National Institute Of Materials Physics - Romania

Gold nanorods (AuNRs) were synthesized and optimized with the aim of obtaining strongly hydrophilic nanomaterials, suitable as a drug delivery system (DDS) for copper-based drugs. After careful purification, AuNRs were characterized by ultraviolet-visible-near-infrared spectroscopy (UV-Vis-NIR), showing two typical localized surface plasmon resonance (LSPR) bands in the range 550-750 nm. Fourier Transform Infrared (FT-IR) and high-resolution X-ray photoelectron (HR-XPS) spectroscopies verified the surface functionalization. Transmission electron microscopy (TEM) showed AuNRs with regular shape and size, with an aspect ratio (AR) of 2.6. Dynamic Light Scattering (DLS) measurements confirmed the size and the stability in water for up to 3 months. The AuNRs were conjugated with copper(I) drugs, i.e., [Cu(PTA)4]BF4 (PTA = 1,3,5-triaza-7-phosphadamantane). The drug loading procedures and efficiency were optimized, and the best loading was eta (%) = 50 +/- 7%. The non-covalent interactions of the Cu(I) complex with the AuNRs were studied by means of UV-Vis-NIR, zeta-potential, HR-TEM, FT-IR, synchrotron radiation-induced X-ray photoelectron (SR-XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. The MTT assay performed on Vero E6 cells showed that AuNRs and AuNR-Cu(I) conjugates had no significant effect on cell viability, being biocompatible, causing a reduction in cell viability only after prolonged exposure.

A set of yttrium-gadolinium ferrite powder and ceramic samples (Y3-xGdxFe5O12, x = 0.0-1.0) was comprehensively investigated to elucidate the mechanisms that govern the formation of garnet structure. The objects of investigation were synthesised by means of precipitation in aqueous solutions followed by annealing and sintering (for ceramic samples) at temperatures up to 1400 degrees C. The employment of X-ray diffraction and Fourier-infrared spectroscopy has enabled to reveal the key features associated with the crystal structure formation in dependence on the concentration of gadolinium. The formation of a garnet structure is demonstrated to occur in two stages, where the initial stage includes the formation of an intermediate orthorhombic perovskite phase. The substitution of yttrium cations with gadolinium ones is shown to exert a non-monotonous effect on these processes. A significant finding of this study is that the presence of Gd dopant results in a substantial decrease in the temperature of the garnet structure formation. This decrease is approximately 100 degrees C within the concentration range that was studied, and for specific concentrations (x = 0.4 and x = 1.0), it reaches 200 degrees C that is technologically relevant for energy-efficient materials processing. In ceramic samples derived from the synthesised particles, the increase in gadolinium concentration is found to result in a decrease in porosity and a non-monotonous transformation of static (saturation magnetization, coercivity) and dynamic (ferromagnetic resonance linewidth) magnetic parameters. This study delineates the critical insights into the development of yttrium-iron garnets-based materials, offering the practical approaches for improving their structural and physical parameters to enhance utilization for microwave applications.

Y-branched TiO2 nanotubes (NTs) were produced by anodizing titanium plates derived from aerospace production leftovers and subsequently engineered to develop an enhanced TiO2-based photocatalytic system. The NTs were electrochemically reduced to obtain reduced TiO2 nanotubes (rTN) with a narrowed bandgap, followed by surface modification with polydopamine (PD) and silk fibroin-derived quantum dots (QDs) to promote enhanced UV and visible-light photocatalysis for wastewater treatment. The QDs were hydrothermally synthesized from Bombyx mori silk fibroin. Scanning Electron Microscopy (SEM) revealed spherical QD agglomerates encapsulated within the PD layer, while Energy Dispersive X-ray Spectroscopy (EDX) confirmed the presence of carbon and nitrogen originating from both PD and QD. The resulting rNT/PD/QD photocatalyst exhibited a significantly reduced bandgap (1.03 eV), increased Urbach energy (1.35 eV), and moderate hydrophilicity. A high double-layer capacitance (C-dl) indicated an enlarged electrochemically active surface due to the combination of treatments. Electrochemical characterization demonstrated reduced electrical resistance, higher charge density, and lower electron-hole recombination, leading to improved interfacial charge transfer efficiency and electrochemical stability during multi-cycle cyclic voltammetry measurements. Preliminary photocatalytic tests show that the rNT/PD/QD photocatalyst achieved a degradation efficiency of 79.26% for methyl orange (MO) and 35% for tetracycline (TC).

