J. P. Stark

Grain Boundary Self‐Diffusion in Nickel

High‐purity nickel bicrystals with controlled grain boundary misorientations have been grown from the melt using an electron beam floating‐zone technique. These bicrystals have symmetrical tilt grain boundaries with 10° misorientation between {111} planes tilted about a 〈112〉 axis, and 10° twist about a {111} axis. The diffusion of nickel‐63 in these boundaries and similar sintered grain boundaries has been studied over the temperature range 600°–970°C using high‐resolution contact autoradiography. Using the dislocation pipe model for low‐angle grain boundaries, edge and screw dislocations were found to have similar activation energies of 40.7 and 44.9 kcal/mole, respectively. The value for the tilt boundaries is shown to agree well with recent work on isolated edge dislocations in nickel. It is concluded that the low‐angle tilt boundaries are composed of 〈112〉 {111} edge dislocation arrays which exhibit the same diffusion behavior as isolated edge dislocations formed by plastic deformation. Also, the hig...

Analysis of Penetration Data from Grain Boundary Diffusion Experiments

The results from computer solutions to the various mathematical analyses of the grain boundary diffusion problem which have previously been developed are presented in a convenient manner for interpretation of grain boundary diffusion measurements using the penetration depth technique. In particular, the results allow a quantitative assessment of the limitations and applicability of the two approximate solutions due to Fisher and Whipple. The present results also permit the use of Whipples exact solution for data analysis using a simple graphical technique. Results of several previous grain boundary diffusion investigations are reevaluated by applying the exact solution to the published penetration data. It is concluded that the activation energy for grain boundary diffusion along 〈100〉 symmetrical tilt grain boundaries is independent of grain boundary misorientation.

IN SITU TRANSMISSION ELECTRON MICROSCOPY STUDY OF PLASTIC DEFORMATION IN PASSIVATED AL-CU THIN FILMS

Plastic deformation in passivated Al-1 wt %Cu thin films was studied in situ using a straining device in the transmission electron microscope. Both edge and screw dislocations were found to have caused slip on inclined {111} planes. Multiple slip was frequently observed as two or more sets of intersecting slip traces. Microstructural investigations of both unpassivated and passivated Al-1 wt %Cu films indicate that grain size and encapsulation by passivating layers are major contributors to strength of a thin film with a particular thickness. Additional strengthening is also provided by interactions between dislocations on multiple slip systems. The roles of grain orientation and precipitates in plastic deformation are also discussed.

In situ transmission electron microscopy study of plastic deformation and stress-induced voiding in Al–Cu interconnects

Plastic deformation in submicron wide Al-1 wt %Cu interconnects was studied in situ using a straining device in the transmission electron microscope. Dislocation motion occurred readily in unpassivated lines but was nonexistent in passivated lines due to the presence of stiff oxide sidewalls. Instead heterogeneous void nucleation occurred on straining to a critical limit. The void morphology was always near hemispherical and the nucleation always took place at the line edges. Further stretching of the lines led to a rupture of the sidewalls away from the lines, resulting in immediate dislocation motion. Void nucleation, cross slip, and operation of dislocation sources at line edges were all recorded on video. It was noted that dislocations almost parallel to the plane of the lines are rarely observed and furthermore, their movement is sluggish. Based on the dislocation configuration observed in these lines, a generalized geometrical model was arrived at in order to determine the significance of grain orientation on yield stress of passivated lines with columnar, bamboo grains. Frequent occurrence of twinning within the grains indicated that plastic deformation was indeed restricted in confined metal lines.

Correlation factor for diffusion in an edge dislocation in a simple cubic crystal

The correlation factor for diffusion is constructed for a vacancy mechanism of tracer diffusion in an edge dislocation in a simple cubic lattice. The method of calculation evaluates a weak and tight binding approximation to the problem. Comparison of the two approximations suggests that the tight binding approximation may be preferable under all circumstances.

Influence of solute pairs on solute diffusion in a substitutional fcc alloy

In a moderately concentrated fcc alloy, the correlation factor for solute jumps becomes increasingly approximate as the probability of solute atom pairs increases. To compensate for this difficulty, a model of solute diffusion is presented which incorporates the number of solute pairs and their contribution to the diffusion coefficient by dissociation.

A proposed model to explain impurity‐induced layer disordering in AlAs‐GaAs heterostructures

Impurity‐induced disordering of III‐V compound semiconductor quantum well heterostructures and superlattices has been extensively studied. However, the theories proposed to explain this phenomenon have dealt primarily with vacancy diffusion mechanisms and have not succeeded in explaining all the experimental observations satisfactorily. In this communication, we propose a two‐atom ring mechanism of diffusion based on a simplified model of covalent bonding in III‐V compound semiconductors and suggest that the phenomenon of intermixing is a consequence of a lowering in the activation energy due to coulombic interactions between the substitutional impurity atoms and the host atoms. This mechanism is consistent with experimental observations and is able to predict the behavior of other dopants. The additive effect of the simultaneous presence of different dopants can also be explained by this theory which could possibly be used to achieve controlled layer disordering for use in device technology.

Mobility and diffusivity for vacancy-solute diffusion in a simple cubic edge dislocation

An edge dislocation in a simple cubic crystal is considered as the basis for a model for vacancy‐induced transport. The Burgers vector for the dislocation is [010], and a solute atom moves along the compressed region of the core by vacancy exchanges along the edge of the extra half plane of atoms. The length of the dislocation is carried to the limit of an infinite number of lattice sites. Consequently, when the vacancy is tightly bound to the dislocation, that limit of tight binding becomes exact. In the tight binding limit, the correlation factor goes to zero for self‐diffusion as expected. With vacancy solute tight binding, this result is not altered. Vacancy‐solute repulsion can override vacancy‐dislocation attraction and change the limit. In the case of dislocation and solute binding to the vacancy, the diffusivity becomes indefinitely large due to the abundance of defects increasing the jump frequency at a rate faster than the correlation factor decreases it. The mobility for electromigration also ...

ON THE USE OF THE BOLTZMANN-MATANO ANALYSIS TO DEDUCE CONCENTRATION-DEPENDENT DIFFUSIVITY

Abstract The Boltzmann-Matano (B-M) analysis has been widely used to extract a concentration-dependent diffusion coefficient to explain any deviations from the classical complementary error function of Gaussian diffusion profiles. Here we show that the use of this technique can be erroneous when applied to the case of implanted semiconductors, where diffusion lengths are small and the initial/boundary conditions cannot be applied to the implantation concentration profile in the direction of diffusion.

Isotope separation during diffusion along an edge dislocation in a simple cubic crystal

During diffusion in crystalline lattices, isotope separation is well known to be proportional to the correlation factor. In a recently published analysis of vacancy‐based transport along an edge dislocation in a simple cubic system, the expression for the diffusion coefficient takes on a much more complicated form than is found in the lattice, and it is uncertain whether the isotope separation factor is indeed proportional to the correlation factor. This effect is studied analytically and numerically, and shown to equal the correlation factor for diffusion along the dislocation. In addition, the isotope separation factor for electromigration is also determined to be proportional to the correlation factor for diffusion.