National Institute Of Materials Physics - Romania

NiO-sensitive materials have been synthesized via the hydrothermal synthesis route and calcined in air at 400 degrees C and, alternatively, at 500 degrees C. Structural, morphological, and spectroscopic investigations were involved. As such, the XRD patterns showed a higher crystallinity degree for the NiO calcined at 500 degrees C. Such an aspect is in line with the XPS data indicating a lower surface hydroxylation relative to NiO calcined at 400 degrees C. An HRTEM microstructural investigation revealed that the two samples differ essentially at the morphological level, having different sizes of the crystalline nanoparticles, different density of the surface defects, and preferential faceting according to the main crystallographic planes. In order to identify their specific gas-sensing mechanism towards CO exposure under the in-field atmosphere, the simultaneous evaluation of the electrical resistance and contact potential difference was carried out. The results allowed the decoupling of the water physisorption from the chemisorption of the ambient oxygen species. Thus, the specific CO interaction mechanism induced by the calcination temperature of NiO has been highlighted.

In this study curcumin was immobilized in a silica matrix to overcome its poor aqueous solubility and rapid degradation profile. Two kinds of sol-gel powders based on colloidal silica were synthesized and characterized, one prepared with an ethanolic solution of curcumin and the other using cethyltrimethylammonium bromide (CTAB) to solubilize the dye. The successful integration of curcumin in the matrix as well as the interaction with the components of the composite powders was validated by different analysis methods (DSC, FTIR). The samples morphology was evaluated by SEM. UV-Vis and fluorescence studies showed that curcumin was stable, in its enol configuration in both matrices. The sensitivity to ammonia was proved by exposing the powders to NH3 vapors in a sealed vessel. Color changes were measured with a colorimeter. UV-Vis spectra showed that the enol form of the dye in EtOH/CTAB based SiO2 matrices was energetically stable under NH3 atmosphere, even after being kept a few days at low temperature. A fluorescence quenching of both samples was noticed due to interaction curcumin-ammonia. Both samples have antimicrobial properties, the CTAB containing one being more efficient. The EtOH/CTAB based SiO2 powders may represent a novel signaling and antimicrobial system, useful for food or pharmaceutical applications. [GRAPHICS] .

An original photodetector system based on self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO-ZnO core-shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO-ZnO core-shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p-n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron-hole pairs at the CuO-ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO-ZnO core-shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.

The present study aimed to assess the feasibility of developing low-cost multipurpose iron oxide/TiO2 nanocomposites (NCs) for use in combined antitumor therapies and water treatment applications. Larger size (approximate to 100 nm) iron oxide nanoparticles (IONPs) formed magnetic core-TiO2 shell structures at high Fe/Ti ratios and solid dispersions of IONPs embedded in TiO2 matrices when the Fe/Ti ratio was low. When the size of the iron phase was comparable to the size of the crystallized TiO2 nanoparticles (approximate to 10 nm), the obtained nanocomposites consisted of randomly mixed aggregates of TiO2 and IONPs. The best inductive heating and ROS photogeneration properties were shown by the NCs synthesized at 400 degrees C which contained the minimum amount of alpha-Fe2O3 and sufficiently crystallized anatase TiO2. Their cytocompatibility was assessed on cultured human and murine fibroblast cells and analyzed in relation to the adsorption of bovine serum albumin from the culture medium onto their surface. The tested nanocomposites showed excellent cytocompatibility to human fibroblast cells. The results also indicated that the environment (i.e. phosphate buffer or culture medium) used to disperse the nanomaterials prior to performing the viability tests can have a significant impact on their cytotoxicity.

A new core-shell pH-responsive nanocarrier was prepared based on magnetic nanoparticle (MNP) core. Magnetic nanoparticles were first modified with hyperbranched polyglycerol as the first shell. Then the magnetic core was decorated with doxorubicin anticancer drug (DOX) and covered with PEGylated carboxymethylcellulose as the second shell. Borax was used to partially cross-link organic shells in order to evaluate drug loading content and pH-sensitivity. The structure of nanocarrier, organic shell loadings, magnetic responsibility, morphology, size, dispersibility, and drug loading content were investigated by IR, NMR, TG, VSM, XRD, DLS, HR-TEM and UV-Vis analyses. In vitro release investigations demonstrated that the use of borax as cross-linker between organic shells make the nanocarrier highly sensitive to pH so that more that 70% of DOX is released in acidic pH. A reverse pH sensitivity was observed for the nanocarrier without borax cross-linker. The MTT assay determined that the nanocarrier exhibited excellent biocompatibility toward normal cells (HEK-293) and high toxicity against cancerous cells (HeLa). The nanocarrier also showed high hemocompatibility. Cellular uptake revealed high ability of nanocarrier toward HeLa cells comparable with free DOX. The results also suggested that low concentration of nanocarrier has a great potential for use as contrast agent in magnetic resonance imaging (MRI).

