Anna Macková

Plasma modification of polycarbonates

Abstract We deposited protective coatings on polycarbonates from hexamethyldisiloxane (HMDSO) and HMDSO/O2 mixtures by the plasma enhanced CVD method. In particular, we studied deposition rate, optical constants in UV/VIS, film composition and mechanical properties dependent on rf power and oxygen to HMDSO flow rate ratio. Plasma polymer HMDSO films (PP-HMDSO) showed good transparency in the visible and increased absorption in UV region. The optical constants of HMDSO/O2 films were similar to the tabulated SiO2. In general, the films were characterised by a relatively high content of hydrogen (22–66%) and a carbon content below 20%. The films deposited at an oxygen-to-HMDSO flow rate ratio higher than 15 exhibited higher tensile stress and higher hardness than those prepared at ratios of 5–10. The nature of the internal stress changed to compressive for PP-HMDSO. Plasma pre-treatment of polycarbonate in argon significantly improved the film adherence, especially when low powers and short treatment times were used.

Uranium- and Thorium-Doped Graphene for Efficient Oxygen and Hydrogen Peroxide Reduction

Oxygen reduction and hydrogen peroxide reduction are technologically important reactions in the fields of energy generation and sensing. Metal-doped graphenes, where metal serves as the catalytic center and graphene as the high area conductor, have been used as electrocatalysts for such applications. In this paper, we investigated the use of uranium-graphene and thorium-graphene hybrids prepared by a simple and scalable method. The hybrids were synthesized by the thermal exfoliation of either uranium- or thorium-doped graphene oxide in various atmospheres. The synthesized graphene hybrids were characterized by high-resolution XPS, SEM, SEM-EDS, combustible elemental analysis, and Raman spectroscopy. The influence of dopant and exfoliation atmosphere on electrocatalytic activity was determined by electrochemical measurements. Both hybrids exhibited excellent electrocatalytic properties toward oxygen and hydrogen peroxide reduction, suggesting that actinide-based graphene hybrids have enormous potential for use in energy conversion and sensing devices.

Deposition of protective coatings in rf organosilicon discharges

The paper discusses the deposition of protective coatings ranging from organosilicon plasma polymers to SiO2-like films and hard diamond-like carbon/silicon oxide (DLC?:?SiOx) coatings in radio frequency capacitively coupled discharges using hexamethyldisiloxane (HMDSO). As a result of the optimization of the deposition conditions it was possible to obtain high performance protective coatings. In the HMDSO/O2 mixture, it was shown that rather than the SiO2-like film a hard cross-linked SiOxCyHz polymer film can be used as a protective coating for polycarbonate. The optimum conditions for the deposition of an almost stress-free film were 17% of HMDSO and dc bias voltage of ?240?V. The film hardness and elastic modulus were 10?GPa and 75?GPa, respectively. The refractive index at 600?nm was 1.5 and the extinction coefficient decreased from 0.02 at 240?nm down to zero at 600?nm.The films deposited from HMDSO/CH4 and HMDSO/CH4/H2 mixtures exhibited the attractive properties of DLC films with the partial elimination of some of their drawbacks, such as absorption in the visible and a high intrinsic stress. The optimum concentration of the HMDSO was approximately 21%. Under these conditions the concentration of SiOx in the films was approximately 9?at.%. The film hardness and elastic modulus were above 22?GPa and 120?GPa, respectively.

Chemical Preparation of Graphene Materials Results in Extensive Unintentional Doping with Heteroatoms and Metals

Chemical synthesis of graphene relies on the usage of various chemical reagents. The initial synthesis step, in which graphite is oxidized to graphite oxide, is achieved by a combination of chemical oxidants and acids. A subsequent chemical reduction step eliminates/reduces most oxygen functionalities to yield graphene. We demonstrate here that these chemical treatments significantly contaminate graphene with heteroatoms/metals, depending on the procedures followed. Contaminations with heteroatoms (N, B, Cl, S) or metals (Mn, Al) were present at relatively high concentrations (up to 3 at%), with their chemical states dependent on the procedures. Such unintentional contaminations (unwanted doping) during chemical synthesis are rarely anticipated and reported, although the heteroatoms/metals may alter the electronic and catalytic properties of graphene. In fact, the levels of unintentionally introduced contaminants on graphene are often higher than typical levels found on intentionally doped graphene. Our findings are important for scientists applying chemical methods to prepare graphene.

Insight into the Mechanism of the Thermal Reduction of Graphite Oxide: Deuterium-Labeled Graphite Oxide Is the Key

For the past decade, researchers have been trying to understand the mechanism of the thermal reduction of graphite oxide. Because deuterium is widely used as a marker in various organic reactions, we wondered if deuterium-labeled graphite oxide could be the key to fully understand this mechanism. Graphite oxides were prepared by the Hofmann, Hummers, Staudenmaier, and Brodie methods, and a deuterium-labeled analogue was synthesized by the Hofmann method. All graphite oxides were analyzed not only using the traditional techniques but also by gas chromatography-mass spectrometry (GC-MS) during exfoliation in hydrogen and nitrogen atmospheres. GC-MS enabled us to compare differences between the chemical compositions of the organic exfoliation products formed during the thermal reduction of these graphite oxides. Nuclear analytical methods (Rutherford backscattering spectroscopy, elastic recoil detection analysis) were used to calculate the concentrations of light elements, including the ratio of hydrogen to deuterium. Combining all of these results we were able to determine graphite oxides thermal reduction mechanism. Carbon dioxide, carbon monoxide, and water are formed from the thermal reduction of graphite oxide. This process is also accompanied by various radical reactions that lead to the formation of a large amount of carcinogenic volatile organic compounds, and this will have major safety implications for the mass production of graphene.

