National Institute Of Materials Physics - Romania

We report a study related to the influence of heat treatment (up to 300 degrees C) on the structure of GaSb \GeTe, SnSe\GeTe and GaSb\SnSe stacked phase change memory films and of their counterparts with Hf thin film barrier between the layers. Samples were prepared by pulsed laser deposition and investigated by X-ray reflectometry and X-ray diffraction in order to evaluate the inter-films diffusion and the temperature threshold where this process is initiated. The thickness and mass density variations of films after each heat treatment, as well as the efficiency of hafnium barrier film, to eliminate potential atomic diffusion issues, were investigated.

In this paper we report on a novel 1-D piezoelectric/ferroelectric nanostructure. Composites of piezoelectric (0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) abbreviated as BNT-BT0.08) and ferromagnetic (CoFe2O4) nanotubes were assembled and studied in order to envisage new multifunctional applications. Using a polycarbonate membrane template and sols precursors of BNT-BT(0.08 )and CoFe2O4, heterostructured BNT-BT0.08/CoFe2O4 core-shell composite nanotubes were created. Selective methods such as SEM, TEM, AFM, PFM and MFM were used for the characterization of the as-prepared hybrid piezoelectric/ferromagnetic coaxial nanotubes structure. This composite shows two crystalline phases: rhombohedral BNT-BT0.08 and cubicCoFe(2)O(4). The piezoelectric and ferromagnetic properties have been characterized. Piezo force microscopy (PFM) images evidenced ferroelectric domains with opposite polarity due to lead free piezoelectric BNT-BT0.08 outer tube. Magnetic force microscopy (MFM) images evidenced magnetic domains attributed to the CoFe2O4 inner tube. Magnetic hysteresis curves demonstrate a weak ferromagnetic behavior, accompanied by a linear variation of the magnetization at higher magnetic fields, especially at room temperature. From dielectric measurements, high tunability values reaching about 70% at 0.5 kHz and E = 80 kV/cm have been obtained. An effective dielectric constant epsilon(r) = 32 has been measured. The results obtained from this work provide a base for the design of tubular multi-layered materials with novel functionalities and applications in various multifunctional electronic devices such as actuators, transducers, and energy storage microsystems. (C) 2018 Elsevier B.V. All rights reserved.

Three phenacyl derivatives have been investigated as potential inhibitors for the aqueous oxidation of sphalerite (ZnS) in air-equilibrated solutions of HCl (pH 2.5 and 25 degrees C) using potentyodynamic polarization, aqueous batch experiments, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. Findings show that the studied phenacyl derivatives are inhibitors of sphalerite aqueous oxidation. Quantum chemical calculations indicate that the adsorption of phenacyl derivatives on ZnS is energetically favorable and accounts for the observed inhibiting effects.

The influence of single-walled carbon nanotubes enriched in semiconductor (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of polyaniline (PANI), electrosynthesized in the presence of the H2SO4 and HCl solutions, is reported. The emission bands peaked at 407-418 and 440-520 nm indicate that the electropolymerization of aniline (ANI) leads to the formation of short and longer macromolecular chains (MCs), respectively. We demonstrate that the reaction product consists of ANI tetramers (TT) and trimers (TR) as well as PANI-salt. Using Raman scattering and IR absorption spectroscopy, a covalent functionalization of SWNTs with shorter and longer MCs of PANI-salt is demonstrated. The presence of S-SWNTs and M-SWNTs induces a decrease in ANI TT weight in the reaction product mass consisting in S-SWNTs and M-SWNTs covalently functionalized with PANI-emeraldine salt (ES) and PANI-leucoemeraldine salt (LS), respectively. A PANI PL quenching is reported to be induced of the S-SWNTs and M-SWNTs. A de-excitation mechanism is proposed to explain PANI PL quenching.

This paper presents a comparative study between the properties of the heterostructures realized with single/multi layer organic (zinc phthalocyanine or/and fullerene) prepared on Si substrate between flat or patterned aluminum (Al) layer metallic electrode and multi layer ZnO/Au/ZnO transparent conductor electrode (TCE). The UV-Nanoimprint Lithography was used for the realization of a 2D array of nanostructures (holes/pillars) characterized by a periodicity of 1.1 mu m and cylindrical shape: diameter = 400 nm and depth/height = 300 nm. The effect of the electrode patterning on the properties of the organic heterostructures was analyzed. For the samples with patterned Al electrode was remarked a slight red shift of the peaks in the reflection spectra determined by an increased interaction between the organic molecules in the delimited region of the patterned holes. The shape of the emission spectra at excitation with UV light showed a narrow intense peak around 500 nm associated with the intense resonance phenomena between the energy of the incident light and the surface plasmons in the patterned Al layer. The TCE followed the morphology of the organic film on which it was deposited. The significant differences between the morphology of the top layer in the heterostructures realized on flat and patterned Al are correlated with the total thickness of the successively deposited layers and with the particularities of the molecular arrangement, leading to the preservation or deleting of patterning. An injection contact behavior was evidence for most heterostructures built on flat and patterned Al. The slight increase in current at an applied bias <1 V in the heterostructure Si/Al/ZnPc/TCE is attributed to the larger interfacial area between the patterned Al electrode and ZnPc layer compared to the interface area between flat Al and ZnPc. A buffer layer of 1,4,5,8-naphthalen-tetracarboxylic dianhydride (NTCDA), sandwiched between the flat metallic electrode and organic film in the heterostructure Si/Al/C60/ZnPc/TCE has determined an increase in the current at low applied voltages. (C) 2018 Elsevier B.V. All rights reserved.

The thermal stress effect on the structure of phase change memory materials, namely single films and double stacked films of GeTe and SnSe, is evaluated. The crystallization temperatures of GeTe and SnSe single films are 138 degrees C and 292 degrees C, respectively. The films are amorphous before annealing and crystallize in rhombohedral and orthorhombic structures afterwards. Ge is tetrahedrally bonded and Se is bivalent after deposition. Both Ge and Se have an octahedral configuration after annealing. The double stacked structure is studied in the as-deposited state and after annealing at temperatures of 100, 210, and 350 degrees C. Pulsed laser deposition produces the crystallization of both as-deposited layers when stacked, mostly of SnSe, but also some crystalline GeTe is present. GeTe fully crystallizes after annealing at 210 degrees C, in the face-centred cubic structure. Annealing at 350 degrees C leads to the evaporation of a significant quantity of Se and to the formation of a cubic Ge0.75Sn0.25Te solid solution. Ge has an octahedral coordination, while Se is tetrahedrally bonded as a result of a combination of bivalent amorphous Se and octahedral Se from crystalline SnSe. The study shows that diffusion between layers at high annealing temperatures might suppress the memory property and determines the formation of irreversible solid solutions.

Data storage needs are increasing at a rapid pace across all economic sectors, so the need for new memory technologies with adequate capabilities is also high. Phase change memories (PCMs) are a leading contender in the emerging race for non-volatile memories due to their fast operation speed, high scalability, good reliability and low power consumption. However, in order to meet the present and future storage demands, PCM technologies must further increase the storage density. Here, we employ a probabilistic cellular automata approach to explore the multi-step threshold switching from the reset (off) to the set (on) state in chalcogenide stacked structures. Simulations have shown that in order to obtain multi-step switching with high contrast among different resistance states, the stacked structure needs to contain materials with a large difference among their crystallization temperatures and careful tuning of strata thicknesses. The crystallization dynamics can be controlled through the external energy pulses applied to the system, in such a way that a balance between nucleation and growth in phase change behavior can be achieved, optimized for PCMs.

Different amounts of TiO2 and ZnO particles were deposited upon wool fabrics, which are among the less studied textiles. The materials were get from industry or were home made. Model samples for these oxide deposition and properties were also considered. Either sputtering or chemical sol-gel/electro less technique was respectively applied. The coated samples were then characterized structurally and morphologically, by XRD, SEM and XPS and were checked for photocatalytic properties. Both UV and vis light beams were used for irradiation. The photocatalytic experiments were performed by photodegradation of methylene blue in the PCC2 checker apparatus. The fabrics were firstly impregnated with the dye solution and then dried: self cleaning of the wool fabric samples took in fact place. Reflectance data in the visible spectral range of highest absorption band served for direct analysis of MB degradation. The photocatalytic properties of the coated fabrics increased much in comparison with the raw materials. The photocatalytic decolorization of methylene blue follows up a simple apparently first order kinetic equation in many studied cases. Thus it was demonstrated that MB decolorization can serve as a test reaction at least for self cleaning of fabrics. (C) 2017 Elsevier B.V. All rights reserved.

We report on the synthesis by PLD of simple and lithium-doped biological-origin hydroxyapatite (HA) films. The role of doping reagents (Li2CO3, Li3PO4) on the morphology, structure, chemical composition, bonding strength and cytocompatibility of the films was investigated. SEM investigations of the films evidenced a surface morphology consisting of particles with mean diameters of (5-7) mu m. GIXRD analyses demonstrated that the synthesized structures consisted of HA phase only, with different degrees of crystallinity, mainly influenced by the doping reagent type. After only three days of immersion in simulated body fluid, FTIR spectra showed a remarkable growth of a biomimetic apatitic film, indicative of a high biomineralization capacity of the coatings. EDS analyses revealed a quasi-stoichiometric target-to-substrate transfer, the values inferred for the Ca/P ratio corresponding to a biological apatite. All synthesized structures displayed a hydrophilic behavior, suitable for attachment of osteoblast cells. In vitro cell viability tests showed that the presence of Li2CO3 and Li3PO4 as doping reagents promoted the hMSC growth on film surfaces. Taking into consideration these enhanced characteristics, corroborated with a low fabrication cost generated by sustainable resources, one should consider the lithium-doped biological-derived materials as promising prospective solutions for a next generation of coated implants with rapid osteointegration. (C) 2018 Elsevier B.V. All rights reserved.

Here we describe an organic electro-optic device, obtained using electrospun hydroxypropyl cellulose (HPC) polymer fibres and nematic liquid crystals (LC). Its working mechanism is similar to that of a classic polymer-dispersed liquid crystal (PDLC) device. The scanning electron microscopy of the HPC deposited fibres shows a mat of fibres with diameters in the nano and micron size range. Dielectric spectroscopy measurements allow the determination of the dependence of the dielectric constant and electric energy loss on frequency and temperature as well as the determination of the activation energy. The electro-optic study shows a very good optical transmission curve, with an "on"-"off" switching voltage of less than 1 V/mu m.