Scielo RSS <![CDATA[Superficies y vacío]]> http://www.scielo.org.mx/rss.php?pid=1665-352120130001&lang=es vol. 26 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.mx/img/en/fbpelogp.gif http://www.scielo.org.mx <![CDATA[<b>Analysis of threshold voltage fluctuations due to short channel and random doping effects</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212013000100001&lng=es&nrm=iso&tlng=es Abstract A two-dimensional (2-D) simulation study of short channel and random dopant effects on threshold voltage lowering and fluctuations in 90 nm MOSFET's is presented. The systematic analysis of short channel and random dopant effects was carried out in 2-D on a scale to provide quantitative predictions. Simulations based on a single multigrid solution of the Poisson equation followed by the solution of a simplified current continuity equation are used in the simulations. Both short channel and random dopant effects, on threshold voltage fluctuations are simulated and discussed in MOSFET's. The simulation results will be the start point for the analysis of threshold voltage fluctuations through the comparison with analytical models based on dopant number fluctuations. The simulations show that the threshold voltage fluctuations are principally determined by the fluctuation in the dopant number. <![CDATA[<b>Design of capacitive MEMS transverse-comb accelerometers with test hardware</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212013000100002&lng=es&nrm=iso&tlng=es Abstract This paper proposes the design of MEMS accelerometers, which include hardware to perform testing in a relatively simple way, with different manufacturing processes, PolyMUMPs™ and SUMMiT V™ of MEMSCAP and Sandia Labs respectively, using a methodology that allows them to be adapted to any of these technologies. This method was created to provide the basis to the designing of micro electromechanical devices, optimizing the learning time. The sensors are one-axis transversal comb accelerometers which use an interdigital capacitors array to measure the capacitance change among three independent comb arrays when the system is exposed to positive or negative G forces. In addition, it includes another set of combs which interact as test devices, due to the fact that a voltage can be applied, which will create an electric field in the electrodes of these combs, producing an attraction force that will shift the mobile mass of the sensor, emulating an acceleration to which the device is exposed. Some physical parameters and dimensions proposed for this accelerometer are presented to show the design methodology of such devices. The accelerometers were designed under constraints set by the manufacturing regulations of PolyMUMPS and SUMMiT V™ The accelerometer layouts were designed using MEMS PRO v4.0™ and AutoCAD® and both were simulated with ANSYS Workbench®. <![CDATA[<b>Síntesis y caracterización de óxido de circonio modificado con ión fosfato</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212013000100003&lng=es&nrm=iso&tlng=es Resumen En este trabajo se efectuó la reacción de descomposición de 2-propanol para obtener propileno usando circonia fosfatada como catalizador. La síntesis del Zr(OH)4 se realizó por el método sol-gel. Los materiales fueron modificados con ácido fosfórico y calcinados a 400°C. Las pruebas de caracterización incluyeron difracción de rayos X, fisisorción de nitrógeno, espectroscopia de infrarrojo y microscopía electrónica de barrido. Se obtuvieron sólidos con estructura tetragonal y la adición del ión fosfato incrementó el área específica en los materiales. Las pruebas de reacción revelaron que los catalizadores fosfatados tuvieron mayor actividad catalítica y los sitios activos dominantes fueron sitios ácidos.<hr/>Abstract In this work was conducted the decomposition reaction of 2-propanol to obtain propylene using phosphated zirconia as catalyst. The synthesis of Zr(OH)4 was carried out by the sol-gel method. The materials were modified with phosphoric acid and calcined at 400°C. Characterization tests included X-ray diffraction, nitrogen physisorption, infrared spectroscopy and scanning electron microscopy. The results indicated that were obtained solids with tetragonal structure and the addition of phosphate ion increased the specific surface area in the materials. On the other hand, reaction tests revealed that the phosphated catalysts had higher catalytic activity and the active sites dominant were acid sites. <![CDATA[<b>Comportamiento estructural de aleaciones AlNi