Publications

Three methods were used to prepare poly(ortho-toluidine)/reduced graphene oxide (POT/RGO) composites: (i) the interaction of the two constituents in the solid state, (ii) the chemical polymerization of ortho-toluidine (OT) in the presence of the RGO sheets, and (iii) the electrochemical polymerization of OT in the presence of the RGO sheets. Combining the results of Raman scattering, FTIR spectroscopy, and X-ray photoelectron spectroscopy, we demonstrated the following: (i) the interaction of POT with RGO in the solid state leads to the non-covalent functionalization of RGO with POT; (ii) the chemical polymerization of OT in the presence of RGO results in the covalent functionalization of RGO with POT in emeraldine base (EB) and leucoemeraldine salt (LS) and (iii) the electrochemical polymerization of OT assisted by RGO sheets leads to the covalent functionalization of RGO with POT-LS and POT-emeraldine salt (ES). The cyclic voltammetry (CV) studies indicated that the values for the voltammetric output currents of the POT/RGO composites are superior to those reported for POT. Electrochemical studies demonstrated a (a) battery-type behavior in the case of the electrodes based on POT-ES and POT/RGO composites prepared by chemical and electrochemical polymerizations and a (b) pseudocapacitive behavior for the electrodes based on POT-EB and composites prepared by the interaction of POT-EB with RGO in the solid state. High capacitance values of up to 1197.23 and 1524.62 mF cm-2 were obtained for the symmetrical supercapacitors based on the electrodes containing the POT/RGO composites prepared by chemical and electrochemical polymerization, respectively, of OT in the presence of RGO sheets.

Organic layers based on metal phthalocyanines (MPc acting as donor) and a perylene diimide derivative compound (PDI acting as acceptor) were deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on rigid and flexible substrates. Hence, blend films based on magnesium phthalocyanine (MgPc), copper phthalocyanine (CuPc), cobalt phthalocyanine (CoPc) or iron phthalocyanine (FePc) and N, N-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide (AMC14) were obtained on indium tin oxide/glass (ITO/glass) and indium tin oxide/polyethylene terephthalate (ITO/PET) substrates. Although the investigated MPcs present low solubility in organic solvents, MAPLE technique enables their deposition as blend films. The organic layers reveal a globular morphology specific to the MAPLE process. The roughness of the blend films is related to the MPc molecular packing arrangement, the optical assessment disclosing the presence of MPc in the stable beta-form. The transmission spectra display the optical signature of both MPc and AMC14 components, their complementary absorption bands assuring the light harvesting over a wide part of the UV-Vis spectral range. The current-voltage characteristics recorded under illumination reveal the best electrical parameters for the structures based on FePc: AMC14 layer prepared on ITO/glass (V-OC=0.22 V, J(SC)=2 & times; 10(- 7) A/cm(2)) and on CuPc: AMC14 layer obtained on ITO/PET (V-OC=0.27 V, J(SC)=1.3 & times; 10(- 7) A/cm(2)). Thus, the properties of MAPLE-deposited MPc: AMC14 blend films on both rigid and flexible substrates endorse them as viable choice for applications in optoelectronic devices.

Cadmium sulfide (CdS) nanostructures were synthesized via sonochemical method with varying cadmiumto-sulfur (Cd:S) molar ratios (1:0.1, 1:0.25, 1:0.5, 1:0.75, and 1:1) to investigate the influence of stoichiometry on their structural, morphological, and optical properties. Scanning Electron Microscopy (SEM) analysis revealed that Cd-rich conditions (1:0.1) produced large, irregular agglomerates (similar to 254 nm) due to limited nucleation, whereas increasing sulfur content led to granular and anisotropic morphologies (1:0.25-1:0.75), including partially leaf-like/platelet structures (189-302 nm) driven by facet-selective S2- adsorption. Near-stoichiometric Cd:S ratios (1:1) yielded uniform, faceted nanoparticles (63-396 nm) with controlled growth. X-ray Diffraction (XRD) analysis confirmed a phase evolution from pure hexagonal (1:0.1-1:0.25) to mixed hexagonal - cubic (1:0.5), predominantly cubic (1:0.75), and re-emergent hexagonal coexistence (1:1). Crystallite sizes calculated via the Debye-Scherrer and Williamson-Hall methods ranged from 5.94 to 34.9 nm, correlating with phase stabilization and quantum confinement effects, while microstrain peaked at 8.42 x 10(-3) for the 1:0.5 sample, indicating lattice distortion during hexagonal - cubic coexistence. Ultraviolet-Visible (UV - Vis) spectroscopy showed direct band gaps between 5.18 and 5.41 eV, with the largest for the 1:0.5 sample, and indirect band gaps decreased to 3.32 eV at 1:0.25, reflecting defect-induced band distortion. Photoluminescence (PL) spectra revealed enhanced emission intensity at 547 nm for the 1:1 sample, attributed to defect-assisted recombination and improved surface passivation. Raman spectroscopy indicated phonon confinement, including suppression of the 2LO mode at intermediate compositions. Fourier-transform infrared (FTIR) spectra confirmed Cd - S bond formation and the presence of surface-capping 3-mercaptopropionic acid (3-MPA) ligands. Cd:S precursor ratio enables control over particle size, morphology, crystal phase, defect density, and optical properties, offering a versatile strategy to optimize CdS nanostructures for optoelectronic applications.[GRAPHICS].

