National Institute Of Materials Physics - Romania

We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG/Cr4+:YAG composite medium monolithic laser with four-beam output. The energy of a laser pulse was higher than 3 mJ with duration of 0.9 ns. The proposed system has the ability to choose independently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific to aeronautics. (C) 2016 Chinese Laser Press

The crystallization process of Yb3+/Er3+ codoped LiYF4 nanoparticles obtained by sol-gel method was studied using differential scanning calorimetry and X-ray diffraction. Thermal data obtained from differential scanning calorimetry measurements under non-isothermal conditions at different heating rates were examined using both model-free and model fitting approaches. It was shown that LiYF4 phase crystallization occurs at around 383 degrees C as a result of the thermal decomposition of trifluoracetates and is shifted to higher temperatures as the heating rate increases. Both Friedman and Ozawa-Flynn-Wall analyses have indicated that the activation energy and pre-exponential factor decrease slightly as the crystallization proceeds. According to the model-fitting approach (by using extended Prout-Tompkins nth-order, ath autocatalysis reaction), LiYF4 nanocrystalline phase is the result of an autocatalytic process where a second metastable phase YF3 acts as a catalyst that accelerates the crystallization process of the LiYF4 phase. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Self-passivating tungsten based alloys for the first wall armour of future fusion reactors are expected to provide a major safety advantage compared to pure tungsten in case of a loss of coolant accident with simultaneous air ingress, due to the formation of a stable protective scale at high temperatures in presence of oxygen which prevents the formation of volatile and radioactive WO3. Bulk W-15Cr, W-10Cr-2Ti and W-12Cr-0.5Y alloys were manufactured by mechanical alloying followed by can encapsulation and HIP. This route resulted in fully dense materials with nano-structured grains. The ability of Ti and especially of Y to inhibit grain growth was observed in the W-10Cr-2Ti and W-12Cr-0.5Y alloys. Besides, Y formed Y-rich oxide nano-precipitates at the grain boundaries, and is thus expected to improve the mechanical behaviour of the Y-containing alloy. Isothermal oxidation tests at 800 degrees C (1073 K) and oxidation tests under accident-like conditions revealed that the W-12Cr-0.5Y alloy exhibits the best oxidation behaviour of all alloys, especially in the accident-like scenario. Preliminary HHF tests performed at GLADIS indicated that the W-10Cr-2Ti alloy is able to withstand power densities of 2 MW/m(2) without significant damage of the bulk structure. Thermo-shock tests at JUDITH-1 to simulate mitigated disruptions resulted in chipping of part of the surface of the as-HIPed W-10Cr-2Ti alloy. An additional thermal treatment at 1600 degrees C (1873 K) improves the thermo-shock resistance of the W-10Cr-2Ti alloy since only crack formation is observed. (C) 2016 The Authors. Published by Elsevier Ltd.

Be/W and W/Be bilayers, of interest in regard to the specific behavior of plasma facing components (PFCs) were deposited on Si substrates by thermionic vacuum arc, with Fe, Fe-Cr and Fe-Cr-Al interlayers. The interlayers, with compositions approaching the one of the reduced activation steels used in supporting PFCs, were subsequently annealed in hydrogen atmosphere. The multilayers were characterized with respect to morphologic, structural, diffusional and atomic intermixing aspects via XRD, XRR, X-ray photoemission spectroscopy and Mossbauer spectroscopy. All as-prepared samples present partially amorphous structures. A main alpha-Fe phase is observed, as well as (superparamagnetic) secondary Fe oxides, metallic Fe with Si, Cr, W and Be neighbors, Be-rich Fe-Be and Fe-Si phases. High amounts of tungsten and tungsten oxides were also evidenced in the Fe layer. The strong atomic intermixing of W and Be layers was indirectly supported by the unusual densities of Wand Be layers and Fe-57 Mossbauer spectroscopy results. (C) 2016 Elsevier B.V. All rights reserved.

