National Institute Of Materials Physics - Romania

Publications

5714 articles found

1461. Electrochemically shape-controlled transformation of magnetron sputtered platinum films into platinum nanostructures enclosed by high-index facets

Authors: Khalakhan, I; Lavkova, J; Matolinova, I; Vorokhta, M; Potin, V; Kus, P; Vaclavu, M; Maraloiu, VA; Kuncser, AC; Matolin, V

Published: JAN 15 2017, SURFACE & COATINGS TECHNOLOGY, 309, 11, DOI: 10.1016/j.surfcoat.2016.11.017

A new method based on transformation of magnetron sputtered platinum thin films into platinum nanostructures enclosed by high-index facets, using electrochemical potential cycling in a twin working electrode system is reported. The controllable formation of various Pt nanostructures, described in this paper, indicates that this method can be used to control a selective growth of high purity Pt nanostructures with specific shapes (facets or edges). The method opens up new possibilities for electrochemical preparation of nanostructured Pt catalysts at high yield. (C) 2016 Elsevier B.V. All rights reserved.

1462. In-gap corner states in core-shell polygonal quantum rings

Authors: Sitek, A; Tolea, M; Nita, M; Serra, L; Gudmundsson, V; Manolescu, A

Published: JAN 10 2017, SCIENTIFIC REPORTS, 7, DOI: 10.1038/srep40197

We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e., corner-localized states of electron pairs or clusters shifted to energies that were forbidden for non-interacting electrons, but below the energies of corner-side-localized states. We specify conditions allowing optical excitation to those states.

1463. Self-assembled (Ni/Cu, Ti)-YSZ with potential applications for IT-SOFCs: Catalytic and electrochemical assessment

Authors: Somacescu, S; Navarrete, L; Florea, M; Calderon-Moreno, JM; Serra, JM

Published: JAN 5 2017, , DOI: 10.1016/j.jallcom.2016.08.193

1464. Sol-gel preparation and structural investigations of silico-phosphate glasses doped with Fe ions

Authors: Sava, BAC; Elisa, M; Boroica, L; Kuncser, V; Valeanu, M; Vasiliu, IC; Feraru, I; Iordanescu, R

Published: JAN 2017, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 81, 302, DOI: 10.1007/s10971-016-4192-z

Different aspects related to the sol-gel preparation and structural investigation of silico-phosphate glasses (SiO2-P2O5 system) doped with Fe ions are reported. During the preparation process, tetraethoxysilane was used as a precursor for SiO2 and phosphoric acid (H3PO4-HP) for P2O5. Ferric chloride was used as precursor for Fe ions, water as reagent for hydrolysis reaction and ethylic alcohol as solvent. The pH of the sols was modified by adding hydrochloric acid and ammonia. It was observed that a slight increase of the solution temperature (up to 40 degrees C) allows a drastic decrease of the gelation time (from days to hours). The structure of the obtained powders dried in air at room temperature and at 100 degrees C for 10 h and subsequently thermally treated at different temperatures was investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy. Vibration modes specific to Si-O-Et, Si-OH, PO-P, P-O-Si, hydrogen bonds and H2O, as well as combined modes have been observed. The local structure and electron configurations of the doping Fe ions have been investigated by Fe-57 Mossbauer spectroscopy.

1465. Electrical properties of NiFe2O4 epitaxial ultra-thin films

Authors: Boni, GA; Hrib, L; Porter, SB; Atcheson, G; Pintilie, I; Rode, K; Pintilie, L

Published: JAN 2017, JOURNAL OF MATERIALS SCIENCE, 52, 803, DOI: 10.1007/s10853-016-0376-8

Epitaxial thin films of NiFe2O4 are fabricated by pulsed laser deposition on SrTiO3 substrate. Symmetrical capacitor-like structures are formed using SrRuO3 as bottom and top electrodes. Electrical characterizations, including current-voltage, capacitance-voltage and capacitance-frequency measurement, reveal a hysteresis-like behaviour for current and capacitance as function of voltage. This could be assigned to a resistive and/or capacitive switching. A "degradation" process takes place after repeated voltage cycling or after heating the sample to 400 K, leading to the stabilization of different resistive states. These features can be related to the changes observed in the capacitance-frequency characteristics, suggesting the presence of a relaxation mechanism at low frequencies, and can be associated with the presence of a deep donor-type level in the band-gap of the NiFe2O4 layer.

1466. Dynamic electrical behavior of halide perovskite based solar cells

Authors: Nemnes, GA; Besleaga, C; Tomulescu, AG; Pintilie, I; Pintilie, L; Torfason, K; Manolescu, A

Published: JAN 2017, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 159, 203, DOI: 10.1016/j.solmat.2016.09.012

A dynamic electrical model is introduced to investigate the hysteretic effects in the J-V characteristics of perovskite based solar cells. By making a simple ansatz for the polarization relaxation, our model is able to reproduce qualitatively and quantitatively detailed features of measured J-V characteristics. Pre-poling effects are discussed, pointing out the differences between initially over- and under-polarized samples. In particular, the presence of the current overshoot observed in the reverse characteristics is correlated with the solar cell pre-conditioning. Furthermore, the dynamic hysteresis is analyzed with respect to changing the bias scan rate, the obtained results being consistent with experimentally reported data: the hysteresis amplitude is maximum at intermediate scan rates, while at very slow and very fast ones it becomes negligible. The effects induced by different relaxation time scales are assessed. The proposed dynamic electrical model offers a comprehensive view of the solar cell operation, being a practical tool for future calibration of tentative microscopic descriptions. (C) 2016 Elsevier B.V. All rights reserved.

