Laser-induced short- and long-range orderings of Co nanoparticles on SiO2

Laser irradiation of ultrathin Co films leads to pattern formation by dewetting with short-range order (SRO) as well as long-range order (LRO). When a 1.5nm thick Co film is irradiated by a single laser beam, a monomodal size distribution of particles with average diameter of 31±10nm and nearest-neighbor spacing of 75nm is observed. Moreover, melting by two-beam interference irradiation produces LRO as well as SRO giving a quasi-two-dimensional arrangement of nanoparticles. The SRO is attributed to spinodal dewetting while the LRO is conjectured to be induced by in-plane interfacial tension gradients. Laser-induced dewetting of metals could be a simple technique to fabricate ordered metal nanoarrays.