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Conference Presentations by J.A. Torres-Ochoa

Absorption studies are important in understanding contaminant retention behavior in soils, partic... more Absorption studies are important in understanding contaminant retention behavior in soils, particularly soils at waste sites 1. Some studies suggest that the use of long chain surfactants incorporated into clays improves adsorption heavy metal cations 2–5. In this work the results of the comparative study of the functionalization with HDTMA of two mineral clays with a high proportion of montmorillonite and hematite are reported. Clays were characterized by atomic absortion spectroscopy (AAS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Functionalization was carried out in a BATCH process at 25ªC for 3 hours using a ratio of HDMTA correlated with the three times the cation exchange capacity of clays (40-42 meq/100g). Fourier transform spectroscopy to determine the binding of the organic chains and replacement of ions on the surface and interlayer spaces of clays was used. The bands observed between 2970-2850 cm-1 are attributed to-CH2 HDTMA incorporated in the interlayer space. Functionalized clays were added to solutions of potassium dichromate of 50 mg/L in BATCH systems, sampling and measuring by UV-Vis spectroscopy. We observed that the functionalized clays have a removal ratio of 32mg/g of clay into a maximum removal time of 10 min, compared with the natural clays with 26mg/g of clay of chromium (VI) removal.

Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is... more Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is used to prevent crystallization during annealing [1]. The thickness and composition of HfO x N y films is susceptible to the processing parameters. In this work we present an study of HfO 2 nitridation through remote plasma. P-type crystalline silicon substrates were cleaned with a RCA I-II process. The oxide films were grown with an ALD Savannah Cambridge 100 using tetrakis (dimethylamino) hafnium (TDMA-Hf) as Hf precursor and water (Type I) as the oxidant precursor. The reactor was set to 250°C with an ultra high purity N 2 flow (20 sccm) as purging gas. The exposure time to TDMA-Hf and water were 0.08s and 0.04s per cycle respectively, resulting a growth rate of 1 Å per cycle [2]. The characterization of the film was done through ARXPS with an instrument assembled by Intercovamex equipped with an XR5 monochromatic X-ray source (TermoFisher-VG). To enhance resolution, we employed 10 eV as the pass energy of the spectrometer. The analysis was done employing the multilayer model (MLM) [3]. It was possible to identify the formation of an oxygen-rich hafnium silicate ~9 Å interface (Hf 0.81 Si 0.18 O 2.46 N 0.26) and an hafnium oxide layer with almost no nitrogen. This indicates that nitridation is preferential in regions where silicon is present.

In this work we reports the nitridation degree, carried out through remote plasma processing (LIT... more In this work we reports the nitridation degree, carried out through remote plasma processing (LITMAS), of 2 nm films of silicon oxide and hafnium oxide. The plasma power was 2500 W and the substrate temperature 400 °C. The working pressure and nitrogen flow were kept at 5.0×10-2 Torr and 110 sccm, respectively. The nitridation of silica saturates at a 1:3 N to O ratio. 6 This condition was obtained at 2,500W and 400°C after 10 min. The nitridation of hafnia, under the same parameters only reached a 1:12 N to O ratio. We are exploring the processing conditions for substitutional nitridation without perturbing the original structure of hafnia. Abstract SiO 2 SiO 2 At conditions of plasma power 2500W and substrate temperature of 400°C, the nitriding of silicon oxide reaches a saturation in replacing one of the oxygen atoms by one nitrogen 6 , found by XPS analysis composition SiO 1.67 N 0.46 , while hafnium oxide have a lower degree of nitriding finding a composition of HfO 1.8 N 0.15 under the same conditions of silicon oxide. The nitriding of the silicon oxide related to the peak N1s found in 398.8eV while the hafnium oxide is related to 396.7eV

En el presente trabajo se estudió el mecanismo de consolidación entre una base de arcillas con un... more En el presente trabajo se estudió el mecanismo de consolidación entre una base de arcillas con un alto contenido de caolinita-cuarzo y una solución de silicato de sodio comercial ( = 1.3898, R SiO2/N2O=3.09). Esta reacción da lugar a la síntesis de un geopolímero. Las arcillas, el silicato de sodio y el geopolímero consolidado se caracterizaron por espectrometría de absorción atómica (AAS), difracción de rayos X en polvos (PXRD), espectroscopia molecular infrarroja (FTIR) y microscopía electrónica de transmisión (TEM). Los resultados sugieren que, en la consolidación del geopolímero el silicato de sodio envuelve a las estructuras de caolinita, alunita y cuarzo encontradas en las arcillas naturales. Al ser sometido a un tratamiento térmico entre 70 y 250 C el silicato de sodio se deshidrata, iniciando un proceso de geopolimerización. Al incrementar la temperatura entre 337-550 C el silicato de sodio se deshidroxila, formando enlaces Si-O-Si identificados por FTIR con una vibración en 1085 cm-1.

