Interface Formation and Percusory Dynamics
Final rept. 15 Nov 1986-14 Feb 1990
MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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A completely ab-initio investigation of grain boundaries in solids has been performed for the first time. The electronic and structural properties of two short-period twist boundaries in Ge have been explored and found to be extremely complex. Boundary bonds are found to be distorted and weak, three-fold and five-fold coordinated defects appear to exist, and topological disorder in the form of odd and even numbers of rings of bonds is found to prevail. Complete total energy surfaces as a function of displacement of one grain over the other have also been mapped out. The results predict that there is a large degeneracy in the number of local energy minima, that tunneling-like modes should exist in these boundaries, that the formation energies of the boundaries lie in the range between 4 and 7 eV per unit cell, that the boundary volumes involve expansions in the range of 0.1 to 0.3 Aunit area, that trends toward dimerization exist parallel to the boundary planes, that electronic states will exist deep in the fundamental gaps of these systems.