We approach a cost effective, environmentally friendly, synthesis route of a non-precious electrocatalysts for the anodic oxidation of bioethanol. SnO2 and SnO2-Graphene Nanoplatelets are decorated with nano-crystallized Ni filaments and clusters with peculiar surface chemistry. The electrocatalysts are obtained by subsequently depositing different Ni species by wet impregnation in the presence or absence of a reducing agent (Na borohydride). The effect of the Ni deposition parameters on the crystalline and porous structures, on the surface chemistry and on the electrochemical behavior is highlighted. It is found that the use of a lower temperature (200 degrees C) thermal treatment in the presence of a reducing agent leads to an increase of more than five times of the specific surface area. Electrocatalytic performance is assessed in alkaline medium and, apparently, graphene addition to the SnO2-nickel support allows diminishing the Tafel slope with ca. 20 %, down to 106 mV decade(-1). Such value, that favorably compares to those in the literature, together with the good resistance to fouling that the results of the chronoamperometric and electrochemical impedance spectroscopy (EIS) measurements demonstrate, show that the composites are worthy of development as active materials for biofuel cell applications.

ZnO is recognized as one of the most versatile semiconductor materials, due to its adjustable properties, making it ideal for various applications. Herein, C-doped ZnO nanoparticles were obtained by thermal decomposition and tested as photocatalysts for water depollution and electrode materials in a symmetric supercapacitor device. These nanoparticles exhibited polyhedral shapes with sizes ranging from 95 to 104 nm. The impact of the doping level on the evolution of defect centers was analyzed using EPR and PL spectroscopy. Under visible light, the photocatalytic performance was tested against two contaminants, Rhodamine B (RhB) dye and oxytetracycline (OTC) antibiotic. A 1% C doping level provided the optimal photocatalytic performance, achieving degradation rates of 80% for RhB and 50% for OTC. The photodegradation process was elucidated by examining ROS species generated, linked to the measured valence band position and defect levels. Additionally, the same sample showed superior electrochemical performance when tested in a symmetric supercapacitor device, achieving a maximum specific capacitance of 104.16 F/g at a 2 mV/s scan rate, with an energy density of 14.46 Wh/kg and excellent cyclic stability, retaining 99% capacity after 2000 cycles. These findings highlight the versatility of C-doped ZnO nanoparticles, making them effective in environmental remediation and energy storage applications.

Layers of HfO2 and (Hf,Zr)O2 crystalline nano-particles are synthesized via direct liquid injection atomic layer deposition, and a comprehensive set of structural, chemical, and electrical characterizations is employed to elucidate their phase composition and functional behavior. X-ray photoelectron spectroscopy revealed a compositional contrast between the films: (Hf,Zr)O2 layers contained up to 45% stoichiometric oxide, while pure HfO2 films are dominated by sub-oxides, especially under strongly reducing conditions, in which exclusively sub-oxide phases and p-type semiconducting behavior is revealed. Electrical measurements indicated room-temperature stabilization of polar phases and tetragonal-to-orthorhombic phase transition with a Curie temperature near 200 K. FTIR spectroscopy confirmed the presence of tetragonal and orthorhombic HfO2 phases, providing insight into minor features observed approximate to 30 degrees (2 theta) in X-ray diffraction patterns. Notably, devices incorporating an AlN interlayer demonstrated a significant enhancement in pyroelectric performance, suggesting this strategy to advance the pyroelectric performance of HfO2-based materials, supporting their development for lead-free sensor technologies.

Chronic inflammation and persistent infections represent major obstacles to effective wound healing, underscoring the urgent need for innovative, eco-friendly biomaterials capable of combating microbial contamination and oxidative stress. In this study, we investigated the in vitro biological activities of a gold-titanium dioxide (AuNPs/TiO2) composite, synthesized via an environmentally friendly approach, employing an ethylenediamine-hyaluronic acid derivative as both a reducing and stabilizing agent. The composite was analyzed using various techniques, including Transmission Electron Microscopy, X-ray elemental mappings, X-ray diffraction, and X-ray spectroscopy. We evaluated the biological properties of the material through antimicrobial and anti-adherence assays, alongside hemolysis, cytotoxicity, oxidative stress levels, and wound healing potential. The green-derived AuNPs/TiO2 demonstrated moderate to potent antimicrobial and anti-adhesion activity (minimum inhibitory concentrations ranging from 0.625 to 5 mg/mL) against both standard and clinical isolates. The material showed low hemolysis rates (<5 %) at bioactive concentrations. Additionally, keratinocyte viability and membrane integrity were largely preserved at the tested concentrations, with no detectable increase in pro-inflammatory nitric oxide levels. Intracellular antioxidant defenses were maintained, and lipid peroxidation was minimal. In an in vitro scratch assay, AuNPs/TiO2 promoted keratinocyte migration, suggesting a promising potential to enhance tissue repair. In summary, the biomaterial exhibits promising multifunctional properties, including effective antimicrobial and anti-adhesion activity, excellent biocompatibility with minimal hemolysis, and the ability to enhance keratinocyte migration and intracellular antioxidant defenses. These findings highlight its potential as a safe and effective biomaterial for accelerating wound healing and addressing infection-related challenges.

