National Institute Of Materials Physics - Romania

A designed experimental configuration for the simultaneous study of magnetization reversal and giant magnetoresistance effects in layered systems is reported. The suitability of the device, designed mainly for didactical purposes, to prove giant magneto-resistance effects is exemplified in case of exchange coupled spin valve structures. The multilayer structures were prepared by theromo-ionic vacuum arc methods and initially characterized by X-ray diffractometry and energy dispersive Xray spectroscopy. According to the performed experiments, it has been clearly proven the presence of magnetoresistance maxima ever ranges of applied fields inducing antiparallel magnetizations of the two ferromagnetic layers interfacing a thin conductive layer.

The first step of the smartcut (TM) process consists in inducing structural defects below the free surface of a silicon wafer, usually by implantation of light elements, such as hydrogen or helium. An alternative way to induce subsurface defects is by plasma treatment. In this work, we present a morphological and structural study on silicon wafers submitted to hydrogen plasma treatment, using two plasma-processing geometries. The parameters of the plasma treatment have been varied in order to limit the surface roughness and to confine the induced defects in a narrow region (50 nm) below the wafer surface. The morphological and structural investigations have been performed by AFM and TEM.

Many nanovectors used for therapy (drug targeting radiation therapy) or diagnostic such as Magnetic Resonance Imaging (MRI) have a composite structure consisting of an organic core or organic coverage encapsulating magnetic nanoparticles and they are commonly dispersed in liquid suspensions for intravenous injection Here is presented the application of a new Environmental Scanning Electron Microscopy (ESEM) mode in transmission so called Wet-STEM for transmission imaging of droplets of such suspensions This is illustrated by Wet-STEM images from PLLA/Re nanospheres (about 100-300 nm in diameter) loaded with magnetite nanoparticles (about 10 nm in diameter) and from iron oxide core (about 5 nm in size) MRI contrast agents both examples in aqueous suspensions It is shown that the Wet STEM mode allows both the collective behavior of such nanovectors in suspension to be characterized and the inner composite structure of individual vectors to be revealed Such experimental results are discussed by comparison with Monte Carlo computer simulations of the distribution of the electrons scattered through the samples in rather large solid angles (between 20 degrees and 47 degrees) corresponding to the detection conditions (C) 2010 Elsevier Inc All rights reserved

The interaction between CO and WO3 based gas sensors was investigated in operando conditions by using resistance, catalytic conversion and DRIFTS measurements. The experimental results are showing that the sensing involves the reduction of the metal oxide, which is the opposite of the case of SnO2, the other extremely relevant material for semiconducting oxides based gas sensors. (C) 2010 Elsevier B.V. All rights reserved.

Undoped and neodymium doped quartz glasses were obtained by the hybrid sol-gel method. The vitrification was performed in He atmosphere. The Nd(3+) characteristic absorption bands in the UV and VIS were put into evidence. Investigations in the NIR range revealed a small amount (86 ppm) of OH(-) in the vitreous matrix. FTIR and Raman spectra exhibit the SiO(2) glass characteristic vibrations and also the characteristic vibrations of Si-OH and Si-Cl bonds. The photoluminescence peaks at 640, 920 and 1080 nm belonging to the Nd(3+) doped quartz glass were evidenced.

Low-frequency (X-band) electron spin resonance (ESR) investigations on commercially available large-grained cubic boron nitride (cBN) superabrasive powders of various coloration, combined with high-frequency (W-band) ESR measurements on oriented submillimeter-size single crystallites selected from the same powder samples, resulted in a clear identification of several types of paramagnetic point defects. The resulting spin Hamiltonian parameters describing the ESR spectra observed in the 3-293 K temperature range and the photosensitivity of the paramagnetic defects observed in amber-colored cBN samples are reported. It is shown that the nature of the paramagnetic centers depends on the color of the investigated samples and that, in many cases, uncontrolled impurities seem to be involved in their structure.

Nanocrystalline cubic ZnS doped with 0.2% mol manganese, exhibiting a stable mesoporous structure, was synthesized at room temperature by a non toxic surfactant-assisted liquid liquid reaction. The X-ray diffraction measurements demonstrate the formation of a sponge-like mesoporous material built from cubic ZnS nanocrystals of 1.8 nm average sizes, with a tight distribution of pores of 1.8 nm mean diameter. The transmission electron microscopy images confirm the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from cubic ZnS nanocrystallites of 2.1 nm average size. The resulting tight distribution of crystallites and pores yields a well resolved Electron Paramagnetic Resonance spectrum, with the narrowest reported component lines attributed to three types of isolated Mn2+ centers, called Mn2+ (I), Mn2+ (II) and Mn2+ (III). From the analysis of the spin Hamiltonian parameters it is shown that in the Mn2+ (I) centers the paramagnetic ion is situated at substitutional Zn sites in the ZnS nanocrystals, being also subjected to a small axial distortion. The relative concentration changes under thermal treatment experiments strongly suggest that in both Mn2+ (II) and Mn2+ (III) centers the Mn2+ ion is localized on the surface of the ZnS nanocrystallites, being bond to an oxygen ion in the first case and to an additional water molecule in the second case.

Cobalt-aluminate spinel, CoAl2O4, has been synthesized by two synthesis variants of the complexation method: tartarate and gluconate routes. The complex precursors have been characterized by IR, UV-vis spectroscopy and thermal analysis. The cobalt-aluminate spinet has been investigated by XRD, IR, UV-vis and luminescence spectroscopy and TEM. The results indicated that in both cases the single-phase nanocrystalline CoAl2O4 spinet was formed. The average crystallite size from TEM images was in the range 50-60 nm. The emission spectra of CoAl2O4 in the visible region confirmed the presence of tetrahedral coordinated Co2+ ion. (C) 2010 Elsevier B.V. All rights reserved.

The nonlinear optical (NLO) crystal Y0.6Lu0.4Ca4O(BO3)(3) (starting composition) of good quality has been grown from the melt by the Czochralski pulling method. X-ray diffraction experiments show that the structure of grown crystal belongs to the monoclinic system with space group Cm and its unit cell parameters have been measured to be a = 0.80711(2)nm, b = 1.60132(1)nm, c = 0.35230(8)nm and beta = 101.166(1)degrees. The crystal possesses a wide transmission range from UV to IR, which is advantageous for applications as new NLO material for frequency doubling of solid state lasers operating in the near infrared range.

Macroporous polyacrylonitrile/hydroxyapatite (PAN/HAp) composite bead was studied for cadmium removal in a fixed-bed column. The morphology of PAN/HAp composite bead was measured. The adsorption performance of PAN/HAp composite bead in the column was examined by varying bed height and HAp amount in PAN bead. The maximum adsorption capacity and the exhaustion time were determined from the breakthrough curves. Experimental data was described using the Adams-Bohart model. Bed height did not exert large influence on the maximum adsorption capacity and the exhaustion time. The kinetic rate constant and the adsorption capacity of the bed were found to be affected by the total HAp amount.