Copper-zinc-tin-sulfide (Cu2ZnSnS4, CZTS) kesterites a promising earth-abundant and non-toxic absorber for next-generation thin-film photovoltaics. However, sulfur-based CZTS solar cells remain limited in performance, largely due to intrinsic defects and interfacial recombination losses. Here, we systematically investigate the impact of solvent chemistry and extrinsic doping and compositional engineering on the quality of solution-processed CZTS absorbers. A comparative study of three solvents, 2-methoxyethanol (MOE), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) reveals that all yield phase-pure, and compact films due to a robust Cu+-Sn4+ molecular precursor system, with MOE producing the most uniform morphology and superior optoelectronic properties. Rather than focusing on pure CZTS, the solvent screening is conducted on Cd-alloyed CZTS (CZCTS), as Cd incorporation substantially alters precursor coordination and crystallization behavior. Building on the optimized processing route, a synergistic compositional strategy combining silver (Ag) - cadmium (Cd) co-alloying with lithium (Li) doping is introduced to suppress cation disorder, passivate grain-boundary defects, and enhance carrier transport. As a result, the optimized he optimized absorber delivers a champion device with a power conversion efficiency of 10.6%, placing it among the highest efficiencies reported for solution-processed, selenium-free CZTS solar cells. These results highlight the critical role of solvent engineering coupled with targeted extrinsic doping in overcoming the long-standing limitations of CZTS photovoltaics and provide a scalable pathway toward environmentally benign thin-film solar technologies.

We present a simple and intuitive tabletop experiment designed to generate gravitational wave-like signals. This toy model serves as a physical analogy for the motion of compact astrophysical objects in curved spacetime and is intended primarily for educational and outreach purposes. The experimental setup consists of a circular solid frame over which an elastic fabric is tightly stretched and secured with clips. Solid spheres of different masses represent astrophysical objects, and their motion is recorded using a webcam connected to a laptop running the TableTopGW software. A heavy sphere is placed at the center of the fabric to simulate a massive compact object, such as a black hole or neutron star, that distorts the surrounding spacetime. A lighter sphere is then released onto the curved surface, where it spirals inward toward the central mass under the influence of Earth's gravity and friction with the fabric. The webcam continuously records the motion of both spheres. From this video data, the separation between the two masses is computed. Using the quadrupole formalism from general relativity, as applied to binary systems, the TableTopGW software uses this separation to simulate gravitational wave-like signals. This setup establishes a direct and visually engaging connection between the physical motion of orbiting bodies and the corresponding gravitational waveform, offering students and the general public an accessible and hands-on introduction to complex astrophysical concepts.

In a two-dimensional electron gas in a periodic lateral superlattice subjected to an external homogeneous magnetic field and in a cylindrical far-infrared photon cavity we search for effects of broken symmetries: Static ones, stemming from the unit cell of the system, and the external magnetic field together with the dynamic ones caused by the vector potential of the cavity promoting magnetic types of transitions, and the chirality of the excitation pulse. The Coulomb interaction of the electrons is described within density functional theory, but the electron-photon interactions are handled by a configuration interaction formalism within each step of the density functional approach, both for the static and the dynamic system. In the dynamical calculations we observe weak chiral effects that change character as the strength of the electron-photon interaction and the external magnetic field are increased. From the analysis of the chiral effects we identify an important connection of the para- and diamagnetic electron-photon interactions that promotes the diamagnetic interaction in the present system when the interaction strength is increased. Furthermore, the asymmetric potential in the unit cell of the square array activates collective oscillation modes that are not present in the system when the unit cell has a higher symmetry.

