National Institute Of Materials Physics - Romania

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5714 articles found

1681. 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.

1682. 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.

1683. 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%).

1684. Nano and Microtechnology for Monitoring Stem Cell Differentiation

Authors: Cheran, LE; Cheran, A; Lupu, AR; Popescu, T

Published: 2016, STEM CELLS BETWEEN REGENERATION AND TUMORIGENESIS, 320, DOI:

This chapter gives an overview of the new micro- and nano-technologies designed to monitor SC differentiation in the context of their potential applications in disease modeling, tissue engineering, regenerative medicine, as well as drug screening and toxicology. Representative examples of such applications are presented and the crucial importance of the differentiation processes for the safety of SC therapies is discussed. The roles of the main factors that influence SC differentiation are briefly summarized and the vital need to control and monitor the differentiation process using non-invasive methods is emphasized. The basic principles of new micro- and nano-technologies for monitoring SC differentiation are presented, with special focus on the use of acoustic vibrational fields to characterize SC. Literature studies on SC differentiation, involving methods based on Impedance Sensing (IS), Surface Enhanced Raman Spectroscopy ( SERS), Fourier Transformed Infrared (FTIR) spectroscopy, Microelectrode Array (MEA) sensors, Light-addressable Potentiometric Sensors (LAPS), Field-effect Transistors ( FET), Surface Plasmon Resonance (SPR) and Quartz Crystal Microbalance (QCM), are briefly described.

1685. FTDT investigations for fabrication of sub-wavelength metal wire-grid polarizes and quarter waveplate

Authors: Cotirlan-Simiontuc, C; Logofatu, C; Iordache, G; Rizea, A; Ursu, DV

Published: NOV-DEC 2016, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 18, 927, DOI:

Ultracompact polarization components modeled and analyzed with Finite Difference Time Domain Photonics Simulation Software (FTDT) are: a wire-grid linear polarizer and a quarter waveplate for infrared (IR) domain. They will be integrated into a polarization state analyzer (PSA). The components will be manufactured with metamaterials (MTMs). These are composite materials consisting of artificial meta-atoms, i.e. conductive nano- or micro-structures regularly arranged in a dielectric or semiconductor matrix. These conductive structures are made-up smaller than the wavelength of the radiation work. MTMs show extraordinary electromagnetic properties, typically not found in nature, such as negative refractive index. They increase the interaction between radiation and matter. The use of optical polarization components in IR imaging systems dedicated to difficult conditions of visibility is a must, as it allows improving performance and reducing the dimension of optoelectronic devices used in air, car and naval navigation. We will focus on developing the components for applications of imaging polarimetry in long-wave infrared (LWIR) range.

1686. Transparent Nd doped YAG ceramics

Authors: Stanciu, CA; Dascalu, T; Stanciu, G; Pavel, N

Published: 2016, 3RD INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2016), 741, DOI: 10.1088/1742-6596/741/1/012074

The reasearch main objective is to obtain ceramic laser materials based on pure YAG (Y3Al5O12) and Nd doped YAG (Y-3-xNdxAl(5)O(12), with x = 0.5 and 1.0 at. %), by conventional solid state reaction method. Stoichiometric compositions of Y3Al5O12 (YAG), Y2.985Nd0.015Al5O12 (0.5 at.% Nd: YAG) and Y2.97Nd0.03Al5O12 (1.0 at.% Nd: YAG) were prepared using high purity Y2O3 (99.999%), Al2O3 (99.999%) and Nd2O3 (99.999%) nanopowders. Green bodies were sintered at 1750 degrees C for 16 h under vacuum (1.0 x 10(-3) Pa) and then annealed at 1450 degrees C for 10 h in the air.

1687. BIOLOGICAL STUDIES ON DEXTRIN COATED IRON OXIDE NANOPARTICLES

Authors: Iconaru, SL; Turculet, C; Le Coustumer, P; Bleotu, C; Chifiriuc, MC; Lazar, V; Surugiu, A; Badea, M; Iordache, FM; Soare, M; Prodan, AM

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 1544, DOI:

