Vol. 58 No. 4 (2012): Revista Mexicana de Física.

Published: 2012-01-01

Articles

  • Photoinduced shape transformation from nanospheres to silver triangular nanoprisms and nanodisks: citrate ion concentration and stirring effects

    I.A. López, I. Gómez
    289-292
    Abstract:
    Silver nanospheres were transformed into triangular nanoprisms and nanodisks via a photoinduced growth process. In order to show the citrate ion concentration effect, the silver nanospheres were prepared in three different silver/citrate ratios (1:1, 1:2 and 1:3). The photoinduced shape transformation was carried out under magnetic or ultrasonic stirring with the purpose of showing the stirring effect. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) images of the obtained nanoplates show nanoprisms and nanodisks of 50 and 30 nm, respectively. The formation of silver nanoplates is very sensitive to the citrate ion concentration, which is confirmed by the UV-Vis spectra. Higher concentrations of citrate ion produce triangular nanoprisms with more sharp vertices. The ultrasonic stirring limits and controls the nanoplate growth.
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  • Caracterización de nanopartículas magnéticas de CoFe$_{2}$o$_{4}$ y CoZnFe$_{2}$O$_{4}$ preparadas por el método de coprecipitación química

    J. Lopez, F.J. Espinoza-Beltran, G. Zambrano, M.E. Gómez, P. Prieto
    293-300
    Abstract:
    Magnetic cobalt ferrite nanoparticles of CoFe$_{2}$O$_{4}$ and CoZnFe$_{2}$O$_{4}$ were prepared by co-precipitation technique from aqueous salt solutions of Co (II), ZnSO$_{4}$ and Fe (III), in an alkaline medium. CoFe$_{2}$O$_{4}$ powder samples were structurally characterized by X-ray diffraction, showing the presence of the most intense peak at 2$\theta $ = 413928$^{\circ}$ (Co K$\alpha $1) corresponding to the (311) crystallographic orientation of the CoFe$_{2}$O$_{4 }$spinel phase. The mean size of the crystallite of CoFe$_{2}$O$_{4}$ y CoZnFe$_{2}$O$_{4 }$nanoparticles determined from the full-width at half maximum (FWHM) of the strongest reflection of the (311) peak by using the Scherrer approximation was calculated to be 11.4 and 7.0 ($\pm $~0.2) nm, respectively. Transmission Electron Microscopy (TEM) studies permitted determining nanoparticle size of CoZnFe$_{2}$O$_{4}$. Fourier Transform Infrared Spectroscopy was used to confirm the formation of Fe--O bonds, allowing identifying the presence of ferrite spinel structure. Magnetic properties were investigated with the aid of a vibrating sample magnetometer (VSM) at room temperature Herein, the sample showed superparamagnetic behavior, determined by the hysteresis loop Finally, due to the hysteresis loop of the CoZnFe$_{2}$O$_{4 }$is very small, our magnetic nanoparticles can be considered as a soft magnetic material. These magnetic nanoparticles have interesting technological applications in biomedicine given their biocompatibility, in nanotechnology, and in ferrofluid preparation.
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  • Multi-point quasi-rational approximants for the energy eigenvalues of two-power potentials

    P. Martin, E. Castro, J.L. Paz
    301-307
    Abstract:
    Analytic approximants for the eigenvalues of the one-dimensional Schrödinger equation with potentials of the form $V(x) = x^a + \lambda x^b$ are found using a multi-point quasi-rational approximation technique. This technique is based on the use of the power series and asymptotic expansion of the eigenvalues in $\lambda$, as well as the expansion at intermediate points. These expansions are found through a system of differential equations. The approximants found are valid and accurate for any values of $\lambda>0$ (with $b>a$). As an example, the technique is applied to the quartic anharmonic oscillator.
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  • Efecto de la temperatura de substrato en las propiedades estructurales, ópticas y ferroeléctricas de películas delgadas de BaTiO$_{3}$ depositadas por RF sputtering

    A. Márquez-Herrera, E. Hernández-Rodríguez, O. Calzadilla-Ama, a., M. Meléndez-Lira, M. Zapata-Torres
    308-312
    Abstract:
    Thin Films of Barium Titanate (BaTiO$_{3}$) were grown on nichrome and quartz substrates, using a BaTiO$_{3}$ target, by RF-sputtering technique. We varied the substrate temperature in order to study its effect on the structural, optical and ferroelectric properties of the samples. The results of the X-Ray diffraction showed tetragonal structure with increases of the cristallinity as increases the substrate temperature. Furthermore, it observed by ultraviolet-visible (UV-VIS) spectroscopy that the band gap decreased as the substrate temperature increases showing abrupt sharp decrease at 494.8$^{\circ}$C. The ferroelectric properties of the films showed a dependence with substrate temperature, the best ferroelectric answer was obtained at 494.8$^{\circ}$C.
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  • Current saturation in In$_{2}$O$_{3}$-SrO ceramics: a role of oxidizing atmosphere

