National Institute Of Materials Physics - Romania

Hydrogenated amorphous carbon (a-C: H) films were grown by radio-frequency (1.78 MHz) plasma enhanced chemical vapour deposition technique onto medical grade Ti6Al4V substrates. By varying the deposition pressure (13.33 Pa and 53.33 Pa, respectively) and methane dilution (20% and 60%, respectively) several types of carbonic films were obtained, presenting different bonding structures, surface energies and morphological features reflected in their biological behaviour. FTIR, Raman, UV-Vis, XPS and AFM measurements were used for characterizing these structures. The surface energy was determined by contact angle measurements, and their thrombogenicity was tested by the activated partial thromboplastin time (aPTT) method. We have noticed that at the same values of methane in argon dilution but at different pressure values, the film structure was totally changed: soft polymer-like carbon (PLC) type at the higher pressure and hard diamond-like carbon (DLC) type at the lower pressure. Raman spectroscopy and XPS suggested that the highest sp(3) ratio (similar to 52%), was found for DLC films prepared in a 60% methane dilution in argon. It has been found that for both PLC and DLC structures the surface energy has a decreasing tendency with the methane concentration increase in the deposition atmosphere. Excellent aPTT results were obtained for the DLC-60 (18.6.+/- 0.3 min) and PLC-20 (17.4 +/- 0.5 min) structures, superior to those recorded for Ti6Al4V and PMMA commercial materials. These values recommend the prepared carbonic structures for medical applications: harder coatings (DLC) for metal prostheses (heart valves, acetabular cups etc.), while softer and flexible coatings (PLC) for the textile vessels or stents biofunctionalization.

The ability of a sol-gel route for the synthesis of cobalt doped ZnO (Zn 1-xCoxO, x = 0.04-0.11) films grown on Si (100) and glass substrates is investigated. A homogeneous and stable Zn (1-x) CoxO sol was prepared by dissolving zinc nitrate hexahydrate and cobalt acetate tetrahydrate in a PVP (polyvinylpyrrolidone) solution, followed by annealing at 800 degrees C. Local structure studies of the Zn1-xCoxO thin films by XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure) proved the co-existence of a few amount of small metal cobalt aggregates with Co in non-stoichiometric ConOm aggregates, with n > m, and m similar to 4. Low temperature magneto-optical Kerr effect (Faraday rotation) measurements of the magnetization versus field give a direct proof of a superparamagnetic behavior of the magnetic aggregates and allowed an estimate of the number of magnetically active atoms in Co aggregates, which is close to the number of Co excess atoms inferred from XANES and EXAFS considerations: n - m similar to 3 atoms per aggregate. To this main superparamagnetic phase, a weak ferromagnetic phase with coercitive field of similar to 50 Oe is superimposed, most probably due to metal cobalt nanoclusters.

Various approaches have been reported during the last decade to enhance the photo-catalytic and super-hydrophilic characteristics of the intrinsic TiO2 materials. Results on the photo-degradation activity of RF-sputtered nitrogen-doped titania thin films are presented here with respect to two environmental pollutants in gas- and liquid phases, as a function of dopant concentration. This study was accomplished by monitoring the time dependence of pollutant concentration in contact with the films, both under UV and solar light illumination. The synergic effects of surface morphology, crystalline and electronic structure of the materials are discussed in relation with the observed experimental facts. The results presented here show a close correlation between the oxidative power of the films and their previously reported wettability features. (C) 2009 Elsevier B.V. All rights reserved.

The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker structures under various stresses and temperatures ranging from +15 degrees C to -15 degrees C. Comparison with simulation shows that the achieved alignment precision in the barrel part of the tracker leads to residual distributions similar to those obtained with a random misalignment of 50 (80) mu m RMS in the outer (inner) part of the barrel.

TiO2 nanopowders, doped with Fe3+ and Eu3+ were obtained by high-energy ball milling and their physical properties were investigated as a function of the doping content and ball milling time. A noticeable red shift and high photoactivity in the degradation and catalytic oxidation reactions of styrene and phenol were found for all doped specimens.

In March 2007 the assembly of the Silicon Strip Tracker was completed at the Tracker Integration Facility at CERN. Nearly 15% of the detector was instrumented using cables, fiber optics, power supplies, and electronics intended for the operation at the LHC. A local chiller was used to circulate the coolant for low temperature operation. In order to understand the efficiency and alignment of the strip tracker modules, a cosmic ray trigger was implemented. From March through July 4.5 million triggers were recorded. This period, referred to as the Sector Test, provided practical experience with the operation of the Tracker, especially safety, data acquisition, power, and cooling systems. This paper describes the performance of the strip system during the Sector Test, which consisted of five distinct periods defined by the coolant temperature. Significant emphasis is placed on comparisons between the data and results from Monte Carlo studies.

The subsystems of the CMS silicon strip tracker were integrated and commissioned at the Tracker Integration Facility (TIF) in the period from November 2006 to July 2007. As part of the commissioning, large samples of cosmic ray data were recorded under various running conditions in the absence of a magnetic field. Cosmic rays detected by scintillation counters were used to trigger the readout of up to 15% of the final silicon strip detector, and over 4.7 million events were recorded. This document describes the cosmic track reconstruction and presents results on the performance of track and hit reconstruction as from dedicated analyses.

In a previous paper [C.M. Teodorescu and G.A. Lungu, J. Optoelectron. Adv, Mater. 10, 3058 (2008)] we studied the zero temperature problem of the occurence of band ferromagnetism and of the derivation of the Stoner criterion for systems of variable dimensionality: 1D, 2D, 3D. The dimensionality of the system is reflected by a different shape of the density of states. For ideal 2D systems, the density of states is a constant and this seems to be the simplest case to be modelled. In this paper we integrate to this simplest model of constant density of states the influence of temperature, in order to analyse temperature-dependent ferromagnetism in two-dimensional systems, such as magnetic surfaces. Some surprising results are obtained, namely: (i) in contrast to the common belief, in this case the influence of the temperature is to favour, not to inhibit ferromagnetism, i.e. in some conditions ferromagnetism may be obtained at finite temperature. even for systems where the zero temperature Stoner criterion is not satisfied; (ii) for a careful choice of the ratio between the Hubbard energy parameter U and the equilibrium zero-temperature Fermi level value epsilon(mu) (0), systems nonmagnetic at low temperature which become magnetic at higher temperature may be possible. A short review of the experimental data which may be interpreted within the present formalism is also given.

The obtaining of a good ohmic contacts on the semiconductor material surfaces is strongly depending on the ability of the cleaning procedures to remove the native oxides and also, in the case of the compounds, to keep the surface stoichiometry. In this work, the XPS technique has been used in order to compare the efficiency of both, chemical etching and the Ar+ ion sputtering methods as to be suitable cleaning procedures in the case of n-GaP semiconductor compound surfaces preparation for the optoelectronic devices obtaining. The results have revealed some differences in the final surface composition/stoichiometry. The atomic ratio P/Ga within the outer layer of the single crystalline sample (similar to 100 angstrom) has been evaluated. The presence of residual of surface oxides was recorded after performing the chemical cleaning.