National Institute Of Materials Physics - Romania

Publications

5714 articles found

1711. Laser-induced chemical transformation of free-standing graphene oxide membranes in liquid and gas ammonia environments

Authors: del Pino, AP; Gyorgy, E; Cotet, C; Baia, L; Logofatu, C

Published: 2016, RSC ADVANCES, 6, 50042, DOI: 10.1039/c6ra07109k

Laser-induced chemical conversion of graphene oxide (GO) is an effective way to modify its properties and expand its potential use for numerous applications. In this work, a mechanically stable and flexible freestanding GO membrane is synthesized and further processed by ultraviolet laser radiation in gas and liquid ammonia-rich environments. Electron and atomic force microscopy, as well as X-ray photoelectron spectroscopy analysis, reveal that laser irradiation in gas leads to a large defect-induced morphology modification and high deoxygenation process, accompanied by the slight incorporation of nitrogen functionality to the reduced GO structure. Conversely, irradiation in liquid provokes significant integration of nitrogen groups, essentially amines, into a partially reduced GO structure, without evident modification of the morphology. Electrical measurements on the macro-and nano-scale point to a complex contribution of morphology and oxidized regions to the overall resistance of the rGO.

1712. CEMS MEASUREMENTS ON LOW Fe-57 DOPED ANATASE NANOPARTICLES

Authors: Bibicu, I; Constantinescu, S; Tarabasanu-Mihaila, D; Grecu, MN

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 1512, DOI:

We report the conversion electron Mossbauer spectroscopy (CEMS) used to analyze the iron valence states and magnetic ordering properties in Fe-57 low doped (0.1-1% at.) as prepared and anneale d anatase TiO2 nanoparticles. The spectra evidence the static and dynamic diversity of local defects around the Fe ions, localized mainly on the surface samples.

1713. Effect of thermal treatments in Ni-Fe-Ga with Co substitutions and Ni-Mn-Ga melt spun ribbons

Authors: Tolea, F; Sofronie, M; Crisan, AD; Popescu, B; Tolea, M; Valeanu, M

Published: 2016, 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21), 2, 1480, DOI: 10.1016/j.prostr.2016.06.187

The effect of "in situ" thermal treatments (by DSC measurements) on the martensitic transformation in two representative Ni-Fe-Ga and Ni-Mn-Ga alloys has been studied and discussed by correlating the structural and magnetic properties. The alloys were prepared from high purity elements, by arc melting under argon protective atmosphere as bulk and also as melt-spun ribbons - an alternative preparation route that also allows to assess the influences of grains size and strain induced by this processing method. All samples presented reversible thermo-elastic transformations. The thermal treatments promote a reduction of the martensitic transformation temperatures in the Ni-Fe-Ga investigated samples, as opposed to the stoichiometric Ni2MnGa where the temperatures increase with increasing the annealing temperatures. Interestingly however, the off-stoichiometric Ni-Mn-Ga with increased Ni content recovers the behaviour with reduction of transformation temperatures by thermal treatments. The precipitation of the secondary FCC (gamma) phase is inherently found in Ni-Fe-Ga alloys with Ga <= 27% at, and also-although in lower amounts- in the off-stoichiometric Ni-Mn-Ga. The gamma phase is considered to contribute to the decrease of the MT temperatures (via valence electrons concentration depletion of the main matrix) and of the transformation heat as well as to the final structural degradation if the temperature of the thermal treatments is further increased. In addition, this phase, located mainly at the grain boundaries, is responsible for the improved ductility of Ni-Fe-Ga based alloys. Changes in the transformation heat due to thermal treatments are observed and discussed in both types of alloys, the maxima of the transformation heat being associated with the highest atomic order. Thermo-magnetic measurements show that Ni-Fe-Ga alloys have close magnetic and structural transitions temperatures, with promising applications for magnetic refrigeration. Copyright (C) 2016 The Authors. Published by Elsevier B.V.

1714. INFRARED AND X-RAY PHOTOELECTRON SPECTROSCOPY IN SURFACE CHARACTERIZATION OF POLYDIMETHYLSILOXANE THIN FILMS GENERATED ON METALLIC SUBSTRATES IN MULTIPOINTS TO PLANE CORONA DISCHARGES

Authors: Groza, A; Surmeian, A; Diplasu, C; Negrila, C; Mihalcea, B; Ganciu, M

Published: 2016, ROMANIAN JOURNAL OF PHYSICS, 61, 656, DOI:

By coupling two spectral techniques, namely, X-ray photoelectron and specular reflection infrared spectroscopy at high reflection angles, we identified, in this paper,. the formation of SiO2 respectively SiOx (1 < x < 2) structures on the surface of polydimethylsiloxane thin films. These layers have been obtained as a result of placing a thin liquid film precursor on a germanium substrate under corona charge injection in multipoints to plane electrodes configuration in air at atmospheric pressure for 2 hours.

