J. Hernández-Torres

Biocompatibility and Surface Properties of TiO2 Thin Films Deposited by DC Magnetron Sputtering

We present the study of the biocompatibility and surface properties of titanium dioxide (TiO2) thin films deposited by direct current magnetron sputtering. These films are deposited on a quartz substrate at room temperature and annealed with different temperatures (100, 300, 500, 800 and 1100 °C). The biocompatibility of the TiO2 thin films is analyzed using primary cultures of dorsal root ganglion (DRG) of Wistar rats, whose neurons are incubated on the TiO2 thin films and on a control substrate during 18 to 24 h. These neurons are activated by electrical stimuli and its ionic currents and action potential activity recorded. Through X-ray diffraction (XRD), the surface of TiO2 thin films showed a good quality, homogeneity and roughness. The XRD results showed the anatase to rutile phase transition in TiO2 thin films at temperatures between 500 and 1100 °C. This phase had a grain size from 15 to 38 nm, which allowed a suitable structural and crystal phase stability of the TiO2 thin films for low and high temperature. The biocompatibility experiments of these films indicated that they were appropriated for culture of living neurons which displayed normal electrical behavior.

Cytotoxicity Evaluation of Anatase and Rutile TiO2 Thin Films on CHO-K1 Cells in Vitro

Cytotoxicity of titanium dioxide (TiO2) thin films on Chinese hamster ovary (CHO-K1) cells was evaluated after 24, 48 and 72 h of culture. The TiO2 thin films were deposited using direct current magnetron sputtering. These films were post-deposition annealed at different temperatures (300, 500 and 800 °C) toward the anatase to rutile phase transformation. The root-mean-square (RMS) surface roughness of TiO2 films went from 2.8 to 8.08 nm when the annealing temperature was increased from 300 to 800 °C. Field emission scanning electron microscopy (FESEM) results showed that the TiO2 films’ thickness values fell within the nanometer range (290–310 nm). Based on the results of the tetrazolium dye and trypan blue assays, we found that TiO2 thin films showed no cytotoxicity after the aforementioned culture times at which cell viability was greater than 98%. Independently of the annealing temperature of the TiO2 thin films, the number of CHO-K1 cells on the control substrate and on all TiO2 thin films was greater after 48 or 72 h than it was after 24 h; the highest cell survival rate was observed in TiO2 films annealed at 800 °C. These results indicate that TiO2 thin films do not affect mitochondrial function and proliferation of CHO-K1 cells, and back up the use of TiO2 thin films in biomedical science.

Compliant MEMS mechanism to extend resolution in Fourier transform spectroscopy

A complaint mechanism to extend resolution in the Fourier Transform Spectroscopy (FTS) technique has been designed, fabricated and tested. The mechanism based on the complaint mechanical design strategy has not mobile parts and was fabricated in MEMS technology in a Bosch Process. When this mechanism is used to displacing the mobile mirror in a FTS setup, an extended range travel for the reference mirror is achieved; thus, the optical path difference and hence the resolving power of the FTS system is increased. The fabricated device has dimensions of 5400x4200x400 Microns at the large, width and thickness respectively, with an aspect ratio about 10. Numerical simulations with ANSYS Software were developed to get the Stress limits and the input and output displacements, the mechanical gain and the resonance frequency of the device. Experimental results in both the forced and dynamical regime are presented. It is found that in the dynamical regime when the device is operated at its resonance frequency it exhibits a higher mechanical gain several times its gain in the forced regime.

Production, chemical, physical and technological properties of antioxidant dietary fiber from pineapple pomace and effect as ingredient in sausages

ABSTRACT In this study, fresh and steamed under pressure (SPP) pineapple pomace were used to produce dietary fiber concentrates (DFCs) dried by freeze-drying or hot air-drying. Chemical, physical and technological properties were determined to select one pineapple DFC (PDFC) and to evaluate its mixture effect with meats on characteristics of Vienna-type sausages. The PDFC produced from SPP and hot air-dried (SPDFC-HD) had the highest content of DF, carotenoids, polyphenols such as gallic, cinnamic and p-coumaric acids, antioxidant capacity and hydration properties. Microstructural analysis evidenced a cell wall disruption of the PDFCs matrix by the effect of processing. The cubic model equations showed that with the increase in SPDFC-HD in the ternary mixture, a reducing effect on nitrites, moisture, shear force and shrinkage was obtained in sausages, while carotenoids and antioxidant polyphenols increased. This study demonstrated that SPDFC-HD was produced with characteristics to be used as ingredient in potential functional sausages.

