V.M. Fuenzalida

Toward Tailor-Made Biocide Materials Based on Poly(propylene)/Copper Nanoparticles

A set of poly(propylene) composites containing different amounts of copper nanoparticles (CNP) were prepared by the melt mixed method and their antimicrobial behavior was quantitatively studied. The time needed to reduce the bacteria to 50% dropped to half with only 1 v/v % of CNP, compared to the polymer without CNP. After 4 h, this composite killed more than 99.9% of the bacteria. The biocide kinetics can be controlled by the nanofiller content; composites with CNP concentrations higher than 10 v/v % eliminated 99% of the bacteria in less than 2 h. X-ray photoelectron spectroscopy did not detect CNP at the surface, therefore the biocide behavior was attributed to copper in the bulk of the composite.

Hydrothermal ABO3 ceramic thin films

Abstract Complex oxide thin films of ABO3 type, with one or more different cations on the A site, were prepared on B-metal substrates using the hydrothermal method: barium zirconium oxide, BaZrO3 (BZ), on Zr; barium-strontium titanium oxide, (Ba,Sr)TiO3 (BST), and barium titanium oxide, BaTiO3 (BT), on Ti. The films were prepared in the 200–250°C temperature range using a mixture of 0.5NxBa(OH)2 and (1 - x)Sr(OH)2 solutions (x = 1 for BZ and BT, and x = 0.5 for BST). XPS characterization confirmed that the A cations were incorporated into the B-metal substrate, forming a complex oxide. Dielectric breakdown occurred at 10 MV m-1 in a BST film with an estimated 20 nm thickness. In a 110 nm BZ film the dielectric breakdown was observed at 20 MV m-1. BT breaks down near 6 MV m-1 in a 100 nm film. The dielectric properties exhibit sensitivity to relative humidity.

Water incorporation in BaTiO3 films grown under hydrothermal conditions

The influence of temperature on water incorporation into barium titanate films grown hydrothermally was investigated. The films were prepared using titanium foils that were immersed in 0.5 M barium hydroxide aqueous solutions for 4 h. Working temperatures were 100, 150 and 215°C. The samples were characterized by X-ray diffraction, Auger electron spectroscopy, forward recoil spectrometry and thermal desorption spectrometry. The latter showed that water was incorporated mainly in the molecular form and that this was favored at lower temperatures, leading to a slightly larger unit cell as has been observed in hydrothermal powders. Films grown at lower temperatures exhibited stronger XRD reflections.

Effect of Sulfate Content of Biomacromolecules on the Crystallization of Calcium Carbonate

Natural composite bioceramics such as bone, teeth, carapaces and shells contain organic and inorganic moieties, with the organic matrix components directly involved in the precise formation of these structures. We have previously shown that chicken eggshell contains two main sulfated polymers (proteoglycans), referred to as mammillan and ovoglycan which are involved in nucleation and growth of the eggshell calcite crystals. They differ on their anionic properties due to the carboxylate and sulfate content of their glycosaminoglycan component. Based on biological and biochemical evidences, the putative role of mammillan, a keratan sulfate proteoglycan, is in the nucleation of the first calcite crystals, while that of ovoglycan, a dermatan sulfate proteoglycan, is to regulate the growth and orientation of the later forming crystals of the chicken eggshell. In this communication, a systematic study of the influence of variable concentrations of glycosaminoglycans differing in their sulfation status on the morphology, size and number of calcium carbonate crystals after crystallization on microbridges from a calcium chloride solution under an atmosphere of ammonium carbonate at different pH is presented. Depending on the pH and concentration, the variation of sulfation status drastically changed the morphology, size and number of calcite crystals. The produced calcite particles with various morphologies are promising candidates for some novel materials with desirable shape- and texture-depending properties.

