Au agglomerates observed in the out-diffusion process of supersaturated high-temperature substitutional Au in Si

Out-diffusion profiles of supersaturated substitutional Au in Si annealed at 900 °C for 90 h have been measured by SIMS and ICTS methods over a distance of 80 μm from the specimen surface. The tendency of the profile of total Au atoms measured by SIMS and that of electrically active substitutional Au measured by ICTS agrees well, but the very small regions containing high-concentration of Au atoms, 3 × 10²² cm⁻³, are observed sporadically at the distance deeper than 10 μm from the surface by SIMS method. The size of the high-concentration region is estimated to be about 20 nm and its density is about 2 × 10¹⁰ cm⁻³. The small agglomerates contain 10⁵–10⁷ Au atoms and many of them contain about 2 × 10⁵ atoms. The observed agglomerate is a new agglomeration of Au in Si. The state of the agglomeration (namely, precipitates of Au, agglomeration of substitutional Au in Si, or a new state) is not clear by SIMS measurement.     

SIMS measurement of nano-sized Au agglomerates in Si

The conditions required for SIMS measurement, namely the detection depth of the SIMS signal and an appropriate measurement cycle, to obtain a reliable shape, size and atom number of nano-sized agglomerates in Si have been investigated. Au agglomerates in Si generated during annealing at 900 °C for 360 h are measured by an appropriate SIMS method and it is found that the Au agglomerate has a spherical shape with a concentration of 5.4 × 10²¹ Au atoms/cm³. The SIMS results agree well with the calculation of spherical agglomerates. The size of agglomerates larger than 20 nm and the Au atom number in agglomerates larger than several nm can be measured in a usual SIMS experiment.     

Conditions for the generation of nano-sized Au agglomerates in Si

The conditions for the generation of nano-sized Au agglomerates in Si, which were recently discovered by the author, have been investigated. The agglomerates can be generated under very limited conditions. The agglomerates are generated with a continuous annealing method but are not generated with a typical ordinary annealing method. They are generated at an annealing temperature of 900 °C but not at 930 °C. Agglomerates are not generated in regions less than 6 μm from the surface. They are generated in a sample that is initially supersaturated with Au atoms at 7.5 × 10¹⁶ cm^?3 but are only generated at the boundary of the out-diffusion in a sample that initially contains Au atoms at 2.5 × 10¹⁶ cm^?3. Generation of the agglomerates becomes difficult as the time to cool to the annealing temperature increases in the continuous annealing process. The generated agglomerates dissolve and disappear as the surrounding Au concentration decreases to the thermal equilibrium value, that is, as the sample recovers from the supersaturation of the surrounding Au.     

Point defect configurations of supersaturated Au atoms inside Si nanowires

Aberration-corrected scanning transmission electron microscopy (STEM) is used to reveal individual Au atom configurations inside Si nanowires grown by Au-catalyzed vapor-liquid-solid (VLS) molecular beam epitaxy (MBE). We identify a substitutional and three distinct interstitial configurations, one of which has not been previously identified. We confirm the stability of the observed point defect configurations by density functional theory (DFT) calculations. The observed number densities of the various configurations are in accord with their calculated formation energies. The concentration of Au atoms is larger than the solubility limit, but the effect may be caused by the STEM beam.     

Stress evolution during isochronal annealing of Ni/Si system

Nickel films on Si(001) substrates were annealed in vacuum at a ramp rate of 5°C/min. The total force per unit width (F/W) in the film during isochronal annealing was determined using a laser scanning method for substrate curvature measurements. During heat treatment, several abrupt changes of F/W in the film were observed. A clear correlation between the evolution of F/W and the phase formation sequence was found. X-ray diffraction and sheet resistance measurements revealed that these changes of F/W coincide with the formation sequence of Ni₂Si, NiSi, and NiSi₂.     