In this study, thin films of copper oxide (CuO) were deposited on indium-doped tin oxide (ITO) layers supported on glass substrates using a simple and low-cost home-made pneumatic spray technique at 350 degrees C for different deposition times (5 min, 10 min, 15 min, 20 min). Copper chloride (CuCl22H(2)O) was used as copper source at a concentration of 0.05 mol/l. X-ray diffraction patterns revealed that the films were polycrystalline with a monoclinic structure in the preferred directions (111) and (-111). Increasing the deposition time led to an increase in grain size from 11.85 to 14.73 nm. Surface analysis by scanning electron microscopy revealed improved uniformity and horizontal growth of the CuO films with increasing roughness at a deposition time of 20 min. UV-Visible measurements showed a decrease in transmittance from 73 to 47% for the wavelength range (300-1100 nm) with increasing deposition time, accompanied by a decrease in the reflectance of the films. The energy gap (Eg) decreased from 2.17 to 2.44 eV, while the Urbach energy increased with increasing spray time from 0.145 to 0.33 eV. The prepared films had absorption coefficients greater than 5 x 10(4) cm(-1) in the visible range, which diminished in the near-infrared range. The refractive index ranged between 2.01 and 3.00, whereas the dielectric constant (epsilon(r)) increased from 3.65 to 9.17.

The glass/FTO/TiO2/Sb2S3-x/P3HT/Au solar cells were investigated, with a focus on identifying the origin of performance degradation after exposure to high relative humidity and to mild heat stress. Analyzing the photovoltaic output and Deep-Level Transient Spectroscopy (DLTS) results, we probed the evolution of defect states after thermal exposure and after long-term storage of Sb2S3-x-based devices. The DLTS analysis revealed that shallow hole traps govern the stability of the Sb2S3-x cells. Significantly, it was shown that this shallow defect is not related to chlorine in the absorber, indicating an intrinsic origin. In the broader context of Sb2S3-x photovoltaics, this study underlines the paramount importance of defect engineering towards achieving more stable and efficient Sb2S3-x solar cells.

Alloys (A) of crystalline Ge50Te50 and partially amorphous Ge20Te80 were added to MgB2 superconductor. Samples with composition (MgB2)A0.01 were ex situ spark plasma sintered (SPS) and characterized. Results are compared with pristine and Te ((MgB2)Te0.01) or Ge, ((MgB2)Ge0.01) added samples. Samples with Ge-Te alloys show the fastest densification rate of 3.4 to 5.2 times larger than for the other samples. Although there is a strong influence of Te, alloys synergistically contribute structural and microstructural development and superconducting properties as determined by magnetometry. The proposed methodology of densification curves analysis allows prediction of the final bulk density, MgO and MgB4 amounts, the amount of carbon substituting boron and critical temperature. The alloys addition promotes MgB4 formation and a slightly lower critical current density Jc for Ge50Te50. For Ge20Te80, Jc is approximately similar to pristine sample, while the highest Jc is for Te. Samples with Ge-Te have lower maximum pinning force values.

The present study, presents for the first time the development and characterization of innovative bioceramic samples based on magnesium doped hydroxyapatite (xMg = 0.015 and xMg = 0.05) obtained by a modified coprecipitation method and the lyophilization of the final precipitate (1.5MgHAp-LF and 5MgHAp-LF). The lyophilized powders were thoroughly investigated, obtaining valuable information regarding stability through non-destructive ultrasound measurements, structure, chemical composition, bonding states, surface properties and biological evaluations. The X-ray diffraction (XRD) patterns of the samples revealed peaks characteristic of pure hexagonal hydroxyapatite (P63/m). When calcium ions were substituted with magnesium ions, a reduction in peak intensity and a slight broadening of the peaks were observed as the magnesium concentration increased. Fourier transform infrared spectroscopy (FTIR) was used to investigate the structural and compositional characteristics of the studied samples. Information regarding the surface topography of 1.5MgHAp-LF and 5MgHApLF pellets was obtained using scanning electron microcopy (SEM) and atomic force microscopy (AFM) studies. Additionally, AFM topographies and SEM images provided useful insights into the roughness of the samples. A complementary analysis was performed on a larger surface area using a Scanning Acoustic Microscope (SAM). The biological performance of 1.5MgHAp-LF and 5MgHAp-LF pellets was evaluated using the MG63 osteoblastlike cell line. Surface analyses-including furrow morphology, texture orientation, fractal dimensionality, and frequency spectrum-revealed that increased magnesium content induces greater topographical order and complexity, enhancing the material's potential for osteoconductive applications. The cytotoxicity of the pellets was assessed by determining the cell viability through the MTT assay after an incubation period of 24 h. Also, fluorescence microscopy (FM) visualization was used to determine the cytotoxicity of the pellets. The results demonstrated that both 1.5MgHApLF and 5MgHApLF pellets exhibited good biocompatibility for both tested samples. Furthermore, the interaction of the MG63 cells with the surface of the 1.5MgHAp-LF and 5MgHAp-LF pellets was assessed by metallographic microscopy (MM) and atomic force microscopy (AFM). MM and AFM analyses revealed that the surface morphology of both materials effectively supported cellular attachment and growth. These findings suggest that both 1.5MgHAp-LF and 5MgHAp-LF pellets have a significant potential for being used in the development of advanced biomaterials for biomedical use.