Phosphate glasses are an important group of materials for wide applications. They have received attention as biomaterials, eco-fertilizers, in optoelectronic devices, waste immobilization, etc. The subject of the studies is binary Al2O3-P2O5 glass, seen by ab initio molecular dynamics simulations. In the paper, Mayer's Bond Order analysis was employed as a suitable tool to observe the changes in the network due to Al2O3 substitutions. As well as, the bonding properties across the atoms in the network, which were characterized by electron localization function. The basic structural properties of the glasses are presented. The simulations showed that oxygen atoms in [PO4] tetrahedrons create a weak covalent bond between the atoms. The interaction spreads across the whole phosphate network via bridging oxygens. Whereas, there is no such interaction between the atoms in [AlOx] polyhedrons. In the case of the Al2O3 rich glasses, there are evidence non-network oxygen atoms which influence the distribution of phosphate structural units predicted based on the O/P ratio. The possibility of estimation of the oxygens in an experiment is discussed. The atoms building the network are going to take specific values of the total bond orders and the glass network is an interplay between atoms' affinity to saturate bond orders and the glass network neutrality.
The choice of metals, bonding conditions and interface purity are critical parameters for the performance of metal–metal bonding quality for quantum cascade lasers (QCLs). Here, we present a novel approach for the thermocompression bonding of Cu–Cu thin films on GaAs-based waveguides without having any oxide phase, contamination or impurities at the interface. We designed a hybrid system in which magnetron sputtering of Ta, thermal evaporation of Cu and Cu–Cu thermocompression bonding processes can be performed sequentially under high vacuum conditions. GaAs/Ta/Cu and Cu/Ta/GaAs structures were thermocompressionally bonded in our in-situ homebuilt bonding system by optimizing the deposition parameters and bonding conditions. The grown thin film and the obtained interfaces were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) techniques. The optimum Ta and Cu films’ thicknesses were found to be about 20 nm and 500 nm, respectively. EDX analysis showed that the Ta thin film interlayer diffused into the Cu structure, providing better adhesivity and rigidity for the bonding. Additionally, no oxidation phases were detected at the interface. The best bonding quality was obtained when heated up to 430 °C with an applied pressure of 40 MPa during bonding process.
In this work, the properties of zinc oxide (ZnO) low-dimensional conductive oxide nanostructures in the aspect of their potential applications in microelectronics, in toxic gas sensing, as well as in water remediation, have been determined. ZnO nanostructured porous thin films deposited by DC reactive sputtering (RS) have been deposited on Si substrates at different temperature conditions. For surface properties and chemical morphology analysis, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been used. Thanks to these techniques, it was possible to obtain information on thin film surface modifications caused by the adsorption of atmospheric carbon dioxide, and by the adsorption of photodegradation products following the photocatalysis experiments. The ZnO thin films were tested for their photocatalytic properties under UV light irradiation. For this purpose, methylene blue was used as a dye model pollutant to evaluate the activity of the nanostructures. It was observed that the ZnO thin films are able to photocatalytically degrade methylene blue. These results demonstrate that properly selected zinc oxide nanostructures, currently used in toxic gas sensing, can find application in the removal of micropollutants such as dyes and pharmaceuticals present in wastewater.
High contrast gratings (HCGs) are diffraction gratings whose period is less than the wavelength of light, made of a material with a high refractive index. Monolithic HCGs (MHCGs) are made of the same material as the cladding. They can be made of almost any material used in optoelectronics. We show experimentally and via simulations that shaping the cross-section of the MHCG stripes enables very broad high reflection spectrum.