En el presente trabajo se estudió el proceso de deshidroxilación de un geopolímero sintetizado a ... more En el presente trabajo se estudió el proceso de deshidroxilación de un geopolímero sintetizado a base de una solución de silicato de sodio y una arcilla con alto contenido de caolinita y alunita. Las arcillas, el silicato de sodio y el geopolímero se caracterizaron por TG/DTA y FTIR, encontrando tres procesos endotérmicos; el primero, centrado en 93°C con una pérdida del 10.16% de masa, se asocia a la deshidratación del geopolímero, seguida de una pérdida de masa del 3.54% asociada a la eliminación del agua de cristalización en la consolidación del silicato de sodio, además de un proceso endotérmico centrado en 475°C con una pérdida de masa del 6.92%, esto se asocia a la deshidroxilación del geopolímero. Se observa que, la caolinita presente en el geopolímero consolidado se deshidroxila para dar lugar a metacaolinita a 475°C. El proceso de deshidroxilación se analizó por DRIFT, haciendo un seguimiento de la vibración del enlace O-H en las bandas características de la estructura Alvi-OH-Alvi, centradas en 3694, 3669, 3650 y 3621 cm-1, y de los registros en espectrometría de masas para las fracciones m/z = 17 y 18.

En el presente trabajo se realizó la caracterización química, mineralógica y textural de 2 arcill... more En el presente trabajo se realizó la caracterización química, mineralógica y textural de 2 arcillas del municipio de Comonfort, Gto., con el fin de obtener información relevante sobre sus características específicas y poder determinar con base en estas sus potenciales campos de aplicación industrial. Las arcillas estudiadas se nombran como arcilla A1 y A2. En la caracterización de las arcillas de estudio se utilizaron las técnicas de análisis de: espectrometría de absorción atómica (AAS), espectroscopia infrarroja (FTIR), difracción de rayos-X en polvos (PDRX), microscopía de transmisión electrónica (TEM) y análisis de adsorción-desorción de nitrógeno (BET). Con base en los resultados obtenidos de la caracterización, se obtuvo que las arcillas de estudio son de materiales conformados esencialmente de óxidos de silicio y aluminio (aluminosilicatos). En los cuales se identificó la presencia de metales como Ca ++ , Fe +++ y Mg ++ . Se identificaron enlaces Si-O, Si-OH, Al-OH que dan forma a estructuras minerales como Caolinita, Cuarzo y Alunita principalmente. En cuanto a las características texturales se obtuvo que las dos arcillas son materiales mesoporosos que poseen una considerable área superficial específica con un diámetro de poro promedio ligeramente mayor a los 3nm.

Resumen En este trabajo se realizó la extracción de hierro (Fe) para determinar la presencia y di... more Resumen En este trabajo se realizó la extracción de hierro (Fe) para determinar la presencia y distribución de este elemento en arcillas minerales de la comunidad de Delgado de Abajo, Comonfort, Guanajuato. Se utilizaron dos tipos de arcillas nombradas como AB y AF compuestas principalmente por Caolinita, Cuarzo y Alunita. Los ensayos experimentales para la extracción de Fe se dividieron en dos fases. La primera enfocada a la extracción del Fe contenido en la toda la estructura arcillosa (Fe total) mediante una fusión alcalina con metaborato-tetraborato de litio a una temperatura de 900ºC. La segunda fase enfocada a la extracción de Fe contenido solo en la superficie de la arcilla (Fe superficial) mediante la lixiviación del Fe con HCl, siguiendo un diseño de experimentos factorial multinivel en el que se evaluaron diferentes concentraciones de ácido, tiempos de lixiviación y temperaturas. La cuantificación del Fe extraído se realizó mediante las técnicas de Espectrometría de Absorción Atómica (AAS) y Espectrometría de Absorción Molecular Visible (VIS) utilizando el método de orto-fenantrolina. Los resultados obtenidos muestran que el Fe contenido en las arcillas de estudio se encuentra distribuido entre su estructura interna y su superficie, teniendo una presencia mayor en la estructura interna con un porcentaje del 59.81% para la arcilla AB y del 52.36% para la arcilla AF. Para analizar el cambio estructural de las arcillas se realizaron análisis de Microscopía de Transmisión Electrónica (TEM) de las arcillas antes y después de la extracción de Fe.

Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is... more Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is used to prevent crystallization during annealing [1]. The thickness and composition of HfO x N y films is susceptible to the processing parameters. In this work we present an study of HfO 2 nitridation through remote plasma. P-type crystalline silicon substrates were cleaned with a RCA I-II process. The oxide films were grown with an ALD Savannah Cambridge 100 using tetrakis (dimethylamino) hafnium (TDMA-Hf) as Hf precursor and water (Type I) as the oxidant precursor. The reactor was set to 250°C with an ultra high purity N 2 flow (20 sccm) as purging gas. The exposure time to TDMA-Hf and water were 0.08s and 0.04s per cycle respectively, resulting a growth rate of 1 Å per cycle [2]. The characterization of the film was done through ARXPS with an instrument assembled by Intercovamex equipped with an XR5 monochromatic X-ray source (TermoFisher-VG). To enhance resolution, we employed 10 eV as the pass energy of the spectrometer. The analysis was done employing the multilayer model (MLM) [3]. It was possible to identify the formation of an oxygen-rich hafnium silicate ~9 Å interface (Hf 0.81 Si 0.18 O 2.46 N 0.26) and an hafnium oxide layer with almost no nitrogen. This indicates that nitridation is preferential in regions where silicon is present.

Absorption studies are important in understanding contaminant retention behavior in soils, partic... more Absorption studies are important in understanding contaminant retention behavior in soils, particularly soils at waste sites 1. Some studies suggest that the use of long chain surfactants incorporated into clays improves adsorption heavy metal cations 2–5. In this work the results of the comparative study of the functionalization with HDTMA of two mineral clays with a high proportion of montmorillonite and hematite are reported. Clays were characterized by atomic absortion spectroscopy (AAS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Functionalization was carried out in a BATCH process at 25ªC for 3 hours using a ratio of HDMTA correlated with the three times the cation exchange capacity of clays (40-42 meq/100g). Fourier transform spectroscopy to determine the binding of the organic chains and replacement of ions on the surface and interlayer spaces of clays was used. The bands observed between 2970-2850 cm-1 are attributed to-CH2 HDTMA incorporated in the interlayer space. Functionalized clays were added to solutions of potassium dichromate of 50 mg/L in BATCH systems, sampling and measuring by UV-Vis spectroscopy. We observed that the functionalized clays have a removal ratio of 32mg/g of clay into a maximum removal time of 10 min, compared with the natural clays with 26mg/g of clay of chromium (VI) removal.

In this work, the formation of oxide film on metallic copper was studied using X-ray photoelectro... more In this work, the formation of oxide film on metallic copper was studied using X-ray photoelectron spectroscopy (XPS). Metallic copper was sublimated on Si (100) wafers in a high vaccum chamber. Early stages of oxidation were achieved by exposing the copper film to oxygen flow from 1 L to 10 GL at room temperature. The fitting of the spectra was carried out by using a double-Lorentzian line-shape [1]; this function fits the high asymmetry of the main peak more precisely than the traditional forms. The pronounced background of the transition metal XPS spectrum was modeled employing a combination of a Shirley and a Tougaard-type backgrounds [2].

En el presente trabajo se estudió la adherencia de un geopolímero sintetizado a partir de una bas... more En el presente trabajo se estudió la adherencia de un geopolímero sintetizado a partir de una base de arcillas refractarias y una solución de silicato de sodio comercial ( = 1.3898, R SiO 2 /N 2 O=3.09). Se utilizó un diseño de experimentos para mezclas simplex con centroide y, para su optimización una metodología de superficie de respuesta; manteniendo el porcentaje de silicato de sodio constante a 50%, analizando la adherencia como variable de respuesta. Esta propiedad fue medida en una maquina de pruebas universales; encontrándose que, el mejor ajuste es un modelo cuadrático, con interacciones sinérgicas entre todos los factores; obteniendo una adherencia promedio de 28.11 MPa. Se obtuvieron micrografías TEM para observar los cambios en la morfología de geopolímero antes y después un tratamiento térmico a 950ºC por 8hr.

