National Institute Of Materials Physics - Romania

The analysis of the sequence of electron paramagnetic resonance (EPR) spectra of trace amounts of substitutional probing paramagnetic ions incorporated in (nano)crystalline samples submitted to isothermal and isochronal pulse annealing treatments can offer a wealth of information on the thermally induced compositional and structural changes of the host material. The potential of this new thermal analysis method is illustrated here with results of such investigations on the thermal decomposition of crystalline zinc hydroxide (Zn(OH)(2)) and anhydrous zinc carbonate basic (Zn-5(CO3)(2)(OH)(6)) precursors containing trace amounts of substitutional Mn2+ probing ions into nanostructured zinc oxide-ZnO. The quantitative analysis of the sequence of isochronal pulse annealing EPR spectra could provide, besides the thermal decomposition curves of the two precursors, additional information about the structure of the resulting nanostructured ZnO, some of it hard to get by standard structural diffraction techniques. The analysis of both isochronal and isothermal pulse annealing EPR data was further used to investigate the crystallization mechanism of the initially formed nanostructured disordered ZnO and to quantitatively describe the further growth of the resulting ZnO nanocrystals with the increasing annealing temperature and duration.

YBa2Cu3O7-delta films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Delta(omega), of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T-c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Delta(omega) vs. buffer thickness and T-c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00l) texture) and other defects generated by agglomeration supply a low fraction of (00l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.

We report about the contribution of thermally grown SiOx overlayer on the SiOx/Si interface (with oxidation states Sin+, where n = 1, 2, 3, 4) to the optical losses of a resonant spectroscopic cavity. The experiments on Si oxide thin films were performed in evanescent wave for Si samples in contact with a total internal reflection surface of a BK7 prism. The evanescent field can be exploited to investigate properties and processes such as the absorption of thin film or solid/air interface reactions. The results show that the oxide overlayer thickness grows with the thermal exposure time and is limited after more than 7 h of treatment. Transmission electron microscopy has been used for the native oxide thickness measurement and angle-resolved X-ray photoelectron spectroscopy used to determine the thermal oxide thickness. A change of absorption coefficient Delta alpha in the range 100-200 cm(-1) is obtained by evanescent-wave cavity ring-down spectroscopy (EW-CRDS) for thermal silicon oxide overlayer, in agreement with the general trend from literature. The evaluation from the EW-CRDS experiments presents the used setup as a competitive method for measuring the absorption properties of thin overlayer.

Micro-supercapacitors have attracted considerable research attention for on-chip energy storage due to their unique properties and potential applications in various smart electronic devices. Although significant advances have been reported on their power performances, they still cannot compete with micro-batteries in terms of energy densities for mobile, portable and self-powered applications. Herein, we demonstrate the fabrication of vertically aligned carbon nanowalls (CNW) decorated with porous ruthenium oxide as a high-performance electrode for all-solid-state micro-supercapacitors. The decorated CNW electrode, essentially consisting of thin carbon sheets assembled from graphene domains, delivers specific capacitance in excess of 1000 mF cm(-2) (which is three orders of magnitude higher than state-of-the-art micro-supercapacitors) and energy density comparable to that of lithium-ion micro-batteries, but with superior power and cycling stability. Our findings demonstrate a route towards the integration of microfabricated supercapacitors combining fast charge/discharge rates with high energy densities. (C) 2014 Elsevier Ltd. All rights reserved.

Cobalt chromites (CoCr2O4) powders have been synthesized via thermal decomposition of oxalate precursor compounds (NH4)(4)[CoCr2(C2O4)(4)(OH)(4)]center dot 7H(2)O (I) and (Na-4)(12)[CoCr2(C2O4)(8)(OH)(4)]center dot(NH4)(2)C2O4 center dot 12H(2)O (II). The oxalate precursors have been characterized by infrared (IR) and ultraviolet visible spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. The structure, morphology and magnetic properties of CoCr2O4 powders have been investigated by XRD, SEM, IR and Raman spectroscopy (RS), UV-vis and magnetic measurements. XRD patterns confirmed the formation of spinel-type cobalt chromite, with average crystallite sizes calculated from XRD patterns of 38 nm and 58 nm, for spinel chromites from precursors I and II, respectively. SEM micrographs revealed particle sizes between 30 and 130 nm, with a low degree of aggregation of primary nanocrystallites. Both CoCr2O4 powders presented ferrimagnetic ordering below the Currie temperature (T-c) and a phase transition at T-s similar to 20 K attributed to the onset of long-range spiral magnetic order. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

