This figure shows the core of a dislocation (the so-called 30 degree partial) in crystalline silicon as seen from the perspective of its electrons.  The spheres (white and light green) represent the atomic cores, whereas the translucent gold and red surfaces represent contours (lower and higher, respectively) of the electron density. The build up of charge corresponding to bonds appear as red regions outlined in gold between each pair of atoms. The figure shows that the dislocation core maintains the expected four-fold, tetrahedral bonding network of silicon.  The atoms highlighted in green make up the core of the dislocation, which prefer to have atoms bonded together in pairs as do the two green atoms in the left half of the figure. The green atom on the right represents the most common defect of the dislocation, a soliton. Rather than pairing with another core atom, it "reaches" up and to the left to bond with a white, non-core atom, which already had four bonds and now forms a "floating-bond" defect, a silicon atom with five bonds.  Floating bonds are usually only found in amorphous silicon, and the unusual structure of the this soliton defect explains the unusual symmetry of the primary component of the magentic resonance observed in plastically deformed silicon. This resonance had remained a mystery for several decades and was oft noted to resemble resonance signatures found in amorphous silicon. (See "Paramagnetic structure of the soliton of the 30 partial dislocation in silicon," Reference: Gábor Csányi, Sohrab Ismail-Beigi and T.A. Arias, Physical Review Letters 80, 3984 (1998).)

Submitted by Sohrab Ismail-Beigi