Heiddy P. Quiroz

Synthesis of self-organized TiO2 nanotube arrays: Microstructural, stereoscopic, and topographic studies

In this work, titanium dioxide nanotubes were prepared by using titanium foils via electrochemical anodization in ethylene glycol solutions containing different amounts of water and fluoride in the ranges of 1%–3% and 0.15%–0.5%, respectively, to determine their effects on morphology, optical, and crystalline structure properties. Annealing processes were performed on all samples in the range between 273 and 723 K. Morphology and structure properties of the samples were studied by scanning electron microscopy, X-ray diffraction (XRD), and transmission electron microscopy. Titanium dioxide (TiO2) nanotubes, through anodization method, are strongly influenced by conditions, like fluoride concentration and applied voltages. Tube lengths between 2 and 7 μm were obtained, exhibiting different diameters and wall thicknesses. When alternating voltage was applied, the outer surface of the nanotubes exhibited evenly spaced ring-shaped regions, while smooth tubes were observed when constant voltage was applied. Ref...

Nanocrystalline Cu2ZnSnSe4 thin films for solar cells application: Microdiffraction and structural characterization

This work presents a study of the structural characterization of Cu2ZnSnSe4 (CZTSe) thin films by X-ray diffraction (XRD) and microdiffraction measurements. Samples were deposited varying both mass (MX) and substrate temperature (TS) at which the Cu and ZnSe composites were evaporated. CZTSe samples were deposited by co-evaporation method in three stages. From XRD measurements, it was possible to establish, with increased Ts, the presence of binary phases associated with the quaternary composite during the materials growth process. A stannite-type structure in Cu2ZnSnSe4 thin films and sizes of the crystallites varying between 30 and 40 nm were obtained. X-ray microdiffraction was used to investigate interface orientations and strain distributions when deposition parameters were varied. It was found that around the main peak, 2ϴ = 27.1°, the Cu1.8Se and ZnSe binary phases predominate, which are formed during the subsequent material selenization stage. A Raman spectroscopy study revealed Raman shifts asso...

Optical and structural properties of GaSb-doped Mn based diluted magnetic semiconductor thin films grown via DC magnetron sputtering

In this work, diluted magnetic semiconductor GaSb:Mn thin films were grown via DC magnetron Co-sputtering on glass substrates. The effect of synthesis parameters on the optical and structural properties was determined through spectral transmittance measurements and X-ray diffraction (XRD), respectively. Substrate temperature was changed from 373 to 523 K and layer thicknesses were obtained between 200 and 330 nm. All samples were subjected to annealing process to 623 K in situ. It was found that the optical constants (refractive index (n), absorption coefficient (), extinction coefficient (), and energy gap (E1)) are significantly affected by the temperature and target power used during the synthesis process. In particular, a variation of the energy gap between 0.58 and 0.98 eV was obtained when the target power of GaSb varied between 80 and 140 W. GaSb, Mn2Sb and SiO2 phases were observed for lowest values of target power, where SiO2 phase is a contribution of the substrate. The dielectric function of the compound with a dependence on synthesis parameters such as, the substrate temperature and deposition time was obtained, both real () and imaginary part (). Analysis of the XRD measurements allowed to find that the (GaSb)Mn films grow with a mixture of the GaSb and Mn2Sb phases, and an amorphous halo associated with the glass substrate. A correlation between synthesis parameters and optical properties is presented. Diluted magnetic semiconductors, like GaSb:Mn, are considered among promising materials for the development of new spin-electronic devices, high speed quantum-mechanical in computational information, other more; in this case, studies on magnetic properties in digital alloys of GaSb/Mn can be realized around of the optimization of Curie temperature. Copyright

Effect of Annealing Process on Natural Zeolites from Volcanic Ash for Environmental Applications: Structural and Morphological Characterizations

This work presents a study of morphological, structural, and compositional properties of volcanic ash obtained from Nevado del Ruiz volcano in Colombia. The volcanic ash samples were subjected to hydration and annealing processes at atmospheric pressure to obtain zeolite-type natural structures for different applications, like water decontamination and air pollution control. The strong influence of hydration and annealing processes on the formation of zeolite phases was observed. Rietveld refinement was performed with X-ray diffraction (XRD) patterns, obtaining the presence of natural zeolites: gismondine, hydrated calcium aluminosilicate, litosite, clinoplitolite-Na, and phillipsite-K. From scanning electron micrographs, a morphological change of the ash sample was observed with increasing annealing temperature (290 K < T < 673 K). The surface was dominated by the presence of agglomerates or granules around 5 µm in size; other regions with tubular form or flake-type structures were observed with less presence on the surface ash, associated with the formation of the labradorite phase.

