelires, and E. Kaxiras, J. Appl. Phys. 112, 103503 (2012).

Resume : Deposition of metal vapour on insulating substrates commonly proceeds in the so-called Volmer-Weber growth mode, in which isolated islands nucleate, grow in size, coalesce, form an electrically conducting network (percolation) and eventually form a continuous structure. The initial formation stages, i.e., island nucleation, growth and coalescence set characteristic length scales on the growing surface. Therefore, fundamental understanding of the dynamics of those formation stages and of their complex interplay is paramount of knowledge-based design and synthesis of thin films and nanostructures. By establishing the effect of growth conditions on the scaling behaviour of characteristic transition thicknesses, e.g., the percolation transition thickness, theoretical research has suggested the existence of two regimes; one in which growth is dominated by coalescence and a second one in which growth behaviour is determined by island growth and impingement. Here we use kinetic Monte-Carlo growth simulations and analytical expressions to derive the universal condition for the transition from one regime to another as a function of adatom arrival rate, adatom surface diffusivity and coalescence completion rate. Experimental evidence for the existence of both regimes is provided by monitoring in-situ the growth of Ag on SiO2 both by continuous and pulsed vapour fluxes. The implications of our findings for surface science and surface engineering communities are discussed.

Resume : ZrC thin films were grown on Si substrates by the Pulsed Laser Deposition technique. By changing the substrate temperature and ambient gas nature and pressure during deposition, films having a wide range of crystal grain sizes, mass densities and C/Zr ratios were obtained. We investigated the IR optical properties of ZrC films by measuring the optical reflectance from 30 cm-1 (4 meV) to 30 000 cm-1 (4 eV), using a Bruker-113v FTIR spectrometer and a Carl Zeiss microscope photometer. The resistivity values extracted from the optical data were similar to those measured using a four point probe technique. The results indicated that ZrC films exhibited high reflectivity in the mid IR range regardless of the structure and composition. Very low resistivity values of around 5×10-5 .cm and slightly lower wear rates were measured for films having the highest ratio of C/Zr, while higher hardness values were measured for films having the largest crystal grains. These excellent qualities recommend the ZrC films for applications as thermal radiators working at very high temperatures in the outer space.

Resume : Remote plasma assisted vacuum deposition is a novel a versatile deposition methodology, which permits the fabrication of organic films from non-chemically polymerizable organic or organometallic molecules.[1-3] The technique is based in the effective control of the interaction between the sublimated precursor molecules and a remote glow discharge. Thus, the technique has some similarities with the vacuum deposition and the plasma polymerization processes. Once formed, the films are solid cross-linked organic structures typically insoluble in organic solvents and thermally stable at temperatures higher than the sublimation temperatures of the precursor molecules. The technique also permits the direct fabrication of microstructures and low dimensional nanostructures. The optical properties of the films (light absorption, luminescence, sensor response, etc) depend on the precursor molecules and on the particular thin film nanostructures and final composition. Examples of multifunctional films and microstructures deposited from laser dyes and other relatively complex molecules for the fabrication of photonic structures, gas sensors, optical films, lasing media and optoelectronic components will be presented and studied. [1] A. Barranco, P. Groening, Langmuir 22 (2006) 6719. [2] I. Blaszczyk-Lezak et al. J. Phys. Chem. 113 (2009) 431. [3] F.J. Aparicio et al. Adv. Mater. 23 (2011) 761.

Resume : Enhanced toughness in hard and superhard thin films is a primary requirement for present day ceramic hard coatings, known to be prone to brittle failure during in-use conditions, in modern applications. In our previous Density Functional Theory (DFT) investigations, we predicted significant improvements in the hardness/ductility ratio of several pseudobinary B1 NaCl structure transition-metal nitride alloys, obtained by alloying TiN or VN with NbN, TaN, MoN and WN [1, 2]. The initial calculations, which were carried out on model, highly ordered configurations with Cu-Pt ordering on the cation sublattice, reveal that the electronic mechanism responsible for toughness enhancement stems from the high valence electron concentration (VEC) of these alloys, and ultimately allows a selective response to tetragonal and trigonal deformations. Recently, these results have been validated experimentally. Single-crystal V0.5Mo0.5N/MgO(001) [3] and V0.6W0.4N/MgO(001) [4] alloys, were grown by dual-target reactive magnetron sputtering, together with VN/MgO(001) and TiN/MgO(001) reference samples. The V0.5Mo0.5N films exhibit hardness >50% higher than that of VN, and, in contrast to nanoindented VN and TiN reference samples, which suffer from severe cracking, the V0.5Mo0.5N films do not crack. No ordering on the cation sublattice is observed in the V0.5Mo0.5N films, however, the onset of W ordering on adjacent {111} planes of the metal sublattice, is observed in V0.6W0.4N alloys. Here we present new DFT results, which address the issue of lattice ordering effects on the mechanical properties of these pseudobinary alloys. Our investigations concentrate on V0.5Mo0.5N, V0.5W0.5N, Ti0.5Mo0.5N and Ti0.5W0.5N alloys obtained by alloying TiN and VN with WN and MoN. Our calculations, carried out for structures with increasing levels of disorder, reveal that while the degree of electronic structure layering, i.e. the formation of alternating layers of high and low charge density upon shearing, becomes less pronounced in disordered configurations, the overall VEC effect is not affected. The essential feature in the disordered alloys, as initially predicted for highly ordered configurations, remains the increased occupancy of electronic d-t2g metallic states, which allows the selective response to tensile/shearing stresses, and explains the enhanced toughness confirmed experimentally for V0.5Mo0.5N films. [1] D. G. Sangiovanni et. al. Phys. Rev. B 81 (2010) 104107. [2] D. G. Sangiovanni et. al. Acta Mater. 59 (2011) 2121. [3] H. Kindlund et. al. Appl. Phys. Lett. Materials, 1 (2013) 000000. [4] H. Kindlun et. al. J. Vac. Sci. Technol. A 31 (2013) 040602.

