Magnetic disorder induced enhanced magneto-resistance in La0.5Sr0.5Co1−xRuxO3

We observe a sharp increase in negative magneto-resistance ratio up to 40% for x=0.1, in La_0.5Sr_0.5Co_1−xRu_xO₃ which is due to the magnetic disorder induced by an anti-ferromagnetic interaction between Co and Ru ions. We also observe a metal to insulator and a ferromagnetic to anti-ferromagnetic transition for 0≤x≤0.3. Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co³⁺:t_2g⁵e_g¹), forcing a double exchange mediated ferromagnetic state to an anti-ferromagnetic spin state for x≥0.2.     

Enhanced excitation of giant pairing vibrations in heavy-ion reactions induced by weakly bound projectiles

The use of radioactive ion beams is shown to offer the possibility to study collective pairing states at high excitation energy, which are not usually accessible with stable projectiles because of large energy mismatch. In the case of two-neutron stripping reactions induced by ⁶He, we predict a population of the giant pairing vibration in ²⁰⁸Pb or ¹¹⁶Sn with cross-sections of the order of a millibarn, dominating over the mismatched transition to the ground state. Received: 30 November 2001 / Accepted: 25 February 2002     

Asymptotic normalization coefficients and astrophysical direct capture rates

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANCs). These coefficients, which specify the normalization of the tail of the nuclear overlap function, determine S-factors for direct capture reactions at astrophysical energies. A variety of proton transfer reactions involving both stable and radioactive beams have been used to measure ANCs. Tests have demonstrated that ANCs determined from proton transfer reactions can be used to calculate astrophysical direct capture rates to within 9%. The ¹⁰B(⁷Be, ⁸B)⁹Be and ¹⁴N(⁷Be, ⁸B)¹³C reactions have been used to measure the ANC appropriate for determining the ⁷Be(p,γ)⁸B rate, and the ¹⁴N(¹¹C, ¹²N)¹³C reaction has been used to measure the ANC required to calculate the ¹¹C(p,γ)¹²N rate. Received: 1 May 2001 / Accepted: 4 December 2001     

Nitrogen incorporation in amorphous SiCN layers prepared from electron cyclotron resonance plasmas

Electron cyclotron resonance plasma chemical vapor deposition with nitrogen, methane, and argon-diluted silane as precursors has been used to prepare SiCN thin films. Optical emission from CN species in the plasma has been observed. Infrared measurements show that most of the nitrogen is incorporated to the thin solid films in the form of Si-N, C=N and C≡N bonds suggesting a basic structure of incomplete SiN tetrahedra with C=N and C≡N bridging bonds. The deposited films are nearly transparent in the visible range with a weak absorption threshold between 2.2 and 3.5 eV. Received: 3 April 1998 / Accepted: 5 January 1999 / Published online: 31 March 1999     

Nanocrystalline CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> powder by PVA sol–gel route: synthesis,characterization and its giant dielectric constant

Nanocrystalline CaCu₃Ti₄O₁₂ powders were synthesized by a simple PVA sol–gel route and calcined at 700 and 800°C in air for 8 h. The diameter of the powders ranges from 40–100 nm. The calcined CaCu₃Ti₄O₁₂ powders were characterized by TG-DTA, XRD, FTIR, SEM, and TEM. Sintering of the powders was conducted in air at 1100°C for 16 h. The XRD results indicated that all sintered samples had a typical perovskite CaCu₃Ti₄O₁₂ structure although the sintered samples contained some amount of CaTiO₃. SEM of the sintered CaCu₃Ti₄O₁₂ ceramics showed the average grain sizes of 13–15 μm. The samples exhibit a giant dielectric constant, ε′∼10⁵ at 150 to 200°C with weak temperature dependence below 1 kHz in the sample sintered using the powders calcined at 700°C. The Maxwell–Wagner polarization mechanism is used to explain the high permittivity in these ceramics. It is also found that all sintered samples have the same activation energy of grains, which is ∼0.122 eV.     

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W₂B target at various N₂/(Ar + N₂) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.     

Fabrication and characterization of suspended single-walled carbon nanotubes

Suspended single-walled carbon nanotubes (SWCNTs) between SiO₂ pillars via a direct lithographic route using a simple mixture of catalyst precursor [Co(III) acetylacetonate, Co(acac)₃] and conventional electron beam resist (ma-N2403) were fabricated. The catalytic electron beam resist (Cat-ER) layer plays dual roles as a catalyst and a resist layer for the growth and alignment of CNTs, respectively. The structure of the grown nanotube was characterized by Raman spectroscopy (633 nm laser excitation). Nanotubes grown from Cat-ER with Co(acac)₃ show the typical Raman spectra of SWCNTs which are characterized by the strong tangential bands near to 1590 cm⁻¹ and radial breathing modes (RBMs) in the low frequency region (<300 cm⁻¹). The calculated diameter of the probed nanotubes individually corresponds to the range 0.86-1.77 nm.     

La1−xCaxCoO3 perovskite-type oxides: Identification of the surface oxygen species by XPS

A detailed study of the La_1−xCa_xCoO₃ perovskites surface by XPS was carried out since this is a potentially useful tool to identify the oxygen species involved in the catalytic reaction and discriminate them. Mainly, the concentration of surface oxygen vacancies (λ′) can be estimated from the XPS atomic ratio.     

Italian Renaissance and Hispano-Moresque lustre-decorated majolicas: imitation cases of Hispano-Moresque style in central Italy

An investigation was carried out on Renaissance lustre-decorated majolica shards, found during excavations made in Umbria (central Italy) and defined by experts, on the ground of the surface decoration, as imitations of the Hispano-Moresque style. A comparison between this particular kind of samples, produced in central Italy, and some Hispano-Moresque lustre shards has been performed. The ceramic bodies as well as the lustred surfaces have been analysed by means of several techniques: inductively coupled plasma optical emission spectrometry, X-ray diffraction (XRD), atomic absorption spectrometry with electrothermal atomisation and scanning electron microscopy. By means of XRD analysis the presence of cosalite (Pb₂Bi₂S₅) has been disclosed in the Italian lustre decorations but was not observed in the Hispano-Moresque ones. A hypothesis has been made, considering bismuth as a discriminating element, between lustres produced in central Italy and the Hispano-Moresque ones. We thought that the Italian artisans were able to manage the use of bismuth. Therefore a recipe, quite similar to the one employed by the Spanish artisans, was used by the Italian ceramists if their aim was to imitate the Hispano-Moresque style. Received: 4 November 2002 / Accepted: 6 November 2002 / Published online: 28 March 2003 RID="*" ID="*"Corresponding author. Fax: +39-06/9067-2316, E-mail: pad@mlib.cnr.it     

The Average Lifetime of Giant Composite Systems Formed in Strongly Damped Collisions

The dynamic, adiabatic and diabat ic entrance potentials in strongly damped reactions of ^238 U＋^238 U, ^232 Th ＋ ^250Cf are calculated and compared. The feature of the dynamical potential implies that it is possible for the composite systems to stick together for a period of time. By means of the improved quantum molecular dynamics model the time evolution of the density and charge distributions of giant composite systems and their fragments for reactions ^238U＋^238U, ^232Th＋^250Cf are investigated, from which the lifetimes of giant composite systems at different energies are obtained. The longest average lifetime of ^238U＋^238U is found when the incident energy is about Ec.m =1080 MeW, which is about 1200 fm/c.