Publications

Bilayer metallic electrodes of magnesium and zinc-aluminum alloys Mg/Zn:Al were prepared using combined laser-thermionic vacuum arc methods. Plasma diagnosis suggests laser-plasma interaction by increasing the discharge voltage when the laser is on, which is converted by thermal annealing of plasma ions. A magnesium thin film with a lower work function, covered with a Zn:Al (4:1) layer was successfully used for efficient charge injection into electroluminescent diodes. The zinc-aluminum combination preserved the electrical conductivity of the thin magnesium film and protected it against oxidation. The capacitance-voltage measurements confirmed the integrity of the magnesium layer, whereas the work function was not affected. The zinc-aluminum alloy obtained through a thermionic vacuum arc exhibits good conductivity compared to pure zinc layers and better stability against degradation.

Synchrotron-based small- and wide-angle X-ray scattering is used to elucidate the structure of low-dimensional lepidocrocite-titanate-based nanofilaments. In the colloidal state, they consist of quantum-confined 1D NFs, loosely associated into nanoribbons, one lepidocrocite sheet thick (about 4 & Aring;), 30-40 & Aring; wide (5-8 NFs), and more than 300 & Aring; long. In the dry state, they reach a final state of extended sheets, stacked three to about twenty high, whose crystallinity increases with stack height, in parallel with a decrease in photocatalytic activity. These findings suggest a kinetic pathway for the self-assembly of initially 1D titanate nanoribbons into 2D and ultimately 3D structures, providing context for a recent body of work on these low-dimensional materials.

In this study we present the effect of the irradiation of sintered MgB2 with protons of intermediate energies, from 8.6 to 15.07 MeV, at a constant fluence of 2.86 x 10(16) p/cm(2). We found clear evidence that the disorder generated by irradiation leads to a weak suppression of the critical temperature T-c and an increase of the critical current density J(c) with increasing proton energy, as expected. However, it was found that thermomagnetic instabilities and vortex creep phenomena strongly depend on the ratio between proton range and the sample thickness. The number of the macroscopic flux jumps (MFJ) is highest and manifest up to 28 K in the sample with the proton range shorter than sample thickness (P-1) and decrease as the proton energy increases. Similarly, the relaxation rate of the irreversible magnetization is the lowest in the sample P-1 and increases with proton energy. We tentatively attribute this effect to the protons that stop within MgB2 and interact with the local structure/atomic composition.

This study aims to investigate the impact of clays on the quality of the Nubia reservoir in the Saqqara field, Gulf of Suez, Egypt. The research will contribute to a broader knowledge of reservoir characterization, offering valuable insights for similar geological settings in other regions, thereby aiding in the optimization of resource management in global petroleum industries. The shale evaluation procedure involves three primary steps: estimating shale volume, identifying clay minerals, and assessing shale distribution. The neutron-density (N-D) method was employed to estimate the shale volume in the Nubia reservoir, yielding an average of 0.6% across four wells, with a maximum recorded value of 2.2% in well GS323-3. These values represent that the Nubia reservoir contains a negligible amount of shale, indicating that the porosity and permeability are high. Clay mineral analysis, based on a Potassium-Thorium (K-Th) and Potassium-PEF cross-plots, identified the presence of chlorite, illite, montmorillonite, and heavy thorium-bearing minerals, where chlorite and illite enhance the mechanical stability of the reservoir, while montmorillonite may cause issues with swelling and pressure. Thorium-bearing heavy minerals are typically associated with reduced permeability due to their influence on chemical interactions. The shale distribution analysis, conducted using the Thomas and Stieber model, confirms the overall cleanliness of the Nubia reservoir. Most formation data points align with the 0% shale line, indicating high total porosity, while only a few points fall along the dispersed shale line. In conclusion, the findings indicate that the Nubia reservoir exhibits minimal shale content, predominantly clean lithology, and favorable porosity and permeability characteristics. Consequently, the reservoir is classified as high-quality, making it suitable for efficient hydrocarbon production.

This study presents annealing time variation as an alternative approach for tuning structural and ionic defects in SnO2 nanoparticles (NPs) synthesized by a modified Pechini method, to modulate charge transfer and the formation of reactive oxygen species (ROS), enabling a correlation of these with photocatalytic activity. Structural refinements of the X-ray diffraction (XRD) data, combined with Raman and infrared (IR) spectroscopy, revealed that the samples adopted a tetragonal P42/mnm symmetry, with a distinct short-range structural order (associated with intraoctahedral [SnO6] distortions), which strongly depends on the annealing time. Field emission scanning electron microscopy (FE-SEM), scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (STEM/EDX), high-resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) analyses showed the formation of homogeneous NPs smaller than 50 nm in the SnO2 samples, with a surface area between 12.072 and 14.102 m2 g-1. The presence of unusual reduced Sn3+ species associated with oxygen vacancies (VO) was evidenced by electron paramagnetic resonance (EPR) spectroscopy, and Sn2+ was characterized by Sn MNN Auger electron emission. The amount of these defects also depends on the annealing time. The synergistic effect and the photocatalytic mechanism were then elucidated. The degree of intraoctahedral [SnO6] distortions and the amounts of Sn3+:VO defects play a fundamental role in the charge transfer mechanism to modulate ROS generation during photoexcitation, as indicated by the photohydroxylation of terephthalic acid (TA) and in situ spin-trapping EPR measurements. Specifically, we show the formation of two main ROS, center dot OOH and center dot OH, which leads to a different photocatalytic pathway in SnO2 NPs. In conclusion, our study enlightens and uncovers the importance of choosing appropriate conditions for materials processing to fine-tune structural and electronic properties to design other functional materials.