Resume : A comprehensive study on the influence of the Al content on TiAlN coating microstructure and related mechanical and tribological properties are presented. A layered structure of TiAlN and AlN is obtained applying an average power density of 2.468 W/cm2 and 1.234 W/cm2 to a TiAl and Al target respectively, by the RF modulated pulse power. X-ray diffraction reveals fcc single-phase coatings at low Al contents and dual-phase or hcp phase at higher Al contents. As-deposited TiAlN and TiAlN/AlN film compositions are determined by X-ray Photoelectron Spectroscopy (XPS). The single TixAl1-xN film has x = 0.36 which remains unchanged even in the multilayer. The Ti 2p 3/2 peak can be fitted with two components, whose relative areas vary along the sample depth, and are ascribed to the fcc and hcp phase of the ternary compound. The peak at lower B.E. is shifted respect to the TiN peak at about 455.3 eV. The second peak is associated to a ternary structure like hcp-TiAlN. The presence of two different chemical states on Ti 2p does not induce any variation on Al 2p and N 1s spectra. Hardness measurements show high values for x=0.36, decreasing with increasing Al to values of 17 GPa at x=0.76. Friction coefficients are around 1.5 at room temperature but decrease significantly at higher temperatures to 0.88 at 700 °C. This investigation clearly shows the relations between coating composition and the resulting structure explains their mechanical and tribological properties.

Resume : The electronic properties of sp2 carbon nanostructures are very sensitive to local perturbations, such as surface charges and adsorbed gas molecules, so that the grafting of functional groups in a controllable way has been proposed as a feasible reproducible solution for band gap engineering and controllable doping, in order to exploit and tailor the extraordinary properties of these materials. Plasma-based functionalization methods have the advantage to be solvent-free, time efficient and flexible. Within this context, we will discuss the functionalization of vertical aligned carbon nanotubes (v-CNTs) via nitrogen plasma treatment. Valence band (UPS) and scanning X-ray photoelectron spectromicroscopy (SPEM) measurements were performed at ELETTRA Synchrotron. The creation of defects induced by ions drives the grafting of nitrogen species (pyridinic, pyrrolic and graphitic) on the CNTs. A depth of functionalization up to 4 μm was evaluated by SPEM, beyond which the properties of the v-CNTs remain unperturbed. Furthermore, an intriguing different behavior of the grafting at the CNT tips with respect to the sidewalls was observed. This indicates a different reactivity of the CNT tip, where the presence of natural defects may be involved in different bonding formations between carbon and nitrogen. The effect of the temperature has been evaluated both during the plasma treatment and with post synthesis annealing, showing variations in the ratio between the nitrogen species.

Resume : We report high current density explosive electron emission from a copper cathode with diameter of 50 mm with pre-deposited pyrolytic carbon (PyC) films being from 70 to 150 nm thick. In the diode configuration, we demonstrate the current density as high as 300A/cm2 under applied voltage below 400 kV. The Raman measurements reveal that the PyC film survives after 7 shots. In order to study the cathode degradation we compared optical microscope images of the cathode before and after shots. We observed that the pre-deposited PyC film cathode prevents copper evaporation and oxidation. This property ensures a higher explosion emission stability and longer lifetime of the PyC/Cu-cathodes in comparison with conventional graphitic/Cu ones. Our results show that PyC/Cu cathodes are most promising for applications that require electric field strengths from 50 to 60 kV/cm.

Resume : Undoped, Cu and Mn doped aluminium nitride (AlN) nanostructures were synthesized using a chemical vapour condensation (CVC) method. The raw materials were a mixture of Al and NH4Cl powder with different weight ratios and Cu and Mn powders, which were used as a dopant. Field emission scanning electron microscopy (FE-SEM) results showed different nanostructures, including nanowires and nanoparticles of different sizes. Photoluminescence (PL) spectroscopy of as-prepared samples show intense peaks in red, blue-green and blue regions in the Mn doped, Cu doped and undoped samples, respectively. These results are important for optoelectronical applications.

