National Institute Of Materials Physics - Romania

The principal obstacle to long-time operation of silicon detectors at the highest energies in the next generation of experiments arises from bulk displacement damage which causes significant degradation of their macroscopic properties. The analysis of the behaviour of silicon detectors after irradiation conduces to a good or reasonable agreement between theoretical calculations and experimental data for the time evolution of the leakage current and effective carrier concentration after lepton and gamma irradiation and large discrepancies after hadron irradiation and this in conditions where a reasonable agreement is obtained between experimental and calculated concentrations of complex defects. In this paper, we argue that the main discrepancies could be solved naturally considering as primary defects the self-interstitials, classical vacancies and the new predicted fourfold coordinated silicon pseudo-vacancy defects. This new defect is supposed to be introduced uniformly in the bulk during irradiation, has deep energy level(s) in the gap and it is stable in time. Considering the mechanisms of production of defects and their kinetics, it was possible to determine indirectly the characteristics of the Si-FFCD defect: energy level in the band gap and cross-section for minority carrier capture. In the frame of the model, the effects of primary defects on the degradation of silicon detectors are important in conditions of continuous long-time irradiation and/or high fluences.

Amorphous SnSe2 films were prepared by pulsed laser deposition (PLD) and pulsed electron deposition (PED) from solid polycrystalline targets. The atomic scale structure has been revealed by X-ray diffraction. Hardness properties and electrical properties were measured. The peculiarities of the structures of the films prepared by PLD and PED methods were investigated discussed.

Electrochemical polymerization of N-vinyl carbazole (VC) on carbon nanotube (CNT) films was studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when single- or multi-walled carbon nanotube (SWNT or MWNT) films were previously deposited onto the Pt electrode, a downshift of the VC reduction peak potential is observed in the latter case. The influences of monomer concentration, type of solvent, and supporting electrolyte on the polymerization conditions and electrochemical properties of these composite materials are also investigated. The morphological aspects of poly(N-vinyl carbazole) (PVC)-functionalized CNTs are revealed by transmission electron microscopy (TEM) studies. A covalent functionalization of carbon nanotubes with PVC is invoked as a result of attenuated total reflection infrared (ATR-IR) spectroscopic studies. Using PVC-functionalized CNTs as a positive electrode and an electrolytic solution containing LiPF6, the charge-discharge characteristics of the rechargeable lithium cells are determined. High specific discharge capacity (approximate to 45 and 115 mA h g(-1)) is reported for PVC-functionalized single- and multi-walled carbon nanotubes, respectively.

Fe-Ni-Co-Ti shape memory alloys were prepared by various techniques. A comparison between samples prepared by classical metallurgy and by melt spinning technique is performed in respect to the microscopic mechanisms responding for the shape memory effects. X-ray diffraction, thermomagnetic measurements and Mossbauer spectroscopy were applied for a complete structural and magnetic characterization. Only samples supporting an aging treatment gave evidence for shape memory effects and correlated structural transformations.

PbZr1-XTiXO3 (PZT) film was prepared by addition of polymer polyvinylpirrolidone (PVP) in the PZT precursor and hydrolysis of the PZT precursor sol. Porous thin films were prepared by spin coating on Pt-coated Si substrate. The structure of the films was investigated by X-ray diffraction (XRD). (100)-oriented PZT 20180 film was obtained by hydrolysis of sol. PVP addition leads to the (110)-orientation of the film. The surface microstructure of the films was characterised with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The surface profile indicates a films roughness of 5 nm. No micro-cracks were observed on film surface. The average remnant polarization and the coercive field were obtained from the hysteresis loop measurements. The ferroelectric behavior has been evidenced by the presence of the butterfly shape of the capacitance-voltage characteristics. Experimental results show that the dielectric constant of the PZT porous film is lower than that of the dense film.

The hydrophilicity of RF sputtered thin films of: (a) pure TiO2 and (b) TiO2 doped with 0.3% Ce, 0.4% Nb, and 0.4% N (atomic percents) was investigated macroscopically by measurements of the contact angle between water and film surface. The results are discussed in terms of the connection of the hydrophilic and photocatalytic properties of the materials with their structure, morphology and optical characteristics. The 280 nm thick films were deposited on optical glass substrates at 250 degrees C. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. The surface roughness was derived from atomic force microscopy and ellipsometric data. The contact angle of de-ionized water with film surface was monitored during photo-activation and after irradiating with near-UV light. The surface super-hidrophilicity of all the investigated samples decays, when samples are kept in darkness for 48 h after irradiation. The hydrophilic behavior of the doped TiO2 thin films is discussed in terms of the effects of surface roughness, phase transformations enhanced by doping and charge carrier recombination. (c) 2006 Elsevier B.V All rights reserved.

