National Institute Of Materials Physics - Romania

Abstract: N-doped defective graphene [(N)G] obtained by pyrolysis at 900 degrees C of chitosan contains about 3.7% of residual N atoms, distributed as pyridinic, pyrrolic and graphitic N atoms. It has been found that (N)G acts as basic catalyst promoting two classical C-C bond forming nucleophilic additions in organic chemistry, such as the Michael and the Henry additions. Computational calculations at DFT level of models corresponding to the various N atoms leads to the conclusion that N atoms are more stable at the periphery of the graphene sheets and that H adsorption on these sites is a suitable descriptor to correlate with the catalytic activity of the various sites. According to these calculations the most active sites are pyridinic N atoms at zig-zag edges of the sheets. In addition, N as dopant changes the reactivity of the neigh. bour C atoms. Water was found a suitable solvent to achieve high conversions in both reactions. In this solvent the initial distribution of N atoms is affected due to the easy protonation of the N-py to N-pyH sites. As an effect, C edge sites adjacent at N-PyH with an appropriate reactivity towards the alpha-C-H bond breaking are formed. The present results show the general activity of N-doped graphene as base catalysts and illustrate the potential of carbocatalysis to promote reactions of general interest in organic synthesis. (C) 2019 Elsevier Inc. All rights reserved.

Abstract: The crystallization of ferroelectric (Hf,Zr)O-2 thin films is achieved by playing on the deposition pressure during reactive magnetron sputtering from a Hf/Zr metallic target. Postdeposition annealing was tried at different temperatures in order to optimize the quality of the samples. Structural characterizations are performed by transmission electron microscopy (TEM) and electrical characterizations are carried out. TEM analyses reveal that the samples deposited at a low working pressure show no orthorhombic phase, and thus are not ferroelectric, whereas the samples deposited at higher working pressure show the orthorhombic ferroelectric phase. The maximum remnant polarization is 6 mu C/cm(2) and is obtained for the sample annealed at 600 degrees C. The maximum cycles to breakdown is higher than 2 x 10(10) cycles and is reached for the sample annealed at 400 degrees C. These results are discussed in the matter of phase transition and oxygen vacancies redistribution. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Abstract: The paper describes an innovative bio-design of some hybrid nanoarchitectures containing bioartificial membranes and silver nanoparticles phytogenerated by using a natural extract Caryophyllus aromaticus (cloves) that contains many bioactive compounds. Two kinds of liposomes with and without chlorophyll a (Chla) obtained through thin film hydration method were used to achieve bio-green-generated hybrids by a simple, cost effective bottom-up approach. The characteristic peaks of CE-nAg monitored by UV-Vis absorption have firstly demonstrated the biohybrids formation. The slightly blue shift and fluorescence quenching observed by fluorescence emission spectra highlighted the formation of hybrid systems by biointeraction between lipid vesicles and silver nanoparticles. The incorporation of silver nanoparticles in lipid vesicles resulted in significant changes of FT-IR spectra of liposomes, indicating a reorganization of biomimetic membranes. All the microscopic methods (SEM, AFM and TEM) confirmed the biosynthesis of "green" AgNPs together with associated biohybrids, their spherical and quasi-spherical shapes with nano-scaled size. By TEM assay it was shown that CE-nAg are surrounded by petal like cloud structures that consist of biopolymers like proteins or polysaccharides and other phytochemicals arising from clove extract. EDS spectra confirmed the formation of phyto-nanoAg and also the presence of silver in the biohybrids. In addition, Selected Area Electron Diffraction showed characteristic polycrystalline ring patterns for a cubic structure of the clove-generated AgNPs. The hybrid materials showed efficient physical stability, ie. xi value of - 28.0 mV (for biohybrids without Chla, BH) and of - 31.7 mV (for biohybrids labelled with Chla, Chla-BH), assured by strong electrostatic repulsive forces between particles. The "green" nano-silver particles (CE-nAg) showed remarkable antioxidant activity (AA = 90.2%). The biohybrids loaded with clove-AgNPs proved to be more effective, scavenging about 98.8% of free radicals (in case of ChlaBH), and of 92.6% (in case of BH). The antibacterial effectiveness showed that green AgNPs combine in a synergistic manner the antibacterial properties of clove extract with those of silver, resulting in an enhancement of inhibition diameter, by 20%. Chla-BH proved to be more potent against Escherichia coli, than BH, exhibiting an inhibition diameter of 42 mm. Regarding the in vitro cytotoxicity against tumour cells, the CE-nAg concentration significantly influenced the cell viability, ie. IC50 was 3.6% (v/v) for HT-29 cells. Chla-BH was more effective against HT-29 cancer cells at the concentrations ranging from 0 to 18% (v/v), when the normal cells were not affected. Clove-generated AgNPs exhibited haemolytic activity against hRBCs, while the biohybrids were haemocompatible. The action mechanism on the two cell lines (mouse fibroblast L929 cells and human colorectal adenocarcinoma HT-29 cells) investigated by fluorescence microscopy demonstrated that CE-nAg killed almost all the cells (94%) through necrosis at a concentration of 33.4% (v/v). The treatment of HT-29 cells with BH resulted in: 71.5% viable cells, 19.5% apoptotic and only 9% necrotic cells, while in the case of Chla-BH treatment, only 77.5% cells were viable, 16% cells were apoptotic and 6.5% were necrotic. In this way, the developed silver-based nanoparticles can represent viable promoters to develop new biohybrids with improved features, e.g. antioxidant and antibacterial effectiveness, haemolytic activity and greater specificity towards tumour cells.

