27 April 2012
Vol 336, Issue 6080

About The Cover

Cover image expansion

COVER Overlayed scanning tunneling and atomic force microscopy images of a single atom (width 1.3 nanometers): tunneling current (gray veil) and force (colored surface) between a tungsten atom and a carbon monoxide molecule. The force shows a strong angular dependence and is attractive (blue minimum) in one direction and repulsive (dark red crescent) in others. The angular dependence of single chemical bonds determines the shape of molecules and crystals. See page 444. Image: Joachim Welker, University of Regensburg