    A. Bondarchuk, O. Shpot, uk., A. Glot, H. Kl, m.
    313-316
    Abstract:
    Current-voltage dependence in In$_{2}$O$_{3}$-SrO ceramics contains a region where the current is increased weaker than the voltage. Such behavior is observed in oxygen atmosphere and is not registered in an inert one. Nonlinear current-voltage dependence is explained in terms of a relation between electronic processes at the grain boundaries and adsorption of oxygen in electric field. The role of adsorption processes is discussed on the basis of obtained data (current-voltage dependences, pore size distribution, secondary electron microscopy, and humidity sensitivity of conductance).
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  • Simulación de adsorción en superficies a partir de cálculos ab initio sobre nano--clusters de átomos de oro

    H. Franco, L. Puerta, J. Murgich, V. Mujica
    317-323
    Abstract:
    We have studied a nanosystem consisting of an alpha helix thio-polypeptide of high dipole moment chemisorbed on a Au$_{23}$ cluster surface with sulfur as the linking atom. We have studied a particularly important geometry where the alpha helix is almost perpendicularly oriented with respect to the gold cluster surface for the two possible directions of the molecular dipole moment. We have performed an ab initio quantum chemical study of this system to determine some characteristic properties such as the electric dipole, spin density and electronic population (DOS) near the Fermi level. For the calculation of the surface DOS we have implemented a new methodology based on an algorithm developed by us to analyze the electronic density. Our results give some clues for the understanding of the changes in the DOS, and the appearance of electronic states with high magnetic moments, during the process of formation of self-assembled monolayers of thio-polypeptide molecules chemically inked to the surfaces of gold clusters. These processes are related to both chemisorption-induced magnetism and spin transport in these systems.
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  • Estimation of length scale of RS II-$p$ braneworld model through perturbations in Helium's atom ground state energy

    N. Garrido, H.H. Hernández
    324-327
    Abstract:
    We put to the test an effective three-dimensional electrostatic potential, obtained effectively by considering an electrostatic source inside a (5+$p$)-dimensional braneworld scenario with $p$ compact and one infinite spacial extra dimensions in the RS II-$p$ model, for $p=1$ and $p=2$. This potential is regular at the source and matches the standard Coulomb potential outside a neighborhood. We use variational and perturbative approximation methods to calculate corrections to the ground energy of the Helium atom modified by this potential, by making use of a 6 and 39-parameter trial wave function of Hylleraas type for the ground state. These corrections to the ground-state energy are compared with experimental data for Helium atom in order to set bounds for the extra dimensions length scale. We find that these bounds are less restrictive than the ones obtained by Morales et. al. through a calculation using the Lamb shift in Hydrogen.
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  • Corrosion resistance and biocompatibility of zirconium oxynitride thin film growth by rf sputtering

    G.I. Cubillos, J.J. Ola, a., D. Clavijo, J.E. Alfonso, M. Bethencourt
    328-334
    Abstract:
    Thin films of zirconium oxynitride were grown on common glass, silicon (100) and stainless steel 316 L substrates using the reactive rf magnetron sputtering technique. The films were analyzed through structural, morphological, and biocompatibility studies. The structural analysis was carried out using X-ray diffraction (XRD), and the morphological analysis was carried out using scanning electron microscopy (SEM) and atomic force microscopy (AFM). These studies were done as a function of growth parameters, such as power applied to the target, substrate temperature, and flow ratios. The corrosion resistance studies were made on samples of stainless steel 316 L coated and uncoated with Zr$_{\text{x}}$N$_{\text{y}}$O films, through of polarization curves. The studies of biocompatibility were carried out on zirconium oxynitride films deposited on stainless steel 316L through proliferation and cellular adhesion. The XRD analysis shows that films deposited at 623 K, with a flow ratio $\Phi$N2/$\Phi$O$_{2}$ of 1.25 and a total deposit time of 30 minutes grew preferentially oriented along the (111) plane of the zirconium oxyitride monoclinic phase. The SEM analyses showed that the films grew homogenously, and the AFM studies indicated that the average rugosity of the film was 5.9 nm and the average particle size was 150 nm. The analysis of the corrosion resistant, shows that the stainless steel coated with the film was increased a factor 10. Finally; through the analysis of the biocompatibility we established that the films have a better surface than the substrate (stainless steel 316 L) in terms of the adhesion and proliferation of bone cells.
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  • Single shot phase shifting techniques for 4D radial slope measurements of transparent samples

