ZnMn2O4 as a material for supercapacitors and its stability against the electrolyte

The electrolyte is an essential part of a supercapacitor, conditioning its performance. Thus, the specific capacitance measured for the supercapacitor electrode in the typical three-electrode arrangement of an electrochemical cell is sometimes not reflected in the supercapacitor. For this reason, ZnMn2O4 electrodes have been manufactured by spray pyrolysis on ITO/glass. The electrodes have been characterized electrochemically, and in symmetrical supercapacitors in which three types of electrolyte have been used, studying the effect of the electrolyte on the stability of the electrode and the capacity of the supercapacitorUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Growth and characterization of ZnO thin films at low temperatures: from room temperature to − 120 °C

ZnO thin films have been grown by e-beam evaporation in the range from room temperature to − 120 °C on two types of substrates, Al2O3 (0001) and Si (100). Although the ZnO/Al2O3 system has been thoroughly characterized, including optical and electrical techniques, the morphological, structural and chemical properties show no significant differences between both substrates. Thus, the general features of the ZnO growth mode at low temperature can be generalized. The relatively low growth temperatures reduce the diffusion of atoms at the surface, which leads to morphological and chemical changes. As the temperature decreases, the growth mode changes from a van der Drift model to a gradual bilayer system composed of an interfacial layer in contact with the substrate and a second columnar-based layer. This second well-ordered film disappears for the lowest temperatures while a Zn-rich interface in contact with the substrate emerges. Precisely from this interface, Zn-rich whiskers develop under the ZnO film and cause the loss of adhesion at temperatures below − 100 °C. These extreme temperatures also affect the crystal size, lattice strain, and total amount of oxygen vacancies. The behavior of the optical and electrical properties in terms of band gap, transparency, electrical resistivity, and Seebeck coefficient is discussed in the light of structural and chemical characterization. Samples grown at 0 °C exhibit an enhanced transmittance compared to those grown at room temperature while preserving similar electrical resistivity values and natural n-type doping. These results open a promising route to enhance ZnO films properties below the typical high temperature windowThis investigation has been funded by the Ministerio de Ciencia, Innovación y Universidades of Spain through the FIS2015-67367-C2- 1-P project and by the Comunidad de Madrid through the NANOMAGCOST-CM P2018/NMT4321 project. One of the authors (C.M.) thanks Ministerio de Educación, Cultura y Deportes for FPU014/02020 gran

Imaging the Kirkendall effect in pyrite (FeS2) thin films: cross-sectional microstructure and chemical features

This investigation provides novel data on the structure and chemical composition of pyrite thin films and new hints concerning their formation mechanism. From TEM-HAADF data, it has been found that the films are composed of two different layers: one is very compact and the other one is quite porous with many voids separating a few groups of grains. This porous layer is always in direct contact with the substrate, and its thickness is quite similar to that of the original Fe film. The average size of pyrite grains is equal in both layers, what suggests that the same process is responsible for their formation. Concentration profiles of sulfur, iron and some impurities (mainly sodium and oxygen from the glass substrate) through both layers are given in this work, and thus chemical inhomogeneities of the films are proved by the obtained stoichiometric ratios (S/Fe). Moreover, Na from sodalime glass substrates mainly accumulates at the pyrite grain boundaries and barely dopes them. The obtained results support the hypothesis that the iron sulfuration process essentially induces the diffusion of iron atoms, what leads to the porous layer formation as a manifestation of the Kirkendall Effect. Therefore, it seems that the same mechanisms that operate in the synthesis of surface hollow structures at the nanoscale are also active in the formation of pyrite thin films ranging from several tens to hundreds of nanometersMembers of MIRE Group acknowledge the financial support of the Spanish MICINN under project RTI2018-099794-B-I00. E. Flores acknowledges the intramural CSIC project 2D-MeSes funding and the service from the MiNa Laboratory at IMN, and funding from CM (project SpaceTec, S2013/ICE2822), MINECO (project CSIC13-4E1794) and EU (FEDER,FSE). Financial support through the project UMA18-FEDERJA-041 is gratefully acknowledge

Towards airborne laser-induced breakdown spectroscopy: A signal recovery method for LIBS instruments subjected to vibrations

Sample or instrument vibrations can scatter laser impacts across the sample surface, which increases the uncertainty of laser-induced breakdown spectroscopy (LIBS) measurements. The common sources of noise associated to mechanical vibration are described and a method for isolating LIBS measurements from artifacts introduced by such fluctuations is presented. The approach circumvents the use of mechanical stabilizers by leveraging simple components common in LIBS systems. A camera was used to capture close-up images of the sample for each laser shot and the laser spot position in the sample surface was measured using common image processing techniques. By associating spectra with spatial coordinates in the sample surface, it was possible to reduce the relative standard deviation of the Cu(I) 427.51 nm signal in a patterned Cu/Al sample from 122.0% to 53.31%, similar to that measured for a pure Cu sample in the same vibration conditions. The spatial resolution of the method was found to depend on the laser spot diameter, the illuminance at the sample, the camera sensitivity and trigger insertion delay, and the speed of the laser beam sweeping the sample surface. The spatial resolution obtained with the setup used was ±0.6 mm at 15 m, i.e., 40 μm per meter of separation between the instrument and the sample with a vibration speed limit of 12 cm·s−1.The authors would like to express their gratitude to Carlos Malagon ´of Astroshop (Málaga, Spain) for donating the telescope used in the stand-off LIBS instrument. This work has been partially supported by the Programa Estatal para la Incorporacion ´ Estable de Doctores (IEDI-2017-00828) and by the I Plan Propio de Investigacion ´ de la Universidad de Malaga ´ (Spain). Funding for open access charge: Universidad de Malaga/CBUA

