Spectroscopic Ellipsometry Study on Tuning the Electrical and Optical Properties of Zr-Doped ZnO Thin Films Grown by Atomic Layer Deposition

This work reports the ellipsometry analysis of atomic layer deposition (ALD) films of ZnO doped with Zr to determine parameters like free carrier concentration and mobility. Thin films of zinc oxide (ZnO) and Zr-doped ZnO of thickness similar to 100 nm were prepared by atomic layer deposition on sapphire, SiO2/Si(100), and Si(100) substrates. Variable-angle spectroscopic ellipsometry was used to study their optical properties in the 0.5-3.5 eV spectral range. The optical constants were accurately obtained using a model that combines Drude and Tauc-Lorentz oscillators with Bruggeman effective medium approximations, allowing the inclusion of a roughness layer in the optical model. The effect of Zr doping (ca. 1.9- 4.4 atom %) was then investigated in both as- prepared samples and samples annealed in the temperature range of 100-300 degrees C. All of the films exhibited good optical transparency (ca. 70-90% in the visible region). For doping levels below 2.7 atom %, the real part of the dielectric permittivity reveals a semiconductor-to-metal transition in the near-infrared (NIR) region, as the permittivity goes from positive to negative. Besides, the plasma energy increases with increasing Zr concentration, and both resistivity and carrier concentration exhibit slightly parabolic behaviors, with a minimum of similar to 1.5 x 10(-3) Omega cm and a maximum of 2.4 x 10(20) cm(-3), respectively, at the same critical Zr concentration (2.7 atom %). In contrast, the carrier mobility decreases rapidly from 76.0 to 19.2 cm(2)/(V s) with increasing Zr content, while conductivities and carrier mobilities worsen when the annealing temperature increases, probably due to the segregation of ZnO crystals. Finally, the optical band gap is very stable, revealing its interesting independence of substrate composition and annealing temperature, as it collapses to a single master curve when band gap energy is plotted versus free carrier concentration, following the Burstein-Moss effect. Overall, the Zr-doped ZnO films studied here would be a highly desirable system for developing thermally stable transparent conductive oxides (TCOs)

Boron-doped diamond growth on carbon fibre: Enhancing the electrical conductivity

Carbon fibre reinforced polymers (CRFP) are extensively used in many industrial applications thanks to its mechanical properties and its low weight. Nevertheless, the orthotropic character of CRFP highly reduces its applications. The transversal electrical conductivity in CRFP is two orders poorer than in the longitudinal direction. To improve their electrical properties, this work proposes the use of polycrystalline boron doped diamond (BDD) as coating of the carbon fibres (CF). BDD coating is deposited on CF surface using microwave plasma enhanced chemical vapor deposition (MPCVD) system. The BDD coating forms a rigid conductive coating around the CF as a core–shell structure. Here, an electrical characterization of both, 12,000 filaments (a tow) and a single coated filament, are carried out in the longitudinal and cross-section directions. Macro, micro and local analysis using the Kelvin method, Conductive Atomic Force Microscopy (C-AFM), and Scanning Microwave Impedance Microscopy (sMIM), were carried out to evidence the improvement of the electrical properties. Macro measurement reveals that the BDD coating decreases to half the resistivity of the CF. The BDD coating raises the local electrical conductivity of the CF by an order of magnitude with respect to the uncoated ones. sMIM maps identified BDD locations in ring-like configurations. © 2023 The Author

Fe3O4-TiO2 Thin Films in Solar Photocatalytic Processes

The optical properties of 5wt% Fe3O4-TiO2 thin films were evaluated in detail with the aim of proposing a mechanism for solar photocatalytic processes and highlighting the advantages over the use of bare TiO2. The results showed that the incorporation of 5wt% Fe3O4 enhanced the optical properties by a redshift to a wavelength in the visible range, reducing the anatase/rutile band gap energy from 3.2 eV to 2.8 eV. Photoluminescence studies reveal a superior separation efficiency of photoexcited electron-hole pairs when Fe3O4 nanoparticles (NPs) are present in the photocatalyst. X-ray photoelectron spectroscopy spectra confirm the presence of Fe3O4 and existence of a chemical bonding between TiO2 and Fe3O4 NPs. Moreover, in this study, a mechanism of solar photocatalytic processes involving Fe3O4-TiO2 thin films is proposed and it is supported by experimental results. Finally, solar photocatalytic experiments were carried out, indicating that the effectiveness for the removal of the selected pharmaceutical is considerably improved when the composite material is used as catalyst. Furthermore, it was demonstrated that the photocatalytic activity of the prepared Fe3O4-TiO2 thin films depends on their thickness, achieving the highest pharmaceutical removal yields using the 2 mu m thick sample. The stability and reusability of the catalyst was confirmed studying the photocatalytic activity over three cycles

Controlled grain-size thermochromic VO2 coatings by the fast oxidation of sputtered vanadium or vanadium oxide films deposited at glancing angles