Interdiffusion and growth of chromium silicide at the interface of Cr/Si(As) system during rapid thermal annealing

In this work, the solid-state reaction between a thin film of chromium and silicon has been studied using Rutherford backscattering spectroscopy, X-ray diffraction and the sheet resistance measurements. The thickness of 100 nm chromium layer has been deposited by electronic bombardment on Si (100) substrates, part of them had previously been implanted with arsenic ions of 10¹⁵ at/cm² doses and an energy of 100 keV. The samples were heat treated under rapid thermal annealing at 500 °C for time intervals ranging from 15 to 60 s. The rapid thermal annealing leads to a reaction at the interface Cr/Si inducing the formation and the growth of the unique silicide CrSi₂, but no other phase can be detected. For samples implanted with arsenic, the saturation value of the sheet resistance is approximately 1.5 times higher than for the non-implanted case.     

Kinetics of reactive diffusion between Au and Sn during annealing at solid-state temperatures

The reactive diffusion between Au and Sn was experimentally studied at solid-state temperatures using Sn/Au/Sn diffusion couples prepared by a diffusion bonding technique. The diffusion couples were annealed at temperatures of T = 393 and 473 K for various times in an oil bath with silicone oil. After annealing, compound layers composed of AuSn₄, AuSn₂ and AuSn were recognized to form at the Au/Sn interface. The thickness of the AuSn₄ layer is about six and four times greater than those of the AuSn₂ and AuSn layers at T = 393 and 473 K, respectively. The ratio of the thicknesses of the compound layers is kept constant independently of the annealing time. The total thickness l of the compound layers is described as a function of the annealing time t by the equation l = k(t/t₀)ⁿ, where t₀ is unit time, 1 s. The exponent n is nearly equal to 1/2 at T = 393 K but takes a value between 1/4 and 1/2 at T = 473 K. Such an intermediate value of n at T = 473 K indicates that the grain boundary diffusion contributes to the reactive diffusion and the grain growth occurs at certain rates. As the annealing temperature decreases, the contribution of the grain boundary diffusion should become more remarkable, but the grain growth will slow down. Consequently, n becomes close to 1/2 at T = 393 K. According to the constancy of the ratio of the thicknesses, it is concluded that the same rate-controlling process works in the AuSn₄, AuSn₂ and AuSn layers at a constant annealing temperature.     

Three-dimensional computer modeling of grain growth and pore shrinkage during sintering

This paper deals with modeling of grain growth and pore shrinkage during sintering. The simulation takes as the theoretical basis the curvature of the grain boundaries and the pore surfaces and their mobilities. The movement of the grain boundaries is calculated for each grain separately using the flux equation for grain growth j=c_k(1/r₂−1/r₁), c_k being a rate constant, r₁ and r₂ effective radii for each grain boundary. The modification of these boundaries in a micro structure is calculated in two and three-dimensional space starting with a Voronoy mosaic at the beginning of sintering. Two kinds of pores are distinguished: sphere like pores situated between two grains and non spherical pores between at least three grains. The results of several computer runs are shown and discussed.     

Dimensional shrinkage of supersaturated ZA27Cu1 and ZA27Cu2 alloys

Abstract

The dimensional changes of supersaturated ZA27Cu1 and ZA27Cu2 alloys based on Zn-27 Al-Cu, quenched from 360°C, and the mechanisms influencing the dimensional changes were investigated with a universal tool measuring microscope and X-ray diffraction. It wasfound that the dimensions of the supersaturated alloys shrunk rapidly and considerably after aging at 80°C, and that Cu enhanced shrinkage. The dimensional shrinkage which occurred after aging was a result of rapid precipitation of η (Zn base solid solution) and e (CuZn₄) phases from the supersaturated β phase (Al base solid solution).     

Subgrain growth in Al and Al-1% Mn during annealing

The subgrain growth during annealing of cold-worked Al-1% Mn and Al(4N) has been measured in the temperature intervals 300 to 400° C and 100 to 200° C respectively. For Al-1%Mn the subgrain diameter showed a parabolic growth, while for Al the diameter gradually reached a constant value. The microstructural investigations which included in situ annealing in a high voltage electron microscope demonstrated that the operating mechanism for growth in the higher temperature range was collective migration of sub-boundary dislocations. In the lower temperature range extraction of dislocations was found to be the dominating mechanism, i.e. dislocations partly lying in the boundaries are pulled out by the stress field in the subgrain interior. The observed growth rates were consistent with models for these mechanisms presented in two previous papers.     

