Examinando por Autor "Maestre, David"

Mostrando 1 - 3 de 3

Ethanol gas sensing mechanisms of p-type NiO at room temperature
(Elsevier, 2022-03-30) Bartolomé, Javier; Taeño, María; Martínez-Casado, Ruth; Maestre, David; Cremades, Ana
Conductometric gas sensors based on metal oxide semiconductors (MOS) usually require high temperature operation, increasing their energy consumption and limiting their applicability. However, room temperature operation with these devices still remains a challenge in many sensor-analyte systems due in part to the low or null response and recovery speeds obtained at this temperature. In this work, the conductometric response of p- type NiO ceramic samples to ethanol is studied under room temperature operation. An anomalous response consisting in an unexpected resistance decrease upon ethanol exposure is observed depending on sample texturing, which is tuned by changing the temperature at which the samples are synthesized. This anomalous response is characterized by fast response and recovery times. A model based on two competing mechanisms, consisting in either an electron transfer from NiO to the ethanol molecule or the catalytic decomposition of adsorbed ethanol, is proposed to explain the observed anomalous response. Extending this model to other MOS could pave the way for fast sensors operating at room temperature.
Li2SnO3 branched nano- and microstructures with intense and broadband white-light emission
(Springer, 2018-11-14) García-Tecedor, Miguel; Bartolomé, Javier; Maestre, David; Trampert, Achim; Cremades, Ana
Exploiting the synergy between microstructure, morphology and dimensions by suitable nanomaterial engineering, can effectively upgrade the physical properties and material performances. Li2SnO3 elongated nano- and microstructures in form of belts, wires, rods and branched structures have been fabricated by a vapor-solid method at temperatures ranging from 700 to 900 °C using metallic Sn and Li2CO3 as precursors. The achievement of these new morphologies can face challenging applications for Li2SnO3, not only in the field of energy storage, but also as building blocks in optoelectronic devices. The micro- and nanostructures grown at 700 and 800 °C correspond to monoclinic Li2SnO3, while at 900 °C complex Li2SnO3/SnO2 core-shell microstructures are grown, as confirmed by X-ray diffraction and Raman spectroscopy. Transmission electron microscopy reveals structural disorder related to stacking faults in some of the branched structures, which is associated with the presence of the low-temperature phase of Li2SnO3. The luminescent response of these structures is dominated by intense emissions at 2, 2.5 and 3 eV, almost completely covering the whole range of the visible light spectrum. As a result, white-light emission is obtained without the need of phosphors or complex quantum well heterostructures. Enhanced functionality in applications such as in light-emitting devices could be exploited based on the high luminescence intensity observed in some of the analysed Li2SnO3 structures.
Self-Organized NiO Microcavity Arrays Fabricated by Thermal Treatments
(ACS Publications, 2020-05-05) Taeño, María; Bartolomé, Javier; Gregoratti, Luca; Modrzynski, Pawel; Maestre, David; Cremades, Ana
The potential use of NiO in low-dimensional devices requires the upgrade of appropriate synthesis methods as well as the achievement of a deeper comprehension of the growth mechanisms and the properties of this p-type oxide at the micro- and nanoscale. In this work, arrays of NiO microcavities with potential use in catalysis, sensing, and high temperature templates have been achieved following a single step process based on the use a controlled argon flow during oxidation of metallic Ni. Fabrication of these self-organized cavities can widen the applicability of NiO in new fields of research avoiding large cost post-fabrication treatments and enhancing NiO properties of interest. Formation of these hole arrays at 1000–1200 °C with unique geometrical morphology and preferential (111) texturing has been discussed based on Ni oxidation mechanisms involving Ni lattice diffusion and strain release phenomena at the NiO surface. Moreover, NiO samples have been fabricated in the range of temperatures 800–1500 °C and characterized by a complete group of techniques in order to shed light on physical aspects related to NiO which still remain unambiguous, such as the bandgap or the understanding of the Raman signal. XRD measurements confirm the presence of strain related phenomena and lattice distortions during thermal treatments. Besides, cathodoluminescence analysis shows a wide signal from near-IR to UV commonly dominated by an emission at 2.5 eV related to Ni deficiency. An increase in the Ni3+/Ni2+ ratio together with a higher p-type character, as demonstrated by surface-sensitive X-ray photoelectron spectroscopy, was promoted in the regions with microcavities as well as in the samples sintered at high temperature.