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Bucharest, Romania

Secu C.E.,National Institute of Materials Physics Bucharest | Matei E.,National Institute of Materials Physics Bucharest | Secu M.,National Institute of Materials Physics Bucharest | Damian V.,National Institute for Laser
Radiation Measurements | Year: 2014

Sol-gel template method has been used to prepare BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu2+ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu 2+ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu2+ is a very efficient X-ray phosphor the material might be used as X-ray micro-imaging detector. © 2014 Elsevier Ltd. All rights reserved.

Georgescu N.,National Institute for Laser
IEEE Transactions on Plasma Science | Year: 2011

For water-pollution control, a combined method was used: in situ electrical discharges, ozonized oxygen flow, and a catalyst. The electrical discharges are formed in water, which is inside the ozonized oxygen bubbles. FeCl2 was used as a catalyst (0.25 mmol/L). The streamer discharges in the reactor (with a volume of 1.2 L) were produced with high-voltage pulses. The methylene blue degradation was analyzed from the absorption peak height at 665 nm. In the pollutant-destroying process, an energy efficiency of 9 g/kWh or 8 × 10-9mol/J has been obtained. © 2006 IEEE.

Goktas H.,Middle East Technical University | Kirkici H.,Auburn University | Oke G.,Middle East Technical University | Udrea M.,National Institute for Laser
PPPS 2001 - Pulsed Power Plasma Science 2001 | Year: 2015

Generation of intense electron beams by superposing two discharges, namely a low pressure dc glow discharge and a high current pulsed discharge at pressures and voltages very similar to that of the pseudo-spark gap devices, has been reported previously [1, 2]. The small diameter, high peak current and short pulse length are the characteristics of the electron beam generated using this technique. In this technique, no high vacuum facilities are necessary, and many applications such as micro processing, X-rays generation, preionization for high-power lasers are feasible. The electron beam current is in the range of 10-30 A. A full characterization of the electron beam that is utilized in this work has been given in a previous work [3]. In this work it is reported that the most energetic part of the electron beam is about 5-nanosecond pulse duration. The beam is magnetically deflected to the specific point. The pulse repetition rate is up to 100 Hz. Microprocessing as drilling tenths of microns diameter holes in different materials such as copper, titanium, tantalum has been performed. The microstructure of the irradiated materials has been investigated by means of SEM and AFM. Currently, the possibility of processing a matrix of holes is being considered. In this paper, preliminary studies regarding the interaction of intense short electron beams with different metallic targets are presented. The electron generator consists of a fast filamentary discharge in low-pressure gases, and the filling gases such as helium, argon, or nitrogen at approximately 0.1 Torr pressure is utilized. Some of the important characteristics of the device for t drilling and micro-machining are that the target can be easily changed, and the beam can be deflected by means of magnetic field. The device is capable of drilling micron holes in metallic targets. After the initial device characterization, several holes at different experimental conditions were drilled onto the target materials, and the interaction of the beam with these different targets was investigated by means of a scanning electron microscope. © 2002 IEEE.

Marinescu M.,University of Bucharest | Emandi A.,University of Bucharest | Marton G.,Polytechnic University of Bucharest | Cinteza L.O.,University of Bucharest | And 2 more authors.
Nanoscience and Nanotechnology Letters | Year: 2015

A series of pyrazole-5-ones, potential candidates for nonlinear optical response, (NLO) was synthesized. Pyrazole-5-ones (theoretically occuring as azo-hydrazo tautomers in the solid state), labeled as Azi/AzHi, (i = 1-4), were characterized by elemental analysis, 1H-NMR and FTIR spectra. The analysis of molecular structure and frontier molecular orbitals HOMO-LUMO was performed using the GAMESS 2012 software. It was found that all compounds exist only as hydrazo tautomers, with a planar structure, responsible for nonlinear optical properties. The NLO behavior cannot be classified as in classical push-pull or π-conjugated molecules. The molecular polarizability (firstorder hyperpolarizabilities tot, dipole (tot and quadrupole (Q) moments, were calculated. The NLO efficiency was assessed by the relationship between high tot and low HOMO-LUMO energy gap. Conjugation discontinuity in the hydrazo planar tautomers is concretized in the highest value of tot for AzH2, 17.49×10-30 esu and the lowest value for AzH4, 809×10-30 esu. © 2015 American Scientific Publishers All rights reserved.

Jang J.H.,University of Florida | Son S.Y.,University of Florida | Lim W.,University of Florida | Phen M.S.,University of Florida | And 3 more authors.
Thin Solid Films | Year: 2010

The new route to fabricate compositionally graded and highly-relaxed Si1-xGex layers using thermal oxidation at high temperatures is investigated. Ge atoms behavior during thermal oxidation of Si1-xGex layers is strongly dependent on the oxidation temperature. For low temperature oxidation processes Ge is incorporated as GeO2 in the grown oxide layer, while for higher temperatures it accumulates below the grown oxide into a layer with a higher concentration than the initial Si1-xGex. However, Si1-xGex layers oxidized at 1000 °C did not show such an accumulation layer because Ge diffusion efficiently occurred, resulting in the formation of a compositionally graded and relaxed Si1-xGex layer. Such layers could be used as virtual substrates for the strained-Si and relaxed-SiGe applications. © 2009 Elsevier B.V. All rights reserved.

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