Publications

The structural changes of cubic ZnS (cZnS) nanocrystals (NCs) doped with 0.2 at.% Mn2+ pulse annealed in vacuum and in air, up to 500 A degrees C, were investigated by multifrequency electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The samples, prepared by a surfactant (Tween20)-assisted liquid-liquid reaction at pH = 6, consist of NCs with a tight size distribution around 3 nm and high crystallinity self-assembled into a stable mesoporous structure. The EPR spectra of the as prepared samples contain only the characteristic lines of the substitutional Mn2+(I) centers. No spectra from Mn2+ ions localized in (hydro)oxidized regions of the NCs surface were observed. The absence of such a surface layer could explain the stability of the cubic (sphalerite) structure observed by XRD and TEM in the investigated cZnS:Mn NCs annealed in vacuum up to 500 A degrees C. The observation of the cubic-hexagonal transformation for the same NCs annealed in air supports the role of such layer in promoting this structural transformation. The narrowing of the EPR spectral lines above 200 A degrees C with the increase in the average size of the cZnS:Mn crystallites was observed. The effect was more pronounced for the sample annealed in air. EPR also revealed the formation of minute amounts of substitutional Mn2+-type centers in a hexagonal ZnO structure at T similar to 300 A degrees C, corresponding to the early stages of the thermally induced oxidation of the cZnS:Mn NCs.

0.89(Na0.5Bi0.5)TiO3-0.11BaTiO(3), (BNT-BT0.11) thin film was fabricated by sol-gel/spin coating process, on platinized silicon wafer. Perovskite structure with random orientation of crystallites has been obtained at 700 A degrees C. Piezoelectric activity of BNT-BT0.11 thin film was detected using piezoresponse force microscopy (PFM). Effective piezoelectric coefficient d (33eff) of such film, recorded at 5 V applied dc voltage, was similar to 29 pm/V, which is similar to other BNT-BT (x) thin films. The complex refractive index and dielectric function of BNT-BT0.11 thin films were also investigated. The high leakage current density significantly influences the dielectric, ferroelectric, and piezoelectric properties of the BNT-BT0.11 films.

The synthesis by pulsed laser deposition of ZnO thin films with a Nd:YAG laser system delivering pulses of 40 ps @ 532 nm is reported. The laser beam irradiated the target placed inside a vacuum chamber evacuated down to 1.33x10(-1) Pa. The incident laser fluence was of 28 J/cm(2) in a spot of 0.1 mm(2). The ablated material was collected onto double face polished (111) Si or quartz wafers placed parallel at a separation distance of 7 mm. The AFM, SEM, UV-Vis, FT-IR and absorption ellipsometry results indicated that we obtained pure ZnO films with a rather uniform surface, having an average roughness of 37 nm. We observed by SEM that particulates are present on ZnO film surface or embedded into bulk. Their density and dimension were intermediary between particulates observed on similar structures deposited with fs or ns laser pulses. We noticed that the density of the particulates is increasing while their average size is decreasing when passing from ns to ps and fs laser pulses. The average transmission in the UV-Vis spectral region was found to be higher than 85%.

Silica has been derivatized with aminopropyl groups which subsequently have been chemically modified with N-methoxy-2,6-dinitroaniline derivatives to yield a solid which changes its color in the presence of arginine or lysine, from yellow to blue. Other amino-acids (such as glycine, valine, cysteine, cystine, alanine, phenylalanine, histidine) do not showed this behavior. The same procedure may be applied to silica nanoparticles. The new materials were characterized by UV-Vis, IR, and TEM.

Glass-ceramics containing RE3+-doped BaF2 nanocrystals (RE = Eu, Sm, Dy, Ho and Pr) with the size below 10 nm size have been made by using the controlled crystallization at higher temperatures of the RE3+-doped SiO2-BaF2 xerogels. Photoluminescence measurements have indicated the incorporation of the RE3+ ions in both silica network and in the BaF2 nanocrystals. Thermoluminescence measurements have shown a peak whose position depends on the nature of RE3+-dopant as it follows: 140 degrees C (for Ho3+, Dy3+), 340 degrees C (for Sm3+) and 370 degrees C (for Eu3+); in Eu3+-doped SiO2 glass the TL peak is shifted to 383 degrees C. The peaks in glass-ceramics were assigned to the recombination of the electrons thermal released from the RE3+-electron traps located in both glass-matrix and BaF2 nanocrystals. Within the series the trivalent lanthanide ions act as increasingly deeper electron trapping centres. (C) 2011 Elsevier B.V. All rights reserved.

New polymeric chelate structures derived from maleic anhydride-dicyclopentadiene copolymer (MA-DCPD) were synthesized by chemical modifications with triethylenetetramine ( TETA), from Riedel De HaSn AG Seelze, Hannover. Germany. Both amide and imide forms of these new polymers have been tested in the retention process of Cr (III) ions. Experimental results referring mainly to the retention capacity and retention efficiency, for different values of the working parameters: contact procedure, batch time, concentration of chelators, and pH, are presented. The polymer structures and their metal complexes were characterized by IR spectroscopy. IR spectra proved that the metal was coordinated by nitrogen from TETA. The thermal properties of modified polymers and polychelates were also examined. Based on these experimental results and literature data, we discuss a possible binding mechanism and suggest the polychelate structures. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:1867-1874, 2011

It is shown that the short-circuit photocurrent measured under illumination in Pb(Zr,Ti)O-3 epitaxial films is strongly dependent on the metal used as the top electrode. The magnitude of the photocurrent varies by more than 2 orders of magnitude from Pt (largest signal) to Al (smallest signal). The differences are for both directions of polarization. The imprint is also dependent on the top metal electrode, with a direct effect on the shape of the spectral distribution. The results support the hypothesis that the origin of the photovoltaic effect in ferroelectric thin films is different from that of the anomalous photovoltaic effect observed in bulk ceramics and single crystals. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624738]

Under certain conditions, we prove the existence of a steady-state transport regime for interacting mesoscopic systems coupled to reservoirs (leads). The partitioning and partition-free scenarios are treated on an equal footing. Our time-dependent scattering approach is exact and proves, among other things, the independence of the steady-state quantities from the initial state of the sample. Closed formulas for the steady-state current amenable for perturbative calculations with regard to the interaction strength are also derived. In the partitioning case, we calculate the first-order correction and recover the mean-field (Hartree-Fock) results.

The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl(4)) and fluorine (C(2)Cl(3)F(3)) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400 pulses at 330 mJ/cm(2) laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 mu m, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 mu m in height and with a full width at half maximum of 2.3 mu m with irradiation of 700 pulses at 560 mJ/cm(2) laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3619856]