The current study aims to present and discuss the results obtained by complementary archaeometric methods applied for the first time on white pigments inlaid on excised pottery of the Boian-Vidra tradition (Early Chalcolithic, c. 4900-4600 BCE). The samples came from three settlements located in Southern Romania (Sultana-Ghetarie, Vidra, and Vladiceasca). They were selected considering that the pottery was produced in approximately contemporary sites, located relatively close to each other in the same geographical region, namely the Romanian Plain. The experimental part included the analysis of local samples of carbonate concretions and prehistoric animal bone ash as reference materials. Archaeometric investigations consisted in applying "in-air" PIXE and EDX methods for the chemical composition, XRD and FTIR for mineralogical data, SEM for microstructure observation, and EPR for the characterisation of the paramagnetic centres. Calcite, bone ash, and silica rich sediments were identified as the primary decorating pigments. The mixtures of calcite and bone-ash observed in 13 samples were specific to the sites at Vidra and Vladiceasca. Silica-rich sediments from distant sources were the main whitening materials in two samples from Vladiceasca, while for the samples from Sultana-Ghetarie, calcite was the only whitening mineral. The results show with a high degree of confidence the use of both local (i.e., carbonate neo-formations and bone ash) and exotic (silica-rich sediments) raw materials to obtain the white pigment applied to Boian-Vidra pottery. Thus, the current data show the adaptability of the potters with respect to the surrounding resources and also provide new evidence for a vast trade network of raw materials and/or finished products in the Lower Danube area during the Early Chalcolithic. The deliberate mixing of two whitening materials from different sources could be a technological choice and may highlight complex symbolic behaviours.

AuxFe1-x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mossbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect alpha-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced.

In this work, the ferroelectric characteristics of ZrO2 thin films grown on ITO-coated glass have been investigated. The ferroelectric nature of the ZrO2 films has been studied by polarization-electric field (P-E) hysteresis loops and found to be optimum for the films processed by rapid thermal annealing at 600 degrees C. The increase in the annealing temperature improves the ferroelectric properties through the increase of the in-plane strain that causes the formation of the ferroelectric orthorhombic phase. The formation of the orthorhombic phase was confirmed through high-resolution transmission electron microscopy. The effect of the electric field on the polarization switching kinetics of ZrO2 films has been investigated revealing that the switching kinetics follows the nucleation limited switching (NLS) model. The activation fields estimated from the peak values of the polarization currents (im) and the time (tm) at which im occurs are in good agreement with the values obtained from the switching characteristic time of the NLS model. This work paves the way towards the integration of (pseudo)binary oxide thin films on cheap substrates like glass for the next-generation of non-volatile memories.

Group IV quantum dots (QDs) in HfO2 are attractive for non-volatile memories (NVMs) due to complementary metal-oxide semiconductor (CMOS) compatibility. Besides the role of charge storage centers, SiGeSn QDs have the advantage of a low thermal budget for formation, because Sn presence decreases crystallization temperature, while Si ensures higher thermal stability. In this paper, we prepare MOS capacitors based on 3-layer stacks of gate HfO2/floating gate of SiGeSn QDs in HfO2/tunnel HfO2/p-Si obtained by magnetron sputtering deposition followed by rapid thermal annealing (RTA) for nanocrystallization. Crystalline structure, morphology, and composition studies by cross-section transmission electron microscopy and X-ray diffraction correlated with Raman spectroscopy and C-V measurements are carried out for understanding RTA temperature effects on charge storage behavior. 3-layer morphology and Sn content trends with RTA temperature are explained by the strongly temperature-dependent Sn segregation and diffusion processes. We show that the memory properties measured on Al/3-layer stack/p-Si/Al capacitors are controlled by SiGeSn-related trapping states (deep electronic levels) and low-ordering clusters for RTA at 325-450 degrees C, and by crystalline SiGeSn QDs for 520 and 530 degrees C RTA. Specific to the structures annealed at 520 and 530 degrees C is the formation of two kinds of crystalline SiGeSn QDs, i.e., QDs with low Sn content (2 at.%) that are positioned inside the floating gate, and QDs with high Sn content (up to 12.5 at.%) located at the interface of floating gate with adjacent HfO2 layers. The presence of Sn in the SiGe intermediate layer decreases the SiGe crystallization temperature and induces the easier crystallization of the diamond structure in comparison with 3-layer stacks with Ge-HfO2 intermediate layer. High frequency-independent memory windows of 3-4 V and stored electron densities of 1-2 x 10(13) electrons/cm(2) are achieved.

We report the mechanical behavior of a bulk boron ceramic prepared by spark plasma sintering of commercially available beta-boron powder. In order to fabricate polycrystalline boron ceramic, we used a protective tantalum foil reacted with carbon from the graphite die or graphite foil forming a thin layer of TaB2 and TaC covering the boron specimen. This is the first study to show the high-temperature flexural strength, toughness, and Young's moduli of boron up to 1400 degrees C. At 1600 degrees C and above, boron will react with testing environment forming an outer shell. The flexural strength and fracture toughness at room temperature reached an average of 340 MPa and 4.1 MPa m (1/2) , respectively. Despite showing clear signs of plastic deformation on the strain-stress curves, the yield strength of the monolithic boron ceramic exceed 1 GPa at 1200 degrees C. It was determined that fracture at elevated temperatures follows a quasi-transgranular mechanism, where the sub-grains of the boron fracture as plate-like structures. An interpretation for the observed fracture behavior was proposed.