J. Reyes-Gomez

University of California, Santa Cruz, Santa Cruz, California, United States

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Publications (11)13.85 Total impact

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    ABSTRACT: Novel composite titanium dioxide (TiO2) films of 10 μm thickness were prepared and characterized with an emphasis on evaluating their photovoltaic properties. The films contained 13 nm TiO2 nanocrystals (NCs) with anatase crystalline phase deposited on FTO substrates, composited with CdSe quantum dots (QDs), gold nanoparticles (Au NPs), and poly(3-octylthiophene) (P3OT) in different configurations and combinations. With the introduction of Au NPs or P3OT into the TiO2/QDs films, the photocurrent increased to 85% and 150%, respectively, while the photoconversion efficiency increased by 167% and 177%, respectively. An interesting synergistic effect was observed when Au NPs and P3OT were used in conjunction. The configuration of TiO2/Au/QDs/P3OT film exhibited a photocurrent of 906 μA (an enhancement of 285%) and a photoconversion efficiency of 0.661% (an enhancement of 600%) compared to that of TiO2/QDs films. Such significant enhancement is attributed to the ability of the Au NPs to facilitate charge separation and improve electron injection as well as P3OT’s ability to inject electrons and enhance hole transport. These properties, when combined with the QD’s strong photoabsorption in the visible, led to the overall increase in photocurrent generation, fill factor, and consequently photoconversion efficiency.
    The Journal of Physical Chemistry C 11/2011; 115(46). DOI:10.1021/jp207744n · 4.84 Impact Factor
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    ABSTRACT: Carbon paste electrodes (CPEs) modified with a biosolid, two types of soils with different amounts of organic matter (OM), and two biocomposites (soils mixed with a biosolid) were used to assess and compare the Cu(II) ion retention properties of the organic matter contained in the samples. The accumulation of Cu(II) on the surface of the modified carbon paste electrodes (MCPEs) was performed under open-circuit conditions. When comparing the response of the MCPEs while assessing parameters such as pH, preconcentration time, and adsorption/desorption capacity, it was found that the reaction mechanism of the two soils is different between the soils and dissimilar from the biosolid; while the biocomposites show reaction mechanisms that are intermediate between those of the soils and the biosolid. This was proven with the use of infrared spectroscopy, since the FTIR spectra show similarities between the two soils and significant differences between the soils and the biosolid.
    Journal of Environmental Management 10/2010; 92(3):448-56. DOI:10.1016/j.jenvman.2010.08.033 · 3.06 Impact Factor
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    ABSTRACT: Overactivation of NMDA-Rs may mediate excitotoxic cell death associated with epileptic seizures, and hypoxic-ischemic conditions. We assessed whether repeated subcutaneous administration of l-glutamate to neonatal rats affects the subunit composition of NMDA-Rs. Accordingly, cortical and hippocampal tissue from 14-day-old rats was analyzed by Western blotting and RT-PCR to quantify the protein and mRNA expression of different NMDA-R subunits. In addition, tissue sections were Nissl stained to assess the cell damage in this tissue. Early exposure of neonatal rats to L-glutamate differentially affects the expression of mRNA transcripts for NMDA-R subunits in the cerebral cortex and hippocampus. In the cerebral cortex, a decrease in NR2B subunit mRNA expression was observed, as well as a loss of NR1 and NR2A protein. By contrast, neonatal L-glutamate administration augmented the transcripts encoding the NR1, NR2B, and NR2C subunits in the hippocampal formation. The expression of mRNA encoding the NR2A subunit was not affected by neonatal L-glutamate administration in either of the brain regions examined. This differential expression of NMDA-R subunits following neonatal exposure to L-glutamate may represent an adaptive response of the glutamate receptors to overactivation in order to reduce the effect of high L-glutamate during the early period of life when the animal is more vulnerable to excitotoxicity.
    International journal of developmental neuroscience: the official journal of the International Society for Developmental Neuroscience 10/2008; 27(2):197-204. DOI:10.1016/j.ijdevneu.2008.09.006 · 2.03 Impact Factor
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    ABSTRACT: The isobaric molar heat capacity of NiBOCl boracite at the ferroelectric 43m-mm2 phase transition is reported. Spontaneous birefringence measurements on single crystals of this composition from room temperature up to the transition temperature are also reported. It is shown by detailed analysis that antiphase domains are not to be expected in the cubic phase.
    Ferroelectrics 01/2000; 237(1):89-96. DOI:10.1080/00150190008216236 · 0.38 Impact Factor
