Maria Ronay

Reinvestigation of first phase nucleation in planar metal‐Si reaction couples

It is proposed that the first nucleating phase in planar metal‐silicon reaction couples is that congruently melting phase neighboring the central eutectic in the phase diagram, which is closer in composition to the diffusing species. This phase also must have a low interfacial free energy with one of the elements constituting the phase diagram. The low interfacial free energy is indicated either by eutectic formation with, or, by epitaxial growth on one of the elements. It is suggested that a low‐energy interface is no barrier to diffusion; therefore, phases that nucleate first in metal‐silicon reaction couples are not good as diffusion barriers.

Hillock formation in lead films by grain boundary sliding

Abstract Lead films varying in thickness and grain size were deposited from the vapour onto substrates varying in their coefficient of thermal expansion. This way both the yield stress of the films and the thermal stress arising from temperature change could be varied. Hillock formation brought about by various numbers of thermal cycles between R.T. and 4.2 ? was observed in these films by SEM and the quantitative dependence of hillock volume on stress and grain size determined. These dependences together with detailed observations suggested that, under thermal stresses larger than the yield stress of the film, hillocks form by grain boundary sliding in the superplastic mode. A model is proposed in which the sliding rate is given as a product of slip band density and the rate of climb of absorbed slip dislocations in the grain boundary. Since both quantities depend linearly on stress—with the yield stress as the threshold stress—the experimentally observed second‐power dependence of sliding rate on stress...

Anisotropy of oxygen transport in YBa2Cu3O7: The role of the [½, b,0] tunnels

We calculated the potential of interstitial oxygen in YBa 2 Cu 3 O 7 using effective medium theory. We found that there is no potential energy barrier for oxygen motion in the [½, b,0] tunnel. Oxygen motion in the a and c directions requires overcoming barriers of 1.7 and 1.6 eV. Implications for superconductivity and oxygen diffusion are given.

Development of Aluminum Chemical Mechanical Planarization

The paper describes the development of an aluminum chemical mechanical planarization process that was successfully integrated into the dual damascene technology producing I Gb dynamic random access memory chips meeting all yield and sheet resistance requirements. Three of the major problems of chemical mechanical polishing of Al-0.5 Cu alloys, i.e., copper plate-out on titanium liners, array erosion, and slow polish rate were solved by adding Ce 4+ ions to the polishing slurry.

Determination of the dynamic surface tension of inks from the capillary instability of jets

Abstract A remarkable agreement between Webers linear analysis and experiment makes it possible to determine the dynamic surface tension of viscous liquids from the growth rate of axisymmetric disturbances on excited capillary jets. The method is very accurate and can be used to determine the surface tension at as short as 10 −4 sec surface age. Aqueous glycerol solution and inks developed for inkjet printing were used as test liquids in the experiments. While a dye base ink showed time-dependent surface tension, the surface tension of inks which were colloid suspensions of small pigment particles and contained surfactant micelles equalled their equilibrium value at 10 −4 sec surface age. In the tentative explanation of this phenomenon, the dynamic equilibrium between surfactant molecules in solution and in micelles was substituted for long-range surfactant transport by diffusion. A result of this assumption is that surface tension in nonequilibrium states depends only on the composition of the surface layer.

A new correlation for Tc from Cu 2p absorption

Abstract We studied the Cu 2p x-ray absorption spectra of the superconductor La2−xSrxCuO4 in the doping regime x=0-0.6 and found that the intensity of the satellite peak is a reliable measure of the doping-induced hole concentration. From the Cu 2p absorption spectra taken in this work on the La2−xSrxCuO4 system and from those published for other high-temperature superconductors, we found that the energy separation between the satellite peak and the main peak, which is the ligand-hole energy, increases with Tc.

Reducing the grain size of polycrystalline lead films by the use of nucleants

Thin layers of La, Y, Au, Pd, Pt, Ag, and Sn were evaporated at room temperature as nucleants prior to the evaporation of 2000 A Pb. The correlations of grain size, surface morphology, and the phase diagrams of lead nucleant showed that the grain size of lead was reduced only if the nucleant formed a compound with lead and a eutectic between the compound and lead. In such a case the surface morphology was hemispherical, indicating that crystallization from the vapor took place through the liquid phase. The various sources of undercooling explaining the presence of the liquid phase are discussed. It is shown that the necessary condition for heterogeneous nucleation is the same as the condition for lamellar or rodlike eutectic growth; therefore, the occurrence of such eutectic in the phase diagram indeed indicates the possibility of heterogeneous nucleation. A vapor‐liquid‐heterogeneous nucleation mechanism of crystallization is suggested. Factors affecting the surface morphology of nucleated films are disc...

Reducing the grain size of polycrystalline lead films by the use of barriers to grain growth

The mechanical strength of lead‐alloy films used in Josephson junctions is improved by reducing the grain size. One way to achieve this goal is to reduce the rate of grain growth. The activation energy for barrierless growth during vapor deposition was estimated to be about 540 cal/mole for lead films and is assigned to the ordering of atoms. Because of its small value, instead of reducing the rate of grain growths, it seemed best to stop growth by the application of a barrier layer. This is followed by the nucleation of new grains. Five requirements for a barrier‐to‐grain growth are given out of which the requirement of a high interfacial free energy between barrier and lead is stressed the most. In the experiments Nb, PdSn4, AuIn2, and PdIn3 were used as barriers between lead layers. The grain size of layered films was determined by transmission electron microscopy and was found to be about the same as if the total film thickness were equal to the thickness of one layer. Yet there are small differences ...

Nitridable steels for cold forming processes

Low carbon titanium steels with nickel and/or manganese and silicon additions were developed to combine formability, nitradability with increased strength. The strength, formability, and nitradability of 16 different compositions were investigated. Neither the depth nor the great hardness of nitrided layers, due to TiN particles < 15Å in size, was influenced by the addition of other alloying elements. The high nucleation frequency resulting in the small size of TiN particles is attributed to the coprecipitation of TiN and Fe4N minimizing the strain energy barrier for nucleation. The hardening caused by various volume fractions of TiN precipitate in the nitrided layer was in good agreement with the quantitative estimate of Gerold and Habercorn15 in which the interaction between edge dislocations and coherency strain fields is assumed to be the strengthening mechanism.

Dependence of track width on load and on the number of passes in sliding contact

Abstract The track width has been determined as a function of the weight and the number of passes in unidirectional and in reciprocated sliding contact with a spherical indenter for both work-hardened and annealed copper. It has been found that this function of two variables has a remarkably simple and symmetric structure. The properties of this function yielded a new material constant, the cyclic work-hardening modulus, defined as the mixed partial derivative of the logarithm of track width with respect to the logarithm of the number of cycles and the logarithm of weight. Work-softening was found to occur in reciprocated sliding, providing an explanation for the wider tracks produced in reciprocated as against unidirectional sliding.