Dependence of the features of diamondlike carbon films on their synthesis methods, as analyzed by Raman spectroscopy

The dependence of features of diamondlike carbon (DLC) films on their synthesis methods were clarified by Raman spectroscopy. The DLC films were synthesized by three different methods: photoemission-assisted glow discharge (PAGD), ionized deposition (ID), and unbalanced magnetron sputtering (UBMS). The main difference among these methods was the influence of ions on film formation. Raman analysis in conjunction with the sp2 cluster model led to the elucidation of each film structure. The DLC film synthesized in PAGD with efficient ion assist consisted of dispersed, small, and unstrained sp2 clusters surrounded by a dielectric matrix of sp3 carbon. The clusters were aliphatic, which reflects the methane gas source; however, hydrogen atoms were etched away to some extent because of bond rearrangement caused by the ion assist. The sp2 clusters synthesized by ID were well-grown aromatic clusters, which reflect the benzene gas source; however, the clusters contained certain amounts of defects, and sufficient electrical isolation occurred among the clusters. The well-grown sp2 clusters caused weak internal strain of the film. In UBMS without the ion assist, strongly strained sp2 clusters that included numerous defects from damaged graphite (polyaromatic) radicals by sputtering were created. The density of the clusters was high, and the film was conductive. The defects were removed by introducing methane as a second hydrocarbon source during the synthesis. However, the strain was enhanced further in conjunction with the defect removal.