National Institute Of Materials Physics - Romania

The catalytic chemical vapor deposition (CCVD) method in which the outer furnace is replaced by the high frequency induction heating (IH) has been used for synthesis of carbon nanostructures. Using different catalysts, various types of carbon nanofibers were obtained, with the absence of the catalyst particles at their tip as a common characteristic. The IH mode combined with the CCVD method seems attractive for the synthesis of carbon nanostructures, allowing a significant decrease of energy consumption and of the overall reaction time as compared with the heating mode with outer furnace. (C) 2003 Elsevier Ltd. All rights reserved.

The effect of the NO3- anion on the corrosion of carbon steel in a solution of 0.1M NH4Cl (pH 5.5) was studied by galvanostatic polarization and Mossbauer spectrometry. The anion has an inhibiting effect by decreasing the expansion rate of generalized corrosion of carbon steel in a solution of 0.1M NH4Cl-Mossbauer spectroscopy shows that a superficial compound is formed on the electrode surface as a result of corrosion, presenting no magnetic ordering. Its parameters show the initial stage of corrosion. We assume that at this stage the main corrosion product is a mixture of ferrihydrite Fe(III) and FeOOH (alpha and/or gamma).

Silicon detectors represent an important option for the Large Hadron Collider and for its upgrades in luminosity and energy, especially for the tracking system. The main limitation in their utilisation comes from the degradation in the hostile radiation environment where they, will work for long time, without the possibility to be changed. The main goal of this paper is to study, the role of growth technology on stable defect concentrations produced by long-time continuous irradiation in the radiation field estimated for LHC and SLHC.

CdxPb1-xS (0 less than or equal to x less than or equal to 1) thin films were prepared on glass substrates using the chemical bath deposition method. The structural, electrical, and photoelectrical properties of the films were investigated, and all were dependent on the x value. For x > 0.5 (high Cd content), the films show a poor crystallinity and weak photoconductivity. For x < 0.5 (high Pb content), the films exhibit a good crystallinity, with an average size of the crystallites of 100 nm, and good photoconductivity. The threshold voltage of photoconductivity is shifted to lower wavelengths with increasing Cd content. The experimental results point toward possible ternary deposition on some composition ranges (near pure PbS or CdS); whereas, for the rest, the deposited film is rather a mixture of phases [not CdxPb1-xS but (CdS)(x)(PbS)(1-x)]. (C) 2004 The Electrochemical Society.

The magnetic properties of core-shell-type nanoparticles with non-magnetic core and ferromagnetic shell are modeled using Monte Carlo simulation. The influence of the surface spin disorder on the magnetization and Curie temperature of magnetic states is studied. Due to competition between exchange coupling and surface anisotropy, rotation of the magnetization axis is observed, as the surface anisotropy of the ferromagnetic shell is increased. It is shown that the exchange coupling at the core-shell interface can influence the shape of the temperature dependence of total magnetization. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Thermally stimulated current measurements of silicon particle detectors have been performed for defect characterization after high levels of gamma- and proton-irradiation. Two defects closely correlated with the detector performance were monitored: a deep acceptor (1) and a bistable donor (BD). In oxygen rich silicon the deep acceptor is largely suppressed while the BD generation is strongly enhanced. The influence of the starting material (standard float zone (FZ), oxygen enriched FZ, Cz, epitaxial silicon) on the formation of these two defects is discussed. Identification of the I-defect with the V2O complex, and of BD with the thermal double donor TDD2 is suggested. (C) 2003 Elsevier B.V. All rights reserved.

Isothermal and isochronal annealing experiments have shown that the I defect (the main cause for the changes in silicon diodes characteristics after high levels of gamma-irradiation) is stable up to 325-350degreesC. Possible reactions, which can explain the behavior of different defects formed during the annealing experiments, are discussed. All the experimental results concerning the I center (second-order irradiation induced defect, formed most likely via VO center, suppressed in oxygen rich material, high thermal stability) make it the favorite for being associated with the V2O2 complex. (C) 2003 Elsevier B.V. All rights reserved.

We demonstrate the application of the Landauer-Buttiker formalism (LBF) to MIS (metal-insulator-semiconductor)-type quantum nanostructures and analyze their static and dynamical response properties. For the time-dependent problem, we employ the random phase approximation (RPA) and calculate the irreducible polarization from the one-particle scattering wave functions in the Hartree approximation. For their calculation, we employ the R-matrix approach which we have developed over the past years. We find in the low frequency limit a reasonable agreement with the static Hartree calculations and experimental capacitance data. (C) 2003 Published by Elsevier B.V.

Recent developments of lithographic techniques as well as improved chemical synthesis methods allow researchers to engineer novel nanostructured materials consisting of arrays of self-organized nanocrystals and multilayers grown as patterns on different substrates. In our case, the magnetic nanostructures consist either of multilayers directly deposited on pre-patterned substrates to form regular arrays of stripes and grooves or colloidal solutions of self-organized bimetallic Ag/Co nanoparticles on patterned and nonpatterned substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed in order to study the surface morphology of the 2D patterning arrays and the 3D nanostructures. The development of periodic arrays of magnetic patterns of micrometer size is strongly dependent on technological parameters such as: film, thickness, distances, size and shape of the patterns. Moreover, it is shown that the substrate morphology significantly affects the colloidal crystallization of magnetic nanoparticles and leads to different growth modes. This will ultimately affect the overall magnetic behavior of the nanostructures. Consequently, the combination of self-assembly and patterning allows for the controlled fabrication of the novel magnetic nanostructures at a macroscopic level and the study of fundamental aspects in magnetism such as quantum tunneling magnetization and magneto-transport properties along well-defined nanosized patterns. (C) 2003 Elsevier B.V. All rights reserved.

For the LHC upgrade (fluences up to 10(16) p/cm(2)) epi-Si devices are shown to be a viable solution. No type inversion was measured up to 1.3 x 10(15) 24 GeV/c protons/cm(2) and the charge collection efficiency (CCE) remained close to 100%. For reactor neutrons CCE was measured to be 60% at 8 x 10(15) n/cm(2). Annealing measurements have shown that only moderate cooling during beam off periods would be necessary. As a tentative explanation for the superior quality of these devices, we assume that radiation-induced donor generation leads to compensation effects of deep acceptors. In the future, we will extend the experiments to fluences up to 10(16) p/cm(2) and use also different variants of the epi-Si material and device geometry. (C) 2003 Elsevier B.V. All rights reserved.