National Institute Of Materials Physics - Romania

TiAlZrCN superhard coatings, in which Ti and Al were additions to ZrCN base compound, were prepared by the cathodic arc method. The films were deposited on Si, plain carbon steel and high-speed steel substrates in a mixture of N-2 and CH4 gases. Elemental and phase composition, chemical bondings, texture, surface roughness, hardness, adhesion, tribological characteristics and erosive-corrosive resistance were investigates as a function of gas composition and total gas flow rate, using XPS, GDOES and XRD techniques, surface profilometry, microhardness and scratch adhesion measurements, tribological and erosive tests. It was shown that the properties and performance of the coatings were strongly dependent on the CH4/(CH4+N-2) flow rate and also on the total gas flow. The tribological and anti-erosive characteristics of the TiAlZrCN coatings were found to be superior to those of reference films (ZrN, ZrC, ZrCN, and TiAlCN). Maximum hardness values (42-45 GPa) were obtained for the films prepared at CH4/(CH4+N2) ratios ranging from 0.2 to 0.4. (c) 2008 Elsevier B.V. All rights reserved.

The main objective of this paper is to give a rigorous treatment of Wigner's and Eisenbud's R-matrix method for scattering matrices of scattering systems consisting of two selfadjoint extensions of the same symmetric operator with finite deficiency indices. In the framework of boundary triplets and associated Weyl functions an abstract generalization of the R-matrix method is developed and the results are applied to Schrodinger operators on the real axis. (C) 2008 Elsevier Inc. All rights reserved.

ZnO nanowires were electrodeposited by using a template approach. Ion track polycarbonate foils (30 mu m thick) were used as templates. Current-voltage (I-V) characteristics were recorded in the temperature range 40-300 K. I-V characteristics show a symmetric, non-linear shape, at temperatures greater than 240 K and voltages greater than 15 V. At lower temperatures, linear characteristics were recorded for the voltage range used. The temperature dependence of the electrical resistance is activated, with activation energy of 0.42 eV at temperatures greater than 240 K. (C) 2007 Elsevier B.V. All rights reserved.

Ferromagnetic shape memory alloys have been manufactured by various techniques involving rapid solidification. Bulk alloys have been obtained by extracting the melted alloy in especially designed copper molds; glass coated wires have been obtained by drawing the melt from glass recipients followed by water cooling and ribbons have been fabricated by melt-spinning. Microstructural observations show particular solidification aspects of fractured areas, while ferromagnetic behavior has been detected in glass coated wires obtained by rapid solidification. The martensitic microstructure was observed on Co-Ni-Ga rapid solidified bulk alloys and Fe-Pd ribbons. The memory effect was detected using a Vibran system that allows the detection of the phase transition for the ribbons and by visual observation for other specimens. The conclusions of the observations are related to the comparison between the ferromagnetic behaviors of shape memory alloys solidified using different techniques.

In this paper, we propose an interpretation for an abnormal anti-Stokes Raman emission observed on nanometric thin films of different materials and in particular carbon nanotubes. We demonstrate that under a tight-focusing of the excitation light, a coherent anti-stokes Raman scattering (CARS) emission is produced, resulting from a wave mixing process between the incident laser light (omega(1)) and Stokes Raman light (omega(s)) generated by a surface enhanced Raman scattering (SERS) mechanism. Although the Stokes/anti-Stokes intensity ratio has been explained differently, we present here the results which corroborate the CARS emission. They can be summarized as follows: (i) a square relationship between the CARS signal intensity and the film thickness; (ii) a square relationship between the CARS signal intensity and the exciting laser intensity; (iii) a dependence of the CARS intensity on the numerical aperture (NA) of the microscope objective used for the detection of the anti-Stokes emission. Such effects are not specific to carbon nanotubes and have been observed with other materials accommodated in similar conditions on rough metallic surfaces acting as SERS supports. (c) 2007 Elsevier B.V. All rights reserved.

Composites based on zinc oxide (ZnO) nanoparticles and single-walled carbon nanotubes (SWNTs) were investigated by photoluminescence (PL) and Raman scattering. The room temperature PL spectrum of ZnO at the excitation wavelength of 335 nm displays a narrow excitonic band, peaking at 368 nm (3.36eV), and a wide one, disclosing two components with maxima at about 444 nm (2.79eV) and 560 nm (2.21eV) which are associated to the local oxygen vacancies and oxygen excess, respectively. Regardless the preparation method of the ZnO/SWNTs compound (electrochemical, mechanicochemical and hydrothermal synthesis), PL spectra reveal an increased quenching tendency with the concentration of nanotubes in the composite mass. As distinct feature in the PL spectra of ZnO/SWNTs composites are two bands, one at 450 nm (2.75 nm) and another one attributed to the formation of a donor-acceptor complex at 680 nm (1.82eV). The role of the dispersion of carbon nanotubes in the ZnO/SWNTs composite is observed by Raman scattering with the excitation wavelength of 676 nm. (C) 2007 Elsevier B.V. All rights reserved.

A template method was used to obtain cadmium sulfide (CdS) nanowires. Polymer ion tracks foils (30 mu m tick) were used as templates, after etching with solutions containing NaOH and methanol. CdS nanowires were electrochemically grown in the resulting pores. The nanowires were contacted by sputtering a gold layer on top of the membrane, and the electrical properties were recorded in the temperature range 40-300K. An activated electrical resistance was observed, with activation energy of 0.27eV at temperatures larger than 180 K. I-V characteristics show a symmetric, non-linear shape, in the voltage range used in this experiment. (C) 2007 Elsevier B.V. All rights reserved.

Magnetic relaxation measurements on a series of Y1-xPrxBa2CU3O7-delta (x=0.13, 0.34, and 0.47) single crystals were performed over a large field and temperature range in order to investigate the characteristics of the vortex matter across the second magnetization peak (SMP). The magnitude of the SMP varies nonmonotonically with Pr concentration, i.e., the irreversible magnetization normalized by its value at the onset field H-on displays a maximum for the x=0.34 single crystal. The two characteristic fields, H,,, and H,,, follow different temperature T dependences: H-on proportional to T-nu on and H-sp proportional to [1-(T/T-c)(2)](nu sp). The extracted values of the apparent activation energy U* and the creep exponent mu display a maximum at a field H-on < H* < H-sp. Their field dependences point toward the coexistence of both elastic and plastic creep for H > H-on. The degree of participation of each creep mechanism is determined by the charge carrier density, which controls both the elastic properties of the vortex matter and the pinning potential.

We report on photoluminescence studies on manganese and copper-doped ZnO nanowire array prepared by template method. The ZnO:Mn:Cu semiconductor grown using the electrochemical technique was characterized by electron paramagnetic resonance (EPR) and optical reflection measurements. Morphology and the structure were observed by SEM and X-ray diffraction. The photoluminescence of this system was correlated with manganese and copper concentration in the ZnO matrix. (C) 2007 Elsevier B.V. All rights reserved.