National Institute Of Materials Physics - Romania

Arrays of Ni submicron wires surrounded by poly (vinylidene fluoride) (PVDF) submicron tubes were prepared via solution-processed polymer and Ni electrodeposition into anodic aluminum oxide template. The PVDF solution was filtered in vacuum through the template and the resulting dried structure was used for the electrodeposition of Ni wires. The obtained core-shell submicron wire structure consists of a metallic magnetic nanowire core of about 50 mu m in length and about 300 nm diameter surrounded by a polymer tube shell with thickness less than 10 nm. The specific ferroelectric beta-phase of the polymer was obtained whereas the magnetic behavior of the Ni-cores was proven to be specific to an array of ferromagnetic Ni cylindrical wires (about 0.62 mu(B)/Ni atom) with magnetization reversal mechanisms dominated by dipolar interactions and domain wall displacements. No significant differences of the magnetization reversal mechanism were observed in case of Ni submicron wires surrounded by PVDF tubes and similar Ni wires without PVDF shell, suggesting that magneto-coupling effects in such systems might be observed only by measuring the perturbation of the electric state of the polymer shell under a magnetic excitation of the Ni cores.

Pd nanoparticles are stabilized onto the surface of Fe3O4-entrapped poly(aminoethyl acrylamide) via functionalization of polymer with a new class of NNN-pincer ligand providing a high loading and stable catalyst for aerobic oxidation of alcohols to aldehydes. Varieties of alcohols are oxidized to the corresponding aldehydes with good selectivity using 0.95 mol% Pd catalyst. The catalyst is reusable (5 runs) without loss of activity and leaching or agglomeration of Pd nanoparticles while structural regularity of the catalyst is preserved. Oxidation of benzyl alcohol is also scaled up to a few grams. (C) 2018 Elsevier B.V. All rights reserved.

A series of liquid crystals with various lanthanide ions (Eu-III, Sm-III, and Tb-III) was designed and prepared starting from the corresponding lanthanide nitrates and N-alkylated 4-pyridone derivatives bearing mesogenic 3,4,5-tris(alkyloxy)-benzyl moieties (alkyl=hexyl, octyl, decyl, dodecyl, tetradecyl, or hexadecyl). These new lanthanidomesogens were investigated for their mesogenic properties by a combination of differential scanning calorimetry, polarizing optical microscopy, and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was assessed by thermogravimetric analysis. All of these complexes show enantiotropic liquid-crystalline behavior with lamellar (SmA) phases in the case of shorter-chain complexes (C-6 and C-8) or hexagonal columnar phases (Col(h)) for complexes with longer alkyl chains (C-12, C-14, and C-16), which were assigned on the basis of their characteristic textures and XRD studies. For complexes with an intermediate number of carbon atoms in the side chains (C-10), both a lamellar phase at lower temperatures and a Col(h) phase at higher temperatures were evidenced. In the solid state, all these complexes show characteristic emissions assigned to the corresponding lanthanide ion. In addition, the luminescence decay curves showed single-exponential decays with characteristic times in the millisecond range (0.75-0.90 ms for Eu-III, 0.045-0.060 ms for Sm-III, and 0.75-1.05 ms for Tb-III).

We investigate the effect of the nature of the substrate and the bottom interface on the out-of-plane polarization orientation of ultrathin (10-nm) lead zirconate titanate (PZT) thin films of (001) orientation by photoelectron spectroscopy of samples without surface contamination. The substrate nature is varied between insulator (strontium titanate, STO) and semiconductor (Nb-doped STO, STON) and finally to a metal with a work function lower than that of PZT (strontium ruthenate, SRO). Outward polarization is obtained for PZT/STON(001) and inward polarization is obtained for PZT/STO(001) and PZT/SRO(001). Explanations are given for all these typical cases, the main elements being charge accumulation for compensation of the depolarization field, self-doping of PZT films, and the interface electric field driving the orientation of the polarization of the ferroelectric films. We find p-type self-doping is correlated with the inward polarization, and the driving field is formed between a negatively charged region with negatively ionized acceptors near the interface with the substrate and the p-type degenerate region with holes accumulated inside, toward the surface. This mechanism may be reversed under the assumption of n-type self-doping, positively ionized donors near the interface, and accumulated electrons toward the surface in the case of an interface with a substrate with a higher work function, being in line with recent data (PZT/Pt or BaTiO3/SRO).

