National Institute Of Materials Physics - Romania

Publications

860 articles found

551. Large scale microstructuring on silicon surface in air and liquid by femtosecond laser pulses

Authors: Ulmeanu, M; Jipa, F; Radu, C; Enculescu, M; Zamfirescu, M

Published: SEP 15 2012, APPLIED SURFACE SCIENCE, 258, 9317, DOI: 10.1016/j.apsusc.2011.08.110

Large-scale microstructures were imprinted on the surface of silicon with dimensions of 1 mm x 1 mm by femtosecond laser line-by-line scanning irradiation. The scanning was made under air and under chlor/hydrogen based liquid layers. Scanning electron microscope investigations evidenced homogeneous surface microstructures, such as: ripples with sub-wavelengths dimensions, Si pillars and directional oriented bacilliform structures. The dependence of the surface morphology on laser energy, scanning speed and irradiation media was analyzed. In air, the microstructure changes from directional-arranged bacilliform structures to well-known ripple structures with a width of about 525 nm. When using the liquid media, we observe ripple structures with a width of about 370 nm and an overlapping of those that evolve in certain regions into Si pillars. The surfaces show interesting gradient topography behaviour which could be used as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth. By using chlor and hydrogen based liquids we were able to explore the microstructuring of the silicon by line-by-line irradiation process using the femtosecond laser. (C) 2011 Elsevier B. V. All rights reserved.

552. Sm3+-doped Sc2O3 polycrystalline ceramics: Spectroscopic investigation

Authors: Gheorghe, C; Lupei, A; Voicu, F; Enculescu, M

Published: SEP 15 2012, JOURNAL OF ALLOYS AND COMPOUNDS, 535, 82, DOI: 10.1016/j.jallcom.2012.04.083

Sm3+-doped Sc2O3 translucent polycrystalline ceramics were fabricated by solid-state reaction method in order to evaluate its potential for visible emission. The optical spectra in the UV-IR range of Sm3+ in these samples, at different temperatures (10-300 K), were performed. A series of data on Sm: Sc2O3 system not investigated previously were obtained from the analysis of the absorption and visible emission spectra as well as the emission kinetics: an extended energy level scheme, absorption cross sections for different bands, lifetimes, etc. Additional spectroscopic parameters were evaluated in the frame of the Judd-Ofelt (J-O) theory: J-O intensity parameters, oscillator strengths, radiative transitions probabilities, radiative lifetimes, branching ratios, and the cross sections (by Fuchtbauer-Ladenburg) of the main three visible emissions: (4)G(5/2) -> H-6(5/2) (yellow), (4)G(5/2) -> H-6(7/2) (orange) and (4)G(5/2) -> H-6(9/2) (red). (C) 2012 Elsevier B.V. All rights reserved.

553. Luminescent micro- and nanofibers based on novel europium phthalate complex

Authors: Enculescu, M; Preda, N; Matei, E; Enculescu, I

Published: SEP 14 2012, MATERIALS CHEMISTRY AND PHYSICS, 136, 58, DOI: 10.1016/j.matchemphys.2012.06.018

We synthesized by wet chemical route a novel europium-potassium phthalate complex Eu3+K+[(COO)(2)(C6H4)](2). The compound is a white powder insoluble in water. X-ray diffraction evaluation shows that we obtained a new crystalline compound with no traces of the starting materials (potassium hydrogen phthalate and europium chloride). Scanning electron microscopy reveals that the powder consists of fiber-shaped structures with sizes larger than 250 nm in diameter. Energy dispersive X-ray analysis proves that the compound has a 1:1 europium-potassium ratio. Fourier transform infrared spectroscopy confirms the presence of the phthalate in the new compound. Photoluminescence and cathodoluminescence measurements show that the fiber-shaped structures are intensely luminescent with emission bands corresponding to the D-5(0) -> F-7(J) (J = 1-4) Eu (III) ion's transitions in the region between 580 nm and 700 nm, the most intense maximum being observed around 615 nm. Up-converted luminescence with a maximum at 315 nm was recorded. (c) 2012 Elsevier B.V. All rights reserved.

