More direct evidence of the fcc arrangement for artificial opal

We present a scanning electron microscopy (SEM) investigation of artificial opals prepared by the sedimentation of suspension with sub-micrometer sili ca spheres. An analysis of the SEM images confirms that the fee stacking is the most stable phase for the artificial crystals. Optical diffraction and transmission spectrum indicate a good alignment of the top (111) crystal p lane. We also show that defects and dislocations of opal crystals are cause d mainly by the irregular spheres. Slow sedimentation and uniform size of s ilica spheres may be the key factors for growing high quality opal crystals . (C) 1999 Elsevier Science B.V. All rights reserved.