Contents

29 November 1991
Vol 254, Issue 5036

About The Cover

Cross section of a serpentine superlattice (100 angstrom period) and its three lowest energy electron wave functions as an example of fabrication on a small scale (see page 1326). The cross-sectional view (far right) shows the aluminum-rich regions (dark) that confine electrons to the gallium-rich regions (light) in the segregated aluminum-gallium-arsenic alloy. The most colorful portions of the wave functions (in sections to the left) are regions of maximum electron density; the reddish-brown areas indicate zero density. See the editorial on page 1277 and the special section beginning on page 1300. [Simulations by J. C. Yi of the University of California, Santa Barbara]