Mapping sp(sup 2) and sp(sup 3) states of carbon at sub-nanometre spatial resolution

The potential of diverse applications of diamond has been enhanced by the discovery of the chemical vapor deposition process 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 way. Because of the large lattice mismatch, thin intermediate layers (interlayers) are formed between the diamond and silicon phases, which may contain crystalline SiC or amorphous compounds (SiC, carbon and SiO2). An understanding of how diamond nucleates, and the role of these interlayers, requires a detailed knowledge of the nature of carbon bonding (sp(sup 2) or sp(sup 3)) at the interface. Here we report the use of transmission electron energy-loss spectroscopy (EELS) to obtain a map of sp(sup 2) and sp(sup 3) carbon at a spatial resolution of less than a nanometer across the silicon-diamond interface. We find that diamond nucleates on an amorphous carbon layer, with the transition from sp(sup 2) to sp(sup 3) carbon occurring over less than one nanometer.