Spatial Distribution Of Oxygen In Luminescent Porous Silicon Films

Transmission electron microscopy associated with electron energy loss spectroscopy imaging was used to determine structural spatial variations and compositional variation in heavily doped (0.006 Ω cm) and lightly doped (0.4 Ω cm) luminescent porous silicon films.64151986198

Isolated Submicrometer Filaments Formed By Silicon Anodization In Hf Solutions

Porous silicon nanocolumn formation is the result of the merging of nearest-neighbor nanopores. In this paper we describe isolated submicrometer filaments formed by silicon anodization in HF solutions. The merging of nearest-neighbor pores may result in the formation of isolated submicrometer silicon filaments. The filament formation is explained by a model which takes into account filament wall layer passivation by hydrogen atoms. The formation of one isolated wire structure is a consequence of the pore diameter enlargement resulting from the available area decrease with etching time.1435L100L102Uhlir, A., (1956) Bell Sys. Tech. J., 35, p. 333Canham, L.T., (1990) Appl. Phys. Lett., 57, p. 1046Beale, M.I.J., Benjamin, J.D., Uren, M.J., Chew, N.G., Cullis, A.G., (1985) J. Cryst. Growth, 73, p. 622Earwaker, L.G., Farr, J.P.G., Grzeszezyk, P.E., Sturland, I., Keen, J.M., (1985) Nucl. Instrum. Methods Phys. Rev., B9, p. 317Bomchil, G., Halimaoui, A., Herino, R., (1988) Microelectron. Eng., 8, p. 293Smith, R.L., Chuang, S.F., Collins, S.D., (1988) J. Electron. Mater., 17, p. 533Memming, R., Schwandt, G., (1966) Surf. Sci., 4, p. 109Cullis, A.G., Canham, L.T., (1991) Nature, 353, p. 335Teschke, O., Alvarez, F., Tessler, L.R., Kleinke, M.U., (1993) Appl. Phys. Lett., 63, p. 1927Teschke, O., Galembeck, F., Gonçalves, M.C., Davanzo, C.U., (1994) Appl. Phys. Lett., 64, p. 3590Teschke, O., Gonçalves, M.C., Galembeck, F., (1993) Appl. Phys. Lett., 63, p. 1348Scares, D.M., Dos Santos, M.C., Teschke, O., (1995) Chem. Phys. Lett., 242, p. 202Teschke, O., Dos Santos, M.C., Kleinke, M.U., Scares, D.M., Galvão, P.S., (1995) J. Appl. Phys., 78, p. 590Trucks, G.W., Raghavachari, K., Higashi, G.S., Chabal, Y.J., (1990) Phys. Rev. Lett., 65, p. 50

Method For Measuring Ohmic Resistance Of Solution Layers At Gas-evolving Electrodes

A method for measuring ohmic resistance of solution layers at gas-evolving electrodes was developed and tested. The method was applied to hydrogen and oxygen-evolving electrodes, and the resistance of their adjacent solution layers (for a 9 mm electrode separator gap) causes a negligible IR drop. For 3 mm gaps at a current density of 300 mA/cm2, the IR drop of the solution layer increases to 25 mV. Contact resistance at the various electrode connections are shown to have a measurable contribution which increases with electrolysis time.13841028103

Pattern Formation On Aluminum Electrodes

The mechanisms of pattern formation on anodized aluminum electrodes in contact with various acid solutions were investigated. The mechanism is related to solute concentration inhomogeneities at the film-solution interface. The size of cells forming the structure was determined experimentally and successfully matched with a recently developed model.13892763277

Wettability Gradients On Anodized Aluminum Effects Of Surface Chemical Reactions

Wettability variation of aluminum electrode surfaces was determined using a Wilhemly-type apparatus, in which the pull force exerted by the electrolyte solution on the electrode was measured at each switching of the electrode potential, for a periodically reversed step potential. The data obtained for aluminum and amalgamated electrodes show that metal-liquid surface tension is sensitive to the applied potential mainly through its effect on the chemical composition of the interface. The gradient of wettability induced by chemical reactions generates a displacement of the meniscus during the periodic polarization pulses. Wettability of aluminum surfaces in contact with H2SO4 solutions depends on the acid concentration, in agreement with previous results for iron-sulfuric acid systems.137378178

Time Resolved Photoluminescence Of Porous Silicon: Evidence For Tunneling Limited Recombination In A Band Of Localized States

Time resolved photoluminescence of porous silicon at room temperature was measured for several emission energies under 2 ns nitrogen laser excitation. For each emission energy studied there is a broad distribution of lifetimes extending over a few decades. The mean value of the distribution varies with the emission energy, from 3 (2.77 eV) to 50 μs (1.96 eV). The results can be explained by assuming a tunneling limited recombination mechanism between bands of localized states. We associate this behavior with a superficial disordered Si:O:H compound rather than with quantum confinement effects.62192381238

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

EFFECT OF PTFE COVERAGE ON THE PERFORMANCE OF GAS EVOLVING ELECTRODES

13151095109

Buckling Of Anodic Films. A Mechanism For The Breakdown Of Coatings On Aluminum Wires

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Oxide layer mechanical instability on anodized aluminum is reported. The striated structure is formed by a regular arrangement of straight lines parallel to the rod axis. A special cell with an axially symmetric current distribution was constructed in order to generate an isotropic stress distribution. The pattern are only formed when the anodization charge density is larger than a critical value. Our results show that film stress values are a function of the anodizing current density.1392L26L27CAPES; São Paulo Research Foundation; FAPESP; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP