National Institute Of Materials Physics - Romania

Atomic Structures and Defects in Advanced Materials Laboratory

Publications

Year:

780 articles found

1. Low temperature CO sensing under infield conditions with in doped Pd/SnO2

Authors: Stanoiu, A; Ghica, C; Somacescu, S; Kuncser, AC; Vlaicu, AM; Mercioniu, IF; Florea, OG; Simion, CE

Published: APR 1 2020, DOI: 10.1016/j.snb.2020.127717

Abstract: A one-step method assisted by hydrothermal treatment was approached to obtain nanocrystalline 1 and 10 mol. % In doped 2 mol.% Pd-SnO2 powders using a non-ionic surfactant Brij52 and Polyethylene glycol 6000 (PEG) as templates. Depending on In content, the samples were labeled as Pd1InSn and Pd10InSn. The obtained materials consist of nanosized crystallites packed into micrometric grains with a high porosity, as revealed by the morphological and structural investigations (SEM, TEM). A dependence of the grain size with respect to the In content has been revealed i.e. the sample Pd1InSn was showing an average grain size of around 10 nm, whilst for the sample Pd10InSn the average grain size was found to be around 5 nm. The XPS investigations highlighted the differences occurred in the surface chemistry in terms of surface hydroxylation as well as the chemical states of Pd. The sensing properties towards different CO concentrations have been examined under infield background conditions, at low operating temperature of 50 degrees C. The sensing mechanism model for CO was discussed in detail according to the possible interplay between oxygen and water related species based on the experimentally results acquired through simultaneous electrical resistance and work function measurements.

2. Unexpected magneto-functionalities of amorphous Fe-Gd thin films crossing the magnetization compensation point

Authors: Stanciu, AE; Schinteie, G; Kuncser, A; Iacob, N; Trupina, L; Ionita, I; Crisan, O; Kuncser, V

Published: MAR 15 2020, DOI: 10.1016/j.jmmm.2019.166173

Abstract: A complex investigation of the morpho-structural, magnetic, magneto-optical and magneto-transport properties of amorphous Fe-Gd thin films crossing the magnetization compensation point is reported and the unexpected observed magneto-functionalities are discussed. A tendency of magnetic domain formation with increasing the Fe content over the compensation concentration is observed. The switch from a reversed Magneto-optical Kerr Effect loop to a direct loop when increasing the Fe content over the compensation point is explained via the specific contribution to the rotation of the polarization vector from each magnetic sublattice, belonging to Fe and Gd, respectively. Local atomic configurations and magnetic interactions ascertained the amorphous character and revealed an out-ofplane orientation of the magnetic moment of Fe above the compensation point. The thermomagnetic curves prove a concentration dependent behavior, explained by weakly coupled magnetization relaxation processes of the two magnetic sub-lattices. On the other hand, the magnetic hysteresis loops gave evidence of two exchange coupled magnetic phases with different coercive fields. According to structural and Fe-57 Mossbauer Spectroscopy results, the two phases correspond to definite nanosized volumes of two different average concentrations (one of them closer to the compensation point) which are randomly distributed in the film. The unexpected single step-like behavior of the magneto-resistivity curves was explained by dissimilar switching of the spins in these two magnetic phases distributed in nano-sized volumes.

3. Aminopropyl-silica functionalized with halogen-reactive compounds for antimicrobial applications

Authors: Zarafu, I; Al Taweel, AAJ; Limban, C; Popa, M; Marutescu, L; Chifiriuc, MC; Pircalabioru, GG; Culita, D; Ghica, C; Ionita, P

Published: FEB 1 2020, DOI: 10.1016/j.matchemphys.2019.122353

Abstract: Aminopropyl-silica nanoparticles S0 were obtained and further functionalized with eight halogen-reactive organic compounds 1-8, leading to the S1-S8 hybrid organic-inorganic materials, with spherical morphology and having a 50-200 nm size, as showed TEM analysis. These were further characterized by IR and DLS. Biological assays were performed using five microbial strains, belonging to species frequently encountered in the aetiology of human infections (Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia toll and Candida albicans). The obtained materials exhibited promising antimicrobial properties, being active against planktonic, but particularly on biofilm-embedded cells. Among the tested hybrid nanomaterials, S6 seemed to exhibit the most promising antimicrobial profile.

