National Institute Of Materials Physics - Romania

Palladium diselenide (PdSe2) is a two-dimensional (2D) transition metal dichalcogenide van der Waals material that exhibits a unique wrinkled pentagonal structure that results in strong anisotropic layer-dependent properties. Owing to these unique properties the material has a great potential for applications in electronic, optoelectronic, photonic and thermoelectric devices. Here, we study the electronic properties of monolayer (ML) PdSe2 in a Schottky junction by contacting the material with a tungsten scanning tunneling microscope (STM) tip. The STM-induced lifting of the 2D layer leads to structural warping of the top layer, which causes significant changes in the electronic properties of PdSe2 as well as the electrostatic potential across the junction. We compare the STM-determined work function of the warped PdSe2 ML with the work function of bulk PdSe2 as obtained by Kelvin probe force microscopy and electronic structure obtained by synchrotron-based angle-resolved photoemission spectroscopy, and x-ray photoelectron spectroscopy.

Carbon nanotubes (CNTs) represent promising nanoplatforms for drug delivery due to their high surface area, tunable surface chemistry, and unique physicochemical properties. This study investigated the effect of chemical functionalization on the dispersion, drug loading, release behavior, aerosolization, and preliminary in vitro cytotoxicity of CNT-based drug delivery systems, with a view toward potential intranasal applications. Pristine CNTs and CNTs functionalized with hydroxyl (-OH) and carboxyl (-COOH) groups were loaded with methylene blue as a model therapeutic compound. The nanosystems were characterized using Raman spectroscopy, UV-Vis analysis, aerosol deposition measurements, electrical mapping by conductive atomic force microscopy (C-AFM), and MTT cytotoxicity assays. Functionalization significantly enhanced CNT dispersion stability and drug release control, with COOH-CNTs exhibiting the most sustained release profile and improved cytocompatibility, maintaining cell viability above XX% at concentrations up to YY & micro;g/mL. Aerosolization tests demonstrated stable droplet formation compatible with nasal delivery devices. Overall, this work provides a proof-of-concept physicochemical and technological assessment of functionalized CNTs as potential carriers for intranasal drug delivery, laying the groundwork for future in vivo validation.

Graphene oxide (GO) nanosheets (0.5-2.0 phr) were incorporated into nitrile-butadiene rubber (NBR) to clarify how interfacial chemistry and dispersion control macroscopic performance. GO was synthesized by a modified Hummers method, and different filler concentrations of NBR/GO were prepared via solution-coagulation followed by sulfur vulcanization. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed multilayer GO and best sheet dispersion at 1 phr, whereas 2 phr showed initial aggregation. Fourier-transform infrared spectroscopy (FTIR) confirmed that the NBR backbone and nitrile groups remained intact, while weak GO-derived C-O-C/C-O bands appeared at higher loadings. The C equivalent to N band at similar to 2,237 cm-1 preserved its position but showed a slight increase in bandwidth, consistent with the formation of a hydrogen-bonded interphase. X-ray diffraction (XRD) showed loss of GO periodicity in the rubber matrix. UV-Vis/Tauc analysis indicated a non-monotonic band gap (direct 3.01 -> 3.13 -> 3.11 eV; indirect 2.84 -> 2.92 -> 2.96 eV), arising from confinement at well-dispersed loadings and pi-pi stacking at higher loadings. Dielectric measurements (102-106 Hz, 20 degrees C-100 degrees C) evidenced a more stable epsilon ' for GO-filled samples, maximized at 1 phr. Mechanical testing showed simultaneous gains in tensile strength, tear resistance, and rebound elasticity at low GO loadings, while swelling and thermo-oxidative retention improved due to barrier effects and chain immobilization. Overall, similar to 1 phr GO delivers the best structure-property balance, combining hydrogen-bond-mediated interfacial adhesion and optimal dispersion with stable dielectric behavior and reduced swelling/aging sensitivity; 2 phr yields the highest tensile value but also results in incipient aggregation and reduced dielectric stability.