Resume : Achive the fine tuning of the graphene electronic properties is one of the main challenges for optimal fabrication of graphene-based nano-devices. Notably the low carrier density in pristine graphene at the Fermi level means that charge carrier doping is very attractive for nanoelectronics applications. Among these, the introduction of nitrogen atoms into the hexagonal carbon lattice of graphene has attracted interest in the recent years. Within this context, we present an experimental report that combines scanning photoemission microscopy analysis with in-situ nitrogen ion casting on suspended graphene. Nitrogen doping was performed by N2 ions bombardment in ultra-high vacuum. Inclusion of up to 20 at. % nitrogen can be reached through this clean technique with absence of oxygen species in the final product, while maintaining a largely sp2-carbon network. The inclusion was observed by scanning X-ray photoelectron microscopy which can be used to follow the evolution of nitrogen species: pyridinic, graphitic, and pyrrolic, at different doping stages and annealing temperatures. Variations in the ratio between sp2 nitrogen species was observed for increasing treatment time; annealing results in quenching of the sp3 component, suggesting graphitic nitrogen as the most thermal stable species. The occurrence of graphitic species together with the absence of pyrrolic is indicative of N-incorporation into a hexagonal graphene-based lattice.

Resume : Ag thin film is an efficient surface enhanced Raman spectroscopy (SERS) substrate because its quality factor of localized surface plasmon resonance (LSPR) is much larger than other materials, e.g., 10 times larger than that of Au at the wavelength of 500 nm. However, the chemical instability of Ag in ambient environment significantly degrades the SERS properties, and hinders the practical applications. Although conventional protective structures (e.g., silica and alumina barrier) can inhibit the Ag corrosion in ambient, they usually have large light absorption and reduce the plasmonic enhancement. In this work, we transfer monolayer graphene onto Ag SERS substrate, on one hand, to protect Ag from corrosion, and on the other hand, to prevent the photo-induced damages (photocarbonization, photobleaching and metal-catalyzed reaction) on the probed molecules. Firstly, we comparatively study morphological characteristic of the Ag SERS substrates with and without graphene protective barrier, revealing high corrosion-resistance of monolayer graphene to the oxidizing gas and liquid. We further demonstrate the graphene coated Ag thin films as stable SERS substrate. After 35-day exposure in air, the graphene coated Ag thin film maintains high SERS sensitivity. Secondly, we systematically study the resistance to photo-induced damages with graphene barrier. Our results show that Ag SERS substrate with graphene coating significantly improves the SERS reproducibility, and simultaneously inhibits metal-catalyzed reaction. In addition, the graphene layer can form strong interaction with the probed R6G molecules through π-π bonding stack, reducing the possibility of photo-induced desorption. In summary, our results show that graphene coating on Ag substrate effectively enhances the resistance to the corrosion and photo-induced damages.

Resume : We have fabricated reduced graphene oxide (RGO) and functionalized them with metal nanoparticls. To obtain uniform metal-RGO sheets, the supernatant was centrifuged to remove small graphene pieces and water-soluble by product, repeatedly washed with distilled water until the pH = 7. Due to their outstanding physical and chemical properties, graphene and its derivatives have attracted tremendous attention for both fundamental science and possible technological applications. RGO can be efficiently prepared by reducing (i.e. annealing) graphene oxides. Although RGO has irreversible defects, disorder and residual functional groups, it exhibits a sufficient conductivity. Transmission electron microscopy results exhibited the deposition of metal nanoparticles on RGOs. The NO2 gas sensing test was carried out to demonstrate the ability of the metal functionalization to attain the higher sensitivity than bare RGO sheet. We have discussed the possible mechanisms for improvement of the sensing properties by metal-functionalization. We suppose that spillover effect induced by metal nanopartitcles play a significant role in enhancing the sensing properties.

Resume : We report the codeposition of three conjugated polymers, with π molecular orbitals delocalized along the polymer chain, (polyaniline, polypyrrole, polythiophene) and poly-1,4-dichloro-2-butyne from suitable monomers on silicon substrate by plasma polymerization that is aiming to identify the range of negative differential resistance (NDR) behavior in I-V characteristics and their correlation with the conduction mechanisms and space charge distribution. The deposited thin films were characterized by UV-VIS (e.g. band gap), FT-IR-Raman (e.g. structural identification of the structural units) spectroscopy and AFM/STM topography. The polyaniline-poly-1,4-dichloro-2-butyne and polythiophene-poly-1,4-dichloro-2-butyne systems show NDR ranged in 0.5 – 1 V, values that are close to requirements in designing of smart card devices based on tunnel diodes.

Resume : Composites made by polymer blending is an attractive alternative to produce materials with tailored properties intended to industrial applications. Chitosan and polylactide (PLA) are both biodegradable and biocompatible polymers with potential use in medical applications. Their combination to provide new materials with controllable composition and properties is very interesting and promising for specific applications in the medical field. In this work, we present the synthesis of the blends for fabrication of nanocomposite thin films and their characterization by optical spectroscopies. Because of their different polarities, the polymers need to be dissolved in a solvent blends in defined conditions for obtaining a homogeneous solution. We have successfully established a ternary phase diagram using chloroform, acetic acid and water and defined the conditions for obtaining controlled compositions of PLA/chitosan composites. Analysis of the optical spectra of PLA, chitosan and their composites shows that the structure of the polymers is preserved in their blends. This observation suggests that chitosan is fully incorporated to PLA without significant interactions. Degradation study of the blends under prolonged UV irradiation reveals that chitosan is more stable in composites but is decomposed before PLA .