1467. Thermal analysis on C6H10Ge2O7-doped MgB2

Authors: Aldica, G; Matei, C; Paun, A; Batalu, D; Ferbinteanu, M; Badica, P

Published: JAN 2017, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 127, 179, DOI: 10.1007/s10973-016-5877-9

Additives to MgB2 can improve the superconducting functional characteristics, such as critical current density (J (c)) and irreversibility field (H (irr)). Recently, we have shown that repagermanium (C6H10Ge2O7) is an effective additive, enhancing both J (c) and H (irr). To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s(-1), in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric-differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB2 and 3 mol% C6H10Ge2O7. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB2 is not observed. Above this temperature, partial decomposition of MgB2 occurs. Crystalline Ge and MgO are detected before formation of Mg2Ge and MgB4, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB2 is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.

1468. Insight on thermal behaviour of new complexes of Ni(II), Cu(II) and Zn(II) with a bismacrocyclic ligand developed as biologically active species

Authors: Badea, M; Bucur, C; Chifiriuc, MC; Bleotu, C; Grecu, MN; Lazar, V; Marinescu, D; Olar, R

Published: JAN 2017, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 127, 497, DOI: 10.1007/s10973-016-5502-y

A multi-component reaction involving metal ion, amines and formaldehyde has been used for a series of decaaza bismacrocyclic complexes M2L(CH3COO)(4)center dot nH(2)O [(1) M: Ni, n = 2.5; (2) M:Cu, n = 1; (3) M:Zn, n = 10; L:1,3-bis(N,N-1,3,6,9,12-pentaazacyclotridecane)-benzene] preparation. Elemental analyses, ESI-MS, IR, UV-Vis-NIR, NMR and EPR spectra, magnetic susceptibility at room temperature, molar conductivities, as well as thermogravimetric analysis, provided data concerning complexes features. The macrocyclic ligand behaves as bischelate, resulting in either a square planar or an octahedral stereochemistry. The in vitro screening of the antimicrobial activity was performed against both reference and clinical isolates multi-drug-resistant strains. The overall antimicrobial potency of complexes was enhanced in comparison with the free ligand, against both planktonic and biofilm-embedded pathogenic strains. Complexes exhibit no cytotoxicity on the HCT 8 tumour cells. Thermogravimetric curves (TG, DTG and DTA) evidenced in air processes as water elimination, acetate into carbonate transformation as well as oxidative degradation of the bismacrocyclic ligand. The powder X-ray diffraction data indicate MO (M: Ni, Cu, Zn) as final product.

1469. Defect-related light absorption, photoluminiscence and photocatalytic activity of SiO2 with tubular morphology

Authors: Anastasescu, C; Zaharescu, M; Angelescu, D; Munteanu, C; Bratan, V; Spataru, T; Negrila, C; Spataru, N; Balint, I

Published: JAN 2017, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 159, 335, DOI: 10.1016/j.solmat.2016.09.032

The research describes the synthesis, optical, photocatalytic, electrochemical and photoelectrocatalytical properties of highly defected, low surface area, tubular SiO2. High surface density of light-absorbing defects is obtained by conducting the synthesis at low temperature (0 degrees C) and by optimizing the ratios between reactants. The calcined tubular SiO2 is characterized by intense and broad absorption band centered at approximate to 320 nm, spanning from deep UV to green. The formation of Si3+ surface defects by calcination is accompanied by a substantial intensification of light absorbing characteristics. The annealing leads also to appearance of intense photoluminescence bands centered at around 433 and 533 nm for excitation wavelengths 320-380 nm. The photocatalytic generation of H-2 and CO2 from water-methanol mixture under solar (AM 1.5) and visible (lambda > 390 nm) irradiation is performed to probe the capability of light-absorbing defects of SiO2 to work as active sites and to gather indirect information on nature of active sites. The electrochemical and photoelectrochemical activity of tubular SiO2 are highlighted by employing [Ru(bpy)(3)]Cl-2 complex as electron transfer witness. According to our results, highly defected nanotubular SiO2 exhibit uncommon optical, light harvesting, electronic and electrochemical properties with great potential for practical applications in numerous fields. (C) 2016 Elsevier B.V. All rights reserved.

1470. Tuning the transmission phase by the dot size

Authors: Tolea, F; Tolea, M

Published: JAN 2017, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 85, 173, DOI: 10.1016/j.physe.2016.08.034

The phase shift of the electron's wave function after a tunneling event (i.e. the transmission phase) was at first measured for its fundamental or applicative relevance for quantum circuitry, but later the phase study self-motivated due to a number of unexpected results. One such result was the reduced increment of the phase on some resonances - with only fractions of pi - in the few-electrons "mesoscopic" regime. In this paper we address such a regime for a rectangular quantum dot and compute the total phase increase on the first four resonances by means of accurate configuration-interaction method and a generalized Friedel sum rule as proposed by Rontani (2006) [17]. Our findings confirm that the electronic correlations reduce the on-resonance phase growth which is also found to decrease quasi-linearly with the dot size, the decrease being more pronounced as the number of electrons on the dot is raised. Sudden jumps (of small amplitude) of the phase are found to accompany ground states spin transitions. (C) 2016 Elsevier B.V. All rights reserved.