Search

Saddle points on high-dimensional potential energy surfaces (PES) play a determining role in the activated dynamics of molecules and materials. Building on approaches dating back more than 50 years, many open-ended transition-state search methods have been developed to follow the direction of negative curvature from a local minimum to an adjacent first-order saddle point. Despite the mathematical justification, these methods can display a high failure rate: using small deformation steps, up to 80% of the explorations can end up in a convex region of the PES, where all directions of negative curvature vanish, while if the deformation is aggressive, a similar fraction of attempts lead to saddle points that are not directly connected to the initial minimum. In high-dimension PES, these reproducible failures were thought to only increase the overall computational cost, without having any effect on the methods' capacity to find all saddle points surrounding a minimum. Using activation-relaxation technique nouveau (ARTn), we characterize the nature of the PES around minima, considerably expanding on previous knowledge. We show that convex regions can lie on activation pathways and that not exploring beyond them can introduce significant bias in the saddle-point search. We introduce an efficient approach for traversing the convex regions, almost eliminating exploration failures, while multiplying by almost 10 the number of identified unique and connected saddle points as compared to the standard ARTn, thus underlining the importance of correctly handling convex regions for completeness of saddle point explorations. [ABSTRACT FROM AUTHOR]

Hard coatings are commonly used in decorative applications due to their attractive colors and high wear resistance. In most cases only intrinsic colors of the coatings are exploited. Such colors are determined by the stoichiometry of the coating and can be varied only in a limited range. We demonstrate a more flexible concept of color design by utilizing the interference effect in semi-transparent and reflective materials. In this design a thin film of partially transparent hard coating material is deposited over a material with specific reflectivity. Such construction enables wider color control since the interference-based colors can be tuned by the thickness of the interference layer and by the optical constants of the thin film and the reflective substrate. In this work such principle is demonstrated with AlTiN. A single-layer of AlTiN was deposited by DC magnetron sputtering on substrates with different reflectivities. Colors of high saturation, ranging from yellow, pink, violet to blue, were prepared by varying the thickness of AlTiN in the range of 20-55 nm. Optical properties were studied by spectrophotometry and ellipsometry. Only small color shifts were measured with the angle of observation. Interference-based color design is further demonstrated on the tools with complex geometry combining protective and decorative functionality of the coating. A uniform blue color was prepared in an industrial deposition system on drills of different sizes. [ABSTRACT FROM AUTHOR]

Abstract: Molybdenum blue-type materials are usually obtained by partially reducing MoVI+ in acidic solutions, while in the presented method it is formed in ethanol solution of exfoliated MoS2 nanotubes, where the MoS2 flakes are the preferential location for their growth. Material was investigated by means of scanning electron and atomic force microscopy, showing the structure and self assembly, while also confirming that it is stable in high vacuum with molecules as small as 1.6nm and the agglomerates of few tens of nanometres. The ultraviolet–visible and photoelectron spectrometry show the change in absorption properties and oxidation states from MoS2 structure to molybdenum blue, while the presence of sulphur suggests that this is a new type of molybdenum blue material. [Copyright &y& Elsevier]

Silicon paints were prepared from yellow, ochre, dark ochre, green and blue pigments. To improve the solar absorptance, as, of these coatings, an existing black paint was admixed in different ratios. The optical properties of the mixed paints thus formed are expressed in terms of the Kubelka–Munk absorption and scattering coefficients in the spectral region 400–17000 nm. The scattering coefficient obtained for all paints was essentially equal. In the visible region the absorption coefficient follows the spectral characteristics of each respective colour. In the infrared absorption at ∼9000 nm and above 12000 nm are seen in all cases which result in a thickness-dependent increase of the thermal emittance, eT, of the coating. The metric chroma (Cab*) and lightness (L*) in CIELAB colour space were calculated for wide-angle observer in average daylight conditions. A range of non-black spectrally selective solar absorber surfaces with as>0.8 and eT<0.3 have been prepared with L*<45 and Cab*<10. [Copyright &y& Elsevier]

Metallic paints consist of metallic flakes dispersed in a resinous binder, i.e. a light-element polymer matrix. The spatial distribution and orientation of metallic flakes inside the matrix determines the covering efficiency of the paint, glossiness, and its angular-dependent properties such as lightness flop or color flop (two-tone). Such coatings are extensively used for a functional (i.e. security) as well as decorative purpose. The ion microbeam analysis of two types of silver paint with imbedded metallic flakes has been performed to determine the spatial distribution of the aluminum flakes in paint layer. The average sizes of the aluminum flakes were 23 μm (size distribution 10–37) and 49 μm (size distribution 34–75), respectively. The proton beam with the size of 2×2 μm2 at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al Kα map shows lateral distribution of the aluminum flakes, whereas the RBS slicing method reveals tomograms of the flakes in uppermost 7 μm of the pigment layer. The series of point analysis aligned over the single flake reveal the flake angle in respect to the polymer matrix surface. The angular sensitivity is well below 1 angular degree. [Copyright &y& Elsevier]

Presents information on a study which investigated the relationship between the macroscopic properties of plasma-enhanced chemical vapour deposition silicon nitride and oxynitride layers. Details of experimental procedures and calculations; Conclusions.

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]

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]

The degradation of Staphylococcus aureus bacteria during treatment with neutral oxygen atoms was monitored by scanning electron microscopy. Experiments were performed in an afterglow chamber made from borosilicate glass. The source of oxygen atoms was remote inductively coupled radiofrequency oxygen plasma. The density of atoms at the samples was 8×1020 m-3. The treatment was performed at room temperature. The first effect was the removal of dried capsule. Capsule on exposed parts of bacteria was removed after receiving the dose of 6×1023 at./m2, while the parts of capsule filling the gaps between bacteria were removed after receiving the dose of 2.4×1024 m-2. After removing the capsule, degradation continued as etching of bacterial cell wall. The etching was rather nonuniform as holes with diameter of several 10 nm were observed. The cell wall was removed after receiving the dose of about 7×1024 m-2. The etching probabilities were about 2×10-5 for the capsule and 2×10-6 for the cell wall. The results were explained by different compositions of capsule and the cell wall. [ABSTRACT FROM AUTHOR]

Abstract: Interaction of neutral hydrogen atoms with the layer of hydrogenated carbon–tungsten composite was studied. A 1μm thick layer was prepared by sputter deposition from C and WC-targets in Ar/C2–H2 gas mixture. After deposition the samples were treated in weakly ionized highly dissociated hydrogen plasma created in a microwave discharge at a power of 1kW. The gas flow was 13l/h and pressure was 90Pa. Temperature of the samples during treatment was about 850K. After plasma treatment the samples were analyzed by AES (Auger electron spectroscopy) depth profiling, XPS (X-ray photoelectron spectroscopy) and SEM (scanning electron microscopy). It was found that during hydrogen plasma treatment selective etching of the C–W layer occurred. Carbon was preferentially removed from the C–W layer, and after about 10min of treatment practically only tungsten with a huge porosity was detected. [Copyright &y& Elsevier]

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]