In this study, dextrin coated iron oxide nanoparticles were obtained using an adapted chemical co-precipitation method. The size and morphology of the dextrin coated iron oxide nanoparticles (DIO-NPs) were analyzed by transmission electron microscopy (TEM). The scanning electron microscopy (SEM) analysis depicted information on the morphology of DIO-NPs. The elemental analysis was conducted by Energy-dispersive X-ray spectroscopy (EDAX). The iron oxide particles coated with dextrin have a spherical shape at nanometric scale with a narrow size distribution. The cytotoxicity assay was performed by quantification of HeLa cells viability, while the antimicrobial activities of the DIO-NPs were determined against ATCC reference and clinical microbial strains, i.e. Gram-positive bacteria (Staphylococcus aureus ATCC 6538) and yeast (Candida albicans 393). The obtained nanoparticles did not have cytotoxic effect on HeLa cells after a 24 h exposure to DIO-NPs and the morphology of the cells was not affected. A low toxic effect on HeLa cells was noticed after 48 h. The minimal inhibitory concentration of DIO-NPs was 1 mg/mL for both tested microbial strains.

1688. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates

Authors: Oumezzine, M; Galca, AC; Pasuk, I; Chirila, CF; Leca, A; Kuncser, V; Tanase, LC; Kuncser, A; Ghica, C; Oumezzine, M

Published: 2016, DALTON TRANSACTIONS, 45, 15040, DOI: 10.1039/c6dt01914e

Epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO3 (STO) (001) substrates. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) investigations revealed that the films are epilayers with a four-fold symmetry around the [001] direction. Cross-sectional TEM and the presence of Pendellosung fringes in the XRD profiles demonstrate smooth interfaces. The STO substrate induces an in-plane compressive strain, which leads to a slight tetragonality of the film structure. The epilayers exhibit paramagnetic-to-ferromagnetic phase transitions at the Curie temperature T-C (286 K), close to room temperature. The magnetization easy axis lies in the film plane along the [100] direction of the (001) substrate. The magnetic entropy change (Delta S-M) associated with the second-order magnetic phase transition was determined via magnetization measurements in the temperature range between 210 and 350 K under different magnetic fields. The relative cooling power (RCP) of this film is about 220 J kg(-1), somewhat lower than that of bulk Gd (410 J kg(-1)) for a 50 kOe field change, making the LBTMO ferromagnetic thin films a promising candidate for micro/nanomagnetic refrigeration around room temperature. The proposed universal curve provides a simple method for extrapolating Delta S-M in a wide range of fields and temperatures, thus confirming the order of the magnetic transition in this system. The magnetic entropy (Delta S-M)(max) around T-C is proportional to (mu H-0/T-C)(2/3) in agreement with the mean-field theory, indicating the existence of long-range ferromagnetic interactions in epitaxial LBTMO thin films.

1689. Polarized Raman spectra of phosphorene in edge and top view measuring configurations

Authors: Baibarac, M; Nila, A; Baltog, I

Published: 2016, RSC ADVANCES, 6, 58009, DOI: 10.1039/c6ra09682d

We demonstrate the anisotropic features of the A(1g), B-2g and A(2g) vibrational Raman modes of phosphorene by performing for the first time a comparison of two orthogonal polarized Raman scattering studies in edge and top view measuring configurations. Despite the orthogonality between the vibration modes of A(1g) and A(2g), they exhibit intense and very weak Raman intensities under light polarized along and transverse to the armchair edge, respectively, while the B-2g mode is virtually non-existent. The B-2g mode significantly appears only in the top view configuration. The studies performed under different intensities of excited light in the top view configuration are detailed for the sample rotated at 0 degrees, 40 degrees, 80 degrees and 130 degrees about the incident laser beam. The studies reveal a quadratic opposite behavior of the A(2g) and B-2g modes and an unusual angle dependence of the A(1g) vibrational mode. An unexpected behavior of the A(2g) Raman mode at higher intensities, which still persists for the A(1g) mode, is shown. The anomalous behavior of the A(1g) mode from the edge and top view and the A(2g) mode in the top view configuration is explained in terms of the layer stacking structures of phosphorene.

1690. Leakage current for thin film metal-ferroelectric-metal devices

Authors: Filip, LD; Pintilie, L; Tam, WS; Kok, CW

Published: 2016, 2016 5TH INTERNATIONAL SYMPOSIUM ON NEXT-GENERATION ELECTRONICS (ISNE), DOI:

The leakage current for a thin film metal-ferroelectric-metal device was modelled using an electron tunnelling approach. The potential energy through the device was obtained from an electrostatic argument and a balance equation was imposed for the incoming and outgoing currents. Using the obtained leakage current, experimental data was fitted in order to obtain qualitative values for the model parameters. Good agreement between the obtained dielectric constant and numerical calculations performed in the literature.