National Institute Of Materials Physics - Romania

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.

Two series of photocatalysts (TYAu, TYCeAu) were obtained. Ti was incorporated by direct synthesis with zeolite Y, while Ce and Au were immobilized by double incipient wetness impregnation method. The experimental weight percents (XRF analysis) were for titanium (0.7 %, 1.9 %, 3.5 %), Ce (1 %), and Au (0.3 %, 0.1 %). The typical crystalline structure of zeolite Y was preserved in all samples except those with 3.5 % Ti, where XRD revealed reduced pattern intensity. SEM and TEM analyses showed morphological changes at higher Ti contents. CO2-TPD confirmed a decrease in basicity with increasing Ti, consistent with the diminished zeolite contribution. XPS analysis indicated the presence of varying Au0/Au+ and Ce3+/Ce4+ ratios on the surface, depending on the Ti content. The intra- and extraframework TiO2 as amorphous or anatase phases were Raman confirmed in ceriumcontaining samples. For materials with high Ti content, the dominant effect was from the Ce and Ti species, accentuated by gold. The surface plasmon resonance effect of Au nanoparticles and decreasing in band gap energy after Ce immobilization was evidenced by UV-Vis spectroscopy. The photocatalytic properties of the synthesized materials were evaluated in CO2 reduction with water and H2 production via water splitting under visible light (525 nm). Higher Ti content enhanced CO2 conversion and reduced CH4 selectivity, favoring the production of CH3OH and CH2O. A greater amount of hydrogen was produced by the samples with the lowest Ti concentration while the reaction was favored by the presence of cerium in the rich titanium samples.

Cerium dioxide (CeO2) thin films with pyramidal nanostructures exhibiting a fractal aspect are suitable for various applications that require a large surface area. An accurate model of these films is valuable not only for optimizing the properties for specific applications but also for predicting and understanding the growth mechanism. In this paper, we present the foundation of a simulation for the growth of CeO2-x nanostructured thin films. We propose a 3-dimensional model of the surface nanostructures and link the morphology with crystallographic orientations and growth modes. To validate our model, we fabricated CeO2_ x thin films with different thicknesses using pulsed laser deposition (PLD) and characterized their morphological and structural properties. The evolution of our films shows the representative features of the Stranski-Krastanov model. The morphology changes from compact and smooth to dendritic with pyramidal nanostructures. The texture of our film also changes with thickness, and the preferential orientations are (111) and (220). Additionally, we characterize the CeO2_ x thin films from the chemical and optical points of view. The stoichiometry of CeO2 is not fully achieved, our thin films present the Ce3+ oxidation state at the surface. The formation of C-type Ce2O3 with fluorite structure can be associated with a small refractive index and small band gap.

Superoxide plays a significant role in maintaining physiological states of living systems, with major roles in eradicating invading microorganisms and in cell signaling. It is regulated intricately by the enzyme superoxide dismutase (SOD), and when not properly regulated it can lead to cascade biological pathways with severe and irreversible damage to biofilms, tissue, and organs, being linked with many neurodegenerative diseases, atherosclerotic and cardiovascular diseases. Therefore, superoxide anion (O center dot-2 ) detection has a tremendous potential in clinical diagnostics to assess oxidative stress in living cells. This comprehensive review aims to explore, discuss, and analyze recent trends in the electrochemical detection of O center dot-2 in living systems, focusing not only on the recognition mechanism for in vitro assays (living cell cultures/tissues) but also on the importance of the electrode design and operational parameters for in vivo measurements (implantable sensors). By analyzing current in vitro/in vivo electrochemical strategies we gather information that is helpful to overcome existing limitations in the dynamic monitoring of O center dot-2 , and further improve electrochemical strategies that can be adopted and applied to prevent its negative effect, with an insight into the pathophysiology of neurodegenerative disorders and even cellular malignancies that derive from its accumulation in living systems.

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.

This study describes the development of a pyruvate kinase (PyK)-biosensor for the evaluation of PyK activity, as a diagnostic tool for early cancer screening and detection of kinase inhibitors used in cancer treatment, with the evaluation of the inhibition mechanism. The biosensor was constructed by co-immobilizing the enzymes PyK and pyruvate oxidase (PyOx) on Au film electrodes by crosslinking with glutaraldehyde (GA) and evaluated electrochemically by cyclic voltammetry (CV) and fixed potential amperometry (CA). First, the experimental conditions were optimized in terms of applied potential, enzyme ratio PyK:PyOx and enzyme substrate concentration: phosphoenolpyruvate (PEP) and adenosine diphosphate (ADP). The biosensor sensitivity towards PEP detection was 2.11 +/- 0.08 mu A mM- 1 cm- 2, with very high reproducibility and repeatability, which made it suitable for inhibition studies of PyK inhibitor. The inhibition mechanism of shikonin was determined in relation to both PEP and ADP, with the calculation of IC50 values and binding constants (Ki). Detection of shikonin was possible at very low concentrations in the linear range of 0.1-4.0 pM. The electrochemical results were validated by UV-Vis spectrophotometry. The developed biosensor is a valuable tool for drug screening by enabling enzyme catalytic function examination with applicability to identify inhibitors, estimate their affinity, inhibition mechanism linked to their molecular mechanisms of action and evaluate selectivity, of great interest in both pharmaceutical and medical domains.