This study explores synthesizing and characterizing LaPO4:Sb3+/xMn2+ (LSBMx) phosphors (x = 0%-5%) prepared via the co-precipitation method. Structural analysis and luminescence properties reveal that LSBM0 (without Mn2+) emits blue light under UV excitation, while Mn2+-doped samples exhibit tunable emission from blue to orange-red. Under UV excitation, LSBMx phosphors demonstrate a broad visible emission band with multiple peaks attributed to the 4T1(4G) -> 6A1(6S) transition of Mn2+. The broad emission band (520-660 nm) can be deconvoluted into four Gaussian components centered at 564 nm (Mn-I), 595 nm and 616 nm (Mn-II), and 648 nm (Mn-III), corresponding to Mn2+ in La3+sites due to charge inconsistency, crystal field modifications induced by Sb3+ incorporation, and Mn2+- Mn2+ dimers, respectively. Energy transfer efficiency calculations determine the optimal Mn2+ concentration to be approximately 3%. This novel phosphor system demonstrates versatile green, orange, and red emission capabilities, establishing a valuable framework for developing Mn2+-doped luminescent materials with potential applications in LED lighting technology.

The results of experimental investigation of the fundamental optical absorption edge of glassy thin films of the AsS3-GeS4 system are presented and discussed. The films were grown via thermal vacuum evaporation of powder of relevant glasses onto optical quartz substrates. The study was focused on the optical measurements to reveal the character and spectral position of the absorption edge, as well as to the effect of both glass composition and annealing on optical forbidden gaps and characteristic energies (triangle) of glasses in question. The absorption edge was found to concur with usual behavior established for disordered materials: at high photon energy hv > Eg, it is described by a parabolic function but at low energy hv < Eg by an exponential law (Urbach tail). The quadratic part of the absorption edge allowed to determine the optical forbidden gap Eg. It is shown that the glass composition and the thermal treatment influence the spectral position and slope of both parts of the absorption edge, but they especially strongly affect the slope of the exponential tail. The results are explained in terms of topological transformations due to glass composition change and structural self-organization, as well as their effect on concentration and energetic distribution of localized states inside of the forbidden gap.

Zinc oxide (ZnO) semiconducting nanoparticles were added to a nematic liquid crystal (NLC) mixture E7, and the influence of these particles on the spectroscopic and dielectric properties of the E7 mixture was studied. ZnO nanoparticles were obtained using a recently developed green method involving clove extract. The proportion of ZnO:LC in the mixture was varied between 1:99 and 95:5% to ensure accessibility of the particle surface for interactions with LC. These natural compounds not only facilitate the formation of stable nanostructures, but also promote surface functionalization, influencing the resulting morphology, crystallinity, and dispersion behavior of the nanoparticles in the host media. Because the classical fitting models were inadequate in our systems with multiple overlapping relaxation and conduction processes, derivative-based numerical methods were employed. Such approaches enabled the resolution of up to three distinct dielectric relaxation processes and allowed the extraction of characteristic frequencies and activation energies, and insight into the underlying interfacial phenomena between the ZnO nanoparticles and LC molecules was obtained. We assumed that the interaction between the two components of the composites (NLC and ZnO) was weak, which contributes to a deeper understanding of the interplay between biofunctionalized nanostructures and anisotropic soft matter environments.

