Vol. 59 No. 1 (2013): Revista Mexicana de Física.

Published: 2013-01-01

Articles

  • Umbral de percolación en las redes de Kagomé y Dice

    W. Lebrecht
    1-0
    Abstract:
    An alternative way to calculate percolation thresholds of bonds and sites on Kagome (K) and Dice (D) lattices are presented. The methodology used is based on considering the topological structures of these lattices and characterize them by a polynomial function provided by the simplest structures, as are the square lattice (C), the triangular lattice (T), and the hexagonal lattice (H). To obtain the polynomial functions associated to C, T, and H, the technique associated to the growth of small cells is used to determine the exact finite occupation of bonds (or sites). The percolation threshold is obtained through two methods in order to compare and validate results. Techniques related to finite size of lattices are used, including the asymptotic corrections to the laws of scale in each case. The technique allows independently know the percolation threshold for both the problem of bonds, such as sites. The results obtained for the bond (site) percolation threshold for the K lattice is $ 0.52440516 $ ($ 0.65270365 $) and for D lattice is $ 0.47559502 $ ($ 0.58504625 $).
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  • Effect of Cr$_{2}$O$_{3}$ on the microstructure and non-ohmic properties of (Co, Sb)-doped SnO$_{2}$ varistors

    J.A Aguilar-Martínez., M.I. Pech-Canul, M.B. Hernández, A.B. Glot, E. Rodríguez, L. García Ortiz
    6-0
    Abstract:
    The effect of Cr$_{2}$O$_{3}$ addition on the physical characteristics, microstructure, and current-voltage properties of (Co-Sb)-doped SnO$_{2}$ varistors was investigated. SnO$_{2}$-Co$_{3}$O$_{4}$-Sb$_{2}$O$_{5}$ ceramics with additions of 0.0, 0.03, 0.05 and 0.07 mol % Cr$_{2}$O$_{3}$ were sintered at 1350 $^{o}$C under ambient atmosphere and characterized microstructurally and electrically. The characterization by XRD and SEM show that the microstructure remains as a single phase material with multimodal size distribution of SnO$_{2 }$grains. The greatest effect of Cr$_{2}$O$_{3 }$additions is manifested in the electric breakdown field. Additions of high levels (0.07 and 0.05 %) of this oxide promote an increase of approximately 55% in this parameter compared to the Cr$_{2}$O$_{3}$-free sample. Another physical property is affected: the measured density values decreases as the Cr$_{2}$O$_{3}$ content increases. A change in the nonlinearity coefficient value is produced only at the highest Cr$_{2}$O$_{3}$ content while at intermediate levels there is not change at all. Consequently, when seeking high nonlinearity coefficients, intermediate levels of Cr$_{2}$O$_{3}$ are not recommended.
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  • Caracterización superficial y nano estructural de nano multicapas Cr/CrN obtenidas por UBM con diferentes grados de desbalance

    U. Piratoba, J. Arenas-Alatorre, J. J, a.
    10-0
    Abstract:
    Coatings of 25 bilayers of Cr/CrN, with total thickness between 1.32 and 1.67 microns, were deposited by reactive sputtering on silicon and H13 steel, in argon and argon with nitrogen atmospheres. A power of 160 watts, flows of argon and nitrogen of 9 and 3 sccm respectively, and an axial unbalanced magnetron, whose coefficient of geometrical unbalance K$_{G}$ [1] was varied between 0.85 and 1.37. Of these coatings, micrographs of surface and cross section scanning electron microscopy SEM were obtained, was make a micro structural characterization with X-Ray Diffraction XRD, a nano structural characterization by transmission electron microscopy TEM, and surface characterization by atomic force microscopy AFM in tapping mode; analysis showed uniform surface coating with globular and pyramidal formations, which contain some granular inclusions and microscopic craters. With the increase in the unbalance of the magnetic field, the grain size, the roughness and the speed of the coatings growth were increased.
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  • Thermal properties of high order crystalline dielectric mixtures

    G. Moro, oqui-Estrella., R. Rodríguez-Mijangos, R. Pérez-Salas, A. Rodríguez
    16-0
    Abstract:
    Through experiments the heat capacity is determined at constant volume in ternary and quaternary KCl$_{0.5}$KBr$_{0.25}$RbBr$_{0.25}$:Eu$^{2 + }$ and KCl$_{0.25}$ KBr$_{0.25}$RbCl$_{0.25}$RbBr$_{0.25}$:Eu$^{2 + }$ single crystals. The results are compared with calculated values using the low temperature approximation of the Debye Model, in which the Debye temperature is obtained by applying a Kopp-Neumann relation. It is shown that the $C_{v}$ values obtained by the Debye model are in good agreement with the measured ones which demonstrates that the Kopp-Neumann law used for metals and other solids can also be applied to ternary and quaternary alkali halide crystals, that is also an element that strengthens the diffractogram of the quaternary mixture which shows that the crystal has a single phase, thus being a solid solution.
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  • A study of the attack to one water molecule by either aluminum or cadmium atoms

    A. N, J. H
    20-0
    Abstract:
    A study of the attack to a water molecule by either aluminum or cadmium atoms is accomplished for determining their interaction geometry. The existence of certain number of geometrical zones for repulsion and attraction of Al and Cd atoms when these interact with the water molecule is obtained using Density Functional Theory. Our results clearly show the existence of defined geometries where the interaction is the strongest for chemical bonds formation.
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  • Micro sensor-actuador térmico sin baterías para aplicaciones en microelectrónica de ultra-bajo consumo de potencia

