Showing papers by "Cinzia Casiraghi published in 2003"

Dynamic roughening of tetrahedral amorphous carbon.

Abstract: The evolution of the surface roughness of growing thin films of metals or semiconductors provides much information about their growth mechanism. Some systems show stages of nucleation, coalescence, and growth. Some systems show microstructures that vary with the growth temperature and conditions [1]. Others show a self-affine behavior in which the roughness varies in a fractal manner with the film thickness and the measurement scale [2 ‐6]. In this case, the randomness of the incident flux creates roughness, which is smoothed by the presence of surface diffusion or surface relaxation and a minimization of surface energy. It is found that the roughness evolution belongs to certain classes depending on the dominant process. These processes are thermally activated, so the observed behavior class depends on the temperature scaled to the melting point — homologous temperature, � —for a given class of materials. This Letter presents the first measurement of the roughness evolution of a highly sp 3 form of amorphous diamondlike carbon called tetrahedral amorphous carbon (ta-C) grown from energetic ions [7]. It is found to have an extremely small roughness, of � 0: 1n mroot mean square (rms), and an extremely small growth exponent, and to have these at very low homologous temperatures, of order 0.07, based on a melting point of 4000 K [8]. These results indicate that surface relaxation is occurring at very low scaled temperatures. We interpret this as a smoothening that occurs during a local surface melting caused by the incident ions. This is very important technologically, as the remarkable smoothness of ta-C allows it to form pinhole-free films of only 1‐2 nm thickness, and to act as a protective layer on read heads and disks in magnetic disk storage systems [9]. While the traditional carbon coatings for magnetic storage cease to protect below 3‐ 4 nm [10], 1‐2 nm thick ta-C films could be used to achieve recording densities over � 100 Gbit=in: 2 and � 1 Tbit=in: 2 for longitudinal and