Laser-Induced Dewetting Nanomorphologies in Single and Bilayer Metal Films
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0960-N03-02
Laser-Induced Dewetting Nanomorphologies in Single and Bilayer Metal Films Hare Krishna1,2, Christopher Favazza1,2, R. Sureshkumar2,3, and R. Kalyanaraman1,2 1 Department of Physics, Washington University in St. Louis, St. Louis, MO, 63130 2 Center for Materials Innovation, Washington University in St. Louis, St. Louis, MO, 63130 3 Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, 63130
ABSTRACT Spatially ordered patterns result under ns laser-induced dewetting of nanoscopic metallic films like Co and Ag on inert substrates like SiO2. In both cases, the observed ordering length scale is due to thin film hydrodynamic instability with spinodal-like character. However, the morphological pathway during dewetting is different for the two metals: occurring through development of bicontinuous structures in the case of Ag and by progression of cellular networks for Co. Dewetting in bilayer structures of Ag and Co on SiO2 show that the morphology evolution is dictated by the thicker of the two films in the bilayer structure. We applied linear stability analysis to predict the length scales in single and bilayer metal film. The experimental observations are in good agreement with theoretical predictions from the analysis. An important result was that the length scales for the bilayer film were significantly smaller than a single layer of the same thickness suggesting that further control of patterning length scales may be achieved through multilayer dewetting. INTRODUCTION Ordered metal nanoparticles have potential applications in nanophotonics and nonlinear optics below the diffraction limit [1, 2], high density magnetic storage and nanocatalysts [3-5]. However, such applications require cost-effective and reliable techniques, that would allow better control over the particle size and spacings between the particles. Thin film hydrodynamic (TFH) instabilities leading to dewetting with spatial order could be utilized to self-assemble such nanoarrays [6]. Dewetting studies in polymer films [7, 8] have received attention because they are liquids at RT. On the other hand, there have been few studies of dewetting of ultrathin metal films on inert substrates with the motivation to create ordered nanostructures. The primary reason is the high melting point of metals, which makes experimental studies of dewetting, especially in the liquid phase, challenging. Pulsed laser irradiation is a practical approach to investigate the dewetting in metals [9-12]. Pulsed lasers irradiation produce large heating and cooling rates, as well as melting times comparable to the pulse times, which could allow morphological evolution to be captured as a function of multiple instances of phase change, i.e. melting and resolidification. In the case of bilayer liquid films, Pototsky and co-workers [13, 14] have studied the dewetting in bilayer polymer films. However, the literature of dewetting for bilayer metal films is sparse. In this work, we have compared the morphological evo
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