Resume : Nanostructured carbon materials based on graphene are among the most studied materials nowadays, due to interesting properties which allow their utilization in various applications. Previously, we have developed a method for carbon nanowalls (CNW) growth based on downstream deposition from an expanding radiofrequency argon plasma beam discharge injected with acetylene in the presence of hydrogen. So-called ?standard? conditions were defined as: RF power = 300 W, Ar:H2:C2H2 = 1050:25:1 sccm, pressure = 1 mbar, distance from the injection = 5 cm, substrate temperature = 700 ?C. The present study aims to investigate the effect of the nozzle geometry (diameter 2-16 mm) on the material characteristics and to correlate them with the plasma species present during the synthesis process. The main investigation technique was Scanning Electron Microscopy (SEM) for revealing the obtained morphologies and structures, in combination with statistical processing of SEM images for determination of specific length/width ratio of individual CNW. The plasma process was analyzed regarding the excited species by Optical Emission Spectroscopy (OES) performed both at the injection level and on the deposition level. We show that either CNW, or combined nanofibers/nanowalls architectures with various aspect ratios can be obtained, and the OES technique may provide information which allows a correlation between the material characteristics and the internal plasma parameters.

Resume : Organic-inorganic nanocomposites have found extensive range of application in various fields, from energy storage to catalysis or biomedical materials. In particular, metallic nanoparticles embedded in polymeric matrices are of high interest for biomedicine. Plasma polymerized polyethylene glycol films present antifouling properties and low water solubility, while the silver particles are well known for their antimicrobial effect as well as for generation of plasmon resonance effect. This work proposes the deposition of polyethylene glycol ?silver (PEG-Ag) nanocomposites with tunable composition by using low pressure RF plasma system. The study aims the obtainment of a synergistic effect by means of proper control of the composition and density of each component through experimental parameters. The morphology, chemical composition and optical properties of the material were determined by means of Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Spectroscopic ellipsometry, respectively. The antimicrobial effect against various strains as S. aureus, E. coli and C. albicans was demonstrated.

Resume : Electrospinning is commonly used for preparation of polymer nanofibers but the application of the nanofibers usually requires an additional surface treatment. Plasma enhanced chemical vapor deposition (PECVD) is a versatile technique used for surface modification and it is interesting to test it also for highly porous materials such as electrospun nanofibers. Organic/inorganic composites were prepared by PECVD of organosilicon plasma polymers deposited on PVA and PA6 electrospun nanofibers from HMDSO/Ar mixtures. Low pressure RF discharges with capacitive coupling and by cold RF plasma multi-jet working at atmospheric pressure were used. Deposition conditions were varied to get samples with different structure and wettability and their influences on chemical composition of the resulting layers were investigated by IR spectroscopy and the XPS. The values of the WCA were strongly influenced by both chemical composition of deposited layers and overall surface structure. Significant variations in microstructure of resulting composites were revealed by AFM and SEM analysis of composites prepared by different plasma sources.

Resume : Fumed silica A-300 was carbonized by means of pyrolysis of CH2Cl2. The obtained initial SiO2:C nanopowders of black color (d~14-16 nm, carbon concentration 7 wt%) subjected to the oxidation and passivation treatment were studied by electron paramagnetic resonance (EPR) at 4.2-400 K. Two EPR signals of Lorentzian lineshape with nearly equal g-factors and different linewidth were observed in all samples. The two-component EPR spectrum was explained by the presence of the C clusters of different sizes resulting in EPR line of different linewidth due to the spin exchange interaction between paramagnetic centers. The intensive narrow EPR signal was attributed to the carbon related defect (CRD) with non-localized electron hopping between neighboring C-dangling bonds. From the temperature dependence of resonance field position of the CRD EPR signal, caused by exchange interaction between conduction electrons and localized spin system, the parameters of the localized spin system has been determined in oxidized and passivated samples. It was supposed that the conduction electrons are coupled with electrons localized at interface defect. The observed peaks in temperature dependence of the conduction electron EPR signal integral intensity at 200-440 K was explained by ejection of electrons from the confinement energy levels of carbon quantum dots when the temperature become comparable with the confinement energy. The work supported by STCU №5513 and SAFMAT CZ.2.16/3.1.00/22132 projects.

Resume : It is well known that different varieties of carbon-based nanostructures demonstrate facilitated field-induced electron emission, even if they have no high-aspect-ratio surface morphology elements, such as sharp tips or ribs. Macroscopic properties of DLC films strongly depend on relative content of sp3- and sp2-hybridized carbon bonds and hydrogen content. The quality of DLC films and hence their properties can be tailored by tuning the ratio of sp2/sp3 carbon atoms and stress in the films, both of which can be changed by doping metals or non-metals in DLC matrix. In this contribution we report growth and study of properties of sandwich structures comprising layers of both Ni-C nanocomposite and α-C:H layers on (100) crystalline silicon substrates. α-C:H layers were grown using RF plasma of methane and methane-hydrogen mixtures. Process of deposition of α-C:H layers was carried out in the PECVD method. ncNi-carbon layers were grown by the MOCVD technique using bis-(ethylcyclopentadienyl) nickel (EtCp)2Ni as a precursor. The deposition process was carried out in low-pressure tube silica reactor in the temperature range 350-650°C. Nanocomposite layers contained 10-20 nm Ni particles presumably coated by nickel carbide shells were obtained. Results of investigation of DLC films and different sandwich structures by AFM, SEM, XPS and other techniques will be presented. This work was supported by RFBR grants № 12-08-01197 and 13-02-92709.

