Synthesis and characterization of compound-curved graphite

Crystalline graphite with compound curvature has been produced by precipitation of carbon from metal carbide solutions. Nearly spherical graphitic shells hundreds of microns thick have been synthesized on top of millimeter-sized spherical transition metal cores in high vacuum. Raman spectroscopy, backscatter electron diffraction and X-ray analysis shows the shell to be composed of highly crystalline graphite. Upon cooling, these graphite-like shells routinely undergo a reversible transformation in which the initially smooth surface forms striking geometric facets bounded by ridges of triangular cross section. Evaporation rates and other factors suggest that this transformation represents a phase transition from graphite composed of randomly oriented layers of graphene to fully crystalline graphite having layers in registry. (c) 2006 Elsevier Ltd. All rights reserved.