Nucleation Of Cu Research Articles

Thermal stability and grain growth behavior of mechanically alloyed nanocrystalline Fe-Cu alloys

X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry were used to study the thermal stability of highly supersaturated nanocrystalline FexCu100−x alloys (10≤x≤95) synthesized by mechanical alloying. Alloys with x<60 exhibit single-phase fcc structure while single-phase bcc alloys form for x≳80. For 60≤x≤80 fcc and bcc phases coexist. Heating to elevated temperatures leads to structural relaxation, phase separation, and grain growth of the metastable nanocrystalline solid solutions. Single-phase fcc and bcc alloys undergo significant strain release but no appreciable grain growth prior to phase separation. After phase separation pronounced grain growth sets in. In contrast, samples in the two-phase region show some grain growth and significant chemical redistribution even at low temperatures. The phase separation of single-phase fcc and bcc alloys proceeds via different mechanisms: fcc solid solutions decompose by forming small Fe precipitates, while demixing in bcc alloys starts by segregation of Cu atoms to bcc grain boundaries before nucleation of Cu precipitates. These results show that the stability and grain growth behavior of nanocrystalline alloys is strongly affected by the microstructure of the material.

Potentiometric study of the nucleation of Cu2O after its formation from fehling solutions and reducing sugars

AbstractThe oxidation of glucose by Fehling solution was followed by various solid‐state ion‐selective electrode. The shape of the recorded potential vs. time transient curves at three different electrodes (Cu2 + Ph2+, and Ag+/S2−) was explained on the basis of the known mechanisms of formation of precipitates, the growth of crystals, and adsorption/desorption phenomena. The curves are peculiar in shape, are very reproducible, and show three distinct parts. The potential changes of the electrodes are due to the consumption of OH− during the reaction, as well as to its adsorption and desorption on the Cu2O precipitate. The effects on the values of different curve parameters of the concentrations of glucose, OH−, and K, Na‐tartrate, as well as the temperature, were studied.

Epitaxy and Nucleation in Cu and Ag Doped Amorphous Si

AbstractThe competition between solid phase epitaxy and random nucleation during thermal annealing of amorphous Si implanted with the fast diffusers Cu and Ag has been studied. For low concentrations of these impurities, solid phase epitaxy proceeds with small deviations from the intrinsic rate and with the impurity remaining in the shrinking amorphous layer. At a critical metal concentration in the amorphous layer of ∼ 0.12 at.% rapid random nucleation occurs, halting epitaxy and transforming the remaining amorphous material to polycrystalline Si via grain growth. The nucleation rate is at least 8 orders of magnitude greater than the intrinsic homogeneous rate. At higher Cu concentrations nucleation is observed below the temperature needed for epitaxy (400°C). This nucleation, clearly caused by the presence of Cu or Ag in the layer, may be induced by the impurities exceeding the absolute stability concentration and starting to phase separate, leading to enhanced crystal Si nucleation in the metal rich regions.

Nucleation of Cu on Si(111)7 × 7 and atomic structure of the Cu/Si(111) interface

By using scanning tunneling microscopy and spectroscopy we have studied the growth of Cu films in the submonolayer and monolayer range on room temperature Si(111)7 × 7 and the effects of annealing, which produces a long-range 5 × 5-like (noncommensurate) reconstruction. At room temperature deposition Cu mostly condenses in form of nearly triangular shaped two-dimensional islands preferentially on top of the faulted halves of the 7 × 7 unit cells, which apparently does not affect the underlying 7 × 7 reconstructed substrate. For the 5 × 5-like reconstruction a pattern with a repetitive arrangement of unit cells could not be resolved in the STM images. As characteristic details of the reconstruction we find protrusions and depressions in a mean distance of approximately 5 times the Si lattice parameter.

Nucleation of Cu on Si(111)7×7 and atomic structure of the Cu/Si(111) interface

Nucleation of Cu on Si(111)7×7 and atomic structure of the Cu/Si(111) interface

Cu2+-Adsorption Characteristics of Aluminum Hydroxide and Oxyhydroxides

AbstractThe nature of Cu2+ adsorption by boehmite, gibbsite, and noncrystalline alumina was studied over a range of equilibrium pH (4.5–7.5) and Cu2+ concentration (10−3–10−8 M) by electron spin resonance (ESR). Available chemisorption sites at pH 4.5 were the most numerous for noncrystalline alumina (~1 mmole/100 g), less for boehmite, and least for gibbsite as indicated by the relative strength of the rigid-limit ESR signal attributed to Cu2+ adsorbed at discrete sites. The chemisorption process involved immobilization of Cu2+ by displacement of one or more H2O ligands by hydroxyl or surface oxygen ions, with the formation of at least one Cu-O-Al bond. As the pH was raised from 4.5 to 6.0, essentially all of the solution Cu2+ appeared to be adsorbed by the solids. However, the noncrystalline alumina and boehmite chemisorbed much of the total adsorbed Cu2+ (10 mmole/100 g), whereas precipitation or nucleation of Cu(OH)2 in the gibbsite system was indicated. Precipitated Cu2+ was more readily redissolved by exposure to NH3 vapor than chemisorbed Cu2+.