National Institute Of Materials Physics - Romania

Publications

5714 articles found

1311. Local configurations and atomic intermixing in as-quenched and annealed Fe1-xCrx and Fe1-xMox ribbons

Authors: Stanciu, AE; Greculeasa, SG; Bartha, C; Schinteie, G; Palade, P; Kuncser, A; Leca, A; Filoti, G; Birsan, A; Crisan, O; Kuncser, V

Published: 2018, PHILOSOPHICAL MAGAZINE, 98, 1067, DOI: 10.1080/14786435.2018.1425556

Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe1-xCrx and Fe1-xMox ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 degrees C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mossbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mossbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe1-xCrx alloys are structurally more stable than the Mo counterpart under annealing at 700 degrees C. Annealing at 1250 degrees C in He enhances drastically the Cr clustering around Fe nuclei.

1312. ZnHAp Thin Films for Medical Applications

Authors: Iconaru, SL; Groza, A; Chapon, P; Gaianschi, S; Petre, CC; Jiga, G; Beuran, M; Prodan, AM; Lupescu, O; Trusca, R; Predoi, D

Published: 2018, 9TH INTERNATIONAL CONFERENCE ON TIMES OF POLYMERS AND COMPOSITES: FROM AEROSPACE TO NANOTECHNOLOGY, 1981, DOI: 10.1063/1.5045984

The research regarding the properties of thin films of hydroxyapatite doped with various ions such as zinc elaborated by spin-coating technique have rarely been fabricated and studies in recent years. In the present study Zn doped hydroxyapatite (ZrHAp) synthesized by a sol-gel method were coated on Ti substrates using a spin-coating technique. The thin films was characterized by Scanning Electron Microscopy (SEM) and Glow Discharge Optical Emission Spectroscopy (GDOES). The structural characterizations of ZnHAp thin films showed the presence of Zn and apatitic structure. The GD depth profiles revealed the successful embedding of the Zn ions in HAp structure. In addition, in vitro evaluation of the antifungal properties of ZnHAp demonstrated the potential antifungal effect of ZnHAp thin films against Staphylococcus aureus 0364 biofilm.

1313. Polymer Dispersed Liquid Crystals films doped with carbon nanotubes - preparation methods

Authors: Manaila-Maximean, D; Circu, V; Ganea, P; Barar, A; Danila, O; Staicu, T; Loiko, VA; Konkolovich, AV; Miskevich, AA

Published: 2018, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS, AND NANOTECHNOLOGIES IX, 10977, DOI: 10.1117/12.2326186

Polymer Dispersed Liquid Crystals (PDLC) are composite materials consisting of small liquid crystal (LC) droplets surrounded by a polymer matrix. Due to their relatively easy preparation and processing, the PDLC devices found many applications such as displays, architectural windows, energy control devices, projection displays, spatial light modulators, polarizers. Carbon nanotubes (CNT) have excellent mobility and are suitable as doping nanoparticles in order to improve the electrically-controlled orientation of LC. This paper presents the methods of preparation of PDLC doped with CNT. Experimental results are presented for the films obtained by solvent induced polymerization method, using polymethyl methacrylate and a nematic LC, E7. The obtained films are characterized by polarized optical microscopy, differential scanning calorimetry and electro-optical transmission.

1314. Limits and Particularities of the Synthesis of Ba1-xCaxTiO3 for Piezoelectric Applications, by Topochemical Conversion from Molten Salt Solutions

Authors: Vlaicu, ID; Maraloiu, AV; Ghica, D; Mercioniu, IF; Stefan, M; Vlaicu, AM; Negrea, RF; Kuncser, AC; Bulat, S; Krzmanc, MM; Ciobanu, R; Plopa, O

Published: 2018, 2018 INTERNATIONAL CONFERENCE AND EXPOSITION ON ELECTRICAL AND POWER ENGINEERING (EPE), 1050, DOI:

Because of the unique properties of the ferroelectric perovskite particles with a well-defined anisotropic form like shape-and size dependent at low dimensions they have all the attention of the scientific world. Extensive morphostructural techniques will be used to characterize the piezoelectric material.

1315. New Lasing Regimes of High-beta Nanolasers

Authors: Lohof, F; Barzel, R; Gartner, P; Gies, C

Published: 2018, 2018 IEEE PHOTONICS SOCIETY SUMMER TOPICAL MEETING SERIES (SUM), 24, DOI:

We identify new lasing regimes of high-beta nanolasers with extended gain media. There, coherent emission can occur after the typical threshold non-linearity in the I-O-curve due to increased spontaneous emission. As an example for this device-regime, we present room temperature lasing in III-nitride nanobeam cavities.

1316. The effect of H-2/Ar plasma treatment over photoconductivity of SiGe nanoparticles sandwiched between silicon oxide matrix

Authors: Sultan, MT; Gudmundsson, JT; Manolescu, A; Ciurea, ML; Svavarsson, HG

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 260, DOI:

The effect of room temperature hydrogen plasma treatment on the photoconductive properties of the SiO2 matrix containing SiGe nanoparticles is investigated. A considerable increase in photocurrent intensity is observed after plasma treatment. The increase is partly attributed to neutralization of dangling bonds around the nanoparticles and partly to passivation of non-radiative centers and defects in the matrix and at the nanoparticles-matrix interfaces.