Se estudio la remoción de cromo hexavalente utilizando arcillas funcionalizadas mediante tratamie... more Se estudio la remoción de cromo hexavalente utilizando arcillas funcionalizadas mediante tratamientos ácidos (HNO3, H2SO4, H3PO4 y C4H7OOH) buscando incrementar su capacidad de adsorción para potenciar su uso en la remoción de cromo hexavalente. Se realizó el estudio de la adsorción en un sistema batch a un pH constante de 2 y a una temperatura de 25oC, siguiendo un diseño de experimentos factorial. En este diseño se consideró como variable de análisis la proporción Cr6+/arcilla. Se generaron las isotermas de adsorción obteniendo que la máxima remoción fue del 80% para la arcilla funcionalizada con H3PO4 (AAF). Posteriormente se realizó el estudio de las arcillas utilizadas en la adsorción mediante espectroscopia de infrarrojo (FTIR) y microscopía de transmisión electrónica (TEM) para identificar la interacción arcilla-Cr6+, mediante lo cual se presume que el Cr6+ fue removido tanto por adsorción como por reducción de este a Cr3+.

Papers by J.A. Torres-Ochoa

Applied Surface Science, 2021

Abstract A quantitative study of the surface composition of clean metallic and oxidized chromium ... more Abstract A quantitative study of the surface composition of clean metallic and oxidized chromium exposed to atmospheric conditions was carried out employing X-ray photoelectron spectroscopy (XPS). Advanced tools were used for the fitting process and surface composition analysis. We found that, in contrast with most metals, the oxidation does not come about through the formation of an oxide layer. State of the art analysis showed that, even at long exposures, a fraction of the chromium surface retains its metallic nature even at the top layers. Depth profile of XPS spectra shows no shape modulation from angle to angle which strongly suggest both Cr3+ and Cr6+ species coexist with the metallic species throughout the probing depth of XPS. The oxidation mechanism of metallic chromium exposed to ambient is through the partial oxidation of surface regions.

Polymer Degradation and Stability, 2018

Polyethylene/poly (lactic acid)/chitosan films, with and without poly(ethyleneg-maleic anhydride)... more Polyethylene/poly (lactic acid)/chitosan films, with and without poly(ethyleneg-maleic anhydride) (PEgMA) as compatibilizer, were prepared by extrusion and the degradation behavior under different times of standard weathering conditions was analyzed. The materials were characterized by means of infrared spectroscopy, scanning electron microscopy, tensile strength, differential scanning calorimetry and thermogravimetric analysis. It was demonstrated that blends of synthetic and natural polymers have a higher susceptibility to degradation in comparison to neat polyethylene and poly (lactic acid) films. Additionally, it is found that the incorporation of PEgMA into the extruded films apparently favored the polymer degradation, as it deduced from the fall of the mechanical properties when the films are exposed to accelerated weathering simulation.

Applied Physics A, 2018

A technique was developed to measure dielectric constant at microscale based on the system theory... more A technique was developed to measure dielectric constant at microscale based on the system theory approach using an atomic force microscopy (AFM), this makes possible the electrical characterization of dielectric materials using an optimized instrumentation. This technique is capable of measuring capacitance on either metallic contact-insulator-metallic contact or metallic contact-insulator with the AFM tip as the upper contact, the dielectric constant can be calculated from these results. The technique compares the frequency response between the input voltage and the output voltage of an equivalent RC-circuit (resistance-capacitance) in the frequency range 1 Hz-60 kHz. This comparison is analyzed using a transfer function model and a least-squares process to get the time constant involved in this kind of circuit, facilitating the implementation of this technique with any atomic force microscopy equipment. Additionally, the measurements can be carried out in a single point or in a mapping. The measurements were carried out on two hybrid films, PMMA-TiO 2-SiO 2 and PMMA-TiO 2-BT, which were prepared by sol-gel technique and deposited on indium tin oxide (ITO)-coated glass substrates. The results obtained with this technique agreed with conventional measurements that use commercial capacitance-voltage analyzer, and indicated that dielectric constant is 11.31 for PMMA-TiO 2-SiO 2 , and 15.41 for PMMA-TiO 2-BT.

