Improved properties of TiAlN coatings through the multilayer structure

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Short and long term surface chemistry and wetting behaviour of stainless steel with 1D and 2D periodic structures induced by bursts of femtosecond laser pulses

We investigate the short and long term wettability of laser textured stainless steel samples in order to better understand the interplay between surface topography and chemistry. Very different 1D and 2D periodic as well as non-periodic surface patterns were produced by exploiting the extreme flexibility of a setup consisting of five rotating birefringent crystals, which allows generating bursts of up to 32 femtosecond laser pulses with fixed intra-burst delay of 1.5 ps. The change of the surface morphology as a function of the pulse splitting, the burst polarization state and the fluence was systematically studied. The surface topography was characterized by SEM and AFM microscopy. The laser textured samples exhibited, initially, superhydrophilic behaviour which, during exposure to ambient air, turned into superhydrophobic with an exponential growth of the static contact angle. The dynamic contact angle measurements revealed a water adhesive character which was explained by XPS analyses of the surfaces that showed an increase of hydrocarbons and more oxidized metal species with the aging. The characteristic water adhesiveness and superhydrophobicity of laser textured surfaces can be exploited for no loss droplet reversible transportation or harvesting

Synthesis and Characterization of Rutile TiO2Nanopowders Doped with Iron Ions

Titanium dioxide nanopowders doped with different amounts of Fe ions were prepared by coprecipitation method. Obtained materials were characterized by structural (XRD), morphological (TEM and SEM), optical (UV/vis reflection and photoluminescence, and Raman), and analytical techniques (XPS and ICP-OES). XRD analysis revealed rutile crystalline phase for doped and undoped titanium dioxide obtained in the same manner. Diameter of the particles was 5–7 nm. The presence of iron ions was confirmed by XPS and ICP-OES. Doping process moved absorption threshold of TiO2into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence

Metal nanocrystals in amorphous silica matrix by the sol-gel process

Pd and Ag nanocrystals of diameter 1-30 nm embedded in amorphous silica matrix have been prepared by the sol-gel process. In order to correlate the preparation route to the structural and optical properties of the materials and to obtain a deeper insight in the formation and physical properties of the clusters, a detailed structural and optical characterization have been undertaken via transmission electron and high resolution electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy and differential scanning calorimetry. In the case of Pd and PdO, the sol-gel process has been modified by using organofunctional silanes. Thick film and uncracked bulk materials containing uniformly dispersed Pd nanocrystals are obtained by this technique after thermal treatment up to 400 degrees C. The Pd to PdO phase transformation following the annealing beyond 400 degrees C in air is also studied

The influence of hydrogen on the electrical properties of a-GaAs.

The electrical properties of hydrogenated amorphous gallium arsenide prepared by r.f. sputtering have been studied. ConductivitY measurements as a function of T evidence two different behaviours depending on the increasing (heating) or decreasing (cooling) T. Metastable effects are also evidenced at T < 360 K, probably linked to the diffusion of bonded hydrogen in the network. Several conductivity curves show a downward kink at T congruent-to 360 K. The presence of this kink has been explained using a model proposed by Spear and assuming the shift of the conduction band edge as a main contribution to the variation of the mobility gap. The Tauc optical gap, the activation energies of the conductivity and the hydrogen content in the network show a rapid increase when C(H) goes from 0 to 10% in the gas phase

STRUCTURAL CHARACTERIZATION OF HYDROGENATED AMORPHOUS GAAS

The electrical properties of hydrogenated amorphous gallium arsenide prepared by r.f. sputtering have been studied. ConductivitY measurements as a function of T evidence two different behaviours depending on the increasing (heating) or decreasing (cooling) T. Metastable effects are also evidenced at T < 360 K, probably linked to the diffusion of bonded hydrogen in the network. Several conductivity curves show a downward kink at T congruent-to 360 K. The presence of this kink has been explained using a model proposed by Spear and assuming the shift of the conduction band edge as a main contribution to the variation of the mobility gap. The Tauc optical gap, the activation energies of the conductivity and the hydrogen content in the network show a rapid increase when C(H) goes from 0 to 10% in the gas phase

Plasma-treated PET surfaces improve the biocompatibility of human endothelial cells.