Extracellular Matrix Molecules Involved in Barnacle Shell Mineralization

Abstract : Austromegabalanus psillacus is a large (normally up to 30 cm high) sessile balanomorph barnacle from the coast of Chile and South Peru. Its hard shell is composed of twelve calcareous side plates, six parietes and six radii, joined in the form of a truncated cone opened at the top. Plates rest on a basal disk firmly cemented to the substratum. Although the crystalline microstructure of barnacles shell has been studied to some extent, its organic composition and the mechanisms governing the biomineralization of such highly ordered nanocomposite have remained obscure. By using X-ray diffraction, infrared spectrometry, SEM and TEM electron microscopy, histochemistry, immuno-histochemistry and -ultrastructure, biochemistry and a crystallization assay, we have studied the cell-shell interactions, the crystalline microstructure of the inorganic moiety and the localization of particular macromolecules, and tested their influence on crystallization. The mineral of the plates and basal disk was calcite showing a (104) preferential orientation. Plates were not solid but porous. While parietes have longitudinal canals (from the base to the apex), radii have transversal canals arranged parallel to the base. These canals are not in the center of the plates but displaced to the outside of the shell delimiting a thinner solid outer lamina and a thicker inner one. The inner lamina consisted of parallel calcified layers separated by organic sheets. These sheets showed autofluorescence and consisted of chitin surrounded by proteoglycans and of other minor proteins, which seems to be responsible for the fluorescent behaviour. These organic sheets were also organized as several concentric rings around the canals. The shell matrix obtained after decalcification, which surrounded the crystals, also contained a loose net of such proteoglycans. Mantle epithelial cells covered the entire surface of the inner side of the inner lamina and extend to the plate canals.

Nanostructures of crystalline molybdenum trioxide grown by condensation in a carrier gas.

Molybdenum trioxide nanostructures were grown by direct evaporation of MoO3 from a tungsten boat resistively heated in the presence of hydrogen or helium as carrier gas at pressures from 100 to 600 Pa. Crystalline structures such as, nanoribbons, nanofibers, nanoneedles and nanoparticles were obtained at source temperatures below 900 degrees C. On the other hand, at source temperatures above 1000 degrees C, nanoporous structures were obtained. The latter were found more often when hydrogen was used as carrier gas.

Fabrication of BaTiO3 Microstructures by Hydrothermal Growth

Barium titanate microstructures are fabricated on (100) silicon/platinum substrates coated with photoresist and titanium by combination of hydrothermal and lift-off techniques. The microstructures are well defined and adhere well to the substrate. The profiles of the line structure are twice as thick as the starting titanium structures due to the reaction of the titanium layer with the barium ions from the aqueous solution. Analysis by x-ray diffraction shows that the barium titanate grows in its cubic phase and that the titanium layer is not consumed completely by the hydrothermal reaction.

Tetragonal BaTiO3 thin films hydrothermally grown on TiO2 single crystals

Abstract Tetragonal BaTiO 3 films were prepared on single crystal TiO 2 substrates by the hydrothermal method. The films were grown in 0.5 M Ba(OH) 2 aqueous solutions at 150°C and 200°C during 4 h. X-ray diffraction analysis demonstrated the presence of polycrystalline BaTiO 3 in its tetragonal phase, in contrast to hydrothermally grown BaTiO 3 on metallic substrates, which usually results in the cubic phase under similar conditions. Rutherford backscattering measurements in the channeling mode showed that the barium ions did not occupy lattice positions and that there is not a sharp film–substrate interface. The diffusion range of the moving species — either Ti or Ba — was about 1 μ m, and the diffusion coefficient at 150°C was estimated to be about 10 −16 m 2 s −1 .

Pulsed deposition : model for the cluster size distribution after the first pulse

A model is presented for the evolution of the submonolayer cluster size distribution after the pulsed deposition of material onto a smooth surface at low temperature, which is annealed to promote diffusion and nucleation. The system is described by a set of Smoluchovsky equations and solved exactly for clusters of linear shape and numerically otherwise. The condensation exhibits a universal behavior, in which physical parameters such as diffusion coefficient and initial monomer density affect only the time scale of the process but not the final cluster size distribution.

Room-Temperature UHV-Deposited Titanium Monoxide Films on Oxidized Polycrystalline Copper

Polycrystalline copper films thicker than 100 nm were evaporated on silicon wafers with their native oxide under ultrahigh vacuum conditions leading to an rms roughness of ~2 nm of the copper film. X-ray photoelectron spectroscopy (XPS) revealed a clean copper surface with only traces of oxygen. The samples were exposed to air, leading to an oxide film consisting of CuO. TiO films were subsequently deposited onto the oxidized copper films from a resistively heated tungsten boat with the substrate at room temperature. The TiO films exhibited good adherence and were amorphous. XPS measurements revealed that the TiO films were contamination-free and that the first layers of TiO reduced the thin native oxide of the copper substrate from Cu(II) into Cu(I) or Cu(0) and transformed the TiO into TiO2 at the interface.