Papers by Author: Marissa Vargas-Ramírez

Abstract: A three dimensions mathematical modeling was developed with COMSOL 3.2 software of an electroremediation cell. The Navier Stokes and Darcy equations were used to model the behavior of the electrolyte and the sand, respectively. The mass balance for hydrogen ion was carried out with Nernst-Planck equation for the anode and soil regions. The main factors that contribute to the hydrogen ion balance were the diffusive flux and electric migration. The mathematical modeling was validated with an experimental arrangement consisted in an electroremediation cell which contains sand as porous medium and water as electrolyte. A potential of 20 V was applied for 24 hours and the pH was measured continuously. The results of the model are in good agreement with those obtained experimentally.

Abstract: Cadmium Selenide (CdSe) thin films were prepared by pulsed laser deposition using a Nd:YAG laser (355 nm). Films were grown by ablating a sintered pure CdSe target with fluences from 0.1 to 1.5 J/cm² on corning glass, silicon (100) and quartz substrates. Deposition chamber was maintained under vacuum pressure while substrate temperature was increased from room temperature to 500°C in order to control the crystalline phase. All the films show mirror-like surface morphology. Atomic force microscopy (AFM) images shown that films have very flat surfaces with RMS values around 0.7 and 5 nm for room temperature and 500°C respectively. The X-ray diffraction analysis proves the presence of the cubic zinc blend phase for the CdSe films deposited at low temperature, at 400°C and at higher substrate temperature the hexagonal phase is present. TEM analysis shows that at 100°C the films are constituted by particles with an average size of 30nm in diameter. The optical properties of the films were determined from the UV-transmission spectra. The estimated band gap values of the films deposited at room temperature and at 400°C (0.1 J/cm²) were 1.87 and 1.70 eV respectively.