A versatile method based on the matrix assisted pulsed laser evaporation (MAPLE) technique was used for the fabrication of graphene-based electrodes for application in supercapacitors. The simultaneous deposition and chemical transformation of graphene oxide (GO) and GO-NiO nanoparticles was attained by including nitrogen-containing chemically reactive compounds (ammonia, urea and melamine) in aqueous MAPLE targets. Morphological analyses reveal the formation of hundreds of nanometres to tens of micrometres thick porous films on both plastic and metallic flexible substrates. Structural and compositional studies, carried out by transmission electron microscopy, and Raman and X-ray photoelectron spectroscopies, disclose significant deoxidation and nitrogen doping of the GO material. The electrodes reveal remarkable electrochemical performance, showing a maximum volumetric capacitance of 350 F cm(-3) (9 mF cm(-2) areal capacitance) in aqueous electrolyte. Symmetric supercapacitors fabricated with these electrodes reveal excellent long-term stability at high specific intensities. From the obtained results, it can be asserted that the reactive inverse MAPLE method stands out as a promising technology not only for the adaptable fabrication of flexible graphene-based composite electrodes but also for a wide variety of advanced functional materials for diverse applications.

We investigate the spectral and transport properties of a diatomic square lattice with hopping to the next-nearest-neighbors and broken time-reversal symmetry, which behaves as a Chern insulator. In a finite-size approach, the attention is paid to the formation of chiral edge states in the topological insulating phase, but also in the semimetallic one. The edge states are revealed in the ribbon and plaquette geometries by analytical and numerical methods, significant differences being produced by the specific atomic connectivity at the boundary. The Hall resistance R-H is calculated in the plaquette geometry using the Landauer-Mittiker approach. The chiral edge states located in the unique gap of the energy spectrum manifest themselves by quantized values R-H = +/- h/e(2) specific to the Chern insulator. The semimetallic system containing chiral edge states embedded in the quasicontinuum of bulk states shows a disorder-driven AQHE as a consequence of the Anderson localization process.

Co-doped CeO2 thin films were grown from a bulk target with starting composition Ce0.95Yb0.04Er0.01O2 by pulsed laser deposition (PLD) on a p(+)-n-n(+) single crystal silicon diode. The PLD laser fluence was varied between 1.7 J/cm(2) and 3.7 J/cm(2). The device with the film grown for a laser fluence of 2.3 J/cm(2) delivers the highest performance taking advantage of the up conversion (UC) effect provided by this film. Namely, the increase in the relative power conversion efficiency of the device is 12.1% and 39.2% for illumination under 1 and 2.1 sun, respectively, and its relative external quantum efficiency is 8.2% when illuminated with 980 nm light. The film grown for the optimum 2.3 J/cm(2) fluence shows good target-film composition transfer and a granular morphology with a low roughness. The UC mechanism consists of efficient energy transfer between spatially separated Yb3+ and Er3+ ions, i.e. the absorption of infrared light photons by the Yb3+ ions (F-2(7/2) -> F-2(5/2) transition) is followed by a two-step energy transfer process to neighboring Er3+ ions and by their characteristic luminescent emissions ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and (F-4(9/2) -> I-4(15/2)).

Organic heterostructures based on zinc phthalocyanine (ZnPc) and perylene tetracarboxylic dianhydride (PTCDA) were deposited by matrix-assisted pulsed laser evaporation (MAPLE) technique on conductive flexible substrate (ITO/PET) in three configurations: ZnPc/PTCDA (stacked layers), ZnPc:PTCDA (blend) and ZnPc/ZnPc:PTCDA/PTCDA. The effect of the configuration on the optical and electrical properties of the obtained heterostructures was investigated. For all heterostructures was observed an improved optical absorption in visible domain. The I-V characteristics recorded under illumination, revealed higher short circuit current (I (SC)) values for the ZnPc:PTCDA and ZnPc/ZnPc:PTCDA/PTCDA structures in comparison with that of the ZnPc/PTCDA structure. The results proved that by MAPLE can be obtained flexible organic heterostructures (in different configurations) with properties adequate for applications in flexible electronics and solar cell fields.

Chitosan-coated cobalt ferrites were synthesized by wet ferritization method through two different approaches. The nanostructured chitosan-coated cobalt ferrites were characterized by: X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), thermal analysis, infrared spectroscopy (IR) and Mossbauer spectroscopy. X-ray diffraction patterns confirmed the formation of CoFe2O4 cubic spinel structure with an average crystallite size of 1.75 and 5.5 nm, respectively. Mossbauer spectra consist in a central quadrupole pattern. The deconvolution in the hypothesis of Lorentzian line shape evidences the prevailing presence of Fe3+ ions at the nanoparticle surface. The antimicrobial activity of chitosan-coated cobalt ferrites against Gram-positive and Gram-negative bacteria, as well as fungal strains was investigated. Based on the results, chitosan-coated cobalt ferrites are thought to be suitable candidates for the development of novel anti-biofilm agents.

During conflict situations, the combat staff is exposed to a wide variety of aggressions, such as temperature and pressure variations and dynamic impacts (from ammunition or fragments). Textiles used in the manufacture of the military uniforms and devices have always played an important role in defending the military against these hazards, and an adequate level of individual protection equipment is required. In this respect, novel fibre-reinforced polymer composite materials for military application, such as reducing blunt trauma for ballistic protection equipment, have been studied in terms of thermal and mechanical properties and ballistic protection, obtaining very good results.