Resume : Structural damage formation in Si irradiated at room temperature by atomic (P+) and molecular (PF4+) ions is experimentally studied in a wide energy range (0.6-3.2 keV/amu). Strong molecular effect, caused by overlapping of collision cascades created by atoms comprising molecular ion, is revealed close to the sample surface in all cases considered. Theoretical assessments of depths where nonlinear processes are possible have shown good agreement with experimental data. Primary defect generation enhancement in the vicinity of Si surface is estimated about factor of 5. This work was supported by RFBR (grants 13-08-00666 and 14-08-01256).

Resume : Diamond like carbon (DLC) is a metastable form of the amorphous carbon consisting from the sp2 bonded (graphite like) carbon clusters embedded into the sp3 bonded (diamond like) carbon matrix. DLC films remains under considerable interest of the researchers due to the high optical transmittance in visible light and IR ranges, high hardness and wear resistance, corrosion resistance, biocompatibility. Additional control of DLC properties can be achieved by doping with different metals. Particularly surface plasmon resonance effect was observed in group I metal containing DLC films. In addition good hemocompatibility and antibacterial properties were reported for group I metal containing DLC films. Taking into account interesting properties of DLC films mentioned above group I metal containing DLC films can become interesting material for fabrication of the advanced plasmonic biomedical sensors. In present study copper containing diamond like carbon films (DLC:Cu) films were deposited by using reactive high power pulsed magnetron sputtering. High power pulsed magnetron sputtering is novel high density plasma deposition method. High plasma density of the high power pulsed magnetron sputtering is advantageous for deposition of DLC films containing high amount of sp3 bonded carbon. Effects of the acetylene and argon gas flow ratio as well as pulse current density were studied. The dependence of the optical properties of DLC:Cu films on structure and composition was investigated.

Resume : Amorphous diamond like carbon films can be modified by introducing doping compounds during deposition process. As potential candidates for modification usually Si, O, N, Ag, Cu are used. In case of Si, O and N incorporation, organosilicone compounds such as hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) are used. Incorporation of SiOx gives better adhesion and optical properties (transparency, optical band gap) of the films. Using HMDSN one can form silicon carbonitride thin films with high hardness, low friction coefficient, etc. Even though these films show interesting properties, the structure of these films employing multiwavelength Raman scattering was not investigated. In the current research thin a-C:H:SiOx and a-C:H:SiN films were deposited on crystalline silicon and fused silica from HMDSO and HMDSN compounds respectively, using closed drift ion beam source and different ion beam energy. The structure of these films was studied employing multiwavelength (325 nm – 785 nm) Raman analysis. From the Raman spectra analysis, the characteristic parameters such as the positions of D and G peaks, D/G peak ratio as well as dispersion of G peak showing topological disorder of sp2 phase in doped a-C:H films were determined. Optical properties of the films were analysed versus composition and structure as well as doping conditions during deposition.

Resume : In aero engines, coatings are facing severe attack under multiple loading conditions. Sand erosion, e.g., can cause great damage to turbine hardware in the compressor, while hot corrosion and oxidation are of concern in the hotter parts of the engines. Today, coatings are widely applied to protect high pressure turbine airfoils, however, their use in the compressor and the low pressure turbine is scarce yet. The paper will review recent developments in the field of erosion protection of aerospace alloys such as titanium and nickel alloys indicating that Cr2AlC nanolaminate MAX phase coatings can substantially improve the component lifetimes under erosion attack. It has been shown that the Cr2AlC MAX phase exhibits good erosion protection due to its combination of metallic and ceramic properties. Furthermore, Cr2AlC has excellent oxidation resistance, particularly if doped with Y. Recently, for this MAX phase autonomous self-healing behaviour was demonstrated which fostered significant research efforts in this area. The current aim of ongoing research is to assess the potential of Cr2AlC MAX phase coatings as erosion resistant autonomous self-healing material by understanding the basic physical and chemical principles governing multiple crack closure to heal erosion damage.