The formation,migration, agglomeration and annealing of vacancy-type defects in self-implanted Si

The evolution of vacancy-type defects has been studied by variable-energy positron annihilation spectroscopy (VEPAS) in samples of high-quality FZ p-type (001) silicon wafers implanted with 4 MeV Si²⁺ ions at room temperature to doses of 10¹²–10¹⁴ cm⁻². The average vacancy concentration increases as (ion dose)^{0.70 ± 0.06}. Progressive isochronal annealing measurements show that open-volume point defects (having a VEPAS signature close to that for divacancies) anneal between 500–600°C. VEPAS with enhanced depth sensitivity (via progressive etching) verified that single 30 min anneals to 550 and 600°C lead to the formation of buried clusters V _N with an average N of 3.5 lying between depths of 2.2 and 3.6 μm (both ± 2 μm), close to the peak of vacancy damage just shallower than the ion range predicted by simulation. The concentration of these clusters increases as (ion dose)^{2.6 ± 0.1}. Single anneals to higher temperatures reduce all open-volume point defect concentrations to below the limit detectable by VEPAS.     

Breakdown of agglomerates in ideal pastes during extrusion

By separating the matrix from the agglomerate it was possible to determine the nature of agglomerate breakdown during extrusion within a known geometry. Previous attempts at observing agglomerate breakdown have been unsuccessful at relating the properties of the paste to the properties of the agglomerate due to the indistinguishability of the paste and the agglomerates. By using well-characterized materials, it was found that the breakdown probabilities of the agglomerates during extrusion were independent of the position of the agglomerate. This indicated that as the shear strain rate was known to be highly position dependent, the agglomerate breakdown was shear strain rate independent. Following breakdown, the distributive mixing was observed to be position dependent.     

The effect of flow type and chemical functionalization on the dispersion of carbon nanofiber agglomerates in polypropylene

Two melt mixing methods generating flow with different characteristics are compared to study the dispersion of 5% w/w carbon nanofibers in polypropylene, namely conventional twin-screw extrusion and the simple application of a converging/diverging flow sequence to the composite melt. The effect of nanofiber surface modification and compatibilization with polypropylene modified with maleic anhydride is also studied. The dispersion of the nanofiber agglomerates through the polymer, the electrical properties of the resulting composites and nanofiber/polymer interface achieved under the different mixing conditions are analyzed. The converging/diverging flow sequence generated a better dispersion as compared with the twin-screw extruder.     

Mechanical properties of Ni3(Si,Ti) polycrystals alloyed with substitutional additions

The mechanical properties of the L1₂-type Ni₃(Si, Ti) polycrystals, which were alloyed with 1–2 at% of various transition metals and also doped with boron, were investigated over a wide range of temperatures. The addition of Hf enhanced the levels of yield stress whereas the addition of Cr, Mn and Fe reduced the levels of the yield stress over a wide range of temperatures. Ni₃(Si, Ti) alloyed with Cr, Mn and Fe showed a shallow minimum in the yield stress-temperature curves. This result was correlated with the modification of the micro-cross-slip process by the additives. At low temperatures, the addition of Hf and Nb slightly reduced the elongation, while the addition of Cr, Mn and Fe improved elongation. This elongation behaviour was interpreted as the alloying effect on the intergranular cohesive strength of L1₂ ordered alloys. At high temperatures, the elongation of Ni₃(Si, Ti) alloyed with Hf showed a particularly high value. This elongation behaviour is discussed based on the alloying effect on the competition between dynamic recrystallization and cavitation at grain boundaries. The fracture surfaces exhibited a variety of fracture patterns, depending on temperature and the alloy, and were primarily well correlated with the elongation behaviour. The ductilities of most of the alloys at high temperatures were reduced by the tests in air.     

The size of condensation nuclei and the growth of drops in a supersaturated vapor

A derivation based on the condition of dynamic equilibrium between a molecular complex and molecules of a gas is given for equations which allow the determination of the size of condensation nuclei and their subsequent growth within free molecular motion.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 5, pp. 905–911, November, 1970.     

Generation of acoustic oscillations during the growth and breakoff of air bubbles

Problems associated with boiling and bubbling processes are investigated. It is established that acoustic signals occurring in the process of bubble generation are produced by pressure variations at the instant of growth and breakoff of bubbles.