National Institute Of Materials Physics - Romania

We report on the fabrication of silicon-reinforced carbon (C: Si) structures by combinatorial pulsed laser deposition to search for the best design for a new generation of multi-functional coated implants. The synthesized films were characterized from the morphological, structural, compositional, mechanical and microbiological points of view. Scanning electron microscopy revealed the presence, on top of the deposited layers, of spheroid particulates with sizes in the micron range. No microcracks or delaminations were observed. Energy dispersive x-ray spectroscopy and grazing incidence x-ray diffraction pointed to the existence of aC to Si compositional gradient from one end of the film to the other. Raman investigation revealed a relatively high sp(3) hybridization of up to 80% at 40-48 mm a part from the edge with higher Ccontent. Si addition was demonstrated to significantly increase C: Si film bonding to the substrate, with values above the ISO threshold for coatings to be used in high-loading biomedical applications. Surface energy studies pointed to an increase in the hydrophilic character of the deposited structures along with Si content up to 52 m Nm(-1'). In certain cases, the Si-reinforced Ccoatings elicited an antimicrobial biofilm action. The presence of Si was proven to be benign to HEp-2 cells of human origin, without interfering with their cellular cycle. On this basis, reliable C: Si structures with good adherence to the substrate and high efficiency against microbial biofilms can be developed for implant coatings and other advanced medical devices.

Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, and the behavior strictly depends on the prepoling bias. NH typically appears at prepoling biases larger than the open circuit bias, while pronounced IH occurs for negative bias prepoling. The transition from NH to IH is marked by an intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model. Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the accumulated ionic and electronic polarization charge at the interfaces. Introducing a three-step measurement protocol, which includes stabilization, prepoling, and measurement, we put forward the difficulties and possible solutions for a correct photoconversion efficiency evaluation.

In the last decades, the study of magnetic fluids with different biomedical applications such as targeted delivery of a chemotherapeutic solution to the tumor site has been of high interest. For this purpose, ultrasonic and antimicrobial studies were used to characterize the aqueous solutions based on maghemite nanoparticles. The maghemite (-Fe2O3) and dextran-coated maghemite nanoparticles (DMNp) were synthesized by coprecipitation method. The spherical shape of the nanoparticles and uniform size with an average diameter around 9.5 +/- 0.5nm for -Fe2O3 were observed in transmission electron microscopy micrographs. Dynamic light scattering was used to determine the hydrodynamic size of -Fe2O3 nanoparticles and DMNp in suspensions. The hydrodynamic diameter obtained of -Fe2O3 and DMNp was 17 and 21nm, respectively. Moreover, a noninvasive method based on ultrasounds was used to characterize the aqueous solutions. The preliminary results showed the attainable accuracy in determining acoustic wave velocity and attenuation in various solutions. These data could be correlated with particle density and size. More than that, velocity and attenuation can be used as characteristic parameters of a given solution. A finite element model of the dispersed particles, correlated with measured velocity, allowed to solve for the elastic properties of the particles. POLYM. ENG. SCI., 57:485-490, 2017. (c) 2017 Society of Plastics Engineers

Sm3+ doped partially disordered calcium-niobium-gallium -garnet (CNGG) and calcium-lithium-niobium-gallium -garnet (CLNGG) single crystals were grown by the Czochralski method. Spectroscopic characteristics of Sm:CNGG and Sm:CLNGG single crystals were obtained by high-resolution absorption and emission spectra and emission dynamics measurements. Partial energy levels of Sm3+ doped CNGG and CLNGG were extracted from the measured spectra. The Judd-Ofelt theory has been applied to evaluate the Omega(t)(t=2,4, 6) intensity parameters, radiative transition rates A(r) branching ratios beta, and radiative lifetime tau(r), of the fluorescent Sm3+ (4)G(5/2) level. The emission cross-sections for the (4)G(5/2)-> H-6(J) (J=5/2, 7/2, 9/2) transitions of special interest for visible laser application were obtained by the Fucht-bauer - Ladenburg equation. The interaction between Sm3+ ions is dipole-dipole type and the C-DA, microparameter for both crystals was calculated based on Inokuti-Hirayama model. (C) 2017 Elsevier B.V. All rights reserved.

In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.