4. Investigations of BaCl2:Eu2+ nanophosphor using electron paramagnetic resonance, structural analysis and thermoluminescence

Authors: Secu, CE; Rostas, AM

Published: JAN 30 2020, DOI: 10.1016/j.jallcom.2019.152400

Abstract: Structural analysis of the Eu2+-doped BaCl2 nanocrystals and the doping process was monitored and characterized via electron paramagnetic resonance spectroscopy. Structural analysis has shown a slight distortion of the cell which is reflected in the low value of microstrain and the Eu2+-doping effect is limited to the first order chlorine ions neighbors of Ba2+. Electron paramagnetic resonance measurements have indicated the presence of the Eu2+-dopant ions in the BaCl2 host matrix with a solubility limit of about 2%. From the spectra simulation, the isotropic g-value g(iso) = 1.9951(7), the isotropic hyperfine coupling constant A(iso)= 42.4 MHz and the high-order zero-field splitting parameters from the crystal field B-2(0) = 21 MHz and B-2(2)= -493 MHz were obtained. During X-ray irradiation, defects are produced and stabilized by the Eu2+ dopant ions. The single dominant thermoluminescence peak at 132 degrees C (activation energy E = 1.1 eV) was assigned to the recombination of the F(Cl)-center with Eu2+ related hole centers. (C) 2019 Elsevier B.V. All rights reserved.

5. HRTEM analysis of the high-temperature phases of the newly developed high-temperature Ni-base superalloy VDM 780 Premium

Authors: Ghica, C; Solis, C; Munke, J; Stark, A; Gehrmann, B; Bergner, M; Rosler, J; Gilles, R

Published: JAN 25 2020, DOI: 10.1016/j.jallcom.2019.152157

Abstract: VDM 780 Premium is a recently developed Ni-based superalloy designed for working at high service temperatures (above 650 degrees C) while keeping the good workability of alloy 718. VDM 780 Premium is based on the austenitic matrix (gamma phase) strengthened by intermetallic Ni3Al-like precipitates (gamma' phase, fcc L1(2) structure). Other co-precipitates may be formed in function of the applied heat treatment, such as Ni3Nb-based (delta phase, orthorhombic DOa structure) or Ni3Ti-based (eta phase, hexagonal DO24 structure) precipitates. The amount as well as the size and morphology of the different precipitates depend on the heat treatments performed on the alloy, playing an important role in improving the creep properties or the behavior during forging and recrystallization. This work contains a complex study using various techniques of analytical electron microscopy and synchrotron diffraction intended to clarify the structure of the high-temperature phase formed in the newly developed VDM 780 Premium alloy. The atomic structure of the high-temperature plate-like precipitates formed in VDM 780 Premium after two different thermal treatments has been investigated in relation with the surrounding matrix lattice, proving the stacked delta/eta structure of the precipitates. (C) 2019 Published by Elsevier B.V.

6. Modular High-Intensity Monochromatic In Situ Illumination Set-Up for Investigating ESR Photoactive Centers in Semiconductors

Authors: Nistor, SV; Joita, AC

Published: , DOI: 10.1007/s00723-019-01183-z

Abstract: A versatile, modular in situ high-intensity monochromatic illumination set-up installed on a standard Q-band ESR spectrometer equipped with a cryostat and probe head for measurements at cryogenic temperatures, which can be easily assembled from commercially available optical components is presented. Using as monochromatic light sources pig-tailed laser diodes (LDs) or fiber-coupled light-emitting diodes (LEDs), a high efficiency of the light transfer (more than 95%) through an optical guide inserted in the sample holder is achieved in the sample area of the microwave cavity. With various LEDs and LDs, one can perform ESR in situ illumination experiments from UV to far-IR, in both cw and pulse mode. Its operation is illustrated with an experiment revealing the presence of certain ESR silent defects in oxygen-doped floating-zone ultrapure Si samples irradiated at room temperature with high-energy-high-fluence electron beams and pulse annealed up to 300 degrees C. New information is obtained by comparing the ESR spectra recorded at T = 120 K, without and with 1.06 mu m across-the-gap in situ illumination.

7. Bulks of Al-B-C obtained by reactively spark plasma sintering and impact properties by Split Hopkinson Pressure Bar

Authors: Vasylkiv, O; Borodianska, H; Demirskyi, D; Li, P; Suzuki, TS; Grigoroscuta, MA; Pasuk, I; Kuncser, A; Badica, P

