Etching Technique For Transmission Electron Microscopy Observation Of Nanostructure Of Visible Luminescent Porous Silicon

We present a special configuration for the electrochemical etching of silicon, in which thin samples suitable for direct transmission electron microscopy observation are produced. This technique allows the observation of images of an irregular matrix of pores and individual columnlike structures with a ∼15 Å cross-sectional diameter. These images show that the preferential etching directions are the projections of the {100} planes on the (111) plane for the etched <111≳-oriented silicon. The large pore (≳50 nm diam) axis orientation is independent of the preferential etching direction and is parallel to the etching current direction.63101348135

Supramolecular ionics: electric charge partition within polymers and other non-conducting solids

Electrostatic phenomena in insulators have been known for the past four centuries, but many related questions are still unanswered, for instance: which are the charge-bearing species in an electrified organic polymer, how are the charges spatially distributed and which is the contribution of the electrically charged domains to the overall polymer proper-ties? New scanning probe microscopies were recently introduced, and these are suitable for the mapping of electric potentials across a solid sample thus providing some answers for the previous questions. In this work, we report results obtained with two of these techniques: scanning electric potential (SEPM) and electric force microscopy (EFM). These results were associated to images acquired by using analytical electron microscopy (energy-loss spectroscopy imaging in the transmission electron microscope, ESI-TEM) for colloid polymer samples. Together, they show domains with excess electric charges (and potentials) extending up to hundreds of nanometers and formed by large clusters of cations or anions, reaching supramolecular dimensions. Domains with excess electric charge were also observed in thermoplastics as well as in silica, polyphosphate and titanium oxide particles. In the case of thermoplastics, the origin of the charges is tentatively assigned to their tribochemistry, oxidation followed by segregation or the Mawell-Wagner-Sillars and Costa Ribeiro effects.73449551

Systematic study of luminescent properties of new lanthanide complexes using crown ethers as ligand

AbstractThis is a report on the synthesis, characterization and spectroscopic study of 24 lanthanide-crown ether coordination compounds, where Eu(III), Tb(III) and Gd(III) were complexes to 12-crown-4 (12C4), 15-crown-5 (15C5), 1,10-phenanthroline (phen) and 2,2′-dipyridyl (dipy). The compounds were synthesized in an ethanol/acetone solution at room temperature and analyzed using CHN elemental analysis and infrared, absorption and emission spectroscopies. The polarizability that the ligand exerts on the emission process was verified and found remarkable. The Eu-15C5-phen complex showed the highest quantum efficiency (71.6%) because of its low non-radiative rate and highest polarizability with reference to the ligands system

EFFECT OF PTFE COVERAGE ON THE PERFORMANCE OF GAS EVOLVING ELECTRODES

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Photoacoustic Characterization Of A Two-layer System

In this paper the use of the so-called open photoacoustic cell for thermal characterization of two-layer systems of variable thickness is described. It is shown that the thermal diffusivity as well as the thermal conductivity are completely determined, based upon the effective sample model widely used in heat-transfer problems.70117046705

On surface plasmons in porous silicon: Measurements of the electron energy loss in etched silicon nanocrystals

Surface plasmons resulting from the interaction of the electron beam of a transmission electron microscope with porous silicon nanoparticles were measured. The inelastic scattering of fast electrons in H-covered silicon nanocylinders shows a peak at similar to 5.5 eV. A gradual decrease of the first and second order plasma volumetric absorption simultaneous with a constant surface mode absorption amplitude was measured for decreasing silicon-slab thicknesses, Competitions between bulk and surface effects show, for the volume mode peak at 16.9 eV, a damping factor increase of similar to 5 eV. The measured silicon particle diameter was similar to 15 Angstrom and a value of the dielectric constant is estimated from the surface plasmon data at 8.5, which is in agreement with recent theoretical work on the modified dielectric constant in quantum confined systems. (C) 1996 American Institute of Physics.69220620

Wettability Effect On The Corrosion Kinetics Of Iron Anodes In Sulfuric Acid Solutions

The interdependence of electrode wetting and electrode corrosion rate was studied for the iron anode in aqueous sulfuric acid solutions. The effects of acid solution concentration and surface-active agents on the corrosion rate and passive-active transition current oscillation amplitude were measured. The results show that both are dependent on the electrode wetting. The electrode wettability is shown to change as a function of time which results in convective liquid displacement around the electrode and on variable corrosion rates.13592188219

BUCKLING OF ANODIC FILMS ON ALUMINUM - DETERMINATION OF PLASTIC-DEFORMATION ENERGY OF COATINGS

The mechanical instability of oxide layers on anodized aluminum generates a regular arrangement of straight lines parallel to the cylindrical electrode axis. This is analyzed using Euler's equation for buckling of thin cylindrical shells under compressive forces, due to volume expansion concurrent with metal-oxide formation. The coating critical stress is determined as well as the energy dissipated by plastic deformation of the anodic coating. Most of the energy associated with compressive stress of the oxide film is dissipated by plastic deformation.14061667167

Photoacoustic Monitoring Of Magnetite-crystal Formation From Iron(iii) Hydroxide Acetate: Comparison With Esr Results

The formation of crystalline magnetite by 1-h heat treatment of iron(III) hydroxide acetate is described. This amorphous-crystalline solid transformation is monitored by electron-spin resonance and photoacoustic spectroscopies. No significant changes were detected for samples heated below 190 °C. Above this temperature both techniques presented results following a definite pattern, namely, the enhancement of ion mobility leading to particle growth and crystallization for a temperature up to 240 °C and the onset of magnetic ordering of magnetite near this temperature.65125150515

MECHANICAL AND CURRENT OSCILLATIONS IN CORRODING ELECTRODES

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