Field deployment of a man-portable stand-off laser-induced breakdown spectrometer: A preliminary report on the expedition to the Cumbre Vieja volcano (La Palma, Spain, 2021)

This paper reports on the expedition to the Cumbre Vieja volcano (Canary Islands, Spain) in November 2021 to assess stand-off laser-induced breakdown spectroscopy for real-time measurements of the lava streams from a safe point. The paper provides insight on the analytical approach to the problem, the rationale of the instrument design and construction carried out in three weeks, the experience with the new-born instrument at the volcano and the preliminary results. Despite the subtle spectral differences among the samples and the signal variability induced by the strong wind gusts at site, a statistical approach to data processing such as PCA, made possible to extract sufficient information and provide a robust classification tool.We express our sincere gratitude to the Spanish Unidad Militar de Emergencias (UME) for providing essential support, security, and expertise at the field. We would like to thank Carlos Malag ́on (Astro- shop, M ́alaga, Spain) for donating the telescope used in the stand-off LIBS instrument, to the personnel of the Chemical Analysis Area and the Machine Shop of the Central Facility for Research Support (SCAI-UMA) and to Profs. E.R. Losilla and A. Cabeza (Dept. Química Inorgánica, Cristalografía y Mineralogía, UMA) and D. Marrero (Dept. Física Aplicada I, UMA) for their valuable comments and advice with the surrogate samples. This work has been partially supported by the I Plan Propio de Investigaci ́on de la Universidad de M ́alaga, the Extraordinary Funding (RD 1078/2021, 7th December, Núm. 293 Sec. I. P ́ag. 150,995) and PID2020-113407RB-I00 granted by the Spanish Ministry of Science and Innovation (MICINN). Funding for open access charge: Universidad de Málaga / CBU

Spray-grown highly oriented antimony-doped tin dioxide transparent conducting films

Undoped and Sb-doped tin dioxide films of varying thickness with a remarkable crystallographic orientation in the [200] direction were grown by spray-pyrolysis from tin(II) chloride solutions. Films grown on silica-coated glass substrates were completely crystalline and showed a higher degree of orientation with respect to films that were grown on uncoated glass. The presence of the silica barrier was seen to have increased the degree of orientation and to have enhanced the resulting electrical properties. Transmission electron microscopy revealed that the silica layer may have played the crucial role of a nucleation layer. Moreover, the developed microstructures were correlated with the optical and electrical behaviour of the films. Dense conducting films with thicknesses between 280–450 nm and visible transmittances of 80-70 % showed resistivities of about 10−3 Ωcm.Fil: Parra, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Leinen, Dietmar. Universidad de Malaga. Facultad de Ciencias. Departamento de Fisica Aplicada I.; EspañaFil: Ramos Barrado, José Ramón. Universidad de Malaga. Facultad de Ciencias. Departamento de Fisica Aplicada I.; EspañaFil: Martín, Francisco. Universidad de Malaga. Facultad de Ciencias. Departamento de Fisica Aplicada I.; Españ

Electronic Decoupling of Graphene from Copper Induced by Deposition of ZnO: A Complex Substrate/Graphene/Deposit/Environment Interaction

This study presents experimental data of the interactions and reactions that occur during the early stages of the growth of ZnO on graphene supported on polycrystalline copper and the subsequent changes on the electronic properties of the graphene. The combination of substrate, graphene, and intercalated species (such as oxygen and water molecules) between graphene and copper due to air exposure, together to the evaporation of metallic zinc under oxygen atmosphere, induces the electronic decoupling of the graphene from copper by the formation of a nanometric layer of copper oxide. In particular, the final stage consists in the formation of a complex interface formed by ZnO/ZnO /Zn/G/CuO/Cu. The role of each actor is discussed in terms of a galvanic corrosion reaction of the metallic substrate where the graphene is the cathode and the initial deposition of metallic zinc accelerates the kinetics of this reaction, after which ZnO grows on the metallic zinc initially deposited. In this manner, the electronic properties of graphene can be engineered by the combination and interrelation of substrates, environment, and new-deposited materials, revealing a more complex and realistic picture for real fabrication processes. These results may help to improve the real applicability of graphene in mass production devices.This investigation was funded by the Ministerio de Economía y Competitividad of Spain through the FIS2015-67367-C2-1-P project and by the Comunidad de Madrid through the NANOMAGCOST-CM P2018/ NMT4321 project. One of the authors (C.M.) thanks Ministerio de Educación, Cultura y Deporte for a FPU grant. The authors also would like to thank SEGAINVEX (UAM) and SCAI (UMA) for technical suppor