National Institute Of Materials Physics - Romania

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5781 articles found

3271. PHASE CHANGE MATERIALS: CHEMICAL BONDING AND STRUCTURAL PROPERTIES

Authors: Velea, A; Popescu, M

Published: SEP-DEC 2009, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 10, 236, DOI:

The phase change materials are the most important materials in the class of chalcogenides (combination of chalcogens (S, Se and Te) with metalloids or metals). The outstanding property of these materials is the switching from a high electrical resistivity state to low electrical resistivity state and back under a moderate voltage. The thin film materials are used in computer memories, CD and DVD devices with performing speed and storage capacity. We have studied several thin solid films made of Ge-Sb-Te in order to assess the switching quality of different compositions. In order to systemize the whole class of chalcogenide phase change materials we have investigated the correlation between different crystallo-chemical parameters and the ionicity of the elements. Binary and ternary compounds are distributed into several distinct groups. The most favorable phase change materials are situated in a specific range of mean ionicity and mean glass formation ability. The results give the possibility to design new compositions with better switching properties.

3272. Current dependent angular magnetoresistance in strongly Pr-doped Y Ba2Cu3O7-delta single crystal

Authors: Sandu, V; Gyawali, P; Katuwal, T; Almasan, CC; Taylor, BJ; Maple, MB

Published: 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5: SUPERCONDUCTIVITY, 150, DOI: 10.1088/1742-6596/150/5/052222

We report a strong dependence of the angular magneto resistance (AMR) on the current density in Y0.47Pr0.53Ba2Cu3O7-delta single crystal above the critical temperature T-c = 13 K for any applied field up to 14 T. We estimated the current dependence from the angular dependence of the top resistance R-top, as measured on the face where the current is applied, and the bottom resistance R-bot as measured on the opposite face. At any temperature, both below and above T-c, R-top decreases as the field becomes parallel to the current and ab-plane with an angle dependence that suggests an important contribution arising from the vortex flow. R-bot evolves from a monotonic to nonmonotonic angle dependence with three minima and two maxima in the angle range 0 - 180 degrees as the temperature increases. For less Pr-doped samples, Y0.58Pr0.42Ba2Cu3O7-delta (T-c = 39 K) and Y0.68Pr0.32Ba2Cu3O7-delta (T-c = 55 K), where the interplane resistivity is much lower, both R-top and R-bot follow the same monotonic angle dependence in all temperature and field range.

3273. Pulsed laser co-deposition of titania with Fe: chemistry, local atomic structure, and light-dependent magnetic properties

Authors: Negrila, C; Logofatu, C; Socol, G; Macovei, D; Teodorescu, CM

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:

TiO2:Fe thin films prepared by pulsed laser deposition exhibit in some case light dependent saturation magnetization, as determined from Kerr magnetometry measurements performed in dark or by illuminating the sample. This phenomenon is Studied in correlation with local atomic Structure investigated by extended X-ray absorption fine structure, composition and chemical state analyzed by X-ray photoelectron spectroscopy and by Xray absorption near-edge structure. It is found that light-controllable magnetism is a property of a mixture of Fe and oxidized Fe clusters embedded in the anatase TiO2 matrix.

3274. FROM NUCLEAR MATTER TO STRANGE QUARK MATTER - SOME CHARACTERISTICS OF THE INTERACTIONS IN ORDINARY MATTER

Authors: Lazanu, I; Chera, M; Iordanescu, R; Nita, C; Lazanu, S

Published: 2009, ROMANIAN REPORTS IN PHYSICS, 61, 221, DOI:

The existence of Strange Quark Matter as a new stable or metastable form of existence of matter has been postulated by various authors quite a few years ago. Because until now a theory to predict the existence and the properties of these strangelets does not exist, it is absolutely necessary to investigate the peculiarities of their interactions with matter versus ordinary nuclear matter interactions. In the present contribution, some peculiarities of the ionization and nuclear energy loss of strangelets with matter are investigated in comparison with ordinary ions, as a useful tool for their search. The rescattering mechanism could produce sub-threshold reactions and thus it is suggested as a possibility to discriminate between ordinary isotopes and very heavy (candidates for) strangelets with the same charge number.

3275. Fabrication and characterization of nano-structured ferromagnetic Ti1-xFexO2 thin films

Authors: Apetrei, R; Negrila, C; Macovei, D; Dascaleanu, V; Teodorescu, CM; Mardare, D; Luca, D

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:

Nanostructured intrinsic and doped titania materials have long been subject to both basic and applied research, in connection with environment and energy related applications. Apart from beneficial effects. such as widening the wavelength range for surface photocatalytic activation, doping TiO2 materials with 3d ferromagnetic cations is a main route to develop ail important class of diluted semiconductors, with potential applications in spintronics. In all the previous investigations the concentration of the ferromagnetic dopant was limited to a few percents. Here, we initiate ail extended investigation of Ti1-xFexO2 within a, wider iron composition range (x = 0 - 0.55) and discuss the magnetic and optical properties of these materials in thin films in relation with their elemental composition, nano-structure and local atomic ordering.

