Papers by Author: Miguel Meléndez-Lira

Abstract: In this work, the synthesis of manganese oxide nanoparticles was achieved by one-step spray pyrolysis method. The nanoparticles were synthesized just from MnCl₂ aqueous solution. The solution was nebulized to a Si substrate placed at 400 °C for 1, 5 10 and 20 min and transported at a 0.1 L /min rate in a Nitrogen flux. The X-ray diffraction confirms tetragonal Mn₃O₄ as the unique phase in the whole sample. The scanning electron microscopy images proved the achievement of irregular nanoparticles with an average diameter of 280 nm experimentally determined by dynamic light scattering. Energy dispersive X-ray and Raman spectroscopy confirmed that the nanoparticles were obtained with Mn₃O₄ single-phase and the employed methodology prevented any contamination. The nanoparticles proved to induce temperature enhancement on artificial breast tissue by exposition to microwave radiation by achieving an increase in temperature around 8 %.

Abstract: In this work we report the results of the synthesis, structural and optical characterization of SiO₂/Ge/SiO₂ heterostructures by reactive RF sputtering. The SiO₂ films were grown by reactive sputtering employing a plasma mixture of oxygen and argon. The Ge layer was grown employing an Ar atmosphere. The samples were prepared on p-type Si (1 1 1) substrates by reactive sputtering. The effect of the partial pressure of oxygen on the electronic properties of the heterostructure is reported[1]. Structural characterization was carried out by grazing angle X-ray difraction. Surface roughness was quantified by atomic force microscopy. The presence of Ge nanocrystals (Ge-NCs) was evidenced by X-ray diffraction. The vibrational properties were studied by Raman spectroscopy. The Raman spectra showed modes associated to germanium indicating the formation of low dimensionality germanium particles embedded within a SiO₂ matrix. Photoluminescence emission is observed around ~1.7 eV and it is associated to the quantum confinement of carriers in Ge-NCs. Ohmic contacts were deposited using a van der Pauw geometry employing an a AuSb alloy for the contacts. Temperature dependent Hall (T-Hall) measurements were done between 35 K and 150 K, using the van der Pauw method. The results indicated low resistivity values that could be explained due to some variable range hopping conduction mechanism.