Search results for "Surfaces"
showing 10 items of 2837 documents
Influence of Anodic and Thermal Barrier Layers on Physicochemical Behavior of Anodic TiO2 Nanotubes
2011
Electrochemical and photo-electrochemical behavior of self-organized TiO2 nanotubes formed in organic solvents have been studied by taking into account the formation of new barrier layers beneath nanotubes either due to the anodic polarization in aqueous solutions or air exposure during high temperature annealing. It has been shown that before annealing, electrochemical and photoelectrochemical answers are dominantly controlled by the physicochemical properties of the anodic barrier layer. Annealing in air at sufficiently high temperatures changes the initial amorphous structure of as-prepared nanotubes and forms a new oxide layer below them due to thermal oxidation of underneath titanium. …
Positron Microscopy Studies of Wear Tracks on a Copper Surface
2014
Positron microscopy was used for studies of defects induced by ball indentation or sliding on the surface of well-annealed copper samples. A focused positron beam of 24.5-keV energy was used to scan the deformed region of the indenter impression, and measurements of the annihilation line parameter were performed. In the case of ball indentation, the measured defect distribution correlates well with the von Mises stress distribution of the Hertz contact and the von Mises yield criterion. For the wear track produced by pin on disc dry sliding, an asymmetric defect distribution near the wear track is observed. It indicates the presence of a tangential force that additionally deforms the sample.
Tailoring of the Solid State Properties of Al–Nb Mixed Oxides: A Photoelectrochemical Study
2013
Al–Nb containing mixed oxides were grown by anodizing sputter-deposited Al–Nb alloys of different compositions. A photoelectrochemical investigation was carried out in order to estimate the band gap, flat band potential, and conductivity type of these oxides as a function of their composition. The dependence of the band gap on the composition of mixed sp–d metal oxides has been rationalized by using a semiempirical correlation between the difference of electronegativity and band gap of oxides proposed in the literature some years ago and recently tested for regular d–d metal mixed oxides. The band gap increase observed as a function of Al content into the oxides seems mainly depending on th…
Luminescence of Eu ion in alumina prepared by plasma electrolytic oxidation
2015
Abstract Eu ion luminescence in aluminium oxide nanocrystals and layers prepared by plasma electrolytic oxidation (PEO) are investigated in this study. The Eu ion in PEO coatings has intense luminescence allowing such material to be used for preparation of various phosphor materials. In this study, Eu ion doped coatings were prepared with two methods: anodization and pulsed bipolar plasma electrolytic oxidation. Also, for comparative studies, alumina nanocrystals with the same amount of Eu ions were prepared using Sol Gel and molten salts methods. Obtained Eu-doped coatings were studied using luminescence methods. Typical Eu ion luminescence bands were observed, however intensity and spectr…
Ultrathin Anodic Aluminum Oxide Membranes for Production of Dense Sub-20 nm Nanoparticle Arrays
2014
We present a systematic study of membrane structure (pore diameter and arrangement) in anodized aluminum oxide (AAO) layers obtained by anodization voltages 8-20 V in sulfuric and 15-40 V in oxalic acid electrolyte solutions. Anodization of bulk aluminum in sulfuric acid at 10 V potential was found to be optimal for production or ultrathin freestanding membranes with pore diameter in sub-20 nm range. The developed process with slow electrochemical reaction results in AAO membranes with thickness below 70 nm. The minimum required time for formation of continuous AAO membrane was determined and influence of electrolyte concentration on pore diameter in membrane after barrier layer removal ana…
Characterizing the Glassy Phase of a Statistical Copolymer Monolayer
1999
Monolayers of a statistical copolymer with a poly(methacrylate) chain and hydrophilic and hydrophobic side groups are investigated at the air/water interface. The isotherms suggest a fluid and a frozen phase. With in-situ X-ray reflectivity the monolayer thickness is determined to be 2.5 nm or less. The shear viscosity in the fluid phase is extremely high yet can be described in the framework of the free area model. However, the parameter which characterizes the overlap of holes available for a diffusing monomer unit is a factor of 2 higher than expected, suggesting local diffusion barriers formed by nanosized clusters. In the glassy phase single-molecule fluorescence shows anomalous diffus…
Synthesis and Characterization of Nanostructured Cobalt Hexacyanoferrate
2010
Cobalt hexacyanoferrate (CoHCF) nanoparticles have been synthesized by mixing aqueous solutions of K3Fe(CN)6 and CoCl2 under vigorous stirring at different temperatures and following two different procedures, drop-by-drop or immediate mixing. The resulting CoHCF nanoparticles, with dimensions of several tens of nanometers, were characterized using TEM, SEM-EDX, IR, and XRD. Their electrochemical behavior was investigated in comparison with the CoHCF powder bulk compound. The CoHCF nanoparticles exhibit an electrochemically driven conversion to the bulk one that has been investigated by a chemometric approach in order to establish the best synthetic parameters. The rate and the degree of con…
Damping by Bulk and Shear Viscosity of Confined Acoustic Phonons for Nanostructures in Aqueous Solution
2007
International audience; A nanoparticle in aqueous solution is modeled as a homogeneous elastic isotropic continuum sphere in contact with an infinite viscous compressible Newtonian fluid. The frequencies and damping of the confined vibrational modes of the sphere are calculated for the material parameters of a CdSe nanoparticle in water and a poly(methyl methacrylate) nanosphere in water. Although the effects of viscosity are found to be negligible for macroscopic objects, for nanoscale objects, both the frequency and damping of the vibrational modes are significantly affected by the viscosity of the liquid. Furthermore, both shear viscosity and bulk viscosity play an important role. A mode…
Morphology, physical properties, silver release, and antimicrobial capacity of ionic silver-loaded poly(l-lactide) films of interest in food-coating …
2014
In the present study, silver ions were incorporated into a poly-(l-lactide) (PLA) matrix by a solvent casting technique using different solvents and glycerol as plasticizer. The effect of the different formulations on the morphology, thermal, mechanical and color properties were first evaluated. Additionally, a thorough study of the silver ions release to an aqueous environment was also monitored over time by anodic stripping voltammetry and correlated with the antimicrobial performance against S. enterica. The incorporation of silver contents of up to 1 wt % did not affect morphology, thermal or mechanical properties of the films. A sustainable, antibacterial effectiveness was found for th…
Sharing of Na+ by Three −COO– Groups at Deprotonated Carboxyl-Terminated Self-Assembled Monolayer-Charged Aqueous Interface
2018
By combining theoretical calculations and experimental observations, we show that Na+ can be shared by three charged −COO– groups of the deprotonated carboxyl-terminated self-assembled monolayers i...