Absorption studies are important in understanding contaminant retention behavior in soils, partic... more Absorption studies are important in understanding contaminant retention behavior in soils, particularly soils at waste sites 1. Some studies suggest that the use of long chain surfactants incorporated into clays improves adsorption heavy metal cations 2–5. In this work the results of the comparative study of the functionalization with HDTMA of two mineral clays with a high proportion of montmorillonite and hematite are reported. Clays were characterized by atomic absortion spectroscopy (AAS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Functionalization was carried out in a BATCH process at 25ªC for 3 hours using a ratio of HDMTA correlated with the three times the cation exchange capacity of clays (40-42 meq/100g). Fourier transform spectroscopy to determine the binding of the organic chains and replacement of ions on the surface and interlayer spaces of clays was used. The bands observed between 2970-2850 cm-1 are attributed to-CH2 HDTMA incorporated in the interlayer space. Functionalized clays were added to solutions of potassium dichromate of 50 mg/L in BATCH systems, sampling and measuring by UV-Vis spectroscopy. We observed that the functionalized clays have a removal ratio of 32mg/g of clay into a maximum removal time of 10 min, compared with the natural clays with 26mg/g of clay of chromium (VI) removal.

Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is... more Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is used to prevent crystallization during annealing [1]. The thickness and composition of HfO x N y films is susceptible to the processing parameters. In this work we present an study of HfO 2 nitridation through remote plasma. P-type crystalline silicon substrates were cleaned with a RCA I-II process. The oxide films were grown with an ALD Savannah Cambridge 100 using tetrakis (dimethylamino) hafnium (TDMA-Hf) as Hf precursor and water (Type I) as the oxidant precursor. The reactor was set to 250°C with an ultra high purity N 2 flow (20 sccm) as purging gas. The exposure time to TDMA-Hf and water were 0.08s and 0.04s per cycle respectively, resulting a growth rate of 1 Å per cycle [2]. The characterization of the film was done through ARXPS with an instrument assembled by Intercovamex equipped with an XR5 monochromatic X-ray source (TermoFisher-VG). To enhance resolution, we employed 10 eV as the pass energy of the spectrometer. The analysis was done employing the multilayer model (MLM) [3]. It was possible to identify the formation of an oxygen-rich hafnium silicate ~9 Å interface (Hf 0.81 Si 0.18 O 2.46 N 0.26) and an hafnium oxide layer with almost no nitrogen. This indicates that nitridation is preferential in regions where silicon is present.

In this work we reports the nitridation degree, carried out through remote plasma processing (LIT... more In this work we reports the nitridation degree, carried out through remote plasma processing (LITMAS), of 2 nm films of silicon oxide and hafnium oxide. The plasma power was 2500 W and the substrate temperature 400 °C. The working pressure and nitrogen flow were kept at 5.0×10-2 Torr and 110 sccm, respectively. The nitridation of silica saturates at a 1:3 N to O ratio. 6 This condition was obtained at 2,500W and 400°C after 10 min. The nitridation of hafnia, under the same parameters only reached a 1:12 N to O ratio. We are exploring the processing conditions for substitutional nitridation without perturbing the original structure of hafnia. Abstract SiO 2 SiO 2 At conditions of plasma power 2500W and substrate temperature of 400°C, the nitriding of silicon oxide reaches a saturation in replacing one of the oxygen atoms by one nitrogen 6 , found by XPS analysis composition SiO 1.67 N 0.46 , while hafnium oxide have a lower degree of nitriding finding a composition of HfO 1.8 N 0.15 under the same conditions of silicon oxide. The nitriding of the silicon oxide related to the peak N1s found in 398.8eV while the hafnium oxide is related to 396.7eV

En el presente trabajo se estudió el mecanismo de consolidación entre una base de arcillas con un... more En el presente trabajo se estudió el mecanismo de consolidación entre una base de arcillas con un alto contenido de caolinita-cuarzo y una solución de silicato de sodio comercial ( = 1.3898, R SiO2/N2O=3.09). Esta reacción da lugar a la síntesis de un geopolímero. Las arcillas, el silicato de sodio y el geopolímero consolidado se caracterizaron por espectrometría de absorción atómica (AAS), difracción de rayos X en polvos (PXRD), espectroscopia molecular infrarroja (FTIR) y microscopía electrónica de transmisión (TEM). Los resultados sugieren que, en la consolidación del geopolímero el silicato de sodio envuelve a las estructuras de caolinita, alunita y cuarzo encontradas en las arcillas naturales. Al ser sometido a un tratamiento térmico entre 70 y 250 C el silicato de sodio se deshidrata, iniciando un proceso de geopolimerización. Al incrementar la temperatura entre 337-550 C el silicato de sodio se deshidroxila, formando enlaces Si-O-Si identificados por FTIR con una vibración en 1085 cm-1.