Bilayer metallic electrodes of magnesium and zinc-aluminum alloys Mg/Zn:Al were prepared using combined laser-thermionic vacuum arc methods. Plasma diagnosis suggests laser-plasma interaction by increasing the discharge voltage when the laser is on, which is converted by thermal annealing of plasma ions. A magnesium thin film with a lower work function, covered with a Zn:Al (4:1) layer was successfully used for efficient charge injection into electroluminescent diodes. The zinc-aluminum combination preserved the electrical conductivity of the thin magnesium film and protected it against oxidation. The capacitance-voltage measurements confirmed the integrity of the magnesium layer, whereas the work function was not affected. The zinc-aluminum alloy obtained through a thermionic vacuum arc exhibits good conductivity compared to pure zinc layers and better stability against degradation.

This study investigates the influence of different aromatic side groups on the 2D-benzodithiophene (BDT) unit in donor-acceptor conjugated polymers for organic solar cell (OSC) applications. Three new polymers, P1, P2, and P3, featuring phenyl, thienyl, and thienothienyl side chains on the 2D-BDT backbone, respectively, were synthesized using the Stille cross-coupling reaction. The benzotriazole (BTz) unit served as the electron acceptor with a selenophene it-bridge to enhance electronic interactions. The optical band gaps were determined to be 1.79 eV, 1.74 eV, and 1.73 eV for P1, P2, and P3, respectively. OSCs fabricated using these polymers and PC71BM as the acceptor showed the best performance for the thienyl-substituted polymer (P2), achieving a PCE of 4.34 % with a JSC of 10.08 mA/cm2, an VOC of 0.67 V, and a FF of 64 %. Compared to P1 and P3, the P2-based blend exhibited a more defined interpenetrating network with PC71BM, enhancing charge transport and promoting exciton dissociation due to its thinner active layer and optimized morphology. These findings highlight the importance of side-chain engineering in improving the optoelectronic properties, morphology, and photovoltaic performance of OSCs. This study highlights the critical role of side-chain engineering in tuning the optoelectronic properties, morphology, and performance of OSCs. The findings emphasize that thienyl side chains in P2 facilitate better it-it stacking and molecular organization, resulting in superior device performance compared to phenyl and thienothienyl-substituted counterparts.

The development of titania-based hybrid nanostructures with enhanced visible-light photocatalytic activity has been a key research area recently. The present study addresses current limitations of the TiO2 based composite photocatalyst by newly-experimental designing of flower-like multifunctional hybrid nanostructure with visible light capability through Ferrihydrite (Fh) surface TiO2 functionalization. Here, we present a versatile nanocompartimentalization process of which, core anatase TiO2 nanoparticles are emebeded into Fh lamellar shell. Physico-chemical properties related to the chemical structure and morphology of the prepared nanomaterials were comprehensively analysed using complementary analytical techniques, such as powder X-Ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FE-SEM), Ultra-High Resolution Transmission Electron Microscopy (UHR-TEM), X-Ray Photoelectron Spectroscopy (XPS) and soft X-Ray Absorption Spectroscopy (XAS). The conducted visible-light-driven photocatalytic water splitting tests highlights significant enhancement in the Oxygen Evolution Reaction (OER) performance for TiO2-Fh core-shell nanoheterostructure of 25.6 mu mol/L of molecular oxygen after 60 min of visible light irradiation (AM1.5G), and a photocatalytic water oxidation activity rate of 341.3 mu mol L-1 g-1h-1. The biocompatibility assessment of the developed core-shell structures combined with their enhanced photocatalytic water oxidation activity under visible light illumination suits them as excellent candidates for the development of sustainable environmental remediation technologies.

Nb2C MXene, obtained from Nb2AlC by Al3+ etching and exfoliation, was characterized using XRD, HRTEM and AFM, with the data confirming the crystallinity of the sample and the 2D morphology of the sheets with an average layer thickness of 1.5 nm. Surface analysis using XPS revealed the presence of structural defects, and NH3- and CO2-TPD profiles confirmed the low density of acid and basic sites in the range of tens of mu mol gcatalyst-1 of weak and moderate strengths. The combination of acid and basic sites in close proximity on the solid surface was responsible for the remarkable catalytic activity of Nb2C MXene in promoting aldolic condensation with high turnover frequencies of up to 855 h-1, which was comparable to the values of benchmark catalysts, such as MgO or HZSM-5. Nb2C MXene also catalyzed the aerobic oxidative aniline coupling to azo- and azoxy-benzene and hydrogenation of azoxybenzene to azobenzene.