In this collaborative study, the variables that affect the morphology of nanotubular arrays of titanium oxide ͑grown by anodization of titanium substrate͒ were analyzed by a fractional factorial ͑Taguchi͒ statistical experimental design. The growth voltage and water content of the medium were found to have the maximal impact on nanotube length as shown by an analysis of variance. Nanotubular array growth was monitored by electrochemical impedance spectroscopy ͑EIS͒ and the results were corroborated by other measurement probes ͑scanning electron microscopy, transient current-time profiles, voltammetry͒ as needed. Taken as a whole, the EIS data presented above support the validity of the Bojinov equivalent circuit model especially at growth times past a few minutes. Trends in the values of the equivalent circuit elements obtained from fits to the EIS data as a function of the growth variables are rationalized within the framework of a model proposed by Schmuki and co-workers for the growth and self-assembly of titania nanotubes on Ti substrates in fluoride-containing media.In this collaborative study, the anodic growth of nanotubular arrays of titanium oxide ͑on titanium substrate͒ was studied by electrochemical impedance spectroscopy ͑ECIS͒ and the experimental and modeling results were corroborated by other measurement probes ͓scanning electron microscopy ͑SEM͒, growth current density-time ͑ j-t͒ profiles, current density-voltage ͑ j-V͒ curves͔ as needed. Tailoring the structure and morphology of semiconductor materials on a nanometer size scale has fundamental and practical importance. 1 Nanotubular semiconductor arrays ͑NTA͒ are particularly of interest because of their unusual electronic transport and mechanical strength characteristics. In this regard, titania ͑TiO 2 ͒ nanotubes and nanotubular arrays have been the subject of many recent studies; these have been reviewed. 2-4 Array growth and selfassembly is underpinned by a delicate and complex interplay of oxide film growth and its subsequent dissolution processes by fluoride species in the electrolyte. Adding to the complexity are details associated with the adsorption and transport of ionic species and mechanical ͑stress͒ effects from oxide growth on the native metal substrate. 5,6 In spite of the rapidly maturing database on TiO 2 NTAs, the temporal aspects of nanotubular growth and self-assembly and the effect of key variables that affect the NTA morphology are still not completely understood. 7,8 Electrochemical impedance spectroscopy ͑EIS͒ ͑Ref. 6 and 7͒ is a particularly effective approach for the monitoring of oxide growth and dissolution in anodic environments. A recognized advantage of this technique is that the dynamical behavior of a metal/oxide interface can be probed in situ at the cost of a very small ac perturbation so that the observed processes are themselves not significantly affected by the probe unlike in the case of large-amplitude signal perturbations. 9,10 Thus it is not surprising that many examples exist for the use of EIS to study...
Un nuevo campo de Investigación se ha encontrado con el estudio de la familia de Nitruros Metálicos de Transición; desde la aparición en el 2002 por la primera película delgada de AuN, diferentes grupos han comenzado con la sintetización de este nuevo material. En el presente artículo se muestra como el crecimiento de películas delgadas de oro en un ambiente de nitrógeno por medio de un sistema de Deposición Física en Fase Vapor Asistido por Plasma (PAPVD) en arco pulsado, hace que las Líneas de Difracción de Bragg de la fase cubica fcc del oro sean ensanchadas, indicativo posiblemente a la inclusión de átomos de nitrógeno dentro de la red cúbica fcc del oro.
The behavior of an electrochemical cell for anodic formation of titanium oxide nanotubes is calculated from an electrical model obtained from the DC Current-time plot. The result can predict the behavior beyond the voltage source used in the experiment and in conditions that are impossible to achieve in a real experiment. This clarifies the speculation around the cell voltage versus cell current limited experimental data and its behavior is explained in terms of the source used in the experiment.
Durante las líneas de este documento se tratará de abordar una des las problemáticas científi cas y tecnológicas más grandes que hoy por hoy la humanidad experimenta, las fuentes de energía. La supervivencia en este planeta depende de la energía y el problema radica en que más del 80% de dicha energía proviene de fuentes fósiles que son no renovables y que contaminan excesivamente. Desde diferentes perspectivas se argumentará el por qué este problema encabeza la lista de los retos que el hombre afrontará este siglo, y se presentarán algunas de las posibles soluciones que no pueden ser ajenas a los estudiantes en Ingeniería. Con optimismo y motivación para las futuras generaciones, parece que el campo de posibles soluciones se hace cada vez más amplio, y la intervención proviene desde variadas direcciones. Es necesario entonces conocer y difundir la problemática, pero aún mejor, encararla. De alguna manera, para continuar en este planeta con las mismas o mejores comodidades, es necesario diseñar e implementar soluciones radicalesdiferentes, tales como: costo, ambiente y producción en masa.
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