fabricadas por colada y sometidas a molienda mecánica de alta energía</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212013000100004&lng=es&nrm=iso&tlng=es Resumen En este artículo, dos aleaciones intermetálicas se prepararon con las composiciones nominales Al-Ni25 y Al-Ni24 (% at.) mediante la técnica de colada por gravedad y después fueron sometidas al proceso de molienda de bolas en húmedo. Estas aleaciones fueron estudiadas por difracción de rayos X (DRX), microscopía electrónica de barrido (SEM) y microscopía electrónica de transmisión (TEM). Se observó que las muestras de colada consisten de las fases intermetálicas NiAl3 hexagonal y Ni2Al3 ortorrómbica, embebidas en una matriz de aluminio. El proceso de molienda en húmedo aplicado a las muestras prealeadas es más eficaz para la reducción de tamaño del cristal en comparación con el proceso de molienda seca. Esto es como resultado de la reacción de fragilización por hidrógeno que tiene lugar en el molino para producir fase bayerita Al(OH)3 y gas hidrógeno. La cantidad de fase bayerita aumenta con el incremento del tiempo de molienda, este resultado también sugiere un incremento en la cantidad de hidrógeno liberada. Las fases metálicas se encuentran rodeadas por la fase bayerita la cual puede pasivar la generación de hidrógeno.<hr/>Abstract In this paper, two intermetallic alloys with the nominal compositions Al-Ni25 and Al-Ni24 (at %) were prepared by gravity casting technique and then subjected to wet ball-milling process. These alloys were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was noted that the as-cast samples consist of NiAl3-hexagonal and Ni2Al3-orthorhombic intermetallic phases embedded into an aluminum matrix. The wet-ball milling process applied to prealloyed samples is more efficient to crystal size reduction in comparison to the dry-milling process. This is as result of hydrogen embrittlement reaction that takes place into the mill to produce bayerite phase Al(OH)3 and hydrogen gas. The amount of the bayerite phase increases with the increase of milling time. This result also suggests an increased in the amount of hydrogen released. Metallic phases are surrounded by bayerite phase which can passivity the hydrogen generation. <![CDATA[<b>Comportamiento tribológico del acero H13 tratado superficialmente</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212013000100005&lng=es&nrm=iso&tlng=es Resumen En este trabajo se analiza el comportamiento tribológico en términos de fricción y desgaste de las películas delgadas CrN/AlN depositadas sobre el acero H13 mediante plasma. Las películas se prepararon con pulverizado reactivo y mezcla convencional de gases Ar + N2, posteriormente añadiendo más gas reactivo a la mezcla inicial y por último, gas reactivo cerca del substrato. El análisis microestructural se llevó a cabo utilizando microscopía electrónica de barrido así como microanálisis con energía dispersa y difracción de rayos X. Los resultados muestran una clara diferencia en la morfología de crecimiento cuando se añade nitrógeno extra en comparación con la mezcla convencional de gases. La adición de nitrógeno extra resultó el método más efectivo para producir la película AlN. Se utilizó un tribómetro del tipo pin-on-disk en seco para estudiar el comportamiento tribológico. Los resultados evidencian una mejora en las propiedades tribológicas de las capas depositadas en comparación con el acero H13 sin deposición superficial.<hr/>Abstract The microstructure of CrN/AlN films, prepared by reactive magnetron sputtering was analysed and related to the friction and wear behaviour of the films on H13 tool steel. The films were prepared by conventional reactive magnetron sputtering and Ar + N2 conventional gas mixture but also a second set adding an extra amount of reactive gas to the initial mixture and finally, adding an extra source of nitrogen near the substrate during sputtering. The samples were analysed by scanning electron microscopy + energy dispersive microanalysis, and X-ray diffraction. The results of the microstructural analysis revealed a clear difference in the morphology growth of the films when extra nitrogen was used compared to the conventionally prepared films. The most effective method to produce AlN was to introduce extra nitrogen. Pin-on-disk wear experiments were carried out under dry conditions and in ambient air, to investigate the tribological behaviour. The results revealed that tribological properties of the layers improved somewhat unlike those of the untreated H13 steel.