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    ABSTRACT: The domain structure of Ni3B7O13Cl single crystals has been studied in the orthorhombic phase of this ferroic boracite by means of transmission electron microscopy. Calorimetric measurements on this composition are also reported.
    Ferroelectrics 02/1999; 222(1):209-213. DOI:10.1080/00150199908014817 · 0.38 Impact Factor
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    ABSTRACT: The static ferroelectric/ferroelastic domain structure in uncoated samples of Ni3B7O13Cl single crystals has been observed in the orthorhombic phase of this ferroic boracite by means of scanning electron microscopy and polarised light microscopy. Analytical and optical measurements on the crystal faces are also reported.
    Ferroelectrics 01/1997; 190(1):1-6. DOI:10.1080/00150199708014084 · 0.38 Impact Factor
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    ABSTRACT: Crystals of halogen manganese boracite, the mineral Mg3B7O13Cl, which is currently found in bedded sedimentary deposits of anhydrite, gypsum and halite, have been grown by chemical transport reactions and were examined by polarizing light microscopy and scanning electron microscopy. For both methods the same as-grown samples were used without having to metallize the crystal faces. Comparative electron microscope images were useful not only for observing the charging mechanism of an insulating sample bombarded by an electron beam but also for revealing the domain structure of these ferroelectric/ferroelastic materials previously observed between the crossed polars of a light microscope. EDS qualitative analysis of the crystal faces was performed for the three compositions under study, i.e. Mn3B7O13Cl, Mn3B7O13Br and Mn3B7O13I.
    Journal of Microscopy 01/1997; 185(1):1-8. DOI:10.1046/j.1365-2818.1997.1350693.x · 1.63 Impact Factor
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    ABSTRACT: The principal dielectric constant, ε33, and the spontaneous polarization, Ps of the trigonal, monoclinic and orthorhombic phases of Cobalt-Chlorine boracite has been measured between 300 to 623 K. At the onset of the 43m-mm2 transition at about 623 K, upon heating the permittivity undergoes a drastic jump downwards. Specific heat measurements in the vicinity of the cubic-orthorhombic phase transition are also reported.
    Ferroelectrics 01/1996; 185(1):67-70. DOI:10.1080/00150199608210481 · 0.38 Impact Factor
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    ABSTRACT: Fully ferroelectric/fully ferroelastic crystals of Manganese-iodine boracite (Mn3B7O13I) were grown by chemical reactions in the vapour phase. Results of observations of the domain structure in uncoated samples of this composition, both by polarized light microscopy and by scanning electron microscopy are presented.
    Ferroelectrics 10/1995; 172(1):151-155. DOI:10.1080/00150199508018468 · 0.38 Impact Factor
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    ABSTRACT: The phase transition sequence 3m − mm2 in Mn3B7O13Br (Mn-Br) boracite was investigated by means of spontaneous birefringence, dielectric constant, pyroelectric and thermal measurements. Results of calorimetric measurements give evidence of a new phase transition in this compound at about 440 K, however, this is not reconfirmed by dielectric and optical studies.
    Ferroelectrics 09/1994; 159(1):31-36. DOI:10.1080/00150199408007544 · 0.38 Impact Factor
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    ABSTRACT: Recibido el 28 de mayo de 2008; aceptado el 4 de junio de 2008 In this work, the preparation and photovoltaic conversion characterization of 10 µm films of sensitized TiO 2 is reported. The 300 nm TiO 2 particles with anatase crystalline phase were deposited on an ITO substrate and decorated with Au nanocrystals, P3OT or CdSe Quantum Dots (QD's). The photocurrent was measured in a three electrode electrochemical cell. The results exhibited that QD's sensitized TiO2 films have the largest photocurrent (237 µA/cm 2), giving a photo-conversion efficiency of 0.149%, more than fourfold the photocurrent of TiO 2 without sensitized (0.034%). These results are attributed to the ability of QD's to photogenerate charge carriers efficiently giving a great amount of electrons to increase the photocurrent. En este trabajo se reporta la preparación y caracterización de películas de 10 µm de espesor de TiO 2 sensibilizado. Las partículas de TiO 2 de 300 nm con fase cristalina anatasa fueron depositadas en un substrato de ITO y decoradas con nanocristales de Au, P3OT o puntos cuánticos de CdSe (QD's).Después, se midió fotocorriente en una celda elctroquímica de tres electrodos. Los resultados muestran que las películas de TiO2 sensibilizadas con QD tienen la mayor fotocorriente (237 µA), resultando en una eficiencia de fotoconversión de 0.149%, cuatro veces mayor a la eficiencia de las películas de TiO 2 sin sensibilizar (0.034%). Estos resultados se atribuyen a la habilidad de los QD's de fotogenerar eficientemente portadores de carga, que contribuirán para incrementar la fotocorriente.