MAPPING SP(2) AND SP(3) STATES OF CARBON AT SUBNANOMETER SPATIAL-RESOLUTION

THE potential for diverse applications of diamond1 has been enhanced by the discovery of the chemical vapour deposition process2,3 for film formation. The growth of hetero-epitaxial diamond films on silicon is a particularly attractive goal, but only polycrystalline films have so far been prepared in this way4. Because of the large lattice mismatch, thin intermediate layers (interlayers5) are formed between the diamond and silicon phases, which may contain crystalline SiC (refs 6, 7) or amorphous compounds (SiC, carbon8 and SiO2). An understanding of how diamond nucleates5,9-11, and the role of these interlayers, requires a detailed knowledge of the nature of carbon bonding (sp2 or sp3) at the interface. Here we report the use of transmission electron energy-loss spectroscopy (EELS) to obtain a map of sp2 and sp3 carbon at a spatial resolution of less than a nanometre across the silicon-diamond interface. We find that diamond nucleates on an amorphous carbon layer, with the transition from sp2 to sp3 carbon occurring over less than one nanometre.