Distortion and Segregation in a Dislocation Core Region at Atomic Resolution

Abstract

The structure of an isolated, Ga terminated, 30 degree partial dislocation in GaAs:Be is determined by high resolution transmission electron microscopes and focal series reconstruction. The positions of atomic columns in the core region are measured to an accuracy of better than 10 pm. A quantitative comparison of the structure predicted by an ab initio electronic structure total energy calculation to the experiment indicates that theory and experiment agree to within 20 pm. Further analysis shows the deviations between theory and experiment appear to be systematic. Electron energy loss spectroscopy establishes that defects segregate to the core region, thus accounting for the systematic deviations.

Sub-angstrom imaging of dislocation core structures: how well are experiments comparable with theory?

“…On the other hand core loss EELS measurements uncover a possible reason for the projected bond length elongation since we detect higher Ga and Be spectrum signal at the stacking fault (Inset Figure 4) relative to the As and C reference signals that are reasonably constant. Careful investigation of the structure predicted by ab initio methods confirms that the EELS results may be due to double segregation of Ga As and Be Ga , although such effects are not intuitive [21]. [21].…”

“…Careful investigation of the structure predicted by ab initio methods confirms that the EELS results may be due to double segregation of Ga As and Be Ga , although such effects are not intuitive [21]. [21].…”

“…This contribution describes investigations that reach for this goal. Part of the described results was briefly reported in a recent letter [21].…”

“…We take advantage of the large image contrast and small noise levels in reconstructed electron exit wave images to extract column positions. Similarly, we exploit the strength of STEM to simultaneously record an image while stepping a 0.1 nm probe across an area of interest to record EELS spectra [21].…”

Dislocation core radii near elastic stability limits

“…Thus while elasticity theory can predict the driving force for dislocation motion, only an atomic scale theory can reveal the atomic scale motions that determine dislocation mobilities. Consequently, dislocation core studies have become a significant tool in the study of mechanical properties (see, for example, 8,[10][11][12] ).…”