National Institute Of Materials Physics - Romania

Publications

5781 articles found

1741. Non-interacting, sp(2) carbon on a ferroelectric lead zirco-titanate: towards graphene synthesis on ferroelectrics in ultrahigh vacuum

Authors: Apostol, NG; Lungu, GA; Bucur, IC; Tache, CA; Hrib, L; Pintilie, L; Macovei, D; Teodorescu, CM

Published: 2016, RSC ADVANCES, 6, DOI: 10.1039/c6ra12910b

Carbon layers grown on lead zirco-titanate (PZT) weakly interact with the substrate and exhibit a nearly two dimensional character, up to a carbon surface density approaching that of graphene. The first feature is evidenced by X-ray photoelectron spectroscopy, and the second by angle resolved near-edge-absorption spectroscopy (NEXAFS). The binding energies and lineshape parameters of C 1s are similar to that of graphene. The dichroism of C K-edge NEXAFS shows the prevalence of in-plane sp(2) bonds for layers whose effective coverage is below the graphene surface density. The polarization state of the substrate, oriented outwards, is preserved upon carbon deposition. The surface Pb content is strongly affected by the carbon ad-layers.

1742. Structural and Biological Assessment of Zinc Doped Hydroxyapatite Nanoparticles

Authors: Popa, CL; Deniaud, A; Michaud-Soret, I; Guegan, R; Motelica-Heino, M; Predoi, D

Published: 2016, JOURNAL OF NANOMATERIALS, 2016, DOI: 10.1155/2016/1062878

The aim of the current research work was to study the physicochemical and biological properties of synthesized zinc doped hydroxyapatite (ZnHAp) nanoparticles with Zn concentrations x(Zn) = 0 (HAp), x(Zn) = 0.07 (7ZnHAp), and x(Zn) = 0.1 (10ZnHAp) for potential use in biological applications. The morphology, size, compositions, and incorporation of zinc into hydroxyapatite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman scattering, and X-Ray Photoelectron Spectroscopy (XPS). In addition, the cytotoxicity of ZnHAp nanoparticles was tested on both E. coli bacteria and human hepatocarcinoma cell line HepG2. The results showed that ZnHAp nanoparticles (HAp, 7ZnHAp, and 10ZnHAp) have slightly elongated morphologies with average diameters between 25 nm and 18 nm. On the other hand, a uniform and homogeneous distribution of the constituent elements (calcium, phosphorus, zinc, and oxygen) in the ZnHAp powder was noticed. Besides, FTIR and Raman analyses confirmed the proper hydroxyapatite structure of the synthesized ZnHAp nanoparticles with the signature of phosphate, carbonate, and hydroxyl groups. Moreover, it can be concluded that Zn doping at the tested concentrations is not inducing a specific prokaryote or eukaryote toxicity in HAp compounds.

1743. STRUCTURAL AND MAGNETIC PROPERTIES OF Sr2FeMoO6 OBTAINED AT LOW TEMPERATURES

Authors: Bartha, C; Plapcianu, C; Crisan, A; Enculescu, M; Leca, A

Published: JUL-SEP 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 780, DOI:

The double-perovskite Sr2FeMoO6 has been obtained by solid state method at low temperature (1060 degrees C) and a very short time of synthesis (up to 4h). Both, X-ray diffraction and scanning electron microscopy (SEM) confirmed the formation of Sr2FeMoO6 oxide with grain sizes around 160 mm, and a small amount of SrMoO4 as an impurity. Mossbauer spectroscopy revealed a mixed site population with Fe and Mo ions generating a structure type with population inversion. This structure has a critical influence on the magnetic properties, as confirmed by the magnetization and TC values, i.e 3.56 mu(B)/f.u and 415 K, respectively. The Sr2FeMoO6 behavior was interpreted in terms of ferrimagnetic couplings generated by the various distributions of local interactions between Fe and Mo neighbors while comparing the ideal structure should show antiferromagnetic coupling between the two sublattices.

1744. An adamantane-based COF: stability, adsorption capability, and behaviour as a catalyst and support for Pd and Au for the hydrogenation of nitrostyrene

Authors: Trandafir, MM; Pop, L; Hadade, ND; Florea, M; Neatu, F; Teodorescu, CM; Duraki, B; van Bokhoven, JA; Grosu, I; Parvulescu, VI; Garcia, H

Published: 2016, Catalysis Science & Technology, 6, 8354, DOI: 10.1039/c6cy01631f

A bimodal (micro/mesoporous) COF was synthesized by coupling tetrakis-1,3,5,7-(4'-iodophenyl) adamantane with 4,4'-diethynylbiphenyl following a Sonogashira protocol. The COF preparation strategy led, however, to the incomplete recovery of the palladium catalyst and ICP-OES analysis indicated that around 0.1 wt% palladium remained inside the pores. Noteworthily, the remnant palladium catalyst is still accessible and can be valorised in additional catalytic reactions like the hydrogenation of nitrostyrene. Further deposition of 0.5 wt% active metals (like palladium or gold) enhanced the catalytic activity and tuned the catalyst selectivity with respect to analogous metal catalysts prepared using active carbon as a support. The resulting COF-supported metal NPs are stable and recyclable catalysts. Under normal conditions, this COF is also able to adsorb large amounts of weak electrophilic gases like carbon dioxide.

1745. The Influence of the Dielectric Constant in Dielectric Resonator Antennas

Authors: Moni, MV; Tuta, L; Grecu, IV; Turcan, MG; Banciu, G

Published: 2016, 2016 INTERNATIONAL CONFERENCE ON COMMUNICATIONS (COMM 2016), 114, DOI:

This paper presents a comparison between dielectric resonator antennas with different dielectric constant parameter of the resonator. The antenna is fed with microstrip line. The dielectric resonators have cylindrical geometry. In HFSS software program, the simulations are up to compare the antennas' behavior as a function of different parameters, such as: center frequency, gain, frequency bandwidth etc.

