National Institute Of Materials Physics - Romania

The morpho-structural and defect properties of SnO2 nanoparticles, obtained by hydrothermal synthesis at 120 degrees C, 140 degrees C and 160 degrees C, using a SnCl2 precursor, were comparatively investigated and correlated with their NO2 sensing performance for in-field conditions. The constructive contributions of the nanoparticle size, faceting and oxygen vacancy concentrations had a positive effect on the sensor performances for the two samples synthesized at lower temperatures. These samples had almost similar, smaller size and the proportion of the more active, higher-index facets over the {110} facets was significantly larger than for the sample prepared at 160 degrees C. The concentration of paramagnetic defects, associated to complexes of oxygen vacancies in the (101) planes at the SnO2 surface, increased with the synthesis temperature decrease. A sensor signal of 74 for the NO2 detection limit of 3 ppm, at the operating temperature of 100 degrees C, under dynamic air flow with in-field-like relative humidity of 50 %, was obtained for the sample grown at 120 degrees C. The sensor signal was about four times higher compared to the 140 degrees C sample with similar size and morphology and about nine times higher than in the case of the 160 degrees C sample. In addition to its high NO2 sensitivity, the 120 degrees C sample had a low sensor response for potential interfering gases as CH4 and CO2 and was relatively stable over a period of 20 months. Our results evidence the direct correlation between the sensing properties and the surface oxygen vacancy complexes and highlight the importance of an in-depth atomic-level investigation approach for the controlled synthesis of an application-oriented material.

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] .

The rapid growth of the global population has increased the need for efficient fabrication methods and materials to purify polluted water. In this study, we report the fabrication and characterization of reusable and efficient three-dimensional (3D) polydimethylsiloxane (PDMS) sponge composites designed for water treatment applications. By varying the ratios (10/90, 30/70, and 50/50) of large and small sacrificial templates' particles used in the fabrication method, we tailored the sponge's morphology and the interconnected pores' distribution. To achieve an enhanced photocatalytic activity, we incorporated titanium dioxide (TiO2) at different concentrations (1 % TiO2, 5 % TiO2, and 10 % TiO2 w/w) into the PDMS matrix. Scanning electron microscopy (SEM) was used to evaluate the structure of both 3D PDMS and TiO2@PDMS sponges, while energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) confirmed the successful incorporation of TiO2 into the sponge framework. The photocatalytic performance of the 3D TiO2@PDMS composites was assessed by monitoring the degradation of Rhodamine B (RhB) under solar light irradiation, and the results were compared to those obtained using reference (TiO2-free) sponges under identical conditions. Very low Ti leaching effect have been evidenced by using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The reusability of the sponges was demonstrated through complete bleaching of the 554 nm RhB absorption band after four consecutive degradation cycles.

Bulk MgB2 disks (20 mm in diameter and 3.8 mm in thickness) added with 0, 1.5, 3.0, 4.5, 6.0, and 9.0 wt% silver are obtained by in situ spark plasma sintering. Samples are characterized by structural, microstructural, magnetic, and magnetic levitation zero-field-cooling and field-cooling measurements. Superconducting transitions are sharp with critical temperatures being in the range of 36.5-37.9 K. The vertical (F z,ZFC) and lateral (F x) levitation force show maximum values for samples added with 1.5 or 3 wt Ag%. At 20 K they are +17.78 N and 6.37 N, respectively. A maximum for zero field critical current density and pinning force is found for the sample added with 3 wt%. Roughly, as expected, levitation force correlates with zero-field critical current density, but other details influence this dependance. Results indicate that silver is an effective addition to MgB2 for enhancement of levitation performance.

This work examines the influence of milling parameters on the evolution of the microstructure of Ni50Ti50 alloy prepared by high-energy mechanical alloying (MA). The study unveils a particle-folding phenomenon observed through scanning electron microscopy, which diverges from the conventional welding and fracturing mechanisms previously associated with MA. It is found that milling duration is critical, with particle folding being predominant in the initial stages, subsequently becoming less pronounced in favor of traditional processes over extended milling times. The research underscores the importance of processing parameters in achieving desired microstructural characteristics and suggests the potential for better control of nanocrystalline material properties. The outcomes present new opportunities for material synthesis, offering insights into the fabrication of nanomaterials with enhanced and tailored properties for various technological applications.

Terahertz (THz) spintronic emitters represent a novel class of heterostructures composed of ferromagnetic (FM) and non-magnetic (NM) metallic layers that strongly emit terahertz (THz) radiation upon femtosecond laser pulse excitation. The optimal geometric configuration to maximize the strength of the emission is currently considered a trilayer structure, NM1/FM/NM2, where the FM layer is confined between two NM layers with opposite spin Hall angles. To investigate this, ultrathin Ta/Fe/Pt trilayers are fabricated and their THz emission profiles are analyzed. These results show that the highest THz emission is achieved for the sample of Ta (1.5 nm)/Fe (2 nm)/Pt (2 nm), demonstrating a significant enhancement compared to standard FM/NM bilayers. Furthermore, the thickness dependence of the THz emission is modeled in Ta (t1 nm)/Fe (2 nm)/Pt (t2 nm), varying t1 and t2 from 1 nm to 3 nm. From this analysis, spin diffusion lengths of lambda Pt = 1.2 nm and lambda Ta = 0.85 nm are extracted. The structure-property relationship is assessed via transmission electron microscopy, revealing that an epitaxial single-crystalline Ta layer covers the MgO surface with Ta adopting a high-resistivity fcc allotropic phase with a lattice parameter of a = 0.436 nm. This phase, together with the prerequisite for low Ta+Pt thickness, emerges as a key factor in achieving high THz emission from trilayer structures.