This paper presents structural, morphological and preliminary ultrasonic characterizations of the -Cyclodextrin/hydroxyapatite (CD-HAp) composites synthesized by an adapted co-precipitation method. The structural and morphological properties were evaluated by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The specific surface area, pore size and pore volume were determined using the methods of Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH), respectively. The novelty of our study consists in preliminary ultrasonic measurements conducted on CD-HAp composite, uniformly dispersed in distilled water. The benefit of this non-destructive method was to facilitate and simplify the characterization techniques of nanoparticles. Our experiments proved that the efficiency of lead ion removal by CD-HAp composites depended on the initial concentration of lead. The maximum adsorption capacity of the solid phase, for Pb2+ indicated a higher rate of removal by the CD-HAp_2. These adsorption results bring valuable insight into the beneficial contribution of our compounds, for the removal of heavy metal ions from aqueous solutions. Furthermore, in the present study, was evaluated the toxic effect of lead ions adsorbed by hydroxyapatite from contaminated water on HeLa cells.

Compatibility of screen-printed piezoelectric 0.65Pb(Mg1/3Nb2/3) O-3-0.35PbTiO(3) thick films with metalized low-temperature co-fired (LTCC) ceramic substrates is examined. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators, where functional layers are usually Pb-based piezoelectrics. In this study the special attention is given to the influence of the Au, Ag and Ag/Pd electrode materials coated over the LTCC on the functional properties of the films. The best phase purity, dielectric and piezoelectric properties were obtained in the films on gilded substrates. No secondary phases were observed at the film/Au interface by scanning electron microscope. The piezoelectric coefficient d(33) of the films on gilded substrates is equal to 120 pC/N.

Silver-doped hydroxyapatite (AgHAp) was prepared by co-precipitation method at room temperature. The obtained AgHAp was added in different amounts of collagen gel (AgHApC1 and AgHApC2). Afterward, the gel was lyophilized and the final AgHApC1 and AgHApC2 composite was achieved. The purity, crystallinity, and the phase composition of the AgHAp, AgHApC1, and AgHApC2 samples were evaluated by X-ray diffraction (XRD). The planes corresponding to the 2 values for hydroxyapatite were found in the three samples analyzed in agreement with the crystalline hydroxyapatite. In the Fourier transform infrared (FT-IR) spectra of AgHApC1 and AgHApC2 samples the peak characteristic to the presence of (2) phosphate mode at 472/cm was found. The peaks resulting from the (4) vibration of the P-O mode, (1) symmetric P-O stretching vibration and (3) P-O stretching vibration of PO43- were also evidenced in all the samples. The formation of agglomerated particles with uniform particle size was evidenced by scanning electron microscope (SEM). The uniform distribution of the constituent elements was evidenced by mapping analysis. Furthermore, the strong antibacterial activity of AgHAp, AgHApC1, and AgHApC2 samples against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains was shown. The inhibition zone increased drastically with the increase of silver concentration. POLYM. ENG. SCI., 57:537-545, 2017. (c) 2017 Society of Plastics Engineers

The substantial increase in the power conversion efficiency of hybrid perovskite solar cells, to date reaching more than 20% in the laboratory, has strongly motivated research on this class of organic-inorganic materials and related devices, particularly based on CH3NH3PbI3-xXx/TiO2 heterostructures (X = Cl,Br). Taking under consideration that a ferroelectric substrate may act as an efficient electron transporter, positively influencing charge collection across the interface and allowing the tuning of the halide perovskite (HP) - ferroelectric junction, we performed extensive density functional theory calculations on CH3NH3PbI3-xClx layers deposited on tetragonal PbTiO3 (PTO) (001) surfaces, to study their structural and electronic properties. The main findings of this study are as follows. (i) A ferroelectric polarization pointing from the PTO/HP interface to the PTO is favorable for the photogenerated electrons transfer across the interface and their transport to the collecting electrode. (ii) The PTO internal electric field leads to a position dependent energy levels diagram. (iii) The HP gap may be tuned by chlorine concentration at the interface, as well as the by the surface terminations of PbTiO3 and hybrid perovskite layers. (iv) The presence of the PTO ferroelectric surface is likely to have just a slight orientational effect on the (CH3NH3)(+) dipoles.

Based on simulations using the plane-wave expansion method, we show that the position of the first bandgap for TM polarized electromagnetic radiation in a high-filling ratio two-dimensional square photonic crystal is practically insensitive to the shape of dielectric rods with the same cross-sectional area. The width of this bandgap depends on the rod shape, but the difference between photonic crystals with circular and regular polygonal rod shapes with a number of edges higher than six can be neglected. For higher-order bandgaps the difference is larger. These results suggest that the fabrication tolerances related to the shape of dielectric rods in a PBG are not as strict as previously thought. (C) 2017 Elsevier B.V. All rights reserved.