Resume : Nanotechnology is the ability to manipulate atoms and molecules to produce nano- structured materials and functional nano- coatings on biomedical devices and surgical tools. The use of carbon fiber composites (CFC) for surgical applications is widespread due to the exceptional physical properties of this material. Carbon fiber structures provide strength, stiffness, and fatigue resistance. Carbon fiber components are also radiolucent and clinical-chemical resistant. Carbon-based materials show, however, significant oxidative degradation in air beginning at temperatures in the region of 400 degree C. The reinforcement of carbon with carbon fibers, complicates the anti- oxidative coating problem, due to the thermal and elastic anisotropy of the carbon fibers. Therefore, a coating concept for carbon–carbon composites should consist of an inner part, which serves as structural link with stress compensation ability to the carbon substrate, and an outer part, which acts as a diffusion barrier. In the presented paper, as the inner part chromium/ chromim nitride (Cr/CrN) multilayer structure has been selected. The literature data indicates the particular meaning of Cr and CrN multilayer coatings. They are characterized by an appropriate crystallographic adjustment of subsequent constituent layers of Cr and CrN and by the creation of a transition layer between them with a thickness of several dozen of nanometers. This ensures a good connection between particular constituent layers and as a result also good maintenance properties: high adhesion, wear and corrosive resistance. The CrN and Cr lattice parameters, 4.14Å and 2.88Å, respectively, allow a cube-on-cube, close to epitaxial growth with a low mismatch (1.6%). With this idea, Cr/CrN multilayers have been designed and deposited on CFC substrates. The outer part of the coating, in the presented paper, was hydrogenated amorphous carbon (a-C:H). It is well-known that a-C:H coatings have low- friction coefficients and low-specific wear rates. Thus, the amorphous carbon coatings are very promising tribo-materials. However, the poor adhesion strength to substrate, high residual stress and weak thermal stability would limit their application. Currently, many metallic elements (Ti, W, Ag, Cr etc.) have been utilized to modify their structure, and it has been proved that the metal doping is an effective method to reduce residual stress and enhance adhesion strength of the film. Among those doping metals, Cr as one of carbide formed elements possesses an attractive combination of properties (corrosion resistance, wear resistance, etc.). Thus, in the presented paper a-C:H part of the coating was implanted by Cr nanocrystals. Coatings were subjected to complex investigations. Influence of deposition conditions on bio- tribological properties were studied. Mechanisms of a mechanical wear of analyzed systems were presented focusing on the cracking propagation revealed in ball- on- disc and scratch tests. Cell-material interaction was analyzed in the direct cell deposition. Complex microstructure analysis of presented, nano- multilayer coatings, before and after mechanical and biological tests, were performed by means of transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). The bio- tribological investigation in connection with detailed microstructure interpretation were used as a screening tool before coatings could be deposited on medical tools.

Resume : CNx are extensively studied for tribological applications because of their high hardness and low friction coefficients. Considering the need to increase the nitrogen content in the today grown CNx films, increasing the dissociation of the nitrogen molecules in the plasma could be a promising strategy. Compared to other magnetron techniques, HiPIMS (High Power Impulse Magnetron Sputtering) enables a high ionization of the sputtered material and a strong dissociation of reactive molecules. Films have been synthesized using reactive HiPIMS of a graphite target in Ar-N2 and Ne-N2. Ne has been used because of its high ionization energy in order to increase the electronic temperature, and in turn the ionization rate. The results are compared to those obtained with a conventional DC reactive magnetron discharge at identical mean power (PD). We discuss the influence of the gas mixture on the peak current and therefore on the film chemistry, determined by XPS. Optical emission spectroscopy was performed in order to address the evolution of the plasma chemistry and temperature with respect to the gas mixture. In HiPIMS, the deposition rate increases with N2 content in Ne-N2 and is lower than in Ar-N2. In DC, the behaviour, with an opposite trend for the two gas mixtures, can be explained by the variation of the sputtering yield for the different gases. The chemical composition of the film reaches a saturation value in all cases.

Resume : The comprehensive study focuses on the interplay interfaces Ta-Nx, x= [0,1.8] coating/ CNT during the growth by assisted catalyst CVD at 850°C, while using ferrocene as catalyst source. We show that the use of Ta-Nx buffer films grown by High Power Pulsed Magnetron Sputtering HIPPIMS is of special interest because it allows a larger incorporation of nitrogen inside the films and generates specific nanostructures. The CCVD process promotes reactions among C, N, O on one side, Ta, Fe on the other side. The abundant evidences collected in our experiments confirm the strong influence of these chemical reactions occurring during the CVD process, thus justifying a close scrutiny of the chemical and structural changes due to the temperature and the CCVD process. Therefore, we present here the interfaces modifications studied by grazing incidence X-ray scattering GIWAXS, high resolved electron scanning microscopy SEM-Feg and XPS. The together techniques are very helpful for exanimating the temperature effect on the morphology of the interface, giving a good picture of the nanocrystalline evolution of the buffers involved in the CNTs growth process. The CNT morphology and nanostructure is followed by TEM and Raman spectroscopy. We conclude on the huge impact of the nanostructure an surface morphology of tantalum nitride on the CNT morphology and growth, and then its influence on potential applications.

Resume : Off-normal deposition offers very interesting possibilities to tailor the nanostructure of sputter deposited thin films. Under certain deposition conditions, transition metal carbides and nitrides exhibit columnar growth. The orientation, size, and porosity of these columnar structures depend on the deposition angle. The direction of the incoming flux influences also the texture formation and can lead to tilted or biaxial textures. Both the texture and the shape of the columns allow for the control of the mechanical properties of the coating. However, for the prediction of these properties a detailed understanding of the growth process is required. Here we present an in situ X-ray study during reactive magnetron sputtering of VN under various deposition angles. The structure formation of thin films with thicknesses up to 200 nm was followed with sub-nm resolution using in situ X-ray reflectivity (XRR) and X-ray diffraction (XRD) measurements performed at the synchrotron radiation source ANKA (Karlsruhe). The XRR measurements give access to the time-dependent thickness and roughness increase of the coating, while the XRD measurements show the development of the (111) texture. The results were compared with SIMTRA simulations. The in situ study was complemented by ex situ measurements including nanoindentation, atomic force microscopy and pole figure measurements.

