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Puebla de Zaragoza, Mexico

Chavez F.,ICUAP BUAP | Zaca-Moran P.,ICUAP BUAP | Ramos-Garcia R.,National Institute of Astrophysics, Optics and Electronics | Felipe C.,CIIEMAD IPN | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

A study of optically induced Zn/ZnO nanoparticles selective deposition using a coherent light source on single-mode fiber optic end is presented. In the numerical studies, Zn/ZnO spherical nanoparticles are considered dissolved in isopropyl alcohol with different diameters under the influence of a Gaussian beam with fundamental mode and linear polarization. The results of this study show that the gradient force is not sufficient to move Zn nanoparticles toward optical fiber end face, but it is sufficient to move ZnO nanoparticles of a certain diameter. In the experimental studies, Zn/ZnO nanoparticles were mixed with isopropyl alcohol and subsequently deposited on the fiber end face using an infrared laser. The results obtained by atomic force and optical microscopy show a good uniform distribution of nanostructures deposited on the core of the fiber end face. © 2011 SPIE.

Chavez F.,ICUAP BUAP | Perez-Sanchez G.F.,ICUAP BUAP | Goiz O.,CINVESTAV | Zaca-Moran P.,ICUAP BUAP | And 3 more authors.
Applied Surface Science | Year: 2013

In this work, we show a simple way to functionalize tungsten oxide nanowires (WO3-NWs) using a saturated palladium chloride (PdCl 2) solution deposited by a drop-casting method. WO3-NWs were synthesized by close-spaced chemical vapor deposition (CSVT). The morphological and structural characterizations showed that the diameters of WO3-NWs are in the range from 50 to 200 nm with lengths above 10 μm, and correspond to the orthorhombic phase of WO3, respectively. The sensor was fabricated using the WO3-NWs and tested with hydrogen and volatile organic compounds (VCO's). A comparative study was done on the sensing performance, before and after the Palladium functionalization of the WO3-NWs, considering a wide range of gas concentrations and moderate operating temperatures (100-400 °C). The results show that this simple functionalization process significantly increases the sensor sensitivity and reduces the time constants. In addition, it has been shown that at 300 °C the decorated sensor becomes more selective to hydrogen and xylene for all concentrations considered in this research. Finally, the mechanisms involved in improving the gas sensing properties of WO3-NWs functionalized with Palladium are discussed. © 2013 Elsevier B.V.

Goiz O.,CINVESTAV | Chavez F.,ICUAP BUAP | Felipe C.,CIIEMAD IPN | Morales N.,ICUAP BUAP | Pena-Sierra R.,CINVESTAV
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2010

Growth of molybdenum oxide microsheets on silicon (1 0 0) substrates using the close-spaced vapor transport (CSVT) technique is proposed. Molybdenum oxide powder is employed as source, the synthesis is carried out at atmospheric pressure with a nitrogen ambient by employing short times (a few minutes), water as reactant and moderate temperatures. The growth process is efficient, fast, and without the use of catalysts. Changes in morphology and structure of products when temperature varies are reported. The produced molybdenum oxide microsheets are analyzed with SEM, XRD and micro-Raman techniques. © 2010 Elsevier B.V. All rights reserved.

Perez-Sanchez G.F.,ICUAP BUAP | Chavez F.,ICUAP BUAP | Zaca-Moran P.,ICUAP BUAP | Morales-Acevedo A.,CINVESTAV | And 2 more authors.
2013 10th International Conference on Electrical Engineering, Computing Science and Automatic Control, CCE 2013 | Year: 2013

Zinc oxide nanowires (ZnO-NWs) were synthesized through two simple processes on silicon substrates. The first step was to obtain the zinc nanowires (Zn-NWs) by close spaced sublimation (CSS) on a quartz substrate. The second step was the transformation of Zn-NWs to ZnO-NWs by a simple thermal annealing in air environment. In the synthesis process a zinc pellet source was used as the source material, where the temperatures of the source, the temperature of the substrate, and the growth time were fixed at 350°C, 325°C, and 5 minutes respectively, using a nitrogen environment at atmospheric pressure conditions. Afterwards, the as-prepared Zn-NWs sample was heated at 400°C for 30 minutes in open tube conditions. In addition, a conductimetric gas sensor was fabricated using the annealed Zn-NWs based film. The sensor was tested to hydrogen at moderate temperatures (200-400°C) for several concentrations (95-1492 ppm). The results revealed that the ZnO-NWs have a high response to hydrogen at high temperatures and high concentrations. The response and recovery times depend on the hydrogen concentration. The response time for almost all conditions is of the order of 2 minutes. These results are very promising for the development of hydrogen solid state gas sensors based on zinc oxide nanowires. © 2013 IEEE.

Goiz O.,CINVESTAV | Chavez F.,ICUAP BUAP | Zaca-Moran P.,ICUAP BUAP | Ortega-Mendoza J.G.,ICUAP BUAP | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

By using the Hot Filament Chemical Vapor Deposition (HFCVD) technique tungsten thin films were deposited on amorphous quartz substrates. To achieve this, a tungsten filament was heated at 1300 °C during 30 minutes maintaining a constant pressure inside the chamber at 460 mTorr and substrate at 700 °C. Transition from tungsten oxide deposits to tungsten thin films, by varying the substrate temperature, were characterized by means of Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM), X-Ray Diffraction and, micro-Raman spectroscopy. The SEM micrographs reveal that the tungsten films have no more than 200 nm in thickness while XRD show evidence of the films crystallize in the á-tungsten modification. On the other hand, AFM shows that the tungsten thin films exhibit a uniform and smooth surface composed with semi-spherical shapes whose diameters are below than 50 nm. Furthermore, to the naked eye, the as-deposited tungsten films exhibit a high mirror-like appearance. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

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