Copper is an essential micronutrient for plants, but excessive levels can induce toxicity and impair physiological functions. This study evaluates the toxic effects of copper sulfate (CuSO4) on the germination of common wheat (Triticum aestivum), with emphasis on the gas emission dynamics and oxidative stress biomarkers. Seeds were germinated in agar and exposed to CuSO4 at concentrations of 1 mu M, 100 mu M, 1 mM, and 10 mM; distilled water served as the control. Ethylene and ammonia emissions were quantified using CO2 laser photoacoustic spectroscopy, while electron paramagnetic resonance (EPR) spectroscopy was employed to detect free radicals and Cu2+ complexes. Exposure to Cu concentrations >= 1 mM significantly inhibited germination and biomass accumulation. Enhanced ethylene and ammonia emissions, particularly at 10 mM, indicated stress-related metabolic responses. The EPR spectra confirmed the presence of semiquinone radicals and Cu2+ complexes under higher Cu levels. These results demonstrate that photoacoustic and EPR techniques are effective tools for the early detection of metal-induced phytotoxicity and offer a non-invasive approach to environmental toxicity screening and plant stress assessment.

Recent achievements in ultrafast spin physics have enabled the use of heterostructures composed of ferromagnetic (FM)/non-magnetic (NM) thin layers for terahertz (THz) generation. The mechanism of THz emission from FM/NM multilayers has been typically ascribed to the inverse spin Hall effect (ISHE). In this work, we probe the mechanism of the ISHE by inserting a second ferromagnetic layer in the form of an alloy between the FM/NM system. In particular, by utilizing the co-sputtering technique, we fabricate Fe/L1(0)-FePt/Pt ultra-thin heterostructures. We successfully grow the tetragonal phase of FePt (L1(0)-phase) as revealed by X-ray diffraction and reflection techniques. We show the strong magnetic coupling between Fe and L1(0)-FePt using magneto-optical and Superconducting Quantum Interference Device (SQUID) magnetometry. Subsequently, by utilizing THz time domain spectroscopy technique, we record the THz emission and thus we the reveal the efficiency of spin-to-charge conversion in Fe/L1(0)-FePt/Pt. We establish that Fe/L1(0)-FePt/Pt configuration is significantly superior to the Fe/Pt bilayer structure, regarding THz emission amplitude. The unique trilayer structure opens new perspectives in terms of material choices for the future spintronic THz sources.

The development of titania-based hybrid nanostructures with enhanced visible-light photocatalytic activity has been a key research area recently. The present study addresses current limitations of the TiO2 based composite photocatalyst by newly-experimental designing of flower-like multifunctional hybrid nanostructure with visible light capability through Ferrihydrite (Fh) surface TiO2 functionalization. Here, we present a versatile nanocompartimentalization process of which, core anatase TiO2 nanoparticles are emebeded into Fh lamellar shell. Physico-chemical properties related to the chemical structure and morphology of the prepared nanomaterials were comprehensively analysed using complementary analytical techniques, such as powder X-Ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FE-SEM), Ultra-High Resolution Transmission Electron Microscopy (UHR-TEM), X-Ray Photoelectron Spectroscopy (XPS) and soft X-Ray Absorption Spectroscopy (XAS). The conducted visible-light-driven photocatalytic water splitting tests highlights significant enhancement in the Oxygen Evolution Reaction (OER) performance for TiO2-Fh core-shell nanoheterostructure of 25.6 mu mol/L of molecular oxygen after 60 min of visible light irradiation (AM1.5G), and a photocatalytic water oxidation activity rate of 341.3 mu mol L-1 g-1h-1. The biocompatibility assessment of the developed core-shell structures combined with their enhanced photocatalytic water oxidation activity under visible light illumination suits them as excellent candidates for the development of sustainable environmental remediation technologies.

CuO is a p-type semiconductor that can be found useful in various applications, sensing, photocatalysis or photovoltaics. Better material performance can be achieved by doping. In our study the doping was done using Cr ions and implantation method. Thin film samples were characterised with X-ray photoelectron spectroscopy (XPS) technique to study chemical properties of the films' surface and to determine the in-depth compositional profile of the films before and after annealing of an implanted sample. Spectroscopic ellipsometry was used to extract the dielectric function of CuO thin films. Depolarization measurements are shown as a useful method to quickly study differences between similar samples. XPS measurements proved that before annealing there is a peak of Cr concentration in depth of the sample, which is no longer present after annealing. Measurement of film resistance as function of temperature in range of 150-300 degrees C resulted with 0.82 eV bandgap. Electronic structure obtained with density functional theory calculations (DFT) showed that with Cr doping the energy band gap narrows and the material should become metallic.

Superconducting bulk disks, of 20 mm in diameter and similar to 3.5-mm thickness of MgB2 were prepared by spark plasma sintering. Samples are co-added with 10 wt. % hexagonal BN (h-BN) or graphene (G) and other additives (B4C, Te, cubic BN, fullerene C-60, or Repa-C6H10O7Ge2 (GEP)), where h-BN and G are introduced in the composite to provide full machinability by chipping of the composite and the other additives to modify microstructure and superconducting characteristics. Measurements of trapped magnetic field B-tr for a fixed rate of the applied magnetic field decrease (0.00015 T/s) indicate that samples with G show less flux jumps, but a higher thermomagnetic stability is accompanied by lower values of B-tr than for samples with h-BN. The highest maximum B-tr at 12 K for samples added with h-BN or graphene was recorded for MgB2(Te)(0.01) + 10wt.% h-BN (3.48 T) and MgB2(B4C)(0.01) + 10wt.% G (2.73 T), respectively. These values of maximum trapped field were determined for an applied field of - 2.5 and - 1.8 T. Results suggest that machinable MgB2-based composites show potential for bulk superconducting magnet applications.