Published: DEC 20 2019, DOI: 10.1038/s41598-019-55888-z

Abstract: Mixtures of B4C, alpha-AlB12 and B powders were reactively spark plasma sintered at 1800 degrees C. Crystalline and amorphous boron powders were used. Samples were tested for their impact behavior by the Split Hopkinson Pressure Bar method. When the ratio R = B4C/alpha-AlB12 >= 1.3 for a constant B-amount, the major phase in the samples was the orthorhombic AlB24C4, and when R < 1 the amount of AlB24C4 significantly decreased. Predictions that AlB24C4 has the best mechanical impact properties since it is the most compact and close to the ideal cubic packing among the Al-B-C phases containing B-12-type icosahedra were partially confirmed. Namely, the highest values of the Vickers hardness (32.4 GPa), dynamic strength (1323 MPa), strain and toughness were determined for the samples with R = 1.3, i.e., for the samples with a high amount of AlB24C4. However, the existence of a maximum, detectable especially in the dynamic strength vs. R, indicated the additional influence of the phases and the composite's microstructure in the samples. The type of boron does not influence the dependencies of the indicated mechanical parameters with R, but the curves are shifted to slightly higher values for the samples in which amorphous boron was used.

8. Superconducting MgB2 textured bulk obtained by ex situ spark plasma sintering from green compacts processed by slip casting under a 12T magnetic field

Authors: Grigoroscuta, MA; Sandu, V; Kuncser, A; Pasuk, I; Aldica, G; Suzuki, TS; Vasylkiv, O; Badica, P

Published: DEC 2019, DOI: 10.1088/1361-6668/ab4620

Abstract: MgB2 green bodies were prepared by magnetic field slip casting in ethyl alcohol with added polyethyleneimine dispersing agent under a high magnetic field, mu H-0(0) = 12 T. Samples were further processed by spark plasma sintering (SPS) and characterized for superconducting properties. Slip casting provides texturing of MgB2 (the degree of c-axis orientation is approximately 3.5%), which is further increased significantly (to about 21%) in the SPSed sample. The critical current density (J(c)) displays anisotropy relative to the orientation of the measuring magnetic field. Specific features of J(c)(H, T) and of the pinning force extracted from magnetic measurements with the field parallel and perpendicular to H-0 are discussed.

9. Antireflective coatings with high damage threshold prepared by laser ablation

Authors: Filipescu, M; Palla-Papavlu, A; Bercea, A; Rusen, L; Cernaianu, MO; Ion, V; Calugar, A; Nistor, LC; Dinescu, M

Published: DEC 2019, DOI: 10.1007/s00339-019-3110-y

Abstract: Latest developments in the field of high power ultra-short pulse lasers have led to intensive studies dedicated to the fabrication possibility of new antireflective coatings which exhibit high damage threshold. Therefore, this study is focused on the deposition and characterization of metal oxide heterostructures followed by laser-induced damage threshold tests which evidence their application in high power laser optics. Al2O3, SiO2, and HfO2 layers are combined to obtain different heterostructures, i.e. HfO2/Al2O3/HfO2/Al2O3/HfO2 and HfO2/SiO2/HfO2/SiO2/HfO2. The metal oxide heterostructures are deposited in a controllable oxygen atmosphere, either at room temperature or high temperatures (600 degrees C) by pulsed laser deposition (PLD). The morphological, structural and optical properties of the as-deposited heterostructures are first investigated. Atomic force microscopy and spectroscopic ellipsometry investigations reveal a lower roughness of the heterostructures based on HfO2/Al2O3 layers grown at 600 degrees C as compared to those grown at room temperature. Furthermore, following the laser-induced damage threshold (LIDT) tests carried out with a Ti-Sapphire laser, higher LIDT values are obtained for the HfO2/Al2O3-based heterostructures than for the HfO2/SiO2-based heterostructures. The ability to control the morphological and structural properties of the antireflective coatings by modifying the deposition parameters of the metal oxide heterostructures demonstrates that PLD is a suitable technique for the manufacturing of antireflective coatings for high power ultra-short laser systems.

10. Core-shell nanowire arrays based on ZnO and CuxO for water stable photocatalysts

Authors: Florica, C; Costas, A; Preda, N; Beregoi, M; Kuncser, A; Apostol, N; Popa, C; Socol, G; Diculescu, V; Enculescu, I

Published: NOV 21 2019, DOI: 10.1038/s41598-019-53873-0

Abstract: Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. ZnO nanowires with a wurtzite crystalline structure and a band gap of approximately 3.3 eV are obtained by thermal oxidation in air. These are covered with an amorphous CuxO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-CuxO core-shell nanowires emphasizes the charge transfer phenomena at the junction and at the interface between the nanowires and water based solutions. The methylene blue degradation mechanism is discussed taking into consideration the dissolution of ZnO in water based solutions for ZnO nanowires and ZnO-CuxO core-shell nanowires with different shell thicknesses. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.