Search

Nanometer-sized structures, surfaces and sub-surface phenomena have played an enormous role in science and technological applications and represent a driving-force of current interdisciplinary science. Recent developments include the atomic-scale characterization of nanoparticles, molecular reactions at surfaces, magnetism at the atomic scale, photoelectric characterization of nanostructures as well as two-dimensional solids. Research and development of smart nanostructured materials governed by their surface properties is a rapidly growing field. The main challenge is to develop an accurate and robust electronic structure description. The density of surface-related trap states is analyzed by transient UV photoconductivity and temperature-dependent admittance spectroscopy. An advanced application of thin films on shaped substrates is the deposition of catalytic layers on hollow glass microspheres for hydrogen storage controlled exothermal hydrolytic release. Surface properties of thin films including dissolution and corrosion, fouling resistance, and hydrophilicity/hydrophobicity are explored to improve materials response in biological environments and medicine. Trends in surface biofunctionalization routes based on vacuum techniques, together with advances in surface analysis of biomaterials, are discussed. Pioneering advances in the application of X-ray nanodiffraction of thin film cross-sections for characterizing nanostructure and local strain including in-situ experiments during nanoindentation are described. Precise measurements and control of plasma properties are important for fundamental investigations and the development of next generation plasma-based technologies. Critical control parameters are the flux and energy distribution of incident ions at reactive surfaces; it is also crucial to control the dynamics of electrons initiating non-equilibrium chemical reactions. The most promising approach involves the exploitation of complementary advantages in direct measurements combined with specifically designed numerical simulations. Exciting new developments in vacuum science and technology have focused on forward-looking and next generation standards and sensors that take advantage of photonics based measurements. These measurements are inherently fast, frequency based, easily transferrable to sensors based on photonics and hold promise of being disruptive and transformative. Realization of Pascal, the SI unit for pressure, a cold-atom trap based ultra-high and extreme high vacuum (UHV and XHV) standard, dynamic pressure measurements and a photonic based thermometer are three key examples that are presented. [ABSTRACT FROM AUTHOR]

Abstract: The removal rate of carbon from amorphous graphite–tungsten composite during cleaning in oxygen plasma was studied. The composite was prepared by sputter deposition from C and WC-targets in Ar atmosphere. A total thickness of deposited layer was about 1μm. The samples were treated in a weakly ionized highly dissociated oxygen plasma created in a microwave discharge at a power of 1kW. The gas flow was 13slh and the pressure was 200Pa. The temperature of the samples during treatment was about 580°C. After plasma treatment the samples were analyzed by AES (Auger electron spectroscopy) depth profiling, XPS (X-ray photoelectron spectroscopy), SEM (Scanning electron microscopy) and AFM (Atomic force microscopy). It was found that during the plasma treatment selective etching of the composite occurred. Carbon was preferentially removed from the composite. XPS results have shown that during the plasma treatment a layer of WO3 was growing on the surface. After about 15min, carbon was completely removed from the deposited composite layer. [Copyright &y& Elsevier]

Abstract: The stability of commercially available yellow (Bayferrox 3920) and red (Bayferrox 140) micronized iron oxide pigments against highly aggressive treatment with oxygen plasma is examined. The red pigment microparticles with hematite crystal structure are stable, while the yellow pigment changes colour during the treatment. Structural analysis with powder X-ray diffraction and X-ray absorption methods, EXAFS and XANES, shows that the yellow pigment microparticles recrystallize from goethite to hematite crystal structure. Larger hematite particles are composed of small highly anisotropic nano-domains. No nanoclusters or amorphous iron oxide phases are detected. The valence state of iron atoms in the pigments is not affected by the strongly oxidative plasma environment. [Copyright &y& Elsevier]