Resume : Amorphous silicon carbonitride (a-SiCxNy) thin films deposited on the SiO2 substrates by reactive magnetron sputtering from SiC target without and with different nitrogen (N) incorporation have been studied by Raman and electron paramagnetic resonance (EPR) spectroscopy. Raman analysis indicates the presence of C-N, Si-N, C-C bonds in a-SiCxNy films. Three EPR signals were revealed in a-SiCxNy/SiO2. One of them with isotropic g factor at g=2.0033 and Lorentzian lineshape was attributed to the carbon-dangling bonds (CDB) located within a-SiCxNy film. Based on the lineshape and linewidth (~ 1.2 mT) the EPR signal was attributed to the unpaired electron delocalized over the sp2 carbon cluster. With increase of the N content the spin density of the CDB significantly increases. From the temperature dependence of the linewidth and integral intensity of the CDB EPR signal which obey Curie-Weiss law it was concluded that antiferromagnetic ordering occurs in the spin system. The value of the antiferromagnetic exchange constant between dangling bonds was found to be J=–32 K. The second EPR signal having g=2.009 was attributed to the interface defect representing threefold-coordinated Si dangling bond which may appear due to the formation of the oxidized silicon on the top surface of the film. The third EPR signal with g=2.05 was tentatively attributed to the trapped holes at Si atom. The work was supported by GA ČR 13-06697P and SAFMAT project CZ.2.16/3.1.00/22132.

Resume : Hydrogen isotopes plasma/walls interactions in carbon tokamaks lead to a severe safety issue avoiding carbon use in the future ITER project. A complete analysis of the D retention in the Tore Supra tokamak, including both in-situ gas balance measurements and ex-situ post-mortem characterizations, has revealed that deuterium was depleted in the deep layers of the deposits, indicating that an unexpected long term D-release occurs. To mimic the variety of hydrogenated deposits found in Tore Supra, we used several reference samples and heated them to relevant temperatures (120-1000°C). These samples had various C(sp2)/C(sp3)/H content and were PECVD layers with properties ranging from soft to hard films (DC bias from -100 to -300 V corresponding respectively to H/(H+C) equal to 37 and 29 at.%). We have studied the thermal stability of these samples using in-situ Raman microspectroscopy under argon atmosphere, recording their evolution during hours or days. Ultra High Vacuum thermal desorption spectroscopy and ion beam analysis were done separately for comparison. We have identified selected Raman parameters as C(sp3)-H and/or C(sp2)-H sensitive. For example, for the -300 V DC bias sample, carbon reorganization with aromatization and loss of C(sp3) occurs in the first 100 minutes at 500 °C. A similar reorganization is detected in the temperature range of 450 - 600°C. H release occurs on a longer timescale of about 10 hours at 500 °C and H release from C(sp2) is only partial, even after several days. These processes occur more rapidly with higher initial H content. Similar analyses have been done for deposits produced in the Tore Supra tokamak to get insights into their structure and on the long term D release processes.

Resume : The high hardness and the low friction coefficient of transition metal nitride (TMN) films allow their use as protective coatings. These materials exhibit also functional properties that make TMN films suitable for applications in energy storage devices. This talk aims to screen the potential use of nitride thin films in supercapacitors. TMN films were deposited on glass substrates by reactive magnetron sputtering of TM targets (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb and Ru). Only Cu- and Ni-based films crystallized in a TM3N-like structure while most of the deposited films exhibit a metal to nitrogen atomic ratio of 1. Only limited information about the structure of MnN and RuN is available in the literature. Subsequently, the structure of these two nitrides is described for the first time. X-ray diffraction analyses and the Rietveld’s method evidence that both RuN and MnN thin films crystallize in a ZnS-like structure with lattice constant of 0.451 and 0.428 nm, respectively. The electrochemical properties of the deposited films were determined by cyclic voltammetry in electrolytes KOH. ScN, Ni3N, FeN, CrN have shown a poor capacitance suggesting that only double layer is involved in the charge storage mechanism. The large capacitance of MnN, RuN and VN and the nearly rectangular shape of the voltammograms suggest a pseudofaradaic process. These electrochemical results are discussed in connection with the film structure and composition.

Resume : In the low-density regime of carbon materials, nanoporous formation along with nanostructuring and coexistence of various hybridizations give rise to three-dimensional (3D) structures with outstanding properties. Carbon nanofoams (CNFs) belong to this class of materials. They are open, random and light structures resembling a foam. We have recently studied [1] CNFs made up of schwarzites, nanostructures with negative Gaussian curvature. Here, we investigate two other forms of this exciting material. One is made of carbon nanotubes (CNT) and the other of graphene nanoflakes (GNF). These 3D randomly interconnected structures offer an alternative route for promising applications. Our studies are based on Monte Carlo simulations for the network formation, followed by tight-binding molecular dynamics simulations for full relaxation and calculation of the mechanical and optoelectronic properties. We find that both foam types are rigid, despite their porous nature, so they can be utilized in applications (catalysis, tribology, energy storage) as thin films. The GNF foams exhibit high conductivity, approaching that of single-layer graphene, and high optical absorptivity. Similar properties are exhibited by the CNT foams. This makes these 3D manifestations invaluable for applications in electronics and optics. [1] C. Mathioudakis and P. C. Kelires, Phys. Rev. B 87, 195408 (2013).

