Low temperature growth of ultrananocrystalline diamond

Ultrananocrystalline diamond (UNCD) films were prepared by microwave plasma chemical vapor deposition using argon-rich Ar/CH4 plasmas at substrate temperatures from similar to400 to 800degreesC. Different seeding processes were employed to enhance the initial nucleation density for UNCD growth to about 10(11) sites/cm(2). High-resolution transmission electron microscopy, near-edge x-ray absorption fine structure, visible and ultraviolet Raman spectroscopy, and scanning electron microscopy were used to study the bonding structure as a function of growth temperature. The results showed that the growth of UNCD films is much less dependent on substrate temperature than for hydrogen-based CH4/H-2 plasmas. UNCD with nearly the same nanoscale structure as those characteristic of high-temperature deposition can be grown at temperatures as low as 400degreesC with growth rates of about 0.2 mum/hr. The average grain size increased to about 8 nm from 3 to 5 nm that is characteristic of high-temperature growth, but the relative amounts of sp(3) and sp(2) bonding remained unchanged. These results suggest that the activation energy for UNCD growth is about 2-3 Kcal/mole compared with similar to28 kcal/mole for traditional growth chemistries, and that hydrogen plays an important role in the growth of UNCD films using hydrogen-poor plasmas. (C) 2004 American Institute of Physics.