Substrate tilting effect on structure of tetrahedral amorphous carbon films by Raman spectroscopy

Raman spectra at visible and ultraviolet excitation of tetrahedral amorphous carbon (ta-C) films have been studied as a function of oblique angles of substrates while keeping the energy of incident particles stable. The substrate angle is varied from 0 to 60°. The spectra show that the films contain less sp3 content and more ordered sp2 clustering as the substrate tilting angle increases from 0 to 60° for thicker films of 70 nm, and also a decrease of sp3 content for thinner films of 2 nm from 0 to 45°. Raman data indicates the substrate tilting can dramatically lower internal stress while having less influence on hardness because hardness is related to sp3 content, but internal stress is related to not only sp3 content but the order of sp2 cluster. And this is also consistent with the measurement of hardness and internal stress for thicker films of 70 nm. The implications of these results on the mechanisms proposed for the film formation were discussed. It can provide a way for film application in magnetic recording slider that requires less internal stress and suitable hardness.