En el presente trabajo se estudió el proceso de deshidroxilación de un geopolímero sintetizado a ... more En el presente trabajo se estudió el proceso de deshidroxilación de un geopolímero sintetizado a base de una solución de silicato de sodio y una arcilla con alto contenido de caolinita y alunita. Las arcillas, el silicato de sodio y el geopolímero se caracterizaron por TG/DTA y FTIR, encontrando tres procesos endotérmicos; el primero, centrado en 93°C con una pérdida del 10.16% de masa, se asocia a la deshidratación del geopolímero, seguida de una pérdida de masa del 3.54% asociada a la eliminación del agua de cristalización en la consolidación del silicato de sodio, además de un proceso endotérmico centrado en 475°C con una pérdida de masa del 6.92%, esto se asocia a la deshidroxilación del geopolímero. Se observa que, la caolinita presente en el geopolímero consolidado se deshidroxila para dar lugar a metacaolinita a 475°C. El proceso de deshidroxilación se analizó por DRIFT, haciendo un seguimiento de la vibración del enlace O-H en las bandas características de la estructura Alvi-OH-Alvi, centradas en 3694, 3669, 3650 y 3621 cm-1, y de los registros en espectrometría de masas para las fracciones m/z = 17 y 18.

En el presente trabajo se realizó la caracterización química, mineralógica y textural de 2 arcill... more En el presente trabajo se realizó la caracterización química, mineralógica y textural de 2 arcillas del municipio de Comonfort, Gto., con el fin de obtener información relevante sobre sus características específicas y poder determinar con base en estas sus potenciales campos de aplicación industrial. Las arcillas estudiadas se nombran como arcilla A1 y A2. En la caracterización de las arcillas de estudio se utilizaron las técnicas de análisis de: espectrometría de absorción atómica (AAS), espectroscopia infrarroja (FTIR), difracción de rayos-X en polvos (PDRX), microscopía de transmisión electrónica (TEM) y análisis de adsorción-desorción de nitrógeno (BET). Con base en los resultados obtenidos de la caracterización, se obtuvo que las arcillas de estudio son de materiales conformados esencialmente de óxidos de silicio y aluminio (aluminosilicatos). En los cuales se identificó la presencia de metales como Ca ++ , Fe +++ y Mg ++ . Se identificaron enlaces Si-O, Si-OH, Al-OH que dan forma a estructuras minerales como Caolinita, Cuarzo y Alunita principalmente. En cuanto a las características texturales se obtuvo que las dos arcillas son materiales mesoporosos que poseen una considerable área superficial específica con un diámetro de poro promedio ligeramente mayor a los 3nm.

Resumen En este trabajo se realizó la extracción de hierro (Fe) para determinar la presencia y di... more Resumen En este trabajo se realizó la extracción de hierro (Fe) para determinar la presencia y distribución de este elemento en arcillas minerales de la comunidad de Delgado de Abajo, Comonfort, Guanajuato. Se utilizaron dos tipos de arcillas nombradas como AB y AF compuestas principalmente por Caolinita, Cuarzo y Alunita. Los ensayos experimentales para la extracción de Fe se dividieron en dos fases. La primera enfocada a la extracción del Fe contenido en la toda la estructura arcillosa (Fe total) mediante una fusión alcalina con metaborato-tetraborato de litio a una temperatura de 900ºC. La segunda fase enfocada a la extracción de Fe contenido solo en la superficie de la arcilla (Fe superficial) mediante la lixiviación del Fe con HCl, siguiendo un diseño de experimentos factorial multinivel en el que se evaluaron diferentes concentraciones de ácido, tiempos de lixiviación y temperaturas. La cuantificación del Fe extraído se realizó mediante las técnicas de Espectrometría de Absorción Atómica (AAS) y Espectrometría de Absorción Molecular Visible (VIS) utilizando el método de orto-fenantrolina. Los resultados obtenidos muestran que el Fe contenido en las arcillas de estudio se encuentra distribuido entre su estructura interna y su superficie, teniendo una presencia mayor en la estructura interna con un porcentaje del 59.81% para la arcilla AB y del 52.36% para la arcilla AF. Para analizar el cambio estructural de las arcillas se realizaron análisis de Microscopía de Transmisión Electrónica (TEM) de las arcillas antes y después de la extracción de Fe.

Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is... more Hafnium oxide thin films are nowadays employed in CMOS devices. The nitridation of HfO 2 films is used to prevent crystallization during annealing [1]. The thickness and composition of HfO x N y films is susceptible to the processing parameters. In this work we present an study of HfO 2 nitridation through remote plasma. P-type crystalline silicon substrates were cleaned with a RCA I-II process. The oxide films were grown with an ALD Savannah Cambridge 100 using tetrakis (dimethylamino) hafnium (TDMA-Hf) as Hf precursor and water (Type I) as the oxidant precursor. The reactor was set to 250°C with an ultra high purity N 2 flow (20 sccm) as purging gas. The exposure time to TDMA-Hf and water were 0.08s and 0.04s per cycle respectively, resulting a growth rate of 1 Å per cycle [2]. The characterization of the film was done through ARXPS with an instrument assembled by Intercovamex equipped with an XR5 monochromatic X-ray source (TermoFisher-VG). To enhance resolution, we employed 10 eV as the pass energy of the spectrometer. The analysis was done employing the multilayer model (MLM) [3]. It was possible to identify the formation of an oxygen-rich hafnium silicate ~9 Å interface (Hf 0.81 Si 0.18 O 2.46 N 0.26) and an hafnium oxide layer with almost no nitrogen. This indicates that nitridation is preferential in regions where silicon is present.

Absorption studies are important in understanding contaminant retention behavior in soils, partic... more Absorption studies are important in understanding contaminant retention behavior in soils, particularly soils at waste sites 1. Some studies suggest that the use of long chain surfactants incorporated into clays improves adsorption heavy metal cations 2–5. In this work the results of the comparative study of the functionalization with HDTMA of two mineral clays with a high proportion of montmorillonite and hematite are reported. Clays were characterized by atomic absortion spectroscopy (AAS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Functionalization was carried out in a BATCH process at 25ªC for 3 hours using a ratio of HDMTA correlated with the three times the cation exchange capacity of clays (40-42 meq/100g). Fourier transform spectroscopy to determine the binding of the organic chains and replacement of ions on the surface and interlayer spaces of clays was used. The bands observed between 2970-2850 cm-1 are attributed to-CH2 HDTMA incorporated in the interlayer space. Functionalized clays were added to solutions of potassium dichromate of 50 mg/L in BATCH systems, sampling and measuring by UV-Vis spectroscopy. We observed that the functionalized clays have a removal ratio of 32mg/g of clay into a maximum removal time of 10 min, compared with the natural clays with 26mg/g of clay of chromium (VI) removal.

In this work, the formation of oxide film on metallic copper was studied using X-ray photoelectro... more In this work, the formation of oxide film on metallic copper was studied using X-ray photoelectron spectroscopy (XPS). Metallic copper was sublimated on Si (100) wafers in a high vaccum chamber. Early stages of oxidation were achieved by exposing the copper film to oxygen flow from 1 L to 10 GL at room temperature. The fitting of the spectra was carried out by using a double-Lorentzian line-shape [1]; this function fits the high asymmetry of the main peak more precisely than the traditional forms. The pronounced background of the transition metal XPS spectrum was modeled employing a combination of a Shirley and a Tougaard-type backgrounds [2].

En el presente trabajo se estudió la adherencia de un geopolímero sintetizado a partir de una bas... more En el presente trabajo se estudió la adherencia de un geopolímero sintetizado a partir de una base de arcillas refractarias y una solución de silicato de sodio comercial ( = 1.3898, R SiO 2 /N 2 O=3.09). Se utilizó un diseño de experimentos para mezclas simplex con centroide y, para su optimización una metodología de superficie de respuesta; manteniendo el porcentaje de silicato de sodio constante a 50%, analizando la adherencia como variable de respuesta. Esta propiedad fue medida en una maquina de pruebas universales; encontrándose que, el mejor ajuste es un modelo cuadrático, con interacciones sinérgicas entre todos los factores; obteniendo una adherencia promedio de 28.11 MPa. Se obtuvieron micrografías TEM para observar los cambios en la morfología de geopolímero antes y después un tratamiento térmico a 950ºC por 8hr.

