These two really go together. The system of interest are nanowires of silicon along the [100] direction (out of page). The images show cross sections of the wire. The second one (Sibars2x1.jpg) shows the atomic positions color coded with their relation to the wire (white are interior atoms, red are surface atoms, and green are edge atoms [intersection of two surfaces]). The Sibarsnz2x1.jpg shows the electron density for this system; atomic positions are shown by small boxes to aid the eye. There is a clear enhancement of density at the edges, much more than at the exposed surfaces, with important repercussions for the stability and the electronic states of the nanowires. Reference: S. Ismail-Beigi and T. A. Arias, ``Edge-driven transition in surface structure of nanoscale silicon'', Physical Review B 57, 11923 (1998).

Submitted by Sohrab Ismail-Beigi