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

Structure imaging by atomic force microscopy and transmission electron microscopy of different light emitting species of porous silicon

The complex pattern of the nanowire skeletons of different light emitting porous silicon structures is investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Diffraction lines and dark field images are used to identify and determine the crystallite specimen long range order. TEM images give the size and particle orientation, and AFM images show a three-dimensional pattern formed by an interconnecting skeleton of particles. Near infrared photoluminescent porous silicon (0.005 Omega cm) structures show a skeleton of nanosized silicon aggregates which form domains of spatially oriented crystallites. For red photoluminescent samples (4.9 Omega cm) the electron diffraction spots are discontinuously split into tiny intensity maxima. The diameter of the wire structure forming porous silicon as measured by TEM allows us to estimate the distortion of the AFM images due to the finite size of the tip radius. A critical angle alpha(0)=2 arctan[K/(1 - K)](1/2), where K is the ratio of the height of the structure to the tip diameter was defined and it was shown that for structure walls steeper than alpha(0) the distortion may be substantial. (C) 1996 American Vacuum Society.1442432243

Self-opacifying aluminum phosphate particles for paint film pigmentation

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In silico evaluation of the Eucalyptus transcriptome

The expressed sequence tags (ESTs) produced in the Forests project provide an invaluable opportunity to assess the Eucalyptus transcriptome. Besides providing information on the different proteins produced by this plant, it is possible to infer gene expression profiles because non-normalized cDNA libraries were used. The EST frequency from any gene is correlated to the transcript levels in the tissues from which the cDNA libraries were constructed. The goal of this work was to identify Eucalyptus genes that showed either differential expression pattern or were ubiquitously expressed in the tissues sampled in the Forests project. Six robust statistical tests and very restrictive rules were applied to gain confidence in the in silico data aiming to avoid false positives. Several genes with interesting expression profiles were identified and some of them were validated by RT-PCR. Copyright by the Brazilian Society of Genetics.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq