Publications

We present a theoretical study of the interplay between the spin-mechanical coupling and spin-lattice relaxation in the dynamics of a nitrogen-vacancy center in diamond. Single and double-quantum spin transitions are driven by resonant acoustic pulses. In addition, the two-phonon decoherence processes are included in the Lindblad equation of the density operator along with the temperature dependence of the corresponding relaxation rates. Our numerical simulations reveal that these processes activate all spin states of the NV-center. Therefore, an idealized qubit rotation is replaced by a genuine qutrit dynamics. We then show that consecutive single- and double-quantum acoustic pulses operate as an all-acoustic qutrit-shift gate. Besides calculating the time-dependent populations of the spin states, we discuss the cumulative impact of the spin-lattice relaxation and spin dephasing on the fidelity of a sequence of qubit and qutrit operations.

Co-/Cu-co-doped ZnO nanorods are synthesized by electrochemical deposition to investigate the effect of co-doping on their structural, optical, electronic, and electrochemical properties. XRD, Raman, SEM, and photoluminescence analyses reveal that Co/Cu incorporation modifies the ZnO lattice, increases defect-related states, and reduces the band gap from 3.11 to 2.15 eV. Density functional theory calculations further show that Co 3d and Cu 3d states appear near the Fermi level and contribute to the observed band-gap narrowing. Electrochemical measurements indicate that the co-doped nanorods exhibit the lowest charge-transfer resistance and the highest areal capacitance among the samples studied. Together, these results show that Co/Cu co-doping improves charge-transfer kinetics in ZnO nanorods and highlights co-doping as an effective strategy for tuning oxide electrodes for energy-storage applications.

Triboelectric nanogenerators (TENGs) are limited by poor charge retention and unstable output. This study investigates the effect of graphene oxide (GO) incorporation and environmental humidity on a nylon/polysiloxane-based TENG. Structural and chemical properties were analyzed using XRD, Raman, and FTIR, while SEM and photoluminescence (PL) were used to examine morphology and charge-trapping behavior. Electrical performance was evaluated through dielectric and TENG output measurements. An optimal GO loading of 0.05 wt% yields the highest performance, reaching 58.6 V, 5.7 mu A, and 54.6 mu W (34.1 mW/m(2)). SEM confirms uniform dispersion at this concentration, while PL indicates increased charge-trapping sites. Higher GO content leads to agglomeration and reduced performance. The output strongly depends on humidity, with voltage and current increasing as relative humidity decreases from 70-75% to 60%, due to reduced charge dissipation. The device powers 37 LEDs at higher humidity and similar to 60 LEDs at lower humidity, and demonstrates stable capacitor charging. Unlike complex hybrid systems, this work establishes a direct relationship between GO dispersion, charge trapping, and triboelectric performance. These results demonstrate that controlled GO incorporation and environmental conditions provide an effective strategy for improving TENG performance and enabling practical self-powered systems. This work goes beyond previous studies by explicitly linking GO-induced defect states and interfacial polarization to humidity-dependent charge retention mechanisms.

Cobalt-free LiNiO2 (LNO) cathodes promise high-capacity lithium-ion batteries, but they suffer from rapid surface degradation and Nickel (Ni) dissolution, which significantly limit cycle life and rate performance. In this study, we demonstrate that ultrathin (similar to 10 nm) TiOx coatings deposited via high-power impulse magnetron sputtering (HiPIMS) effectively stabilize LNO electrodes. This low-temperature process yields dense, conformal coatings that penetrate porous structures, improving interfacial integrity without compromising bulk conductivity. In half-cells, coated LNO retains 213 mAh.g(-1) after 30 cycles at 0.1C (versus 180 mAh.g(-1) for pristine), with 79% higher capacity at 5C. In graphite based full cells, the coated electrodes retain 77% of their initial capacity after 100 cycles at 0.5C (compared to 63% for the uncoated electrodes). This improvement is attributed to suppressed Ni migration (27% reduction confirmed by GD-OES) and reduced impedance growth. High-resolution TEM and density functional theory (DFT) calculations confirm structural stability at the LNO/TiOx interphase. These findings demonstrate a promising strategy for improving the stability of cobalt-free cathodes for next-generation energy storage.

New approaches for the synthesis of magnetite (Fe3O4) nanoparticles (NPs) are of considerable interest due to their potential applications in various fields, such as biomedicine, industry, environmental remediation, and catalysis. This study presents a novel approach for synthesizing Fe3O4 NPs using high-energy electron beam (EB) irradiation starting from organic (acetylacetonates) iron precursors. EB irradiation is a challenging nanoparticle synthesis method, being at the same time efficient and rapid. The synthesis is carried out at room temperature and is based on the water radiolysis process. This eliminates the need for chemical-reducing agents and may provide precise control over particle formation. Using high-energy EB irradiation of an organic Fe precursor, we demonstrate the successful synthesis of well-dispersed Fe3O4 NPs with controlled size, morphology and magnetic properties, as proven by morpho-structural, M & ouml;ssbauer spectroscopy and magnetic investigations. In particular, using organic iron precursors, such as iron acetylacetonates, NPs with distinct surface characteristics and improved thermal stability compared to those synthesized from inorganic precursors were obtained. These findings suggest that integrating organic precursors in EB-assisted synthesis can enhance the functional properties of Fe3O4 NPs, making them more suitable for specific applications. The versatility of this method opens up new avenues for the targeted design of nanomaterials with specific functionalities, paving the way for advanced applications in various technological fields. The current study is also motivated by the lack of literature data on the synthesis of metallic iron or iron oxide NPs mediated by EB radiolysis.

Hafnia (hafnium oxide) nanostructures, both unmodified and silica-modified with minor and major silica content, were synthesized using an adapted sol-gel method with D-L tartaric acid as an internal template. After thermal treatment, structural non-stoichiometry and light absorptive properties were identified in the resulting hafnium-based nanostructures, indicating their potential for various applications, including photocatalysis. The ability of these materials to photogenerate reactive oxygen species (ROS), namely superoxide anion radicals (center dot O2-) under simulated solar light (AM 1.5) and singlet oxygen (O-1(2)) under visible light (lambda > 390 nm), was evaluated and monitored by UV-Vis and photoluminescence spectroscopy. Functionalization of hafnium-based oxides with protoporphyrin IX was employed to enhance singlet oxygen photogeneration. The reactivity of the generated (O-1(2)) was assessed by quenching of DL alpha-tocopherol photoluminescence under visible light irradiation. Photocatalytic experiments conducted under anaerobic conditions demonstrated the ability of the hafnia-based nanostructures to reduce 1,4-benzoquinone (BQ) to 1,4-hydroquinone (H(2)Q). Furthermore, embedding the hafnia-based powders into polyvinyl alcohol hydrogels enabled the obtainment of photoactive coatings on glass substrates, for which their mechanical properties were evaluated using force-distance spectroscopy measurements. Morphological and structural characterization of the materials was performed using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), atomic force microscopy (AFM), X-ray diffraction and fluorescence (XRD, XRF), X-ray photoelectron spectroscopy (XPS), N-2 adsorption-desorption measurements, UV-Vis spectroscopy, photoluminescence (PL) spectroscopy, and zeta potential measurements. These investigations revealed that adding silica induces significant modifications in the morphology, texture, and structure of the hafnia, thereby enhancing the functional properties of the resulting materials.

This study reports on the physico-chemical and in vitro biological characterization of chromium-doped hydroxyapatite (10CrHAp, Cr3+, Ca10-xCrx(PO4)(6)(OH)(2), x(Cr) = 0.1) and chromium-doped hydroxyapatite in dextran matrix (10CrHAp-Dx) coatings, prepared for the first time via the spin coating technique. X-ray diffraction analysis and Rietveld refinement were used to characterize the materials. Fourier-transform infrared (FTIR) spectroscopy confirmed the presence of functional groups specific to hydroxyapatite. Scanning electron microscopy (SEM) observations revealed the presence of a conglomerate of nanoparticles distributed unevenly across the coatings surface. Atomic force microscopy (AFM) showed that both coatings presented continuous surfaces with uniform morphology. The in vitro biocompatibility of 10CrHAp and 10CrHAp-Dx coatings was evaluated using human osteoblast-like MG63 cell line and MTT assay. SEM and MM visualization assessed the cell adhesion and proliferation and morphological changes in the adhered cells. The antibacterial properties of the 10CrHAp and 10CrHAp-Dx coatings was assessed in vitro against two of the most common bacterial reference strains, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 25923. Overall, the coatings achieved log reductions up to similar to 9.35, corresponding to a bacterial kill rate (for S. aureus) exceeding 99.99%, with 10CrHAp-Dx showing slightly superior performance. Similar behavior (log reductions of similar to 8.6 and similar to 8.9, respectively, indicating a sustained antibacterial effect and >99.99% bacterial elimination) was observed and for Pseudomonas aeruginosa. AFM was used to evaluate the bacterial cells interaction with the coating's surfaces. The biological assays demonstrated that both coatings possess notable antibacterial activity, underscoring their potential in biomedical applications, particularly in the design of new antimicrobial devices.