Resume : Graphene, an atomically thin sheet of sp2-hybridised carbon atoms arranged in a honeycomb lattice, has attracted a great deal of interest among the scientific community primarily because of its extraordinary electronic properties. The introduction of dopants has been proposed for applications in nanoelectronics and sensing. In particular, nitrogen dopants can act as electron donors in nitrogen-doped (N-doped) graphitic systems. N-doping of graphene is advantageous for high frequency semiconductor device applications and this material is considered an excellent candidate for energy storage and solar cell applications. Most recently, N-doped graphene has been reported to act as a catalyst in oxygen reduction reactions (ORR) which are crucial in energy conversion. For chemical functionalisation there are several sub-categories, namely surface doping and substitutional doping which can both give rise to either p-type or n-type electronic behaviour. Substitutional nitrogen doping of graphene has been reported by means of different techniques such as chemical vapour deposition, annealing under ammonia atmosphere, arc-discharge of graphite under pyridine/ammonia ambient, wet chemical routes and nitrogen plasma treatment. In spite of its crucial importance, details on the mechanism of incorporation of heteroatoms into graphene remain unclear. We have developed a downstream plasma doping technique using a custom-built apparatus in which the samples are placed at a location remote from the plasma source, thereby minimising the destructive effect of plasma species. Using this approach, an initial oxygen plasma treatment is performed on the pristine sample creating active sites for accommodating further functional groups. A subsequent plasma treatment is then carried out with a mixture of hydrogen and ammonia which simultaneously reduces and N-dopes the graphene. Elsewhere, a similar approach has been shown to simultaneously reduce and N-dope graphene oxide powder. Here we report on the TEM and energy-filtered TEM characterisation of plasma functionalised CVD graphene. Comparative TEM/EELS studies were performed on three different CVD-grown graphene sample types. Namely pristine graphene, O2 plasma treated graphene and O2 followed by H2+NH3 plasma treated graphene. The results show the evolution of pristine untreated graphene to a disordered oxygenated graphene upon O2 plasma treatment and subsequent partial restoration of crystallinity of the graphene lattice following H2+NH3 plasma. This study further probes our N-doped graphene using several spectroscopic techniques, thus offering further information on the nature of doping in graphene. In conclusion, we report on the application of EELS in conjunction with two other spectroscopic techniques for full characterisation of remote plasma-treated CVD-grown graphene. This allowed for a highly detailed analysis of nitrogen-doped graphene; elucidating the structural evolution, along with the nature and bonding states of dopants present. TEM and EELS studies show distortion of the graphene lattice upon oxygen-plasma treatment which is further confirmed by Raman spectroscopy via the emergence of defect related peaks; as well as XPS, with an increased contribution from sp3 carbon bonds and oxygen functional groups. A subsequent H2+NH3 plasma treatment results in partial lattice restoration which is evident from the electron diffraction pattern; this is further corroborated by the better defined peaks and additional features and shoulders in the EEL spectrum. Again, these results are supported via Raman spectroscopy with the re-emergence of long range order and suppression of defect-related peaks. XPS indicates the restoration of the lattice to a graphitic structure with the removal of oxygen groups and the introduction of nitrogen as a dopant. The nature of the nitrogen functional groups was also established. These results show that EELS can be applied to chemically and crystallographically monitor the chemical changes in graphene and its derivatives and, hence, shed light on an established technique as a new avenue for better understanding of the structural variations of graphene upon chemical treatments. Furthermore, the restoration of the graphene crystalline lattice in conjunction with the introduction of nitrogen dopants following the two-step plasma treatment suggests that this plasma treatment technique is a viable method of producing nitrogen-doped CVD graphene for incorporation into further device applications.

Resume : Composite materials with 2D carbon (graphene and/or single wall carbon nanotubes) are very promising due to their extraordinary electrical and mechanical properties. Graphene and natural rubber composites, which may be used for gaskets or sealants, were prepared by ultrasonically assisted latex mixing exfoliation and in-situ reduction process, varying the distribution of the filler in the samples. They present a low electrical conductivity and barrier properties, in spite of excellent spatial distribution. On the other hand, natural rubber composites, prepared by latex mixing and co-coagulation, exhibit a segregated 3D graphene network where the graphene sheets are stacked within the interstices of the coagulated latex particles. These vulcanized composites exhibit good electrical conductivity and high mechanical strength together with excellent barrier properties. The standards for the compositional characterization of these materials still are not established. In addition to the mostly used techniques, such as Raman spectroscopy and electron microscopy, also Auger electron spectroscopy (AES) can be employed for the identification of graphene. In this study, the shape of C KVV peak, excited by electron beam (AES) and X-ray photons (XAES), has been investigated in different composite materials containing graphene and SWCNTs. A new method for 2D carbon recognition, based on the D parameter, determined from C KVV spectra excited by X-ray photons, was proposed and verified.