En las fronteras de la Materia Condensada

In the last years, a wide range of new carbon structures has been prepared from fullerene C₆₀ under high pressures and temperatures. Recently it has been demonstrated that high-pressure-induced amorphization of solid C₆₀ gives as result a superhard carbon structure. However, is not possible to obtain homogenous and contaminants-free films with this method. Hard hydrogen-free carbon films have been produced accelerating C₆₀ ions on silicon substrates. C₆₀ ions were obtained from fullerene powder at high temperature using a filament-discharge ion source. C₆₀⁺ have been accelerated to different energies (from 100 to 2000 eV) on the substrates. Samples have been vacuum annealed at 600 °C in order to study their thermal behavior. All the films have been characterized by Raman spectroscopy, EELS, PAS, and hardness measurements. The experimental evidence shows that the structure of the resulting material depends on the energy of the ions. Up to 200 eV, the molecules preserve their identity and they are weakly bounded to their neighbors. As deposition energy increases, up to 1000 eV, there is a fragmentation of the C₆₀ molecules, giving as result a coexistence of polymeric and amorphous islands. At higher energies, the characteristics of the material are similar to those of amorphous carbon. Hardness measurements indicate that polymeric films are harder than amorphous ones. These results have been correlated with molecular dynamic simulations as a function of the ion beam deposition energy.