An in situ TEM study of phase formation in gold-aluminum couples

In the gold wire bonding of aluminum in microelectronic devices the presence of aluminum oxide on the metallization surface may be expected. Electron transparent couples containing an oxide layer at the interface were heated in a TEM to determine the effects of a passivation layer on intermetallic formation. Intermetallic phases were evidenced by changes in sample appearance and their structure was determined by electron diffraction. The presence of an oxide at the interface hindered second phase formation at temperatures at which they were usually expected to form. In aluminum rich couples, the formation of the AuAl₂ intermetallic was not observed to form until about 350°C with the oxide present. In a reverse configuration involving a gold rich couple, an amorphous oxide phase was observed between the Al and the advancing Au₂Al front. The movement of the reaction front appeared to be controlled by surface diffusion across this phase.     

Hydrogen gas pick-up mechanism of Al-alloy melt during Lost Foam Casting

The hydrogen gas pick-up problem that can occur during Lost Foam Casting was investigated with reduced pressure tests and real castings.The initial hydrogen concentration of the melt and the contact time between melt and polystyrene had a main effect on the hydrogen gas pick-up of Al melt. The hydrogen gas pick-up of Al alloy depended also on pouring temperature and a proper metal front temperature gave the minimum hydrogen pick-up. At a low pouring temperature, the hydrogen went into the melt mainly from entrapped liquid product of polystyrene but at high pouring temperature it was by the gas as well as the liquid product. The mold flask evacuation down to 710 torr decreased the gas porosity down by around 0.4 vol%. The permeability of coating thickness had a great effect because it affects the filling time and the easy removal of liquid polystyrene.     

Mechanochemical reactions between structural defects in magnetic fields

An influence of steady, pulse and microwave magnetic fields on mechanochemical reactions between structural defects in doped ionic crystals has been studied. The effects of dislocation depinning, dislocation mobility increase, macroplastic unhardening and magnetoresonant softening in magnetic fields have been revealed. It is shown that the magnetosensitive spin-dependent reactions between structural defects is the reason of magnetoplastic effects in nonmagnetic crystals. It means that the electron and nuclear spin states of the paramagnetic defects play an important role in the formation of mechanical properties of crystals in magnetic fields and without them.     

Features of the procedures to obtain ultrafine zirconium dioxide by mechanochemical method

The results of investigation of mechanochemical reactions in the mixtures of hydroxides and carbonates of alkaline and alkaline earth metals with zirconium oxychloride and oxynitrate are presented. It is shown that one of the features of interaction between the components is the formation of the salts of alkaline and alkaline earth metals along with X-ray amorphous zirconium-containing compound. It is demonstrated that the mechanical activation of the mixture of yttrium carbonate and zirconium oxynitrate, followed by thermal treatment of this mechanically activated mixture, results in the formation of solid solution ZrO₂-Y₂O₃ in cubic modification.     

The GENIUS-test-facility—first results on background from Rn daughters

GENIUS-TF (Nucl. Instr. and Meth. A 511 (2003) 341; Nucl. Instr. and Meth. A 481 (2002) 149.) is a test-facility for the GENIUS project (GENIUS-Proposal, 20 November 1997; Z. Phys. A 359 (1997) 351; CERN Courier, November 1997, 16; J. Phys. G 24 (1998) 483; Z. Phys. A 359 (1997) 361; in: H.V. Klapdor-Kleingrothaus, H. Pas. (Eds.), First International Conference on Particle Physics Beyond the Standard Model, Castle Ringberg, Germany, 8–14 June 1997, IOP Bristol (1998) 485 and in Int. J. Mod. Phys. A 13 (1998) 3953; in: H.V. Klapdor-Kleingrothaus, I.V. Krivosheina (Eds.), Proceedings of the Second International Conference on Particle Physics Beyond the Standard Model BEYOND’ 99, Castle Ringberg, Germany 6–12 June 1999, IOP Bristol (2000) 915), a proposed large scale underground observatory for rare events which is based on operation of naked germanium detectors in liquid nitrogen for an extreme background reduction. Operation of naked Ge crystals in liquid nitrogen has been applied routinely already for more than 20 years by the CANBERRA Company for technical functions tests (CANBERRA Company, private communication, 5 March 2004.), but it never had found entrance into basic research. Only in 1997 first tests of application of this method for nuclear spectroscopy have been performed, successfully, in Heidelberg (Klapdor-Kleingrothaus et al., 1997, 1998; J. Hellmig and H.V. Klapdor-Kleingrothaus, 1997).

On May 5, 2003 the first four naked high-purity germanium detectors (total mass 10.52 kg) were installed in liquid nitrogen in the GENIUS Test Facility at the Gran Sasso underground laboratory. Since then the experiment has been running continuously, testing for the first time the novel technique in an underground laboratory and for a long-lasting period.

In this work, we present the first analysis of the GENIUS-TF background after the completion of the external shielding, which took place in December 2003. We focus especially on the background coming from ²²²Rn daughters. This is found to be at present by a factor of 200 higher than expected from simulation. It is still compatible with the scientific goal of GENIUS-TF, namely to search for cold dark matter by the modulation signal, but on the present level would cause serious problems for a full GENIUS—like experiment using liquid nitrogen.     

Synthesis and Properties of NdMCr2O5 (M = Na, K, Cs) and NdMgCr2O5.5 Chromites

NdMCr₂O₅ (M = Na, K, Cs) and NdMgCr₂O_5.5 are prepared by solid-state reactions between appropriate oxides and carbonates and are shown to have a tetragonal structure. The heat capacity of these chromites, measured from 298.15 to 673 K, exhibits sharp changes attributable to second-order phase transitions. The C _p ⁰(T) data are represented by quadratic best fit equations. The electrical resistivity of the chromites is measured between 303 and 493 K. The results attest to semiconducting behavior of the materials in certain temperature ranges.     

Preparation and Properties of Er- and Yb-Activated TeO2–WO3 Glasses

TeO₂–WO₃ glasses coactivated with Er³⁺ and Yb³⁺ are prepared. The effect of Yb content on the efficiency of Er photoluminescence (PL) in the visible and IR spectral regions is studied. The highest PL efficiency is achieved at an Er : Yb atomic ratio of 1 : 1. The PL lifetime for the Er^{3+ 4} I _13/2 level is determined to be 7–9 ms.     

Investigation of Metallic and Ceramic Materials by Small-Angle Neutron Scattering

Small-angle neutron scattering measurements on a double-crystal spectrometer with perfect monochromator and analyzer crystals were used to follow microstructural changes in the aluminum alloy VD-17, refractory alloy ZhS-6, and dispersion-hardened zirconia-based ceramics with yttria additions. The measurements were carried out by the Warren method, involving determination of the small-angle neutron attenuation coefficient. The experimentally determined total macroscopic small-angle scattering cross section is correlated with different parameters characterizing external influences on the material: the number of loading cycles, heat-treatment temperature, and fracture stress. The potential of the proposed approach for optimizing processing technologies is discussed.     

Stability of Equilibria in a Four-dimensional Nonlinear Model of a Hydraulic Servomechanism

Starting from plysical laws a four-dimensional nonlinear model for mecano-hydraulic servomechanisms is deduced. The stability of its equilibria is analysed using a theorem of Lyapunov and Malkin to handle the critical case due to the presence of zero in the spectrum of the matrix of the linear part around equilibria. Stability diagrams are drawn and simulation results are presented through phase diagrams.