Rodrigo Espinoza-González

Plasmon-enhanced optical absorption with graded bandgap in diamond-like carbon (DLC) films

Diamond-like carbon (DLC) films with tunable optical bandgap (Eg) were successfully deposited on glass and n-Si (100) substrates by radio frequency (RF)-sputtering technique in different argon (Ar) and acetylene (C2H2) plasmas. The bandgap of the films can be tuned from 1.41 to 1.28xa0eV, which correlates with the sp2 content, which increases from 56.3 to 63.7xa0%, respectively. The different ratios of sp2/sp3 lead to different bandgaps of the DLC films. Plasmonic nanoparticles of silver (Ag) were also embedded in the DLC matrix by reactive magnetron sputtering to study the enhancement of light absorption in DLC films. The absorption coefficient significantly increased when the DLC films were incorporated with 10 at.% of silver nanoparticles. Raman and X-ray photoelectron spectroscopy (XPS) studies were utilized to determine the bonding nature and sp2/sp3 ratios of DLC–Ag films.

Mechanochemical Processing of CaCu3Ti4O12 with Giant Dielectric Properties

The dielectric properties of CaCu3Ti4O12 (CCTO) ceramic prepared by mechanochemical synthesis (MCS) were investigated. The effect on dielectric properties of ball-to-powder weight ratio and milling time was investigated and compared to the behavior of CCTO prepared by conventional solid state reaction (CSSR). CCTO ceramic was partially obtained after 6h of the milling process, while complete transformation was obtained during the sintering step of milled powders. It was shown that the dielectric properties of CCTO processed by MCS are dramatically improved compared with samples prepared by CSSR.

Phosphate favors the biosynthesis of CdS quantum dots in Acidithiobacillus thiooxidans ATCC 19703 by improving metal uptake and tolerance

Recently, we reported the production of Cadmium sulfide (CdS) fluorescent semiconductor nanoparticles (quantum dots, QDs) by acidophilic bacteria of the Acidithiobacillus genus. Here, we report that the addition of inorganic phosphate to Acidithiobacillus thiooxidans ATCC 19703 cultures favors the biosynthesis of CdS QDs at acidic conditions (pH 3.5). The effect of pH, phosphate and cadmium concentrations on QDs biosynthesis was studied by using Response Surface Methodology (RSM), a multivariate technique for analytical optimization scarcely used in microbiological studies to date. To address how phosphate affects intracellular biosynthesis of CdS QDs, the effect of inorganic phosphate on bacterial cadmium-uptake was evaluated. By measuring intracellular levels of cadmium we determined that phosphate influences the capacity of cells to incorporate this metal. A relation between cadmium tolerance and phosphate concentrations was also determined, suggesting that phosphate participates in the adaptation of bacteria to toxic levels of this metal. In addition, QDs-biosynthesis was also favored by the degradation of intracellular polyphosphates. Altogether, our results indicate that phosphate contributes to A. thiooxidans CdS QDs biosynthesis by influencing cadmium uptake and cadmium tolerance. These QDs may also be acting as a nucleation point for QDs formation at acidic pH. This is the first study reporting the effect of phosphates on QDs biosynthesis and describes a new cadmium-response pathway present in A. thiooxidans and most probably in other bacterial species.