An original, simple and cost-effective oxidation strategy to attain thermochromic vanadium dioxide thin films is reported. This two-step procedure comprises the initial deposition of DC magnetron-sputtered vanadium or vanadium oxide films by the combination of glancing angle deposition and, if needed, reactive gas pulsing process, followed by fast oxidation of such layers in air atmosphere at high temperatures. Thanks to the careful control of the thermal treatment parameters, and taking advantage of the superior reactivity of the high surface-to-volume porous deposited structures, the formation of pure VO2 (M1) layers was achieved. The comprehensive characterization of such oxidized systems by means of scanning electron microscopy, Raman spectroscopy and scanning-transmission electron microscopy techniques such as electron energy-loss spectroscopy, not only confirmed the presence of the VO2 (M1) phase, but also allowed to shed light on the key role that reaction time plays in the selective formation of vanadium dioxide films of adjustable grain size and crystallinity. The optimal conditions to stabilize thermochromic VO2 consists in using large deposition angles (85 degrees) and short oxygen pulses (<= 2 s) during the growth, followed by fast and short thermal treatments (<= 45 s with a heating rate of 42 degrees C s(-1)) in air atmosphere at 550 degrees C. The metal-to-insulator response of the accomplished VO2 layers was finally evaluated by means of temperature dependent Kelvin probe force microscopy measurements, evidencing surface potential drops at heating, greater than those reported in the literature to date for VO2 thin films.A. J. Santos would like to thank the IMEYMAT Institute and the Spanish Ministerio de Educacion y Cultura for the concessions of grants (ICARO-173873 and FPU16-04386) . The "Talent Attraction Program" of the University of Cadiz is acknowledged by supporting B. Lacroix contract code E-11-2017-0117214. University of Cadiz and IMEYMAT are also agreed by financing the mutual facilities available at the UCA R&D Central Services (SC-ICYT) , the UCA projects reference "PUENTE PR2018-040 '' and "PUENTE PR2020-003 '', and the IMEYMAT project references "LINEAS PRIORITARIAS PLP2019120-3 and PLP2021120-1 ''. This work was supported by the Spanish State R&D project (Retos y Generacion de Conocimiento) ref. PID2020-114418RB-I00/AEI/10.13039/501100011033. The regional government of Andalusia with FEDER cofunding also participates through the projects AT-5983 Trewa 1157178 and FEDER-UCA18-10788. M. Dominguez acknowledges financial support from the Spanish Ministerio de Ciencia e Innovacion under project reference EQC 2018-004704-P FEDER 2014-2020, "Modernizacion del Servicio de Microscopia de Fuerza Atomica (AFM) del IMEYMAT"

Low temperature growth of nanocrystalline diamond: Insight thermal property

One of the limitations of materials for high-power devices and structural coatings applications is heat dissipation. Diamond is a suitable material for heat distribution due to its high thermal conductivity. Nevertheless, it is usually grown at high temperature (800–1200 ◦C), which limits its use as a coating for substrates vulnerable to degradation at high temperatures. In this work, it is studied the effect of the distance between the plasma source and substrate on the growth of nanocrystalline diamond layers on silicon substrates at low temperature (<450 ◦C) by microwave linear antenna plasma enhanced chemical vapour deposition (MW-LA-PECVD) in pulse mode. The nanocrystalline diamond films have been analysed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. Finally, the superficial thermal conductivity of the diamond layers was determined by scanning thermal microscopy-AFM (SThM-AFM).6 página

Multiscale Analysis of the Gold Dust Defect in AISI 430 Industrial Stainless Steels: Influence of the Aluminum Content

The "Gold Dust Defect" affects the surface quality of AISI 430 ferritic stainless steels. However, there is a very limited number of studies focusing on it. To better understand its nature, we have combined several techniques, such as x-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy, in order to extract a maximum of structural and compositional information. Our results show that the surface quality, microstructure, and chemistry of the samples are strongly affected by the aluminum content, the severity of the defect being the highest at the lowest Al concentration. Not only is the concentration of the defects at the surface strongly reduced when increasing the Al. at.% but the depth of the cavities is also reduced by a factor of 3 when the Al content is increased from 0.09 at.% to 0.59 at.%. Our results provide new information on the nature of this defect, and show that an increase of the aluminum content allows the Cr concentration to be maintained in the range of values required to maintain the passivity of the steel, thus improving the surface quality

People detection and stereoscopic analysis using MAS

This paper presents a multiagent system that can process stereoscopic images and detect people with a stereo camera. In the first of two phases, the system creates a model of the environment using a disparity map. It can be constructed in real time, even if there are moving objects present in the area (such as people passing by). In the second phase, the system is able to detect people by combining a series of novel techniques. A multi-agent system (MAS) is used to deal with the problem. The system is based on cooperative and distributed mechanisms and was tested under different conditions and environments

Preparación y caracterización de láminas delgadas de óxido de vanadio obtenidas por vía sol-gel y recubrimiento por inmersión

Resumen del proyecto de líneas prioritarias titulado "Preparación y caracterización de láminas delgadas de óxido de vanadio obtenidas por vía sol-gel y recubrimiento por inmersión" del IMEYMAT

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

This work presents results in the feld of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fred Ceramics has been used, as a noncrystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these felds of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using diferent bufer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes