The confinement of phonon propagation in TiAlN/Ag multilayer coatings with anomalously low heat conductivity

TiAlN/Ag multilayer coatings with a different number of bilayers and thicknesses of individual layers were fabricated by DC magnetron co-sputtering. Thermal conductivity was measured in dependence of Ag layer thickness. It was found anomalous low thermal conductivity of silver comparing to TiAlN and Ag bulk standards and TiAlN/TiN multilayers. The physical nature of such thermal barrier properties of the multilayer coatings was explained on the basis of reflection electron energy loss spectroscopy. The analysis shows that nanostructuring of the coating decreases the density of states and velocity of acoustic phonons propagation. At the same time, multiphonon channels of heat propagation degenerate. These results demonstrate that metal-dielectric interfaces in TiAlN/Ag coatings are insurmountable obstacles for acoustic phonons propagation

Interface-Induced Plasmon Nonhomogeneity in Nanostructured Metal-Dielectric Planar Metamaterial

Transformations of the electronic structure in thin silver layers in metal-dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metallic properties of silver in the thin films. A critical layer thickness of 23.5 nm associated with the development of quantum effects was determined by X-ray photoelectron spectroscopy. Scanning Auger electron microscopy of characteristic energy losses provided images of plasmon localization in the Ag layers. The nonuniformity of plasmon intensities distribution near the metal-nitride interfaces was assessed experimentally

Surface topography quantification of super hard abrasive tools by laser scanning microscopy

Non-conventional super hard abrasive tools are made of composite materials containing super hard grains, e.g., diamond or cubic boron nitride (CBN) grains, bound by a metallic constitutive phase. These tools are usually produced by means of sintering, and are widely applied in the abrasive machining processes of modern manufacturing, especially in precision machining. The abrasive grains, which induce the material removal processes, are embedded in the metallic binder. They emerge as a consequence of self-dressing, resulting in a self-sharping effect. Therefore, the cutting surface of the tool displays an irregular topography. Quantification of surface topography scenario may supply valuable information to evaluate and understand its correlation to wear mechanisms. In this study, an experimental protocol consisting of five steps: specimen preparation, surface scanning, image assembly, image digital processing and surface quantification, was proposed and validated by characterizing two CBN honing tools used for precision machining: B151/L2/2010/50 (B151) and B91/128/x44/35 (B91) CBN honing stones. It involved the use of laser scanning microscopy and digital imaging processing for assessing significant dimensional, geometrical, and positional properties of CBN grains at the surface of super hard abrasive tools. It was shown that surface topography quantification is an effective method to evaluate and obtain the defined parameters. However, smaller grains may require images with higher resolution; thus, scanning must be refined. Finally, a critical comparative analysis of the experimental results attained for the studied tools pointed out honing stone B91 as more appropriated than B151 one for achieving a higher machining quality of the workpiece.Peer ReviewedPostprint (author's final draft

Conditioning of hiPSC-derived cardiomyocytes using surface topography obtained with high throughput technology

Surface functionalization of polymers aims to introduce novel properties that favor bioactive responses. We have investigated the possibility of surface functionalization of polyethylene terephthalate (PET) sheets by the combination of laser ablation with hot embossing and the application of such techniques in the field of stem cell research. We investigated the response of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to topography in the low micrometer range. HiPSC-CMs are expected to offer new therapeutic tools for myocardial replacement or regeneration after an infarct or other causes of cardiac tissue loss. However, hiPSC-CMs are phenotypically immature compared to myocytes in the adult myocardium, hampering their clinical application. We aimed to develop and test a high-throughput technique for surface structuring that would improve hiPSC-CMs structural maturation. We used laser ablation with a ps-laser source in combination with nanoimprint lithography to fabricate large areas of homogeneous micron- to submicron line-like pattern with a spatial period of 3 µm on the PET surface. We evaluated cell morphology, alignment, sarcomeric myofibrils assembly, and calcium transients to evaluate phenotypic changes associated with culturing hiPSC-CMs on functionalized PET. Surface functionalization through hot embossing was able to generate, at low cost, low micrometer features on the PET surface that influenced the hiPSC-CMs phenotype, suggesting improved structural and functional maturation. This technique may be relevant for high-throughput technologies that require conditioning of hiPSC-CMs and may be useful for the production of these cells for drug screening and disease modeling applications with lower costs.Fil: Cortella, Lucas R. X.. Universidade de Sao Paulo; BrasilFil: Cestari, Idágene A.. Universidade de Sao Paulo; BrasilFil: Lahuerta, Ricardo D.. Universidade de Sao Paulo; BrasilFil: Arana, Matheus C.. Universidade de Sao Paulo; BrasilFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Rank, Andreas. Technische Universität Dresden; AlemaniaFil: Lasagni, Andrés F.. Technische Universität Dresden; AlemaniaFil: Cestari, Ismar N.. Universidade de Sao Paulo; Brasi

Design Rules for Laser‐Treated Icephobic Metallic Surfaces for Aeronautic Applications

Ice accretion on external aircraft surfaces due to the impact of supercooled water droplets can negatively affect the aerodynamic performance and reduce the operational capability and, therefore, must be prevented. Icephobic coatings capable of reducing the adhesion strength of ice to a surface represent a promising technology to support thermal or mechanical ice protection systems. Icephobicity is similar to hydrophobicity in several aspects and superhydrophobic surfaces embody a straightforward solution to the ice adhesion problem. Short/ultrashort pulsed laser surface treatments are proposed as a viable technology to generate superhydrophobic properties on metallic surfaces. However, it has not yet been verified whether such surfaces are generally icephobic under representative icing conditions. This study investigates the ice adhesion strength on Ti6Al4V, an alloy commonly used for aerospace components, textured by means of direct laser writing, direct laser interference patterning, and laser-induced periodic surface structures laser sources with pulse durations ranging from nano- to femtosecond regimes. A clear relation between the spatial period, the surface microstructure depth, and the ice adhesion strength under different icing conditions is investigated. From these observations, a set of design rules can be defined for superhydrophobic surfaces that are icephobic, too