554. Transparent indium zinc oxide thin films used in photovoltaic cells based on polymer blends

Authors: Besleaga, C; Ion, L; Ghenescu, V; Socol, G; Radu, A; Arghir, I; Florica, C; Antohe, S

Published: SEP 1 2012, THIN SOLID FILMS, 520, 6806, DOI: 10.1016/j.tsf.2012.07.030

Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.

555. The antimicrobial activity of fabricated iron oxide nanoparticles

Authors: Iconaru, SL; Ciobanu, CS; Prodan, AM; Predoi, D

Published: SEP 2012, FEBS JOURNAL, 279, 98, DOI:

556. Synthesis and characterization of bead-like particles based on chitosan and vinyl polymers

Authors: Preda, N; Enculescu, M

Published: SEP 2012, JOURNAL OF POLYMER RESEARCH, 19, DOI: 10.1007/s10965-012-9963-9

Styrene, methyl methacrylate and glycidyl methacrylate vinyl monomers were grafted onto chitosan by surfactant-free emulsion copolymerization using potassium persulfate as initiator. The grafted compounds were characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and zeta potential measurements. X-ray diffraction showed changes in the crystallinity pattern of chitosan after the copolymerization reaction. Evidence of grafting was confirmed by FTIR spectroscopy. From zeta potential measurements it is found that the surfaces of graft copolymers latex particles have positive charges resulting from the cationic chitosan molecules. The morphology evaluated by SEM, TEM and AFM proves that in the absence of chitosan, latexes of vinyl homopolymers contain quasi-monodispersed spheres with average diameter of about 400 nm or 250 nm while the graft copolymers latexes are formed by clustered irregular beads with average diameter around 100 nm.

557. Evaluation of antibacterial effect of silver doped hydroxyapatite nanoparticles

Authors: Prodan, AM; Le Coustumer, P; Predoi, D

Published: SEP 2012, FEBS JOURNAL, 279, 98, DOI:

558. Interaction of NaYF4:Er:Yb Nanoparticles with Phospholipid Monolayers as Models of Biological Membranes

Authors: Petrescu, L; Cinteza, O; Voiculescu, AM; Rosu, T; Enculescu, I; Matei, E; Georgescu, S; Birjega, R; Avram, S; Mihailescu, D

Published: SEP 2012, REVISTA DE CHIMIE, 63, 961, DOI:

Given the evolution of imaging techniques in the biomedical field is becoming more necessary to develop sensitive markers, less toxic and not least more economical. Upconverting luminescent nanocrystals doped with rare earth ions, excited in infrared and emitting in visible, are considered real concurrent to classical fluorescent markers, featuring a number of advantages in rapport with them. The aim of this study is to prepare NaYF4 nanoparticles doped with erbium and ytterbium for biological applications in bioimaging techniques. After synthesis, upconverting nano particles were coated with SiO2 for surface sealing and passivation. The nano particles were characterized by X-ray diffraction, luminescence spectroscopy, electronic microscopy and dynamic light scattering. The interaction of the nanoparticles with mimicking cell membrane models was studied. NaYF4 nanoparticles showed a good size distribution and good emission efficiency. The uncoated nanoparticles increase the fluidity of the lipid monolayer, while the effect of the silica coated nanoparticles is substantially reduced.

559. Assessing toxicity of two types of magnetite nanoparticles in human hepatocarcinoma cells

Authors: Radu, M; Iconaru, SL; Predoi, D; Costache, M; Dinischiotu, A

Published: SEP 2012, FEBS JOURNAL, 279, 205, DOI:

560. Synthesis of CdS nanostructures using template-assisted ammonia-free chemical bath deposition

Authors: Preda, N; Enculescu, M; Gherendi, F; Matei, E; Toimil-Molares, ME; Enculescu, I

Published: SEP 2012, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 73, 1089, DOI: 10.1016/j.jpcs.2012.05.003

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300 nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5 - 2.6 eV and a red luminescence at similar to 1.77 eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array. (C) 2012 Elsevier Ltd. All rights reserved.