Diamond Nucleation By Carbon Transport From Buried Nanodiamond Tio_2 Sol-gel Composites

摘要

The diamond nucleation step is critical for the chemical vapor deposition (CVD) of diamond on non-diamond substrates, i.e., for heteroepitaxial as well as polycrystalline growth on non-diamond (foreign) substrates. This process has been studied intensively over the past 20 years. In general, diamond CVD growth on foreign substrates requires artificial formation of diamond nucleation sites on the substrate's surface. The high surface energy of diamond, usually prevents direct, heterogeneous diamond nucleation from the gas phase, hence diamond growth cannot be initiated without this critical nucleation step. As for the subsequently occurring diamond growth, it is assumed that atomic hydrogen is the only essential mediator required for stabilizing the diamond phase. Nonetheless, it was recently suggested that diamond can also grow in bulk, i.e., in a solid state environment, such as the sub-surface of silicon, if carbon atoms are sub-implanted by low energetic beams and transformed into diamond grains. In this communication, we show that diffusion based transport of carbon atoms from diamond seeds through an interlayer is yet another mechanism by which diamond nuclei can be formed. This process opens further possibilities for the LPLT growth of synthetic diamond on a variety of substrates and gives access to new applications for nanocrystal-line diamonds (NCD), where diamond-like carbon and amorphous carbon are already applicable. Carbon transport and subsequently occurring sp~3 bonded carbon cluster formation originates from dissolving so-called ultra-dispersed nanodiamond particles (UDDs) of 5-10 nm size, which are readily prepared in form of a monolayer beneath a TiO_2 sol-gel thin film on silicon substrate surfaces.