1715. Nematic ionic liquid crystals based on pyridinium salts derived from 4-hydroxypyridine

Authors: Pana, A; Pasuk, I; Micutz, M; Circu, V

Published: 2016, CRYSTENGCOMM, 18, 5069, DOI: 10.1039/c6ce00618c

A series of pyridinium salts with various counterions (Br-, NO3-, BF4-, PF6-, OTf- and SCN-) and different spacer chain lengths, which display a nematic phase, have been designed and prepared. They are derived from 4-hydroxypyridine and possess two mesogenic cyanobiphenyl groups attached to the pyridinium unit via a flexible long alkyl spacer (6, 9, 10). These salts exhibit solely a nematic phase with the thermal range influenced by the counterion employed and spacer length.

1716. BST thin film capacitors integrated within a frequency tunable antenna

Authors: Rammal, M; Huitema, L; Crunteanu, A; Passerieux, D; Cros, D; Monediere, T; Madrangeas, V; Dutheil, P; Champeaux, C; Dumas-Bouchiat, F; Marchet, P; Nedelcu, L; Trupina, L; Banciu, G; Cernea, M

Published: 2016, 2016 IEEE INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY (IWAT), 47, DOI:

Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba(1-x)SrxTiO3, BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.

1717. MAGNETIC AND MOSSBAUER SPECTROSCOPY STUDY OF Fe-Cr-Al THIN FILMS SPUTTERED ON Si SUBSTRATES

Authors: Greculeasa, SG; Schiniteie, G; Palade, P; Filoti, G; Ghita, IS; Kuncser, V

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 258, DOI:

Fe and Fe-Cr-Al thin films, both as sputtered on Si substrates as well as after subsequent annealing treatments in hydrogen atmosphere, have been investigated by means of X-ray reflectometry, magneto-optic Kerr effect and Mossbauer spectroscopy with respect to structural and related magnetic characteristics. The as deposited films are showing chemically disordered bcc structures, assigned to Fe-Si and Fe-Cr-Al-Si phases, respectively, with soft magnetism and magnetic texture, both influenced by the presence of Si, Cr and Al atoms. The softness of the films as well as the magnetic texture are strongly modified via hydrogenation treatments. In addition, such treatments induce the expulsion of Si, Cr and Al atoms from the as deposited phases, providing almost pure Fe films of much well crystallized bcc structure.

1718. Fast atomic diffusion in amorphous films induced by laser pulse annealing

Authors: Teodorescu, VS; Ghica, C; Maraloiu, AV; Kuncser, A; Lepadatu, AM; Stavarache, I; Ciurea, ML; Scarisoreanu, ND; Andrei, A; Dinescu, M

Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 158, DOI:

Fast atomic diffusion was evidenced in the surface layer of amorphous thin films of oxides and semiconductors irradiated with low fluence UV pulse laser. This process takes place in a surface layer with a thickness related to the laser radiation absorption depth in the target material and was revealed by the cross section transmission electron microscopy studies. These high values of diffusivity can be explained by supposing the glass transition transformation in the amorphous structure, triggered by the action of the laser pulse field. This effect can have application for controlling structural modifications at nanoscale of the thin films surface and also for inducing structural modification of interfaces between the film and substrate.

1719. Screen-printed Pb(Mg,Nb)O-3-PbTiO3 Thick Tilms on Ceramic Substrates for Sensor Applications

Authors: Ursic, H; Khomyakova, E; Drnovsek, S; Malic, B; Mercioniu, IF; Bencan, A; Makarovic, K; Schreiner, C; Ciobanu, R; Belavic, D; Bolado, P

Published: 2016, PROCEEDINGS OF THE 2016 INTERNATIONAL CONFERENCE AND EXPOSITION ON ELECTRICAL AND POWER ENGINEERING (EPE 2016), 58, DOI:

In this work the screen-printed piezoelectric 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) thick films were prepared on metalized low-temperature co-fired ceramic substrates. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators. The prepared thick films exhibit the piezoelectric coefficient d(33) equal to 120 pC/N.

1720. STRUCTURAL CHARACTERIZATION AND OPTICAL PROPERTIES OF HYDROXYAPATITE/COLLAGEN MATRIX

Authors: Popa, CL; Albu, M; Bartha, C; Costescu, A; Luculescu, C; Trusca, R; Antohe, S

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 1158, DOI:

This paper presents the synthesis and characterization of hydroxyapatite (HAp) and hydroxyapatite embedded in a collagen matrix (C-HAp6). The aim of this study was to investigate the influence of collagen on the structure and morphology of hydroxyapatite. According to the XRD patterns, the samples have the structure characteristic to hydroxyapatite. The FTIR and Raman spectra proved the successfully embedding of hydroxyapatite in the collagen matrix. Morphologically, the collagen increases the porosity of HAp. The collagen influences the structure and morphology of the hydroxyapatite causing a decrease of the mean particle size and/or a decrease of crystallinity while increasing the porosity.