A sensor based on random connections of single-crystalline SnO2 nanowires (NWs) has been fabricated for ethanol detection. The NW length of ∼10 m leads to the formation of several random node ...connections between the Ag electrodes. The samples were subjected to thermal treatments under a reducing atmosphere of H2/Ar, to generate oxygen vacancies at the surface of the NWs. As a result, the core conduction channel of the NWs, where the conduction is based on electron hopping through the potential barriers at the contact nodes, switch to the surface of the NWs by the creation of an impurity band of shallow donors located at 0.347 eV below the conduction band. We suggest that the H2-rich atmosphere of the thermal treatments induced the formation of interstitial hydrogen (Hi) and substitutional hydrogen (HO), which are shallow donors with low formation energy.
A new process for synthesizing rhodium (Rh) nano-particles by sol–gel processing using acrylamide and microwaves is reported and discussed. Three heat treatments were applied: the first required the ...use of microwaves, with an inert gas (Ar) flux, to decompose the organic material; the second and third treatments, respectively, were carried out into a furnace in air at temperatures of 600 and 1,000 °C. This procedure ensured the removal of by-products produced during the sol–gel reaction. The synthesis of a pure nano-Rh was confirmed by X-ray diffraction (XRD), where the presence of a cubic structure was observed (PDF file 089-7383), and EDX. Thermogravimetric analysis (TGA), in addition to determining the decomposition temperatures, enabled the heat treatment conditions needed to obtain pure nano- Rh to be elucidated. Furthermore, the morphology was observed with a scanning electron microscope (SEM). After the heat treatment at 1,000 °C, SEM images showed grain sizes between 3 and 200 nm. High-resolution transmission electron microscopy (HR-TEM) confirmed the production of those nano- particles, and the beginning of the formation of clusters as a consequence of the high temperature applied to the system.
The effect of Mn doping in the electronic structure of cubic KTaO3 has been studied by first-principles calculations, based on density functional theory. In our study, we analyze different Mn-dopant ...concentrations, namely 6.25 %, 12.5 %, and 25 %, with Mn replacing Ta, K, or both sites, and probe changes in electrical, magnetic, and optical properties. Our results show that for Mn substituting Ta or K atoms, the structures acquire a metallic character and, when Mn substitutes both Ta and K atoms, the structures conserve a semiconductor character. On the other hand, all doped structures acquire a ferromagnetic character and magnetic moment resides almost entirely in Mn atom, being larger when Mn substitutes K atoms.
Analysis of the calculated optical properties, allows us to monitor changes in the absorption coefficient. We show that structures for Mn replacing both Ta and K sites display an increased absorption of electromagnetic radiation in the visible region.
Analyzing the formal oxidation states, following a Bader's analysis of component atoms, allows us to explain changes in electrical, magnetic, and optical properties.
Spiny lobsters have an extended pelagic larval development in oceanic waters, ending in a non-feeding post-larva that swims to coastal habitats to settle and molt to a benthic juvenile. The ...accumulation of energetic reserves by larvae is thought to be challenging, especially in tropical waters. We examined changes in fatty acid (FA) composition of the tropical Caribbean spiny lobster Panulirus argus for successive developmental stages sampled across the shelf and off the eastern Yucatan Peninsula, Mexico. Final-stage larvae accumulate considerable lipid reserves (26 ± 2.8% SD of dry weight), mostly saturated FAs (65.4 ± 2.1% of total FAs). Proportions of the FAs 14:0, 15:0, and 16:1n-7 tended to decrease from final larvae to settled juveniles, consistent with their use as a key energy source, although the dominant energy sources in all developmental stages were 16:0 and 18:0. In contrast, the percentages of 20:4n-6 (arachidonic acid) and 20:5n-3 (eicosapentaenoic acid) tended to increase with development, consistent with being conserved. Bacterial and flagellate FA markers dominated in final-stage larvae, indicating a microbial loop foodweb as the source of lipid reserves. Such foodwebs are characteristic of the oligotrophic waters in which the larvae of both sub-tropical and temperate spiny lobsters species are also found. Similarities in the accumulation and use of FAs between the tropical P. argus and spiny lobsters from cooler regions of the world suggest that their extended larval period is a means of acquiring sufficient energy reserves whilst feeding in oligotrophic oceanic waters.
PDF
