Materials Science

Melting the High Spots

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Science  12 Dec 2003:
Vol. 302, Issue 5652, pp. 1865
DOI: 10.1126/science.302.5652.1865b

Carbon films have been used as the protective layer for magnetic disks and read heads, but they begin to fail when they are thinner than 3 to 4 nm. An alternative material, tetrahedral amorphous carbon, forms a highly sp3 bonded network, yielding pinhole-free films that are only 1 to 2 nm thick and remarkably smooth. Casiraghi et al. used atomic force microscopy to follow the carbon-ion deposition process and to elucidate the growth mechanism responsible for the smoothness. By measuring the change of the height-height correlation function with respect to film thickness, they extracted a roughening exponent α of ∼0.39 and a growth exponent β that ranged from 0.0 to 0.1. These exponents do not correspond to any existing growth models, but such low β values suggest that surface diffusion and relaxation must play a role during growth. The authors argue that diffusion is aided by local heating due to the impact of the carbon ions, and they present Monte Carlo simulations in which impact melts and flattens the film locally. — MSL

Phys. Rev. Lett. 91, 226104 (2003).

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