Abstract: In this work we prepared films of amorphous germanium nanoparticles embedded in SiO2 deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 degrees C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly dependent on the deposition temperature. In the films deposited at 300 degrees C, the Ge content is constant in the depth, while films deposited at 500 degrees C show a significant decrease of Ge content from interface of the film with substrate towards the film free surface. From the absorption curves we obtained the Ge band gap of 1.39 eV for 300 degrees C deposited films and 1.44 eV for the films deposited at 500 degrees C. The photocurrents are higher with more than one order of magnitude than the dark ones. The photocurrent spectra present different cutoff wavelengths depending on the deposition temperature, i.e. 1325 nm for 300 degrees C and 1267 nm for 500 degrees C. These films present good responsivities of 2.42 AW(-1) (52 mu W incident power) at 300 degrees C and 0.69 AW(-1) (57 mW) at 500 degrees C and high internal quantum efficiency of similar to 445% for 300 degrees C and similar to 118% for 500 degrees C.

Abstract: ZnxCo1-xFe2O4/SiO2 (x = 0, 0.25, 0.50, 0.75, 1.00) nanocomposites (NCs) have been investigated through structural, morphological and magnetic measurements. X-ray diffraction and Mossbauer data indicated the presence of nanocrystalline mixed cubic spinel. The lattice parameters gradually decreased with increasing Zn content and follow Vegard's law. The crystallite size, X-ray density and porosity of ZnxCo1-xFe2O4 decreased with increasing Zn content. The ferrite nanoparticles spherical shape and size (32.0-6.5, 17.5-8.1 and 36.2-18.6 nm for the NCs annealed at 500, 800 and 1100 degrees C, respectively) was established by transmission electron microscopy. The Mossbauer spectra showed the characteristic magnetic patterns of Co and Zn spinels. The shape of hysteresis loops revealed the dependence of superparamagnetic behavior on the structural properties. The saturation magnetization (M-s) and coercive field (H-c) were also influenced by Co substitution with Zn, showing the decrease of M-s and H-c. The replacement of magnetic Co2+ with the zero magnetic moment Zn2+ induces a gradual reduction of magnetocrystalline anisotropy and decrease of H-c. (C) 2019 Elsevier B.V. All rights reserved.

Abstract: Nano-size and shape of fluorescent silver nanostructures are important for a wide range of bio-applications, especially as drug delivery systems, imaging and sensing. The aim of the work is to develop a fluorescent silver nano-structured system, synthesized by chemical reduction of aqueous AgNO3 solution by Tryptophan using Dextran 70 as stabilizing agent (SNPs(FL)). The formed fluorescent nano-system was analyzed by UV-Vis absorption, DLS, SEM, TEM, AFM, steady-state and time resolved fluorescence spectroscopy. TEM analysis showed multi-twined nanoparticle, with the size within 15-40 nm. SNPs(FL) shows the fluorescence emission at 346 nm, the fluorescence quantum yield, phi = 0.034 and the integrated fluorescence lifetime, = 1.82 ns. Riboflavin fluorescence behaviour in the RF/SNPs(FL) system, has been also studied. The results have relevance in using SNPs(FL) as a potential marker/emissive system to solve various biological barriers in humans, like drug release and protein structure.

Abstract: This paper presents the synthesis, physico-chemical and biological properties of four new coordination compounds with mixed ligands: acrylate ion (acr) and benzimidazole/benzimidazole derivatives with the general formula [Co(L)(2)(acr)(2)]center dot nH(2)O [(1) L: benzimidazole (HBzIm), n: 0.5; (2) L: 2-methylbenzimidazole (2-MeBzIm), n: 0.5; (3) L: 5-methylbenzimidazole (5-MeBzIm), n: 0; (4) L: 5,6-dimethylbenzimidazole (5,6-Me(2)BzIm), n: 0]. Their chemical formulae were achieved correlating the chemical analysis with mass spectrometry data, the ligands coordination modes were assigned by Fourier transform-infrared measurements, and the trigonal bipyramidal geometry of cobalt ion in complexes was assigned by data correlation of UV-Vis-NIR spectra and magnetic moments measurements. Single-crystal X-ray diffraction reveals a mononuclear structure with a pentacoordinated cobalt (II) ion, connected to two acrylato coordinated in different modes and two unidentate 5,6-dimethylbenzimidazole ligands for compound (4). The biological tests were performed against several microbial strains, the cytotoxicity was evaluated on HCT8 cellular lines and the cell cycle analysis was performed on HT29 cellular lines. Microbiological assays indicated that Co (II) complexes present a very good to good activity against Candida albicans 1760, Enterococcus faecium E5, Bacillus subtilis ATCC 6683 and Escherichia coli ATCC 25922. Predictive pharmacokinetic (ADME), toxicity and drug-likeness profiles were evaluated for Co (II) complexes. Our results highlight that Co (II) complexes depicted in the present study are suitable to be used as efficient pharmacological agents.

