Laser-induced phase separation in the nickel-fullerene nano-composite

Metal-fullerene (Ni-C60) thin film has been synthesized by co-deposition of Ni and C60 on the Ni/Si backing (i.e. on the Ni-coated Si wafer). The hybrid Ni+C60 mixture (with C60 affluent component) was grown as a nano-structured composite which consists of the dispersed Ni clusters and the complex C60/a-C-based matrix (a-C-amorphous carbon). The laser beam irradiation (Nd:YAG, λ=1064 nm, τ=8 ns) led to an unusual restructuring of the hybrid matter. In an area restricted by a small aperture, the single-pulse irradiation resulted in formation of a two-stage protrusion encircled with a-C ring and C60-depleted halo. On the other hand, a broad defocused beam irradiation resulted in extensive Ni/C60(a-C) phase separation with interspersed Ni- and C60(a-C)-rich zones. Surprisingly in the C60(a-C)-rich areas, a number of micrometer-sized periodic surface patterns (so-called LIPSS-laser-induced periodic surface structure) were observed. They consist of a massive central nucleus (made of a-C) surrounded with an array of periodic domains (made of C60(a-C)-Ni). We suggest that the formation of the LIPSS patterns of second kind is due to the coordinated relaxation of the stressed structure during the rapid dissipation of the laser beam energy.