1746. High temperature superconducting materials based on Graphene / YBCO nanocomposite

Authors: Colie, M; Mihaiescu, D; Surdu, A; Trusca, R; Vasile, B; Istrati, D; Ficai, A; Plapcianu, C; Andronescu, E

Published: 2016, MATERIALS TODAY-PROCEEDINGS, 3, 2634, DOI: 10.1016/j.matpr.2016.06.006

New route synthesis of YBCO / graphene composite material is described in the present work. The oxide mixture and graphene were obtained separately and then mixed together by ball milling in the mass ratio graphene: YBCO = 1: 100. The oxide mixture was prepared by modified auto combustion reaction starting from stoichiometric amounts of yttrium acetate and barium and copper nitrates without any other organic compound addition. Graphene materials were prepared by reducing GO (i. e. oxidation of graphite powder by a modified Hummers method) with hidrazine sulphate. The final material resulted by applying the ballmilling method was investigated by XRD, SEM, Raman and HRTEM. (C) 2014 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Conference Committee of 6th International Conference on Advanced Nano Materials.

1747. MOSSBAUER AND MAGNETIC INVESTIGATION OF IRON NITRIDE WITH MARTENSITE STRUCTURE SYNTHESISED FROM OXY-HYDROXIDE TYPE PRECURSOR

Authors: Palade, P; Plapcianu, C; Mercioniu, I; Comanescu, CC; Schinteie, G

Published: JAN-MAR 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 63, DOI:

Fe16N2 fine particles were prepared by reduction in 5% H-2/Ar gas mixture flow, starting from goethite or hematite precursors, followed by nitridation in ammonia gas flow. Small amounts of metallic iron and iron oxide are present besides the main phase which is an ordered iron nitride having martensite structure (alpha''-Fe16N2) as revealed by Mossbauer spectroscopy measurements. However, X-ray diffraction data do not show any traces of oxides due to their high degree of amorphization. When nitridation is performed at about 150 C-0, Fe4N phase begins to form and its presence deteriorates the magnetic properties. The samples prepared by nitridation of goethite present better magnetic properties compared to those obtained by nitridation of hematite. Magnetic and Mossbauer measurements performed at ambient temperature were corroborated in order to extract the magnetization at saturation value for each phase which occurs in the obtained samples. The corresponding values are 226 emu/g for Fe16N2 and 198 emu/g for metallic iron contained in the prepared powders.

1748. SYNTHESIS AND CHARACTERIZATION OF FLUORESCENT HYDROXYAPATITE

Authors: Popa, CL; Ciobanu, CS

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 1177, DOI:

This paper presents the synthesis of cerium doped hydroxyapatite using low concentrations of cerium (x(Ce) = 0.01, 0.03 and 0.05) by an adapted sol-gel method. The structural and optical properties of the obtained powders have been studied by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Photoluminescence (PL) measurements. The cerium ions successfully substituted the calcium ions from the hydroxyapatite structure without inflicting any structural alterations. With the increase of dopant concentration in the sample a decrease of the mean particle size was observed. Also, the vibrational peak intensities decreased while the intensity of the photoluminescence excitation bands increased in intensity when the cerium concentration increased from x(Ce) = 0.01 to x(Ce) = 0.05. Taken together, the results suggest that even low concentration of cerium influence the properties of hydroxyapatite but do not-cause any structural alterations.

1749. STRUCTURAL AND MORPHOLOGICAL EVOLUTIONS INDUCED BY THE ANNEALING OF CaF2 NANOCRYSTALLINE POWDERS BY USING Eu3+ ION PROBE LUMINESCENCE

Authors: Polosan, S; Secu, M; Enculescu, M

Published: APR-JUN 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 624, DOI:

Eu-doped CaF(2)nanocrystalline powders have been prepared by using co-precipitation technique. Structural and morphological modifications induced by annealing are followed by using Eu3+-ion probe. Theluminescence properties are changing gradually together with the morphology of doped CaF2 nanoparticles accompanied by anEu(3+)-> Eu2+ conversion. Cathodoluminescence measurements show uniform distribution of the europium dopant ions in the annealed samples accompanied by a strong increase of the integral photoluminescence signal. During annealing the cubic structure of CaF2 nanoparticles is altered going to the spherical morphology due to the Eu3+ ions incorporation. In the annealed samples Eu3+ ions are incorporated as Eu3+-O dimer centres with the coordination symmetry (C-2 nu); in the sintered samples there are two non-equivalent Eu3+ sites. The thermoluminescence peaks have been assigned to the recombination of the Eu3+ related traps in these sites.

1750. SOL-GEL TEMPLATE ASSISTED SYNTHESIS AND UP-CONVERSION PROPERTIES OF (Yb-Er) DOPED SiO2-LiYF4 GLASS CERAMIC RODS

Authors: Secu, CE; Matei, E

Published: APR-JUN 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 494, DOI:

Up-conversion properties of the glass-ceramics microrods containing (Er3+, Yb3+)-doped LiYF4 nanocrystals have been studied. Under 980 nm laser light pumping, both Yb3+/Er3+ co-doped LiYF4 samplesshow green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion luminescences explained by a two-photon processes. The luminescence decay time of the green luminescence is much shorter in the glass-ceramics microrods (0.9 mu s) compared to the bulk powder (15 mu s) indicating the enhancement of the non-radiative relaxation rate due to the cross-relaxation effects between Er3+-ions. The quantum efficiencies were estimated for the green luminescence being much smaller in the glass-ceramic rods (eta = 0.15%) compared the bulk powder (eta = 2%) or pellet (eta = 46%).