    J. Varona, M. Tecpo, otl-Torres., R. Velázquez
    26-0
    Abstract:
    As an alternative to electrically driven thermal actuators, this work presents a sensor/actuator device that can be operated with an external heat source and, for example, scavenge heat from the surrounding medium. The device herein presented is ideal for ultra-low power and portable applications as it eliminates the need for batteries. The mechanism was implemented using a standard micro-electro-mechanical-systems (MEMS) fabrication process. Experimental results demonstrate the viability of exploiting thermal energy from the environment to power MEMS sensor/actuator devices. Finally, examples of potential applications are also discussed including the design of a fully monolithic temperature sensing system that integrates the MEMS thermal device with CMOS circuitry in a single microchip.
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  • Growth and morphology of tin nanoparticles obtained by the condensation of metal vapors

    M. Francisco Melendrez, C. Vargas-Hernández
    39-0
    Abstract:
    Tin nanoparticles (Sn-Nps) were synthesized using the metal vapor condensation technique (MVC) in a metallic atoms reactor. The parameters used for synthesis in this study were the following: distance to the metal evaporation center (MEC), metal evaporated moles (MEM), and frosting and defrosting temperatures of substrates. The Sn-Np depositions were carried out with Sn bulk over glass substrates positioned vertically at different angles and distances to the MEC. The Sn-Np characterization was performed by TEM, SEM, selected area electron diffraction (SAED), and UV-Vis. The TEM micrographs evidenced particle sizes of 75 and 25 nm for depositions conducted at 3 and 10 cm above the MEC, respectively. The particle sizes depended significantly on the MEC, the substrate, and the MEM. The SAED revealed phases corresponding to SnO (tetragonal) and $\alpha $-Sn in different crystalline orientations. The technique showed good reproducibility in terms of particle size, and it is an important source of nanostructured materials free of impurities, which are widely used for printing electronic circuits.
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  • Bound state solutions of schrodinger equation with modified hylleraas plus exponential rosen morse potential

    A.N. Ikot, A.D. Antia, I.O. Akpan, O.A. Awoga
    46-0
    Abstract:
    We present solutions of the Schrödinger equation with modified Hylleraas plus exponential Rosen Morse potential within the framework of the elegant approximation to deal with the centrifugal term for arbitrary orbital angular quantum number. We obtain the energy spectrum and the corresponding wave function using the parametric form of the Nikiforov-Uvarov method. In many cases of interest the energy eigenvalues and eigen functions have been discussed for different potentials.
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  • Diseño e implementación de un sistema de caracterización para microsensores de efecto Hall

    F. López-Huerta, G. Rojas-Nava, B. S, A. L, .
    54-0
    Abstract:
    This paper presents the design and integration of an electrical characterization system for Hall effect microsensors, which allows the detection and measurement of magnetic field perpendicular to the surface of the microsensors. The proposed system can control and maintain the communication of both the position of the excitation source and the magnitude of the magnetic field. This system includes a mechanism for surface movement $\theta $-Z with two degrees of freedom, sensors, electronic instruments, a computer, interface cards and a graphical user interface (GUI) implemented in Lab-View$^{\mbox{\textregistered }}$. The positioning of the system is made through two motors, a stepper motor, and a servomotor. Which perform the movements in the $\theta $-Z surface. The Z axis has a resolution of 0.03 cm through a stepper motor and the $\theta $ axis has a resolution of 1 cm, which is obtained using a servomotor. As excitation source, we used neodymium iron boron (NdFeB) magnet, which has a magnetic field of 100 mT. The detection field is obtained with microsensors which had a response in the linear range of 1 mT to 100 mT. This system allows a single interface through the detection of magnetic field perpendicular to the surface of the microsensor, as well as the positioning of the excitation source in the $\theta $-Z surface. The GUI has a control environment accessible to the end user. Furthermore, the system can be reconfigured for the characterization of other microsensors, changing only the excitation and detection modules. Its versatility will increment the life time of our system characterization.
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  • Electrical characterization of planarized a-SiGe:H Thin-film Transistors

    M. Dominguez, P. Rosales, A. Torres
    62-0
    Abstract:
    In this work the electrical characterization of n-channel a-SiGe:H TFTs with planarized gate electrode is presented. The planarized a-SiGe:H TFTs were fabricated at 200$^{\circ}$C on corning glass substrate. The devices exhibit a subthreshold slope of 0.56 V/Decade, an on/off-current ratio approximately of 10$^{6}$ and off-current approximately of 0.3$\times$10$^{ - 12}$ A. The results show an improvement of the electrical characteristics when are compared to those unplanarized devices fabricated at higher temperature. Moreover, the simulation of the device using a SPICE model is presented.
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  • Materiales para ánodos, cátodos y electrolitos utilizados en celdas de combustible de óxido sólido (SOFC)

    J. Alvarado-Flores, L. Ávalos-Rodríguez
    66-0
    Abstract:
    Fuel Cell Solid Oxide (SOFC), are electrochemical reactors that can directly convert the chemical energy of a fuel into electrical energy with high efficiency, can substantially reduce oil dependency and environmental impact. The current trend in SOFC research is directed to the use of available hydrocarbon fuels, such as natural gas. Moreover, these cells have additional advantages such as high temperature use in cogeneration or hybrid applications as well as for internal reforming capability. This article show the most commonly used materials for the manufacture of anode, cathode and electrolyte comprising the SOFC.
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