Correlation between SiOx content and properties of DLC:SiOx films prepared by PECVD

Hard diamond like carbon (DLC) films with an addition of SiOx were deposited in capacitively coupled rf discharges from a mixture of methane and hexamethyldisiloxane (HMDSO). The flow rate of HMDSO was changed in order to vary the SiOx content in the films. Complete atomic composition of the films was determined by Rutherford backscattering spectroscopy combined with elastic recoil detection analysis. The thickness and the optical properties were obtained from the ellipsometric measurements. The mechanical properties were studied by a depth sensing indentation technique using Fischerscope H100 tester. The O/Si ratio in DLC:SiOx films was 0.286 and the content of SiOx increased with the HMDSO-to-methane flow rate ratio q. The DLC:SiOx films were close to DLC films as concerning the optical properties in the uv/visible and the high hardness if q was maximum 0.25. However, the compressive stress in the films was reduced, the film fracture toughness was improved and the deposition rate increased.

Gold nanolayer and nanocluster coatings induced by heat treatment and evaporation technique

The paper is focused on the preparation and surface characterization of gold coatings and nanostructures deposited on glass substrate. Different approaches for the layer preparation were applied. The gold was deposited on the glass with (i) room temperature, (ii) glass heated to 300°C, and (iii) the room temperature-deposited glass which was consequently annealed to 300°C. The sheet resistance and concentration of free carriers were determined by the van der Pauw method. Surface morphology was characterized using an atomic force microscopy. The optical properties of gold nanostructures were measured by UV–vis spectroscopy. The evaporation technique combined with simultaneous heating of the glass leads to change of the sheet resistance, surface roughness, and optical properties of gold nanostructures. The electrically continuous layers are formed for significantly higher thickness (18 nm), if the substrate is heated during evaporation process. The annealing process influences both the structure and optical properties of gold nanostructures. The elevated temperature of glass during evaporation amplifies the peak of plasmon resonance in the structures, the surface morphology being significantly altered.

A novel method for biopolymer surface nanostructuring by platinum deposition and subsequent thermal annealing

A novel procedure for biopolymer surface nanostructuring with defined surface roughness and pattern dimension is presented. The surface properties of sputtered platinum layers on the biocompatible polymer poly(l-lactic acid) (PLLA) are presented. The influence of thermal treatment on surface morphology and electrical resistance and Pt distribution in ca. 100 nm of altered surface is described. The thickness, roughness and morphology of Pt structures were determined by atomic force microscopy. Surface sheet resistance was studied by a two-point technique. It was the sequence of Pt layer sputtering followed by thermal treatment that dramatically changed the structure of the PLLA’s surface. Depending on the Pt thickness, the ripple-like and worm-like patterns appeared on the surface for thinner and thicker Pt layers, respectively. Electrokinetic analysis confirmed the Pt coverage of PLLA and the slightly different behaviour of non-annealed and annealed surfaces. The amount and distribution of platinum on the PLLA is significantly altered by thermal annealing.

Formation of surface nanostructures on rutile (TiO2): comparative study of low-energy cluster ion and high-energy monoatomic ion impact

The formation of nanostructures on rutile (TiO2) surfaces formed after the implantation of kiloelectronvolt-energy Ar+n cluster ions and megaelectronvolt- to gigaelectronvolt-energy multiply charge ...

Copper Doped Waveguides in Glass Substrates

We have studied the fabrication and properties of the copper ion exchanged waveguides that were fabricated in special Na 2 O-rich soda-lime silicate glasses and in commercial BK7 optical glass substrates. The ion exchange was performed in melts containing either Cu I or Cu II at temperatures from 350°C to 500°C for times ranging from 5 min to 21 h. Optical properties of the fabricated waveguides were studied using mode spectroscopy and photoluminescence spectroscopy, and composition of the waveguides was determined by using Scanning Electron Microscope (SEM), Rutherford Backscattering Spectrometry (RBS), Electron Paramagnetic Resonance (EPR), and Electron Spectroscopy for Chemical Analysis (ESCA). After the ion exchange the refractive index increased, according to fabrication conditions, up to j n = +0.0693, and the guides supported up to 16 TE and TM modes. The Cu I 5 Cu II redox reaction during the fabrication depended strongly on the composition as well as the temperature of the reaction melts. In the Cu 2 Cl 2 :ZnCl 2 melts, the oxidation of Cu I to Cu II was strongly impeded, so that Cu I prevailed in the waveguiding region. These samples exhibited the most intensive blue-green luminescence in spite of those fabricated by using the Cu II -based reaction melts, where practically no blue-green luminescence was observed. ESCA measurement revealed an easy charge transfer between both oxidation states of copper in the very surface regions of the samples.