3276. NEW TOPOLOGIES FOR PLANAR MICROWAVE BAND-PASS FILTERS WITH STRONGLY ASYMMETRIC CHARACTERISTICS

Authors: Lojewski, G; Militaru, N; Banciu, MG

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

In this paper the problem of designing simple low-cost planar microwave band-pass filters with strongly asymmetric characteristics, filters that can very efficiently attenuate an adjacent channel, is investigated. For a fourth-order filter, the usual quadruplet structure leads to two transmission zeros, located one on each side of the passband For one of the two adjacent channels, a higher attenuation can be obtained by designing filters with two transmission zeros with prescribed positions in the same stopband (upper or lower). The new topology investigated in this paper offers the possibility of designing such quadruplets with two transmission zeroes situated both on the same side of the passband, in prescribed and controlled positions. Filters with this novel structure can provide very high attenuation not only at a single frequency, but in a larger adjacent frequency band.

3277. Radiation induced defects in Pb2+-doped LiF crystals

Authors: Somma, F; Montereali, RM; Vincenti, MA; Polosan, S; Secu, M

Published: 2009, 2008 INTERNATIONAL CONFERENCE ON LUMINESCENCE AND OPTICAL SPECTROSCOPY OF CONDENSED MATTER, 2, 221, DOI: 10.1016/j.phpro.2009.07.013

The influence of Pb2+ doping on the optical properties of LiF crystals before and after irradiation with X-ray was studied by using optical absorption and photoluminescence measurements. After irradiation it was observed an increase of the absorption due to primary and aggregate electronic defects together with a higher photoluminescence signals associated with the F-2 and F-3(+) colour centres in doped samples compared with the undoped ones.

3278. Microwave Bandpass Filters with Multiple Couplings, Designed Using Electromagnetic Simulations and Linear Circuit Optimization

Authors: Lojewski, G; Militaru, N; Banciu, MG

Published: 2009, ISSCS 2009: INTERNATIONAL SYMPOSIUM ON SIGNALS, CIRCUITS AND SYSTEMS, VOLS 1 AND 2, PROCEEDINGS,, +, DOI:

In this paper a bandpass planar filter, with cross-couplings and with a pair of attenuation poles, is investigated. The equi-ripple in-band response and the location of the poles on the frequency axis can be precisely controlled by using a new technique which combines accurate electromagnetic field simulations and fast linear circuit optimization, allowing the design of bandpass filters with improved performances. To illustrate the procedure, a microstrip bandpass filter was designed, verified by em-field simulation, fabricated and tested. The response of the designed filter is in good agreement with the specification, confirming the possibilities of realizing microwave bandpass filters with rigorously controlled characteristics, with reduced design time and non-prohibitive computational effort.

3279. TiO2-CeO2 Nanometric Powders Prepared by Sol-Gel Method

Authors: Zaharescu, M; Wittmar, A; Teodorescu, V; Andronescu, C; Wittmar, M; Veith, M

Published: 2009, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 635, +, DOI: 10.1002/zaac.200900186

Nanometric powders in the TiO2-CeO2 System were synthesized using sol-gel methods aiming at corrosion inhibitor preparation. The precursors employed were Ti(OiPr)(4) as TiO2 source and Ce(NO3)(3)center dot 6H(2)O or Ce(CH3CO2)(3)center dot xH(2)O as CeO2 source. Several parameters were varied, like the cerium precursor (cerium nitrate or cerium acetate) and the TiO2:CeO2 molar ratios. For both cerium sources binary powders with TiO2:CeO2 = 4:1 or 1:1 molar ratios were prepared. The obtained materials were dried 12 h in an oven at 100 degrees C and then thermally treated for 1 h at 400 degrees C with a heating rate of 1 degrees C.min(-1) in order to eliminate the water and organic residues. In all cases, nanometric - predominantly amorphous - powders have been obtained which crystallized after the I h thermal treatment at 400 degrees C. The only exception was recorded for the TiO2:CeO2 = 4:1 composition prepared from the Ce(NO3)(3)-6H(2)O precursor which remained amorphous after the thermal treatment. Even though the primary particle sizes were similar to 4-5 nm, the material is constituted from aggregates larger than 50 nm. The desired presence of cerium in two valence states, necessary in active corrosion protection, was achieved and it was put into evidence by XPS and DTA/TGA for the TiO2:CeO2 = 4:1 binary compositions. Future studies have to be performed in order to reduce the agglomeration of the material.

3280. Magnetic properties of MgB2-Fe sandwiches produced by Field-Assisted-Sintering Technique

Authors: Aldica, G; Sandu, V; Plapcianu, C; Badica, P; Groza, JR

Published: 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5: SUPERCONDUCTIVITY, 150, DOI: 10.1088/1742-6596/150/5/052006

Superconducting SiC and B4C-doped MgB2 samples containing up to three layers of pure Fe have been prepared by Field-Assisted-Sintering Technique (FAST). The adhesion between the Fe and doped-MgB2 layers is excellent due to the enhanced local interdiffusion and increased solubility of Fe into MgB2 grains that are typical for the non-equilibrium processes. Magnetic measurements showed the largest irreversibility, hence, the largest critical current density in the B4C-doped sandwich with one Fe foil. Additionally, the drawback of flux jumps at low temperatures is almost absent for one Fe-layer sandwiches. However, the irreversibility is smaller than in pure MgB2 and SiC-doped MgB2 samples prepared by the same technique, but without the insertion of Fe foil. When the number of Fe foils is increased to three and an excess of 5 % wt. Mg is added, the SiC-doped sandwiches show almost similar irreversibility values and field dependence (at 5 K and at 20 K) as the pristine MgB2 samples without Fe. But, the flux jump is recovered at the same level found for the pristine MgB2 without Fe. An explanation in terms of doping dependence of the ratio between the thermal and magnetic diffusion constants is proposed.