Cryogenic graphitization of submicrometer grains embedded in nanostructured tetrahedral amorphous carbon films

A growth mechanism for submicrometer grains in diamondlike carbon films has been investigated. Films were formed by laser deposition on quartz substrates at 20-573 K. Atomic force microscopy shows that films deposited at 20-100 K consist of a matrix assembled from 40 nm nanoparticles that further aggregate into 400-500 nm grains which become embedded in the matrix. Nanohardness measurements show that these embedded grains possess a lower hardness than that of the matrix. Electronic structure obtained from resonant Raman spectra shows a remarkable clustering of s p2 bonds in the s p3 bonded matrix. It is believed that the s p2 bonded phase is concentrated in these submicrometer grains. X-ray photoelectron spectra show that this segregated structure has an enhanced affinity for oxygen.