This study investigates the optimization of multiwalled carbon nanotube (MWCNT) concentration in polysiloxane-based nanocomposites to enhance the performance of triboelectric nanogenerators (TENGs). Flexible nanocomposite films were fabricated using the doctor blading method, and their triboelectric output was systematically evaluated as a function of MWCNT loading. The results reveal that incorporating MWCNTs significantly improves the electrical performance of the TENG, with the open-circuit voltage (V oc) and short-circuit current (I sc) increasing to 51 V and 5.7 mu A, respectively, at an optimal concentration of 0.05 wt %, compared to 32 V and 3.3 mu A for pristine polysiloxane films. However, further increasing the CNT content to 0.1 wt % led to a notable decline in output, attributed to nanoparticle agglomeration, which hinders effective charge transfer and promotes charge leakage. These findings underscore the crucial role of nanofiller dispersion and concentration control in the development of high-performance TENGs. This work provides valuable insights into the development of flexible, nanocomposite-based energy harvesting systems with enhanced output efficiency for wearable and portable electronic applications.

Diamond traceability has been a major challenge for the gemological industry in recent decades. In this context, this paper presents new studies using UV-VIS-NIR spectroscopy to identify the traceability and geographical origin of diamonds. The aim of the work is to identify characteristic centers of fancy-color diamonds collected from Cullinan Mine, Democratic Republic of Congo (DRC), and the geographical regions with unknown origin. Depending on the origin of the diamonds, the UV-VIS-NIR spectra can be differentiated as follows: (i) the diamonds collected from Cullinan Mine show absorption bands assigned to N10, NV0, NV-, N3V0, N4V2, and N4V centers, which are accompanied by a vibronic structure localized between 415 and 394 nm (2.987-3.147 eV) and (ii) the diamonds from DRC show absorption bands attributed to N10, NV-, N3V0, N1+, and NVH centers. Using Raman spectroscopy, nitrogen concentration values of diamonds collected from the Cullinan mines and DRC between 41 and 185 ppm and 204-336 ppm, respectively, were reported. We prove that the simultaneous applicability of UV-VIS-NIR spectroscopy and Raman scattering as comparative tools for assessing diamond provenance can be a valuable strategy for an initial attribution of diamonds with unknown geographical origin, knowing the optical features of diamonds collected from Cullinan Mine and DRC.

The rational integration of different-dimensional nanostructures offers a powerful platform for engineering synergistic functionalities in photocatalysis. Herein, we report the controllable synthesis of novel 2D/1D graphene/silver-silver sulphide (Ag-Ag2S) hybrid nanocomposites, wherein 1D Ag-Ag2S nanowires (NWs) are uniformly anchored onto conductive graphene sheets, affording a hierarchical hybrid structure with tailored optoelectronic properties. Structural characterization via X-ray Diffraction (XRD) confirmed the coexistence of crystalline Ag, Ag2S, and Ag2O phases, evidencing both hybridization and partial oxidation during growth. Complementary Scanning Electron Microscopy (SEM) imaging revealed a homogeneous distribution of NWs across the graphene scaffold, ensuring maximized interfacial contact. Optical investigations demonstrated distinct band gap features (2.5 eV for Ag2S, 3.8 eV for Ag NWs, and 4.6 eV for Ag2O). In comparison, the composite exhibited dual transitions at 3.28 eV and 4.72 eV, attributed to interfacial charge transfer between Ag2S and graphene, alongside enhanced plasmonic carrier dynamics. FTIR analyses further corroborated the hybrid composition, highlighting O-H and C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 C stretching vibrations of graphene, CO bands from surface PVP ligands, and Ag-S/Ag-O vibrational modes consistent with XRD assignments. Harnessing these tailored structural and electronic attributes, the graphene/Ag-Ag2S heterostructures exhibited markedly superior photocatalytic activity toward methylene blue (MB) degradation, achieving a maximum efficiency of 89.55% under acidic conditions (pH 3) after 300 min of irradiation. Kinetic analysis revealed the highest rate constant (0.386 min-1) for the graphene/Ag-Ag2S nanocatalyst in acidic medium, surpassing both pristine Ag NWs and Ag-Ag2S. This work highlights the potential of spatially engineered graphene-based heterostructures to modulate band structures, enhance charge carrier transport, and thereby improve selective photocatalytic dye removal.

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] .