Se estudio la remoción de cromo hexavalente utilizando arcillas funcionalizadas mediante tratamie... more Se estudio la remoción de cromo hexavalente utilizando arcillas funcionalizadas mediante tratamientos ácidos (HNO3, H2SO4, H3PO4 y C4H7OOH) buscando incrementar su capacidad de adsorción para potenciar su uso en la remoción de cromo hexavalente. Se realizó el estudio de la adsorción en un sistema batch a un pH constante de 2 y a una temperatura de 25oC, siguiendo un diseño de experimentos factorial. En este diseño se consideró como variable de análisis la proporción Cr6+/arcilla. Se generaron las isotermas de adsorción obteniendo que la máxima remoción fue del 80% para la arcilla funcionalizada con H3PO4 (AAF). Posteriormente se realizó el estudio de las arcillas utilizadas en la adsorción mediante espectroscopia de infrarrojo (FTIR) y microscopía de transmisión electrónica (TEM) para identificar la interacción arcilla-Cr6+, mediante lo cual se presume que el Cr6+ fue removido tanto por adsorción como por reducción de este a Cr3+.

Applied Surface Science, 2021

Abstract A quantitative study of the surface composition of clean metallic and oxidized chromium ... more Abstract A quantitative study of the surface composition of clean metallic and oxidized chromium exposed to atmospheric conditions was carried out employing X-ray photoelectron spectroscopy (XPS). Advanced tools were used for the fitting process and surface composition analysis. We found that, in contrast with most metals, the oxidation does not come about through the formation of an oxide layer. State of the art analysis showed that, even at long exposures, a fraction of the chromium surface retains its metallic nature even at the top layers. Depth profile of XPS spectra shows no shape modulation from angle to angle which strongly suggest both Cr3+ and Cr6+ species coexist with the metallic species throughout the probing depth of XPS. The oxidation mechanism of metallic chromium exposed to ambient is through the partial oxidation of surface regions.

Polymer Degradation and Stability, 2018

Polyethylene/poly (lactic acid)/chitosan films, with and without poly(ethyleneg-maleic anhydride)... more Polyethylene/poly (lactic acid)/chitosan films, with and without poly(ethyleneg-maleic anhydride) (PEgMA) as compatibilizer, were prepared by extrusion and the degradation behavior under different times of standard weathering conditions was analyzed. The materials were characterized by means of infrared spectroscopy, scanning electron microscopy, tensile strength, differential scanning calorimetry and thermogravimetric analysis. It was demonstrated that blends of synthetic and natural polymers have a higher susceptibility to degradation in comparison to neat polyethylene and poly (lactic acid) films. Additionally, it is found that the incorporation of PEgMA into the extruded films apparently favored the polymer degradation, as it deduced from the fall of the mechanical properties when the films are exposed to accelerated weathering simulation.

Applied Physics A, 2018

A technique was developed to measure dielectric constant at microscale based on the system theory... more A technique was developed to measure dielectric constant at microscale based on the system theory approach using an atomic force microscopy (AFM), this makes possible the electrical characterization of dielectric materials using an optimized instrumentation. This technique is capable of measuring capacitance on either metallic contact-insulator-metallic contact or metallic contact-insulator with the AFM tip as the upper contact, the dielectric constant can be calculated from these results. The technique compares the frequency response between the input voltage and the output voltage of an equivalent RC-circuit (resistance-capacitance) in the frequency range 1 Hz-60 kHz. This comparison is analyzed using a transfer function model and a least-squares process to get the time constant involved in this kind of circuit, facilitating the implementation of this technique with any atomic force microscopy equipment. Additionally, the measurements can be carried out in a single point or in a mapping. The measurements were carried out on two hybrid films, PMMA-TiO 2-SiO 2 and PMMA-TiO 2-BT, which were prepared by sol-gel technique and deposited on indium tin oxide (ITO)-coated glass substrates. The results obtained with this technique agreed with conventional measurements that use commercial capacitance-voltage analyzer, and indicated that dielectric constant is 11.31 for PMMA-TiO 2-SiO 2 , and 15.41 for PMMA-TiO 2-BT.