Photoreflectance and Raman Study of Surface Electric States on AlGaAs/GaAs Heterostructures

Photoreflectance (PR) and Raman are two very useful spectroscopy techniques that usually are used to know the surface electronic states in GaAs-based semiconductor devices. However, although they are exceptional tools there are few reports where both techniques were used in these kinds of devices. In this work, the surface electronic states on AlGaAs/GaAs heterostructures were studied in order to identify the effect of factors like laser penetration depth, cap layer thickness, and surface passivation over PR and Raman spectra. PR measurements were performed alternately with two lasers (532 nm and 375 nm wavelength) as the modulation sources in order to identify internal and surface features. The surface electric field calculated by PR analysis decreased whereas the GaAs cap layer thickness increased, in good agreement with a similar behavior observed in Raman measurements ( ratio). When the heterostructures were treated by Si-flux, these techniques showed contrary behaviors. PR analysis revealed a diminution in the surface electric field due to a passivation process whereas the ratio did not present the same behavior because it was dominated by the depletion layers width (cap layer thickness) and the laser penetration depth.

Photoluminescence and Raman Spectroscopy Studies of Carbon Nitride Films

Amorphous carbon nitride films with N/C ratios ranging from 2.24 to 3.26 were deposited by reactive sputtering at room temperature on corning glass, silicon, and quartz as substrates. The average chemical composition of the films was obtained from the semiquantitative energy dispersive spectroscopy analysis. Photoluminescence measurements were performed to determine the optical band gap of the films. The photoluminescence spectra displayed two peaks: one associated with the substrate and the other associated with films located at ≈ eV. Results show an increase in the optical band gap from 2.11 to 2.15 eV associated with the increase in the N/C ratio. Raman spectroscopy measurements showed a dominant band. ratio reaches a maximum value for N/C ≈ 3.03 when the optical band gap is 2.12 eV. Features observed by the photoluminescence and Raman studies have been associated with the increase in the carbon sp2/sp3 ratio due to presence of high nitrogen content.

Synthesis of europium-doped ZnS nano-crystalline thin films with strong blue photoluminescence

Eu2+-Doped ZnS (ZnS:Eu2+) thin (∼550 nm) films with strong and stable blue photoluminescence have been successfully synthesized by a simple and fast ultrasonic spray pyrolysis method. According to X-ray diffraction (XRD) and high resolution scanning electron microscopy (SEM) analysis, the as grown ZnS:Eu2+ films are composed of hexagonal wurtzite nanocrystals with average size of ∼25 nm, which are preferentially oriented along the (002) direction and agglomerate to form hexagonal facet nanobars with diameters from 50 to 200 nm. These films show a strong blue emission centered at 454 nm, which can be observed with the naked eye under ambient illumination. The intensity of this peak is ∼185 times higher than the maximum photoluminescence peak observed from the undoped ZnS films. The presence of the Eu dopant in the valence state Eu2+ was confirmed by electron spin resonance (ESR) measurements. The comparison of the high-resolution UV-vis absorption spectra and the PL characteristics of the ZnS:Eu2+ films with the pure ZnS films, indicate that the strong blue emission of the ZnS:Eu2+ films comes from Eu2+ 4f65d → 4f7 intra-ion transitions.

Magnetic moments in Ni clusters with deformations

Abstract We have studied the influence of geometrical deformations on the magnetic moments of Ni N clusters. Initial geometries of the clusters are taken from molecular dynamics and Monte Carlo calculations based on semi-empirical potentials. We only consider deformations, keeping the surface area of the clusters constant. The spin-polarized electronic structure has been calculated within a self-consistent spd tight-binding method in a mean-field approximation. The results indicate that changes in the d component of the magnetic moment as a consequence of the deformation can be explained in terms of the coordination number and inter-atomic distance whereas changes in the sp component cannot be explained in terms of these geometrical parameters. The complex dependence of the total magnetic moment is determined mainly by the sp component. Our results have been compared with available experimental data.

Deformation Effects in the Magnetic Moments of Ni Clusters

We study the effects of the geometric deformations on the magnetic moments in free NiN with different geometrical shapes. Initial geometries of the clusters come from Molecular Dynamics and Monte Carlo calculations based on semi-empirical potentials. We only consider deformations that keep constant the surface area of the clusters. The spin-polarized electronic structure has been calculated within a self-consistent tight binding method considering the 3d, 4s, and 4p valence electrons in a mean field approximation. The results indicate that the changes in the d component of the magnetic moment as a consequence of the deformation can be explained in terms of the coordination number and interatomic distance, whereas the changes in the sp component can not be explained in terms of those geometrical parameters. Our results are compared with the available experimental data.