Surface properties of ultra-thin tetrahedral amorphous carbon films for magnetic storage technology

Diamond-like carbon (DLC) films form a critical protective layer on magnetic hard disks and their reading heads. Film thickness below 2 nm and roughness well below 1 nm are needed for storage density of 200 Gbit/inch(2). We use atomic force microscopy to study the roughness evolution vs. thickness of highly sp(3) hydrogen-free tetrahedral amorphous carbon (ta-C). The roughness of films r generally follows fractal scaling laws, increasing with film thickness h as r=ah(beta), where beta is the growth exponent. For a fixed film thickness and scan length 1, the roughness varies as l(alpha), where alpha is the roughness exponent. We find alpha similar to 0.39 and beta similar to 0-0.1. We performed Monte Carlo simulations, modelling the smoothing effects caused by the thermal spike. The simulation results closely match the experimental findings and define a new growth mechanism for ta-C films. The structural evolution of these ultra-thin films is monitored by Raman spectroscopy. A linear relation between G-peak dispersion and Young's modulus is found. The 2-nm-thick ta-C films are pin-hole free, corrosion resistant, have a Young's Modulus of similar to 100 GPa, sp(3) content of similar to50% and roughness of similar to0.12 nm. So, data storage density of 1 Tbit/inch(2) could be achieved. (C) 2003 Elsevier B.V All rights reserved.