Abstract: The most important parameter in reactive hydrogen plasma is the density of neutral hydrogen atoms. The density can be measured by different means including a variety of optical emission and absorption spectroscopy methods, titration and catalytic probes. Recently, it was shown that catalytic probes have some advantages over the other methods. The main advantage is the ability for real time measurement of the atom density. A catalytic probe was used to measure the H density in an afterglow of a plasma reactor. Plasma was created in a mixture of argon and hydrogen. At a constant H2 and Ar flow rates, the H density was found to increase with increasing power. At a low concentration of hydrogen in the gas mixture, saturation in the H density was observed. The lower the hydrogen concentration the lower the power at which the saturation was observed. At high hydrogen concentrations, no H saturation was observed. The results were explained with collision phenomena in ionized gases and heterogeneous recombination of H atoms on surfaces. [Copyright &y& Elsevier]

The technology of selective plasma etching was applied in order to study particle distribution in powder coatings. Etching was performed in pure oxygen plasma. Plasma parameters were measured with a double Langmuir probe and a catalytic probe. At the neutral gas temperature of approximately 50 °C, the electron temperature was approximately 60 000 °C, the density of positive ions approximately 1×1016 m-3, and the density of neutral oxygen atoms 2×1021 m-3. In order to prevent sample overheating, plasma was applied in time intervals of 20 s. The removal of the polymer matrix was accomplished within 2–4 min. After plasma treatment, the samples were analyzed with a scanning electron microscope. All the pigment and filler particles were left intact thus enabling the determination of the original distribution of the particles in the coating. [Copyright &y& Elsevier]

Low pressure inductively coupled plasma was investigated with a combination of two diagnostic techniques: catalytic probes and optical emission spectroscopy (actinometry). Three working gases were used: oxygen, oxygen–argon mixture and hydrogen. Concentrations of oxygen and hydrogen atoms were determined in a wide range of plasma parameters, with pressure ranging from 10 Pa to 70 Pa, applied power in the range from 50 to 250 W and at many different positions throughout the system (including the coil and afterglow in sample chamber). Concentrations of oxygen atoms were measured to be 1.3 × 10 15 cm −3 in the middle of the coil and 4 × 10 12 cm −3 in the regions of the chamber furthest from the coil. These spatially resolved concentrations are very important in plasma processing of materials, because radical concentrations over the sample determine plasma–material interactions. This work demonstrates that a relatively simple detection system can be practical and sufficiently successful in many plasma applications. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous hydrogenated carbon deposits are a present problem in fusion devices with carbon walls. They act as an unpredictable source of hydrogen retention and thus have to be regularly removed. In our experiment we studied removal of hard carbon deposits in an atmosphere of partially dissociated room temperature oxygen. The source of oxygen atoms was a radiofrequency glow discharge in oxygen at pressures in the vicinity of 100Pa. The etching efficiency was observed as surface emissivity variations. Etchings rates are compared to those measured in the discharge region in presence of charged particles. Etching rates in the discharge region are of the order of 1nm/s, etching rates in a neutral oxygen atmosphere were found to be strongly temperature dependent and reached the value of 10nm/s at 300°C. [Copyright &y& Elsevier]

Abstract: The quantitative method for the evaluation of the degree of pigment dispersion in powder coatings is described here. The quantitative information is obtained using selective oxygen plasma etching, scanning electron micrography and image analysis. This procedure was used in order to analyse the influences of the input power of the extrusion equipment on the pigment dispersion in powder coatings. The correlation between the particle size distribution graphs and the energy input during the extrusion process is discussed and compared to the colorimetric analysis. [Copyright &y& Elsevier]

Abstract: We present a study of the interaction of amorphous hydrogenated carbon deposits (a-C:H) with neutral oxygen atoms. Samples of a-C:H were exposed to an atomic oxygen rich atmosphere at surface temperatures from 473 K to 623 K. The source of atomic oxygen was microwave plasma, created in oxygen at pressures between 50 Pa and 200 Pa by means of a surfatron. The density of neutral oxygen atoms reached up to 4 ∙ 1021/m3. The densities of neutral atoms were measured by means of a catalytic probe. The erosion process was monitored by means of an infrared pyrometer. At each sample surface temperature, the erosion rates were found to linearly increase with the atomic oxygen density. This allowed us to calculate the reaction rate coefficient at corresponding surface temperatures. The reaction rate coefficient was found to increase exponentially with the sample surface temperature. [Copyright &y& Elsevier]