We have recently observed that ns pulsed laser irradiation of ultrathin metal films leads to robust nanoscale pattern formation. Detailed investigations for Cobalt films (thickness ranging between 1 and 10 nm) on silica substrates showed that single-beam laser irradiation results in short-range ordering (SRO) in nearest-neighbour spacing between the nanoparticles [1, 2]. We identified the mechanism as the spinodal dewetting instability, which leads to a predictable particle size and spacing [3]. Irradiation by two-beam laser interference conditions resulted in various ordered morphologies, including nanowires and nanoparticle arrays. The nanoarrays showed quasi-2D ordering resulting from long-range ordering (LRO) and SRO [1]. Here we show that in the two beam case, the morphology evolution is dictated by the competition between three instabilities: spinodal dewetting, Rayleigh break-up of the nanowires and Marangoni transport due to temperature gradients. The instability having the shortest time scale was found to dominate the morphology. Since the time scale of each instability had a different behavior with film thickness h , it was possible to access different particle size and spacings by varying the choice of h. These results indicate that robust nanomanufacturing of metal nanoarrays can be achieved by accessing and manipulating hydrodynamic instabilities of nanoscopic metal film.

1.C. Favazza, J. Trice, H. Krishna, R. Kalyanaraman & R. Sureshkumar, Laser induced short and long range ordering of Co nanoparticles on SiO2, in press, Applied Physics Letters (2006) to appear in vol. 88.

2.C. Favazaa, J. Trice, H. Garcia, R. Kalyanaraman & R. Sureshkumar, Nanoparticle ordering by dewetting of Co on SiO2, in press, J. Electronic Materials (2006)

3. C. Favazza, R. Kalyanaraman & R. Sureshkumar, Robust nanopatterning by laser-induced spinodal dewetting in ultra-thin Co films, submitted, Applied Physics Letters (2006)