Fullerene-like (FL) solid compound materials are relatively unexplored. Yet FL-CNx coatings prepared by reactive magnetron sputtering have shown remarkable mechanical properties in terms of resiliency. To improve their applicability as protection coatings and make them adequate to be used as a solid lubricant further improvements in C based FL solid compounds are necessary. By substituting P for N as dopant element a wider variety of bonding configurations is expected. Thus, structural and consequently macroscopic properties might be modified with respect to FL-CNx. However, a more complex structure and greater diversity in growth mechanism for FL-CPx is presumed. Instead of directly proceeding to synthesis, it is useful to apply a theoretical approach involving first principles DFT calculations in order to guide the growth process. Here, we present the results of theoretical simulation of synthetic growth of FL-CPx structures, as well as initial experimental results of the synthesis of the CPx coatings. Our theoretical results present much wider variety of potential precursor species in a general deposition flux compared to CNx. Simulations of FL-CPx structural evolution show that the substitution of N with P makes energetically favorable the formation of tetragon defects and the plausibility of P-P bonds. This implies stronger curvature and interlocking of graphene planes, as well as P-atom induced inter- and cross-linkings between them, leading to cage- and onion-like structures. This kind of structural features promises improved mechanical properties in the FL solids.
The necessity to impede the formation of predominantly P-containing species in the deposition flux, and as a consequence P-segregation in the solid CPx, dictates the use of low proportions of P (≤10 at.%) during CPx thin film deposition by magnetron sputtering, in particular. |