Nanostructural study of the thermal transformation of diamond-like amorphous carbon into an ultrahard carbon nanocomposite

We studied the structural transformation of diamond-like amorphous carbon ( a-C) films into ultrahard carbon nanocomposites via postannealing to 600 de greesC using transmission electron microscopy, x-ray reflectivity, and smal l-angle scattering. Film density decreases monotonically above 200 degreesC . Film surfaces roughen upon annealing to 300 degreesC; however, a-C recove rs its smoothness with higher temperature annealing. Finally, there exists some quasiperiodic nanostructural feature with a lattice spacing that incre ases with annealing, correlating well with purely a-C nanocomposite structu res imaged from samples annealed at 600 degreesC. We propose that these ann ealing-induced nanostructural changes are a derivative of localized stress fields in as-grown a-C films. (C) 2001 American Institute of Physics.