Three novel mu(3)-oxo trinuclear carboxylates [Fe2CaO(CCl3COO),(THF)(4)] center dot THF (1), [Fe2SrO(CCl3COO)(6)(THF)(6)] center dot 0.5H(2)O center dot 0.5THF (2) and [Fe2BaO(CCl3COO)(6)(THF)(6)] center dot 0.5H(2)O center dot 0.5THF (3) have been synthesised and subsequently characterised by X-ray structure analysis, thermal gravimetry (TG), infra red (IR) spectroscopy and magnetic measurements. Compounds I and 3 are molecular complexes with s- and d-metals displayed in the apexes of isosceles triangles with a triply bridging oxygen atom at its centre. The Ca center dot center dot center dot Fe and Ba center dot center dot center dot Fe separations have the values 3.750(1) and 4.177(1) angstrom, respectively. In comparison with these. Fe center dot center dot center dot Fe separations, 3.229(2) angstrom in 1 and 3.201(1) angstrom in 3, appear much shorter. The molecular complexes obey C-2 symmetry with the twofold axis passing through s metal and mu(3)-oxo atom. The coordination numbers are 6, 7 and 9 for iron. calcium and barium correspondingly. Magnetic studies reveal the presence of an antiferromagnetic exchange in the isosceles triangular skeletons of the trinuclear species. Using the spin Hamiltonian H = -2J(12)[S1S2], the fitting parameters g(Fe) = 2.00. J(Fe-Fe) = -58.90 cm(-1) for 1 and -60.40 cm(-1) for 3; g(Fe) = 2.14, J(Fe-Fe) = -75.40 cm(-1) for 2 have been estimated. (c) 2006 Elsevier Ltd. All rights reserved.

We investigate the order parameter of noncentrosymmetric superconductors Li2Pd3B and Li2Pt3B via the behavior of the penetration depth lambda(T). The low-temperature penetration depth shows BCS-like behavior in Li2Pd3B, while in Li2Pt3B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-singlet and spin-triplet pairing, are responsible for this behavior. The triplet contribution is weak in Li2Pd3B, leading to a wholly open but anisotropic gap. The significantly larger spin-orbit coupling in Li2Pt3B allows the spin-triplet component to be larger in Li2Pt3B, producing line nodes in the energy gap as evidenced by the linear temperature dependence of lambda(T). The experimental data are in quantitative agreement with theory.

We report successful growth of high-quality thin films with clean and completely precipitate-free surface, suitable for device applications, by applying a new concept and method to the substrates. The concept consists in generation of artificial steps of controlled height and width, and desired shape on the surface of the substrate. The width of the step is chosen so that it is equal to the double of the migration (surface diffusion) length of the atomic species in the growth process of the film. If precipitates occur, they will be selectively gathered to the step edge where the free energy is lowest. Using this new method, we have successfully obtained by MOCVD high-quality precipitate-free Bi-2223 and Bi-2223/Bi-2212-superlattice thin films on (100) SrTiO3 substrates with artificial steps of controlled width and height. These as-grown films have been further used to fabricate patterned intrinsic Josephson junctions. Completely precipitate-free films offer a strong advantage for integration, and generate new possibilities for the device fabrication.

The series of compounds RFe11.3W0.7, where R = Dy, Ho, Er, and Lu, has been measured by Mossbauer spectroscopy between 15 and 295 K. A model which takes into account the Wigner-Seitz cell local environment of each iron site, the distribution of tungsten atoms on the 8i site, and the temperature-dependent magnetic structures of the compounds has been used to analyse the spectra. The assignment and the temperature dependencies of the hyperfine fields and the isomer shifts are in complete agreement with the Wigner-Seitz; cell analysis of the three iron sites in RFe11.3W0.7 compounds. The plausible orientations of the iron magnetic moments in the canted magnetic phase of ErFe11.3W0.7 compound have been established by a thorough Mossbauer spectral analysis. The Mossbauer spectra of DyFe11.3W0.7 clearly show the influence of the two spin re-orientations occurring in this compound and indicate the directions of the iron magnetic moments in both canted and planar magnetic arrangements. (c) 2005 Elsevier B.V. All rights reserved.