Optical properties are reported for composites based on single-walled carbon nanotubes (SWNT5) and copolymer poly(3,4-ethylenedioxythiophene-co-pyrene) (PEDOT-Py) prepared by chemical polymerization of two monomers in the presence of carbon nanotubes. A charge transfer between SWNT5 and the PEDOT-Py copolymer was demonstrated by Raman scattering. The increase in the relative intensity of the Raman lines peaked at 440-577 cm(-1), which were assigned to the ethylenedioxy ring vibrational modes, indicated a significant hindrance steric in the case of the composites based on the PEDOT-Py copolymer and metallic SWNTs. The increase in the absorbance of IR band peaked at 984 cm(-1) occurred simultaneously with the disappearance of the IR band at 1639 cm(-1). This finding was a consequence of the formation of new covalent bonds between SWNTs and the thiophene and benzene rings of the repeating units of the PEDOT-Py copolymer. The photoluminescence (PL) quenching process of the PEDOT-Py copolymer was induced by semiconducting SWNTs. The PL quenching of PEDOT-Py copolymer in the presence of SWNT5 was. demonstrated based on the energy level diagrams of the two constituents of the PEDOT-Py/SWNTs composite material. (C) 2016 Elsevier B.V. All rights reserved.

The specific morphology and magnetic properties of magnetite-based glass-ceramics obtained by crystallization of Fe-containing borosilicate glassmelts in the presence of P2O5 as nucleating agent are investigated. We found that the distribution of the tiny nanoparticles of magnetite determines the low temperature response to magnetic field. The observed effects are discussed with respect to the following factors: (1) the existence of a multimodal size distribution of the tiny grains as revealed by Mossbauer spectroscopy, magnetometry, and high-resolution electron microscopy; (2) the existence of a disordered layer at the grain surface which is driven by field in a magnetically ordered state; and (3) the interplay between the relaxation mechanisms in different temperature ranges.

The aim of this study consisted to develop novel synthetic magnetite nanoparticles (nFe(3)O(4)) with preferential reactivity to trace elements (TE) for possible environmental applications as adsorbents. The synthetic magnetite materials obtained through the co-precipitation of both Fe3+ and Fe2+ ions (Fe2+ / Fe3+ = 0.5) were characterized by a set of complementary techniques: X-ray diffraction, transmission and scanning electron microscopy, Fourier transform infrared and Raman spectroscopy, and BET adsorption method. The resulting nFe(3)O(4) displayed a wide specific surface area (100 m(2) g(-1)) with particles reaching a size of about 10 nm, smaller than those of the well-crystallized commercial ones (cFe(3)O(4)) estimated at 80 nm while showing a BET surface area of 6.8 m(2) The adsorption properties of the synthetic nFe(3)O(4) magnetite nanoparticles were characterized and compared to the commercial analogous with the adsorption of both As and Cu. The equilibrium adsorption isotherms were properly fitted with Langmuir and Freundlich equation models and suggested that the developed iron oxides nanoparticles display a certain potential for removal and/or immobilization of TE from contaminated waters and/or soils, with an increase of 69.5% of the adsorbed amount compared to that of the commercial ones. (C) 2016 Elsevier B.V. All rights reserved.

Single ZnO nanowires prepared by wet and dry methods are used as channels in high performance back-gated field effect transistors working in low power operation mode, with on-off ratios up to 10(5) and mobilities up to 167 cm(2) V-1 s(-1). The nanowires' properties, generated by the growth techniques, influence the parameters of the transistors, therefore a throughout comparison is made.

We develop a manifest non-Hermitian approach of spectral and transport properties of two-dimensional mesoscopic systems in a strong magnetic field. The finite system to which several terminals are attached constitutes an open system that can be described by an effective Hamiltonian. The lifetime of the quantum states expressed by the energy imaginary part depends specifically on the lead-system coupling and makes the difference among three regimes: resonant, integer quantum Hall effect, and superradiant. The discussion is carried on in terms of edge state lifetime in different gaps, channel formation, role of hybridization, and transmission coefficients quantization. A toy model helps in understanding non-Hermitian aspects in open systems.

Thermal behavior of repa-germanium (C6H10Ge2O7, Ge-132) during heating in air or in argon is investigated using DSC-TGA, XRD, SEM,TEM, and FT-IR measurements. Nine domains of thermal transformations were identified from room temperature to 1200 degrees C, in air or argon. The first reversible transformation is below 220 degrees C and it was assigned to an isomerization process, based on DSC, XRD and IR measurements. The next five transformation domains (220-910 degrees C) are decompositions accompanied by weight loss. The main product of thermal decomposition is Ge. The next transformation domain (910-970 degrees C) corresponds to melting of Ge, both in argon and air. In the air, this step is followed by oxidation of Ge (970-1100 degrees C) and, finally, by melting of GeO2. Amorphous phases formed between 220 and 720 degrees C. Observed processes are discussed based on crystal chemistry and bonds dynamics considerations. (C) 2016 Elsevier B.V. All rights reserved.