Propiedades Estructurales y Ópticas de Nanoestructuras de TiO2 Depositadas por el Método de Deposición en Baño Químico para Aplicaciones en Sensores UV

espanolSe fabricaron peliculas delgadas nanoestructuradas de dioxido de Titanio (TiO2) a partir del metodo de deposicion en bano quimico (CBD por sus siglas en ingles) variando en un amplio rango los parametros de sintesis: tiempo de deposito, temperatura y pH de la solucion. A partir del estudio de las propiedades estructurales se establecio la existencia de las fases Rutilo y Brookita en el material, siendo esta ultima favorecida por la presencia del Hidroxido de Amonio (NH4OH) como reactivo en la solucion. Usando medidas de microscopia electronica de barrido (SEM por sus siglas en ingles) se pudo evidenciar la dependencia del metodo con la formacion de nanoestructuras tipo nanoflores o nanorrodillos. Por medio de espectroscopia UV-Vis-NIR (transmitancia y reflectancia) se obtuvo la brecha energetica de las muestras y se evidencio una alta absorcion en la region del ultravioleta del espectro de radiacion. EnglishNano-structured thin films of titanium dioxide (TiO2) were fabricated using the chemical bath deposition method or CBD, varying in a wide range the synthesis parameters: deposition time, temperature and pH of the solution. From the study of the structural properties, the existence of the Rutile and Brookite phases was established in the material, the latter being favored due to the presence of Ammonium Hydroxide (NH4OH) as a reactive in the solution. Using scanning electron microscopy measurements (SEM) the dependence of the method with the formation of nanoflowers or nanorod-like structures was corroborated. Through UV-Vis-NIR spectroscopy (transmitance and reflectance), the energy gap of the samples was obtained and evidence of high absorption in the UV region of the radiation spectra was found.

Effect of fluoride and water content on the growth of TiO2 nanotubes synthesized via ethylene glycol with voltage changes during anodizing process

In this work, titanium foils were anodized in ethylene glycol solutions containing different amounts of water and fluoride to determine their effects on the top morphology and crystalline structure of the formed titania nanostructures. Anodizing was performed for 2 h by using titanium foils as both anode and cathode applying a squared-pulse voltage profile composed of one step at 80 V for 3 min followed by another at 20 V for 5 min; constant voltage conditions were also used to study the nanostructure formation on the surface. We found the formation of nanostructured titania on the surface of the anodized foil when small amounts of water and fluoride are present in the anodizing solution. The top of these nanostructures is irregular when no water is added, but is expected to change with different amounts of water and fluoride in the ranges of 1 - 9% and 0.05 - 0.5%, respectively. Synthesis parameters also change nanotube morphology. The morphology and structure properties of the samples were studied by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Formation of TiO2 nanotubes by anodization method are strongly correlated to conditions like fluoride concentration and applied voltages. Tube length varying between 2 and 7 μm, exhibiting different diameters and wall thicknesses were obtained. When an alternate voltage was applied, the wall of the nanotubes presented evenly spaced rings while nanotubes with smooth wall form were observed when constant voltage was applied. Reflection peaks corresponding to Brookite, Anatase, and Rutile of TiO2 phases were observed from XRD measurements. A correlation between the effects of synthesis parameters on nanotube formation and morphological properties is presented. TiO2 nanotubes prepared by electrochemical anodization have excellent performance in various applications such as photocatalysts, solar cells, gas sensors, and biomedical applications.

Optical Properties of Cu2ZnSnSe4 Nanocrystalline Thin Films for Photovoltaic Devices

Presents a study of optical properties from transmittance measurements as a function of wavelength to CZTSe thin films (Cu2ZnSnSe4) using Bhattacharyya model and basic elements from the Swanepoel theory. The optical constants such as the absorption coefficient (α), the refractive index (n), the extinction coefficient (k) and physical properties such as gap (Eg), the real and imaginary part of the dielectric function (ε1 and ε2) and the film thickness (d), were determined. Gap values between 1.2 and 1.7 eV were obtained for compound when the mass (MX) of ZnSe was varied during the deposition stage. Inhomogeneity and high surface roughness were observed by SEM measurements for all samples. Size grain varying between 458.16 and 630.28 nm were obtained while the ZnSe binary mass varied from 0.171 to 0.153 g. Refractive index and extinction coefficient of Cu2ZnSnSe4 films were obtained for λ = 800 nm. A decrease of ε1 and ε2 was observed as the wavelength increases; it is associated with the presence of binary phases in the XRD patterns.