Morphology transitions in bilayer spinodal dewetting systems

Abstract

In spontaneous pattern formation by spinodal dewetting, attractive intermolecular forces overcome surface tension and cause an ultrathin liquid film on a low energy substrate to produce ordered structures. Spinodal dewetting in single-layer film on a substrate, is usually manifested by an early stage surface deformation and a highly non-linear ripening stage that results in characteristic morphologies, typically bicontinuous-or hole-like states. Here we have experimentally constructed the dewetting morphology phase diagrams for a bi-layer (Ag, Co) liquid film system on SiO 2 . Nanosecond pulsed laser melting was used to initiate and foster the dewetting as a function of film thickness and arrangement. The early stage ripening morphology was observed by scanning electron microscopy from which the phase diagrams were constructed. Unlike single-layer films, which only show one morphology transition between the bicontinuous to hole states as the film thickness is increased, the bi-layer system can have multiple transitions. We have utilized the thickness-dependent free energy curvature approach (Sharma and Khanna, Phys. Rev. Lett. 81 p3463 1998) to analyze the phase diagram. The location of the multiple transitions cannot be predicted from the curvature minima, as was the case for single-layer films. Nevertheless, despite the complexity from multiple interacting forces and different surface deformation mode in bi-layer systems , the phase diagram can be completely generated by knowledge of the free energy curvature of the respective single-layer films. These results can permit improved modeling of the non-linear dynamics in naturally driven self-organized phenomenon and help design nanomaterials for advanced applications.

Pulsed laser dewetting of Au films: Experiments and modeling of nanoscale behavior

“…Theoretically, h T for a single layer film is strongly correlated to the minima of the free energy curvature, which, in turn, is the second derivate of the thicknessdependent free energy of the film/substrate system. 7,13,42 The free energy G and its curvature for a single layer film on a substrate are given by 13,42 :…”

Laser-Induced Self-Assembled Nanostructures on Electron-Transparent Substrates

“…This laser energy density also ensured minimal evaporation and/or ablation of the various metals and/or carbon film. As described in great detail in previous works, by controlling the number of pulses it is possible to obtain different morphologies of the single layer or bilayer films . Here, we made different Ag NSs by irradiation with 1, 50, or 100 pulses.…”

“…As described in great detail in previous works, by controlling the number of pulses it is possible to obtain different morphologies of the single layer or bilayer fi lms. [ 14,20 ] Here, we made different Ag NSs by irradiation with 1, 50, or 100 pulses. For both the bilayer cases investigated, we applied 100 pulses to form nearly hemispherical-shaped NSs.…”

Controlling Nanoparticles Formation in Molten Metallic Bilayers by Pulsed-Laser Interference Heating

“…Note that (i) we include gravity terms in the pressures, since it has been shown that these terms may be important in a certain range of parameters [28,34], and (ii) we do not include the electronic component in the disjoining pressures [60], since for a single layer as well as for a bilayer system the inclusion of the electronic component does not result in the noticable improvement in matching of the theoretical predictions to the experiment, such as, for instance, the prediction of the critical film thickness at which the transition from bicontinuous structures to holes takes place [13,61]. The surface tension gradients, ∂ x σ 1,2 in Eqs.…”