    N.I. Toto-Arellano, D.I. Serrano-García, A. Martínez García, G. Rodríguez-Zurita, A. Montes-Pérez, J.M. Mir, a-Gómez., G. Reséndiz López, A. González Rosas, L. García-Lechuga
    335-338
    Abstract:
    Through the use of non-destructive optical techniques to measure surfaces with high accuracy, a Mach-Zehnder Radial-Shear interferometer (MZRI) was implemented to analyze the radial slope of phase objects using simultaneous phase-shifting interferometry (SPSI). This optical configuration allows one to simultaneously obtain n-shearograms in order to retrieve the optical phase data map with higher accuracy. Phase reconstruction is performed using a well-known four step phase shifting algorithm. The experimental results for transparent samples are presented in this paper.
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  • Foto-transceptor para sistemas RoF y RoFSO usando un mezclador optoelectrónico basado en PHEMT

    A. Arvizu, J.A. Re, noso-Hernández., M.A. Chávez, J. de D
    339-347
    Abstract:
    This paper deals with the application of self-oscillating optoelectronic mixers based on the use of a pseudomorphic high electron mobility transistor (PHEMT's) in radio over optical fiber (RoF) and radio over free space optics (RoFSO) systems. We describe the development of photoreception stages (down conversion) and up-conversion stages for such systems for two different wavelengths: 1550 nm using a mixer based on a PHEMT on InP substrate as active device for detection and another one with a PHEMT on GaAs substrate at 850 nm. We report the characterization results both for not illumination and illumination conditions. We also describe the results obtained on a typical application of GSM over optical fibers.
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  • Fractional mechanical oscillators

    J.F. Gómez-Aguilar, J.J. Rosales-García, J.J. Bernal-Alvarado, T. Córdova-Fraga, R. Guzmán-Cabrera
    348-352
    Abstract:
    In this contribution we propose a new fractional differential equation to describe the mechanical oscillations of a simple system. In particular, we analyze the systems mass-spring and spring-damper. The order of the derivatives is $0< \gamma \leq 1$. In order to be consistent with the physical equation a new parameter $\sigma$ is introduced. This parameter characterizes the existence of fractional structures in the system. A relation between the fractional order time derivative $\gamma$ and the new parameter $\sigma$ is found. Due to this relation the solutions of the corresponding fractional differential equations are given in terms of the Mittag-Leffler function depending only on the parameter $\gamma$. The classical cases are recovered by taking the limit when $\gamma=1$.
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  • Scattering of a ball by a bat in the limit of small deformation

    A. Cabo, L. Soler, C. González
    353-371
    Abstract:
    The problem of the mechanical evolution of a shock between a cylindrically symmetric object and a spherical one is solved in the strict rigid (small deformations) approximation for arbitrary values of the initial conditions. The friction during the impact is assumed to satisfy the standard rules. Firstly, when it is assumed that the only source of energy dissipation is friction, the problem is fully solved by determining the conditions at the separation point between the two bodies. A relation determining whether the contact points of the two bodies slides between them or become at rest (to be $pure\,rotation$ state) at the end of the impact, is determined for this case of the purely frictional energy dissipation. In second place, the solution is generalized to include losses in addition to the frictional ones. It follows that, whatever the mechanism of the additional form of dissipation is, assumed that it did not affects the usual forms of the laws of friction, the complementary losses only can change the ending value of the impulse $I$ done by the normal force of the bat on the ball at separation. Then, the dynamical evolution of all the mechanical quantities with the value of $I$ during the shock process remains invariable. Thus, under the adopter assumptions of strict rigidity and validity of the standard rules for friction, the solution of the problem is also exactly found, whenever the total amount of dissipated energy is considered as known (by example, measuring the ending mechanical energy of the system). The analysis allows to determine the values of the tangential and normal coefficients of restitution for the class of shocks examined. Finally, the results are applied to the description of experimental measures of the slow motion scattering of a baseball by a bat. The evaluations satisfactorily reproduce the measured curves for the output center of mass and angular velocities of the ball as functions of the scattering angle and the impact parameter, respectively.
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