Failures of small internal diameter vascular grafts have been caused by the lack of a stable endothelial lining to form on their artificial surfaces. Polymer surfaces can be optimized by means of proper treatment to allow a homogeneous and uniform coverage in artificial prosthesis applications. Several solutions were studied to improve cell attachment and growth on artificial materials. In the present study, polyethyleneterephthalate (PET) surfaces were treated by plasma processes with oxygen and ammonia and also in the presence of a gas mixture to verify the effect of functional groups grafting onto the endothelial cell growth. Related surface chemical modifications were investigated by X-ray photoelectron spectroscopy (XPS). Then using cytotoxicity and cytocompatibility tests, the biocompatibility of the modified PET surfaces was assessed by studying the behavior of human umbilical vein endothelial cells (HUVEC). The results showed that plasma- treated PET samples have no toxic effect on HUVEC. The cytocompatibility tests revealed an increase in cell growth with incubation time and the presence of well-spread and flattened cells (SEM analyses). Thus it is reported that plasma treatments can improve PET biocompatibility to HUVEC. (C) 2000 John Wiley and Sons, Inc. Failures of small internal diameter vascular grafts have been caused by the lack of a stable endothelial lining to form on their artificial surfaces. Polymer surfaces can be optimized by means of proper treatment to allow a homogeneous and uniform coverage in artificial prosthesis applications. Several solutions were studied to improve cell attachment and growth on artificial materials. In the present study, polyethyleneterephthalate (PET) surfaces were treated by plasma processes with oxygen and ammonia and also in the presence of a gas mixture to verify the effect of functional groups grafting onto the endothelial cell growth. Related surface chemical modifications were investigated by X-ray photoelectron spectroscopy (XPS). Then using cytotoxicity and cytocompatibility tests, the biocompatibility of the modified PET surfaces was assessed by studying the behavior of human umbilical vein endothelial cells (HUVEC). The results showed that plasma-treated PET samples have no toxic effect on HUVEC. The cytocompatibility tests revealed an increase in cell growth with incubation time and the presence of well-spread and flattened cells (SEM analyses). Thus it is reported that plasma treatments can improve PET biocompatibility to HUVEC

CdS and ZnS nanoparticles growth in different reaction media: Synthesis and characterization

In this work we report on the growth of cadmium sulfide and zinc sulfide nanocrystals by thermolysis, starting from a metal thiolate in a (i) solventless way, (ii) by a novel route in tryoctilphosphine oxide (TOPO), and (iii) by direct synthesis in a polystyrene matrix. The x-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the nanocrystals fabricated by the different methods are under optimized growth conditions single crystals of zincblende structure and of regular spherical shape. The average size was estimated to be between 2.0-3.0 nm with a size dispersion that depends on the synthesis route and is in the range between 10% and 20%, The XPS results indicate that for the nanoparticles obtained via solventless strategy the sulfur is present both as bonded to the metal atom and to the organic residue, while in the TOPO synthesized nanoparticles the sulfur signal has only one component associated to the metal-sulfide bond. The photoluminescence spectroscopy (PL) analysis of CdS crystals clearly evidences the typical emissions of nanosized zincblende CdS monocrystalline particles. Furthermore, the optical spectroscopy data indicate that the size distribution of the Cd-sulfide - TOPO nanoparticles seems to be generally larger than that ones grown directly in polymer matrix. For all the CdS samples, the metal-sulfide nanocrystals exhibit a trap-related radiative transition at about 2eV that can be attributed to the hole-electron recombination at particle surface defect-center

Formation of amorphous silicide nanoclusters in chromium- and titanium-implanted silica

Amorphous nanoclusters of chromium and titanium silicides have been synthesized by implanting 35 keV chromium and 30 keV titanium ions, at a fluence of 1X10(17) cm(-2) in amorphous silica. The cluster stoichiometries were [Cr]/[Si]=1.6+/-0.3 and [Ti]/[Si]=1.1+/-0.3, respectively, as obtained by energy dispersive spectroscopic x-ray microanalysis and confirmed by x-ray photoelectron spectroscopy analysis, Titanium-implanted ions are more reactive than chromium ones in terms of the formation of chemical bonds with silicon of the host silica matrix. (C) 1995 American Institute of Physics