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Mexico City, Mexico

Mancilla J.E.,SEPI | Rivera J.N.,SEPI | Hernandez C.A.,SEPI | Zapata M.G.,CICATA Legaria IPN
Journal of the Australian Ceramic Society | Year: 2012

The ferroelectric behavior of Ba 0.75Sr 0.25TiO 3 (BST) thin films deposited on nichrome substrates by RF-Sputtering sintered in situ at 673-1023 K temperature range has been studied. The thin films microstructures were observed using atomic force microscopy to determine rugosity and grain size. Extensive grain growth was observed at temperatures of 822 and 1023 K, varying from 75 to 95 nm, respectively. The ferroelectric properties were determined by the hysteresis loops applying an electric field of 100 kV/cm. The films sintered in the temperature range of 822-1023 K show a reduction of the remnant polarization Pr from 9.87 °C/cm 2 to 2.23 °C/cm 2, and the coercive field strength E c decrease from 57.75 kV/cm 2 to 19.85 kV/cm 2. In situ heat treatments let to have more uniform grain size distribution, and relative low rugosities. Source

Aguirre C.I.,CICATA Legaria IPN | Reguera E.,CICATA Legaria IPN | Stein A.,University of Minnesota
ACS Applied Materials and Interfaces | Year: 2010

Poly(methyl methacrylate) (PMMA)-based colloidal photonic crystals have an incomplete photonic band gap (PBG) and typically appear iridescent in the visible range. As powders, synthetic PMMA opals are white, but when infiltrated with carbon black nanoparticles, they exhibit a well-defined color that shows little dependence on the viewing angle. The quantity of black pigment determines the lightness of the color by controlling scattering. The combined effects of internal order within each particle and random orientation among the particles in the powder are responsible for this behavior. These pigments were employed as paints, using a mixture of polyvinyl acetate as a binder and deionized water as the solvent, and were applied to wood and paper surfaces for color analysis. © 2010 American Chemical Society. Source

Aguirre C.I.,CICATA Legaria IPN | Reguera E.,CICATA Legaria IPN | Stein A.,University of Minnesota
Advanced Functional Materials | Year: 2010

Colloidal photonic crystals and materials derived from colloidal crystals can exhibit distinct structural colors that result from incomplete photonic band gaps. Through rational materials design, the colors of such photonic crystals can be tuned reversibly by external physical and chemical stimuli. Such stimuli include solvent and dye infiltration, applied electric or magnetic fields, mechanical deformation, light irradiation, temperature changes, changes in pH, and specific molecular interactions. Reversible color changes result from alterations in lattice spacings, filling fractions, and refractive index of system components. This review article highlights the different systems and mechanisms for achieving tunable color based on opaline materials with closepacked or non-close-packed structural elements and inverse opal photonic crystals. Inorganic and polymeric systems, such as hydrogels, metallopolymers, and elastomers are discussed. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Marquez-Herrera A.,CICATA Legaria IPN | Hernandez-Rodriguez E.,CICATA Legaria IPN | Cruz-Jauregui M.P.,CNyN UNAM | Zapata-Torres M.,CICATA Legaria IPN | Zapata-Navarro A.,CICATA Legaria IPN
Revista Mexicana de Fisica | Year: 2010

The heater was constructed mainly of stainless steel, ceramic and a resistance of khantal-Al. The body of the heater is cooled using a system of fins and cooling liquid which is isolated completely of the vacuum chamber. The design of the heater also incorporates a rotation system that allows that the substrate turns during the process of growth providing uniformity to the film. Temperature of the substrate is recorded by a type "K"thermocouple which feeds back a temperature controller that provides a modulated voltage to the heating resistance. In order to evaluate the functionality of the heating system, this was mounted in a rf-sputtering equipment and thin films of BaTiO3 were grown under different substrate temperatures in an off-axis geometry. The heating system is able to provide an uniform temperature to the substrate as well as to operate by long periods of times. Source

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