Results 1 - 10 of 1392
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[en] To clarify the vague points appeared in the literature, it was discussed that fractal analysis of electrode surfaces based on the concept of 'diffusion toward electrode surfaces' is only able to monitor surface roughness in scales larger than 10 nm. When inspecting fractality in atomic scale (and even up to 10 nm), electrochemical measurements are not reliable due to the presence of surface defects, which affect the electrochemical reaction. In other words, for fractal analysis of electrode surfaces, the diffusion layer width which acts as yardstick length, should be sufficiently large, incomparable to the scale of atomic inhomogeneities. To this aim, the experiment time should be sufficiently long or the diffusion coefficient should be sufficiently large
[en] Highly conducting polymers have attracted much interest because of their potential applications in sensors and electronic devices. By the use of templates like porous membranes during polymerization conducting molecular wires can be formed with highly anisotropic properties which can be used as interconnecting layers in a three-dimensional (3D)-chip stacking. We focussed on two electrochemical polymerization (ECP) techniques to produce molecular wires based on polypyrrole (PPy) embedded in isolating porous polycarbonate membranes as self-supporting layers. The growth of the polymer through the membrane pores was investigated in order to achieve a good conductivity through the pores, but with a small cross-talk between them. A new polymerization technique based on a structured cathode has been developed in order to control the polymerization locally. By that technique micro-patterned membranes with separated conducting polymer wires could be produced
[en] Highlights: • We investigated the deposition mechanism of zirconium conversion layer on zinc. • In situ FTIR and electrochemical measurements are conducted. • The initial hydroxyl fraction plays an important role in the deposition process. • Deposition starts with hydroxyl removal by fluoride ions. • An increase of alkalinity adjacent to the surface promotes deposition of Zr. - Abstract: This study is focused on the deposition process of zirconium-based conversion layers on Zn surfaces. The analysis approach is based on a Kretschmann configuration in which in situ ATR-FTIR spectroscopy is combined with open circuit potential (OCP) and near surface pH measurements. Differently pretreated Zn surfaces were subjected to conversion treatments, while the Zr-based deposition mechanism was probed in situ. It was found that the initial hydroxyl fraction promotes the overall Zr conversion process as the near surface pH values are influenced by the initial hydroxyl fraction. Kinetics of the early surface activation and the subsequent Zr-based conversion process are discussed and correlated to the initial hydroxyl fractions.
[en] Several new materials and patterns are studied for the formation and etching of intraocular lenses (IOLs), in order to improve their optical properties, to reduce the diffractive aberrations and to decrease the incidence of posterior capsular opacification. The aim of this study is to investigate the use of UV (λ = 266 nm) laser pulses to ablate the intraocular lenses materials, and thus to provide an alternative to conventional surface shaping techniques for IOLs fabrication. Ablation experiments were conducted using various polymer substrates of hydrophobic acrylic IOLs and PMMA IOLs. We investigated the ablation efficiency and the morphology of the ablated area by imaging the surface modification with atomic force microscopy (AFM) and scanning electron microscopy (SEM). The morphological appearance of IOL samples reveals the effect of a photochemical and photothermal ablation mechanism.
[en] In this paper the optical-functional properties of integrated-optical waveguides in a planar polymer chip prepared by UV-laser irradiation have been investigated. Particularly the refractive index distribution of the waveguide is examined by a two-beam interferometric method. Also the waveguiding effect of this integrated-optical structure has been proved. The study shows that the refractive index depth profile strongly depends on the UV-irradiation dose. Several mostly independently occurring photochemical processes competing with one another can explain the formation and shape of the refractive index distribution
[en] The dynamic processes during ablation are studied by nanosecond-interferometry and shadowgraphy. Most commercial polymers exhibit poor laser ablation properties, therefore special triazene polymers, with superior ablation properties were developed. The photochemical active triazene group absorbs around 330 nm whereas the absorption around 200 nm is due to the photostable aromatic groups. The ns-interferometry shows that the etching of the triazene polymer starts and ends with the laser beam after irradiation at 193 and 308 nm. Shadowgraphy of the triazene polymer and polyimide reveal that the speed of the aerial shockwave increases with fluence and is higher for irradiation at 193 nm than for 308 nm. Shockwaves with equal or higher velocities are observed for the triazene polymer compared to polyimide
[en] Some applications of SIMS in conservation science, archaeometry and cosmochemistry are described. Ultra-low energy SIMS depth profiling and TOF-SIMS imaging are used to study the corrosion of low-lime glass vessels from the V and A museum. Static SIMS and focused ion beam (FIB) SIMS are used to study the effects of laser cleaning on museum artefacts. Archaeological glass from Raqqa, Syria is studied with FIB-SIMS and micrometeorite impacts on space vessels are studied with FIB and FIB-SIMS. The new analytical challenges provided to the SIMS community by these materials are presented and the ethical issues associated with sampling and destructive analysis discussed
[en] Highlights: • Patterning of multilayer graphene shell encapsulated gold nanoparticles (GNPs). • Binding of quantum dots to GNPs resulted in GNP-QD heterostructures. • The heterostructures were characterized for their electrochemical properties. - Abstract: A simple technique for patterning multilayer graphene shell encapsulated gold nanoparticles (GNPs) on the silicon substrate and their further surface decoration with semiconducting quantum dots (QDs) is reported. This leads to the fabrication of a novel silicon electrode decorated with GNP-QD hybrids or heterostructures. The morphology, structure, and composition of the GNPs and GNP-QD heterostructures were evaluated using microscopic and spectroscopic techniques. The heterostructures decorated silicon electrode was also evaluated for the electronic and electrochemical properties. The results showed that the electrical characteristics of the silicon substrate were significantly improved by decorating with GNPs and quantum dots. Furthermore, GNP-QD heterostructure electrode was observed to show significantly increased electrochemical charge transfer activity
[en] Highlights: • The urchin-like NiCo_2O_4 nanostructures are fabricated. • Growth mechanism is proposed based on the morphology evolution process. • The specific capacitance is 1484.1 F g"−"1 at the current density of 1 A g"−"1. • The capacitance retains 90.1% even after more than 2000 cycles. - Abstract: The urchin-like NiCo_2O_4 nanostructures were synthesized by a mild hydrothermal method. A possible growth mechanism is proposed based on the morphology evolution process upon reaction time. The effect of the concentration of metal salt on the electrochemical performance was investigated. The high electrochemical performance was achieved by optimizing the concentration. The corresponding specific capacitance is as high as 1484.1 F g"−"1 at the current density of 1 A g"−"1. Furthermore, the capacitance retains 90.1% even after more than 2000 cycles. The resulting high performance is due to the unique three-dimensional structure constructed by nanorings and nanowires, which increases the amount of electroactive sites and facilitates the electrolyte penetration and electron transfer
[en] Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.