Abstract: The annealing of crystalline defects in Si single crystals created by ion implantation at room temperature was investigated. Silicon single crystals were firstly implanted at room temperature with 1.345 MeV Au1+ ions at fluences from 1 x 10(13) to 1 x 10(14) at/cm(2) to induce damage. A second implantation at room temperature was afterwards performed with 10 MeV Co3+ ions at a fluence of 3 x 10(14) at/cm(2). All samples were analyzed afterwards by Rutherford backscattering in random and channeling geometry to assess the crystalline damage present in the surface region. The results showed a significant reduction of the degree of damage or a reduction of the size of damaged region. The morphology and local atomic structure, studied using high -resolution electron microscopy, selected area electron diffraction and high resolution X-ray diffraction confirmed the reduction of damage degree and volume caused by Au implantation after Co implantation.

Abstract: Oxide dispersion-strengthened ferritic steels (ODSFSs) are promising structural materials for applications in fusion and fission power reactors, but further improvement in their (high-temperature) mechanical properties and ferrite phase stability is required. This work demonstrates that an approach to produce Fe14Cr ODSFSs with a stable ferrite phase and improved strength could involve grain size strengthening by long-term milling with a tiny amount of nitrogen. Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) powders were ball-milled up to 170 hours under an argon atmosphere. In addition to X-ray diffraction, the change in product quality during milling and upon heating was thoroughly investigated by more sensitive magnetic and thermal analysis by measuring the saturation magnetization sigma(s), coercivity H-c, Curie temperature T-c, and temperature of ferrite-austenite (alpha ->gamma) transition T-alpha ->gamma. A pronounced modification of magnetic and microstructure parameters was observed when milling over 70 hours and upon heating above 800 degrees C and was found to be generated by long-term milling with a tiny amount of nitrogen. Upon heating, the nitrogen, incorporated during milling, developed a transition region, with the decomposition of nitrides precipitated at the earlier stage of heating followed by austenite decomposition, nitrogen degassing, and microstructure refinement to a grain size of a few tenths of a nm (e.g., 28 nm by heating at 910 degrees C of 100-hour milled powder). The resulting ferrite phase with refined grains is highly stable to (further) heating. The powders milled for 70 and 100 hours containing 0.175 and 0.500 wt pct nitrogen, respectively, were consolidated at 1100 degrees C with subsequent annealing at 1050 degrees C and subjected to Vickers hardness and 3-point bending tests. The steel produced from the powder milled for 70 hours shows lower hardness, higher density (close to the theoretical value of 7.8 g/cm(3)), and fracture strain. The ductility of this ODS alloy (0.075 fracture strain) is comparable with Eurofer97 (0.075 fracture strain), whereas its strength (2070 MPa ultimate stress) is significantly higher than that of Eurofer97 (1222 MPa ultimate stress). This improvement was attributed to grain size strengthening-the refined grains (promoted by milling with nitrogen) could be effectively pinned by Y-Ti-O dispersoids.

Abstract: Multi-layered structures, composed of thin films from materials with different compositions or physical properties, represents a way to obtain enhanced properties or even new functionalities. In this work, lead zirconate titanate PbZrxTi1-xO3 (PZT; x = 0.20, 0.52, 0.80) multilayers were grown by pulsed laser deposition (PLD) on a single crystal strontium titanate (SrTiO3, STO) substrate, using a strontium ruthenate (SrRuO3, SRO) film as buffer layer for epitaxial growth, and also as back electrode. Up and down multi-layers were grown and their physical and structural properties were compared, up being the structure in which Zr concentration was varied from 20% near the STO substrate to 80% at the surface, while down is for the structure in which the Zr concentration starts with 80% near the substrate and ends with 20% at the surface. It was found that the electric and pyroelectric properties of the two graded structures are significantly different. The up structure presents electric properties that are comparable with those of single composition PZT films while the properties of the down structure are deteriorated, especially in terms of the leakage current magnitude. Pyroelectric signal could be measured only for the up structure. These differences were attributed to larger density of structural defects in the down structure compared to the up one. This is due to the different growth sequence: Lop structure starts with tetragonal PZT on cubic substrate (lower lattice mismatch, 1.1%) while down structure starts with rhombohedral PZT on cubic substrate (larger lattice mismatch, almost 5%).