1317. Martensitic transformation and related properties of Fe69.4Pd30.6 ferromagnetic shape memory ribbons

Authors: Tolea, F; Sofronie, M

Published: NOV-DEC 2018, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 20, 706, DOI:

Ferromagnetic shape memory alloys (FSMA) have attained strong interest over the last years and Fe-Pd alloys seems to be more suited for engineering and medical applications, due to their improved ductility and biocompatibility compared to the well-known Ni2MnGa alloy. The shape memory effect in disordered Fe-Pd (30 at.% Pd) is associated with FCC-FCT thermoelastic martensitic transformation. The melt-spinning technique enables to get ribbons with the FCC meta-stable structure preventing the precipitation of undesirable BCT irreversible phase and subsequent proper thermal treatments could improve the characteristic parameters of the martensitic transformation. The present work reports the effect of the rapid solidification (via melt-spinning technique) and the different thermal treatments on the microstructure, martensitic transformation and magnetic properties of the Fe69.4Pd30.6 ribbons. The samples were investigated by calorimetry, X-ray diffractometry, scanning electron microscopy and magnetometry. Two different structures induced by the distinct thermal treatments and responsible for the characteristic behavior of the martensitic transformation, were noticed and discussed in details. The high temperature treatment for short time stabilized the FCC phase and slightly decrease the martensitic transformation temperature, while the annealing at low temperature for longer time promotes the reduction of the amount of transforming FCC phase by its partial decomposition in the stable phases, causing the fall of the heat of transformation.

1318. MOS DOSIMETER BASED ON Ge NANOCRYSTALS IN HfO2

Authors: Palade, C; Slav, A; Lepadatu, AM; Stavarache, I; Dascalescu, I; Cojocaru, O; Stoica, T; Ciurea, ML; Lazanu, S

Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 90, DOI:

Trilayer MOS capacitors gate HfO2 / floating gate of Ge nanocrystals in HfO2 / tunnel HfO2 / Si substrate were prepared in the aim to be used for the detection of ionizing radiation. Magnetron sputtering and rapid thermal annealing were used for their fabrication. Capacitance-voltage measurements showed that Ge nanocrystals are the most important charge storage centres in our structure. The possibility to use these trilayer MOS capacitors as dosimeters was investigated, and the sensitivity to alpha particle irradiation was extracted.

1319. Flux Channeling in YBa2Cu3O7 Superlattices

Authors: Mollatt, HJS; Dang, VS; Qureishy, T; Mikheenko, P; Crisan, A

Published: 2018, PROCEEDINGS OF THE 2018 IEEE 8TH INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATION & PROPERTIES (NAP-2018), DOI:

We report unusual effect of channeled magnetic flux motion in YBa2Cu3O7-delta/PrBa2Cu3O7-delta superlattices grown by pulsed laser deposition. Magneto-optical imaging reveals that flux moves along a set of parallel and perpendicular lines, while optical microscopy does not show any features on the surface that may be linked to this effect. In contrast, scanning electron microscopy registers sub-micron fractures in the superlattices corresponding to these flux lines, but the magnetic flux channels are much wider than the width of these fractures. To further clarify the origin of flux channels, electrical transport measurements on the superlattices have been performed. Their current-voltage characteristics reveal the presence of distinctive branches related to the flux motion along the selective channels, following which magnetic flux crosses sample in a shortest and least resistive way. The application of very large current overheated the superlattice along these channels, evaporating superconducting material and exposing, wider than in the superconductor, fractures in the substrate. It is concluded that motion of flux in the channels is controlled not only by the presence of nano-fractures in YBa2Cu3O7-delta/PrBa2Cu3O7_delta, but also by stress developed in the superconducting material due to the fracturing of the substrate.

1320. Origin and chemical composition of the amorphous material from the intergrain pores of self-assembled cubic ZnS:Mn nanocrystals

Authors: Stefan, M; Vlaicu, ID; Nistor, LC; Ghica, D; Nistor, SV

Published: DEC 31 2017, APPLIED SURFACE SCIENCE, 426, 350, DOI: 10.1016/j.apsusc.2017.07.172

We have shown in previous investigations that the low temperature collective magnetism observed in mesoporous cubic ZnS:Mn nanocrystalline powders prepared by colloidal synthesis, with nominal doping concentrations above 0.2 at.%, is due to the formation of Mn2+ clusters with distributed antifer romagnetic coupling localized in an amorphous phase found between the cubic ZnS:Mn nanocrystals. Here we investigate the composition, origin and thermal annealing behavior of this amorphous phase in such a mesoporous ZnS:Mn sample doped with 5 at.% Mn nominal concentration. Correlated analytical transmission electron microscopy, multifrequency electron paramagnetic resonance and Fourier transform infrared spectroscopy data show that the amorphous nanomaterial consists of unreacted precursor hydrated zinc and manganese acetates trapped inside the pores and on the surface of the cubic ZnS nanocrystals. The decomposition of the acetates under isochronal annealing up to 270 degrees C, where the mesoporous structure is still preserved, lead to changes in the nature and strength of the magnetic inter actions between the aggregated Mn2+ ions. These results strongly suggest the possibility to modulate the magnetic properties of such transition metal ions doped II-VI mesoporous structures by varying the synthesis conditions and/or by post-synthesis thermochemical treatments. (C) 2017 Elsevier B.V. All rights reserved.