Hafnium oxide (HfO2) thin films were deposited on n-type gallium arsenide (GaAs) substrates by Oxide-Molecular Beam Epitaxy (Oxide-MBE) method using Hafnium (Hf) metallic flow in an oxidizing atmosphere of 10-6 mbar molecular oxygen. The Hf metallic flow was provided by an e-beam evaporator and a deposition rate 10 nm/h was established. Semiconductor surface preparation was done prior to deposition, beginning with chemical wet etching and aggressively adjusted by in treatments until a desired stoichiometry was reached. Heterojunctions with HfO2 thin layers of 1 nm, 3 nm, 10 nm and 20 nm were fabricated. X-Ray Photoelectron Spectroscopy (XPS) and ARXPS(Angle Resolved XPS) in-situ analyses provided a clear picture of the structure of the interfaces, the chemical bonds and composition. The interfaces are chemically stable and abrupt. A small amount of Ga2O3 provides a passivating effect of the semiconductor surface. The electrical properties of the heterostructures were determined using the Kraut method and Reflection Electron Energy Loss Spectroscopy (REELS) technique. Band offsets Delta EC=1.75 eV and Delta EV=2.62 eV confirm a high application potential. Additionally, data on the morphology and continuity of the layers were obtained by Atomic Force Microscopy (AFM) technique while the amorphous growth was monitored by XRD(X-ray Diffraction), GIXRD (Grazing Incidence XRD) and XRR(X-ray Reflectivity) measurements. The dielectric layers showed values of the constant k in the range of 19-22, established by electrical measurements on MOS capacitors.

Background: Hepatocellular carcinoma is associated with high mortality and increasing incidence. Sorafenib, a cornerstone of therapy for advanced hepatocellular carcinoma, presents certain disadvantages, including low bioavailability and poor water solubility. This work describes a new strategy for sorafenib-targeted delivery aimed at improving treatment efficiency and reducing side effects. Methods: Magnetic nanoparticles coated with azelaic acid were modified with aptamer molecules that specifically recognize human liver cancer cell line HepG2, ensuring specificity for the tumor tissue. The nanoparticles were further loaded with sorafenib. The obtained drug delivery system was extensively characterized using UV-Vis spectrophotometry, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. Results: The drug delivery system demonstrated a higher release of sorafenib at acidic pH compared to pH 7.4. The cell internalization of the bare and aptamer-modified magnetic nanoparticles was assessed in HepG2 and human normal foreskin fibroblasts BJ cell lines, demonstrating that the aptamer significantly enhances internalization in tumor cells, while having no impact on healthy cells. Conclusions: The sorafenib-modified nanoparticles exhibited excellent cytocompatibility with BJ cells across all tested concentrations, while showing cytotoxicity towards HepG2 cells at higher concentrations, confirming the selectivity of the system.

Despite the promise of high-k dielectrics, inherent limitations persist in transistor scaling and enhancing energy efficiency, including a fundamental threshold of 60 mV/dec for increasing drain current by an order of magnitude. Proposed solutions involve negative capacitance at the gate oxide to overcome this barrier using ferroelectric structures. Efforts to understand and regulate the switching dynamics and intricate electrostatic configurations of ferroelectric structures towards achieving negative capacitance regimes have intensified. While standalone ferroelectric capacitors cannot stabilize negative capacitance without external fields, multilayered thin films offer a promising solution. Typically, ferroelectric layers are paired with dielectrics/insulator, demonstrating steady-state negative capacitance, often at nanoscale or specific temperature domains. This study aims to stabilize negative capacitance in ferroelectric structures by inducing internal electric fields, aligning the system near coercivity, particularly in bilayer structures formed by two ferroelectric layers with slight differences in polarization values, such as p-n heterojunctions using Pb (Zr,Ti)O3 PZT) with different doping as Fe, Nb, Bi. Most of these structures exhibit evident amplification of capacitance compared to the equivalent series-connected capacitance, across a large temperature domain. The complex capacitance-frequency characteristic of these structures indicates a complex equivalent circuit. Analysis of these complex circuits compared with simple component layers concludes that at least one of the FE layers in these bilayer structures is in a negative capacitance (NC) state.