Number 164 (Story #3), February 10, 1994 by Phillip F. Schewe and Ben Stein ATOMIC DREIDLS, structures resembling the child's toy top of that name, may exist at the intersections of edge dislocations at a Ge-Si semiconductor interface. Like a game of musical chairs, the process of matching up planes of atoms in a layer of germanium with planes in a silicon layer (whose lattice constant is slightly different) will result in the termination of certain planes at the interface. The termination lines are called edge dislocations and they form a checkerboard pattern at the interface. New simulations show that 18-atom dreidl-shaped structures (with half the atoms on the germanium side of the interface, half on the silicon side) are to be found at the intersections of the dislocations. The dreidls constitute a sort of lattice with a spacing of 96 angstroms and a density of up to 10**12/sq.cm. The Oak Ridge scientists performing the simulations (contact Ted Kaplan, 615-574-5790) believe that dreidls may be electrically active, a property that might be significant for electronics applications. Future x-ray scattering and photoluminesence experiments may be able to verify the existence of these structures. (UPCOMING ARTICLE: Mark Mostoller et al., Physical Review Letters.)