Composite x-at.% Yb:Y2O3/y-at.% Yb:Y2O3 (x = 0, 3, 5; y = 3, 5, 8) transparent ceramics with a graded doping profile of Yb3+ ions were obtained by solid-state reaction and multi-step sintering method. The multilayer ceramic compositions, consisting of two- and three-layers, were prepared by direct dry pressing of the constituent powders. Phase identification revealed that all sintered ceramics are well crystallized with a cubic structure similar to pure Y2O3, without impurity phases. Microstructural investigations have shown that the composite ceramics have a uniform morphology, with an average grain size of approximately 20 mu m, indicating that increasing the concentration of Yb3+ ions in the corresponding layers has no visible effect on the microstructure of the Y2O3 ceramics. Yb cations diffusion across the contact boundaries was investigated by the Energy Dispersive X-ray Spectroscopy analysis. Laser emission at 1.03 mu m was obtained from all ceramic samples, using quasi-continuous pumping at 971 nm with a fiber-coupled diode laser. This technique can be used to obtain multilayer ceramic structures, which could ensure for high-power lasers a controlled profile of the power absorbed in the active medium, or an efficient transfer of the heat generated during laser emission.

Overexpression of pyruvate kinase (PyK) is linked to many kinds of malignant tumors, representing therefore one of the most promising therapeutic targets for cancer treatment. Inhibition of PyK slows down tumor growth or causes tumor cell death, minimizing cancer cell proliferation, and understanding inhibitor mechanism of action can significantly improve cancer therapy. The present work describes the use of an amperometric bienzymatic biosensor, based on PyK and pyruvate oxidase (PyOx), in enzyme inhibition studies of four kinase inhibitors, CPG77675, Nilotinib, Ruxolitinib, Cerdulatinib. Their inhibition mechanism is studied and discussed in detail, with a thorough evaluation of their enzyme-inhibitor complex binding constants (Ki) and the inhibitor concentration required for 50% inhibition (IC50), employing standard inhibition procedure graphical methods. The biosensor is successfully applied for the quantification of the inhibitors by fixed potential amperometry, with excellent detection limit values in the pM range. It is the first detection method reported for the anticancer drugs CPG77675 and Cerdulatinib. The electrochemical assay based on the biosensor brings several advantages over the available assay kits for high-throughput screening (HTS) of kinase inhibitors, namely: low cost, easy operability and robustness demonstrated by biosensor high reproducibility and both operational and storage stability, offering an opportunity to discover new inhibitors and optimize their therapeutic index.

Sensing of volatile organic compounds (VOCs) not only in exhaled air but also in environmental air is essential in rapid diagnostication and in identifying potential hazards related to air quality, respectively. In particular, respiratory diseases like influenza and tuberculosis and other conditions like ketosis and diabetes can be investigated based on the detection of specific biomarkers in the exhaled products. At the same time, airborne pollutant contamination and air toxicity must be strictly and efficiently monitored. A practical and accurate VOC sensing device can be obtained using conductance changes induced in properly functionalized phosphorene active layers, which ensure specific binding sites for the targeted biomolecules. We develop here a multiscale approach that embeds an atomistic description based on density functional theory into a macroscopic transport model. In this way, we account for the electronic structure modifications induced in the active layer by the attached biomarkers with different configurations, which are extracted from ab initio molecular dynamics simulations. For the description of the device operation at the macroscopic level, we introduce a statistical model, which takes into consideration the proportion of the binding sites in the pristine active layer and the fractions of attached molecules. Perturbing factors like carbon dioxide, nitrogen, oxygen, and water molecules are investigated, and biomarker detection limits are evaluated. To improve the specificity of the biosensor, multiple sensing elements are employed, differently customized by transition metal impurities, which enhance the biomarker recognition capability. This allows the precise determination of the proportions of the molecules adhered to the device with the accuracy strictly dependent on the measurement resolution. Our results indicate that acetone and cyclohexanone detection is possible down to a few tens of ppm.

In this study, porous polysiloxane (PS)/multi-walled carbon nanotube (MWCNT) nanocomposite films were developed as high-performance triboelectric layers for flexible triboelectric nanogenerators (TENGs). TENGs convert mechanical motion into electricity and offer a promising solution for self-powered electronic systems. The nanocomposites were fabricated using a doctor blading method, and porosity was introduced via a simple, scalable salt-leaching technique. Sieved salt particles of varying sizes produced films with fine, medium, and large pores. Raman spectroscopy confirmed uniform MWCNT dispersion and strong interfacial interaction within the PS matrix. SEM analysis verified controlled pore morphology. Dielectric measurements showed reduced permittivity with increasing pore size due to air void incorporation. Triboelectric performance improved significantly with porosity; the medium porosity sample exhibited the best output with an open-circuit voltage of 65 V, short-circuit current of 6.9 mu A, and a power density of 280.6 mW m-2. This enhancement is attributed to the optimized combination of surface roughness, contact area, and dielectric behavior, promoting efficient charge generation and transfer. These results highlight the potential of microstructural engineering in porous nanocomposites for next-generation energy harvesting applications.