Showing papers by "S. A. Tomás published in 2019"

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO3 Thin Films Deposited by Physical Vapor Deposition

Abstract: The influence of a cadmium selenide (CdSe) layer on the thermochromic and photochromic properties of molybdenum trioxide (MoO3) thin films was studied. The films were deposited on glass substrates ...

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO3 Thin Films Deposited by Physical Vapor Deposition

Abstract: The influence of a cadmium selenide (CdSe) layer on the thermochromic and photochromic properties of molybdenum trioxide (MoO₃) thin films was studied. The films were deposited on glass substrates by thermal evaporation in vacuum using two different bilayer configurations, namely, substrate/MoO₃/CdSe (SMC) and substrate/CdSe/MoO₃ (SCM). The film thicknesses for the MoO₃ and CdSe layers were ca. 250 and 20 nm, respectively. The thermochromic effect was evaluated in the annealing temperature range from 25 to 225 °C, in the presence of air. The characteristic optical absorption band attributed to the color center formation, centered at 820 nm, indicated enhanced thermo- and photochromic effects for both bilayer systems relative to monolayer MoO₃ thin films. For the thermochromic effect, this improvement was more pronounced when CdSe was the upper layer, i.e., for the SMC system. Regarding the photochromic effect, the films were irradiated with UV light for several exposure times within the lapse of 30–180 min. While both bilayer systems presented better photochromic response than pure MoO₃ thin films, the SCM system exhibited better photochromic response. These results are explained in terms of the optical, structural, and surface chemistry properties of the films.

Effect of the indium myristate precursor concentration on the structural, optical, chemical surface, and electronic properties of InP quantum dots passivated with ZnS

Abstract: In this work, we present results on the synthesis and characterization of InP and InP@ZnS quantum dots (QDs), grown using a single-step chemical synthesis method without injection of hot precursors, varying the concentration of indium myristate in both cases. It was found a color variation of the QDs in solution due to the quantum confinement effects when the nanoparticle sizes are smaller than the exciton Bohr radius. The band-gap energy of the samples was determined from the absorption spectra. From the photoluminescence (PL) spectra, emission peaks located in the range from 2.1 to 3.0 eV were observed. Furthermore, an enhanced PL emission due to a passivation effect in the ZnS-covered InP QDs was obtained. From X-ray diffraction (XRD), it was shown the presence of crystalline phases of the InP, ZnS, and In2O3 nanoparticles, with sizes ranging from 8 to 10 nm as determined by high resolution transmission electron microscopy (HR-TEM). From X-ray photoelectron spectroscopy (XPS) analysis, it was confirmed the formation of InP, ZnS, and In2O3; moreover, by means of a valence band analysis, the electronic structure of the samples was further investigated. The effect of the indium myristate precursor concentration on the optical, structural, surface chemical, and electronic properties of InP and InP@ZnS QDs will be discussed.