It is shown experimentally that, in contrast to the stable configuration of (interstitial carbon)-(interstitial oxygen) complexes (CiOi), the corresponding metastable configuration (CiOi*) cannot be found in n-Si based structures by the method of capacitance spectroscopy. The rates of transformation CiOi* -> CiOi are practically the same for both n- and p-Si with a concentration of charge carriers of no higher than 10(13) cm(-3). It is established that the probabilities of the simultaneous formation of stable and metastable configurations of the complex under study in the case of the addition of an atom of interstitial carbon to an atom of interstitial oxygen is close to 50%. This is caused by the orientation dependence of the interaction potential of an atom of interstitial oxygen with an interstitial carbon atom, which diffuses to this oxygen atom.

By implanting Bi in Si, a strong strain field due to the bigger atomic mass and size of stopped Bi ions than Si lattice ones is produced, together with irradiation defects. The controlled doping of Si with Bi leads to modern applications such as quantum information processing. Here we show that the parameters of trapping centres are modified under the strain field. In the literature there are no reports on this subject. We irradiated Si wafers with Bi6+ ions of 28MeV kinetic energy, 3 degrees off [100] axis orientation. The depth distributions of stopped ions and of primary defects were simulated. The traps produced by irradiation were investigated using the thermally stimulated currents method without bias. We recorded and modelled the discharge current curves. The strain field was modelled as a permanent and temperature-independent electric field. The traps of V-2, VO/CiCs, and CiOi and other two not assigned were evidenced. We have found that all trapping levels are broadened, and all capture cross-sections are temperature dependent which we attribute to the strong strain field produced by Bi. These results are important and must be taken into account in designing and manufacturing microelectronic devices incorporating strain, including the topical spin qubit ones. Copyright (C) EPLA, 2014

The electronic structure and magnetic properties of Zr2CoAl bulk material were investigated within the Density Functional Theory (DFT) framework. The material, basically a complete spin polarized half-metallic ferromagnet in the ground state, crystallizes in the ordered full-Heusler inverse structure (Hg2CuTi-type structure). The energy band gap, localized in minority spin channel is 0.48 eV at equilibrium lattice parameter, 6.54 angstrom. The total magnetic moment calculated, equal to 2 mu(B)/f.u., is an integral, in agreement with the Slater-Pauling curve for full-Heusler alloys. (C) 2014 Elsevier B.V. All rights reserved.

A case where the electrode polarization occurs in dielectric spectroscopy measurements carried out on a liquid crystal cell in which there are paired ions with different transport properties in the presence of generation-recombination processes is discussed. The processes of adsorption/desorption take place at blocking electrode surfaces with different features. The theoretical approach consists in introducing new independent variables with simple significance and in reformulating the fundamental equation for the concentrations of charge carriers and Poisson equation for the electric field. The main purpose of the present mathematical method is to obtain a more convenient analytical expression of admittance and complex permittivity in a form that is easy to use for the interpretation of the experimental data. The expression of the admittance allows suggesting an equivalent electrical circuit according to the processes occurring in the sample volume and at the surface electrodes. The analytical form of the admittance highlights a distinctive term that is proportional to one adimensional parameter which estimates the relative effects of the bulk process in comparison with the interfaces process. Several cases are analyzed and for each an analytical expression is found. In some cases the formulas are available in a simple form.

The aim of this study was to obtain membranes with antimicrobial activity presenting a complex sandwich-type structure. The outer layers are comprised of poly(methyl methacrylate) membranes, whereas the inner active layer consists of a modified commercial membrane to achieve antimicrobial properties. This activity arises due to the presence of silver nanoparticles in a material with a hybrid composition deposited on a commercial membrane. This hybrid material consists of polymer colloids and multiwall carbon nanotubes used for both the stabilization of the active layer by the interconnections of the polymer particles and as active component. The filtration tests revealed a good stability of the materials and an increased hydrophilicity of the hybrid membranes. The antimicrobial properties have been evaluated using Staphylococcus aureus and Escherichia coli, and have been correlated with the content and migration rate of silver ions.