30 October 1998
Vol 282, Issue 5390

About The Cover

Cover image expansion

COVER Carbon and phenolic inverse opals can be more opalescent than gem opals because cages replace the periodic silica spheres of the natural gem. The colors change when liquids fill the cages, as for the pictured water-filled phenolic inverse opal (image width ~17 mm). The ability to form periodic arrangements of cages on the scale of optical wavelengths for many materials, including diamond, may be important for obtaining useful electronic and optical properties. See page 897. [Image: A. A. Zakhidov, I. Khayrullin]