In this work, Cu2Zn1-xNixSnS4 (CZ1-xNixTS) thin films were successfully synthesized via the solution-based spin-coating technique, and the effects of partial substitution of Zn by Ni (x = 0.2, 0.4, and 0.6) on their structural, morphological, optical, and photovoltaic properties were systematically investigated. Structural analyses demonstrated that Ni substitution in CZTS leads to lattice contraction and partial structural distortion due to the smaller ionic radius of Ni2+. Increasing Ni content enhances these effects until a solubility limit is reached at x approximate to 0.6, beyond which secondary phases such as NiS and Cu2SnS3 emerge. Raman spectroscopy further supports these findings, indicating compositional inhomogeneity and phase segregation at high Ni concentrations. Scanning Electron Microscope (SEM) micrographs further show that moderate Ni incorporation (x = 0.2) promotes improved surface compactness and grain growth, while excessive substitution results in grain fragmentation and increased surface roughness. Optical characterization reveals a tunable band gap, decreasing from 1.42 eV (x = 0) to 1.08 eV (x = 0.2), followed by a slight increase at higher doping levels, consistent with the formation of secondary phases. SCAPS-1D simulations of Mo/C2Z1-xNixSnS4/CdS/ZnO:Al/Al solar cell structures indicate improved photo-generated current and optical absorption at x = 0.2, whereas higher Ni substitution reduces the open circuit voltage (Voc) and the fill factor FF due to increased carrier recombination. Overall, moderate Ni incorporation enhances light absorption and carrier transport, whereas excessive Ni incorporation induces structural disorder, degrading device performance. These findings contribute to understanding the structural and compositional stability of Ni-doped CZTS thin films and their optimization for solar energy applications.

We report a detailed investigation of flux dynamics in YBa2Cu3O7-x (YBCO) superconducting thin films with strong synergetic pinning centers, using complex AC susceptibility measurements over a wide range of frequencies and DC magnetic fields. A new method is proposed to determine the characteristic pinning energy Uc from the electric field-current density (E-J) characteristics extracted at short time scales from AC susceptibility data. This method overcomes the limitations imposed by the use of standard Arrhenius plots, which rely on assuming a linear temperature dependence (p = 1) of the effective energy barrier UeffT,Hdc, J=Uc0 K,HdclnJc(T,Hdc)/J1-T/Tcp . Our results provide a more accurate approach for evaluating the magnetic field dependence of Uc, yielding a power-law dependence on the magnetic field induction Uc proportional to Bdc-0.32 , consistent with strong pinning behavior.

The scarcity of water resources demands the development of technologies to remove contaminants from industrial wastewater in order to reclaim and reuse the water in other fields like agriculture. In this study, 3D macroporous structures are additively manufactured from commercial ZnO nanopowder to be used in the photocatalytic removal of environmental pollutants from water. Direct Ink Writing (DIW) is used for deposition of the photocatalytic 3D structures that were subsequently consolidated by Spark Plasma Sintering (SPS) using temperatures in the range 425-900 degrees C. The fabricated structures are microstructurally (XRD, nitrogen physisorption, SEM and EDX) and mechanically (uniaxial compression test) characterized and their photocatalytic efficiency is evaluated by analyzing the degradation of Rhodamine B (RhB). Reusability of the DIW structures is also evaluated for structures sintered at selected temperatures by determining the photocatalytic degradation of RhB during five consecutive cycles. The results prove that increasing sintering temperature increases grain size, decreases microporosity and BET specific surface area, generates oxygen vacancies, and improves compressive strength of the 3D structures, but overall, these changes do not significantly affect photocatalytic efficiency. 3D structures require higher catalyst loading and take longer to fully degrade the dye compared to the commercial nanoparticles, but the DIW 3D photocatalysts have some clear advantages in terms of easy removal from the water -avoiding costly post-treatment precipitation, filtration or centrifugation processes typically needed to remove the catalyst nanoparticles- and extraordinary reusability: despite the evident surface corrosion occurring during the photocatalysis, neither their photocatalytic efficiency nor mechanical resistance are reduced. This will translate into significant reductions in the total cost of the treatment and a reduction in the potential toxicity of the reclaimed water due to contamination from any residual catalyst nanoparticles. These findings highlight the potential of reusable DIW ZnO catalysts for sustainable industrial wastewater treatment.