Pulsed laser induced self-organization by dewetting of metallic films
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N. Shirato Department of Material Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996
C. Favazza Department of Physics, Washington University in St. Louis, St. Louis, Missouri 63130
R. Kalyanaramana) Department of Material Science and Engineering, Department of Chemical and Biomolecular Engineering, and Sustainable Energy Education and Research Center, University of Tennessee, Knoxville, Tennessee 37996 (Received 5 May 2010; accepted 12 July 2010)
Reliable and cost-effective techniques to process surface nanoscale metallic structures with controllable and complex nanomorphologies is important toward progress in technologies related to sensing, energy harvesting, information storage, and computing. Here we discuss how pulsed laser melting and the ensuing self-organization by dewetting of ultrathin films can be utilized to fabricate various nanomorphologies in a predictable manner. Ultrathin metal films (1–100 nm) on inert substrates like SiO2 are generally unstable, with their free energy resembling that of a spinodal system. The energy rate theory of self-organization, which is based on balancing the rate of thermodynamic free energy change to the rate of energy dissipation, predicts the appearance of characteristic length scales. This is borne out in experiments of nanosecond pulsed laser melting of a variety of metal films. We review this laser-based self-organization technique with various examples from the behavior of Ag and Co metals on SiO2 substrates. Specifically, film thickness and film roughness can be used to control dewetting length scales, whereas knowledge of the intermolecular forces responsible for the free energy of the system control the type of morphology. Furthermore, novel dewetting is observed that is attributable to nanoscale heating effects resulting from the thickness-dependent pulsed laser heating. These results help elucidate the basic mechanisms of pulsed laser induced dewetting of metal films, but they also provide potential routes for cost-effective nanomanufacturing of metallic surfaces for applications in sensing, energy harvesting, and information processing. I. INTRODUCTION
Nanoscale materials have unique properties compared with both macroscopic bulk materials and individual atoms or molecules. Research in nanoscience focuses on the fundamental study and manipulation of materials to design, fabricate, and characterize structures on the nanometer scale. The ultimate goal is to develop materials and devices that will overcome the existing technological limitations and even create new and novel functionalities. In this respect, the ability to manipulate and measure matter at the nanometer level is making it possible to synthesize a new generation of materials with enhanced mechanical1, optical2, plasmonic,3,4 magnetic,5–7 and magnetoplasmonic8 properties. Nanostructure devices can be based on tailoring these properties starting, at the molecular level9,10, in the structures comprising three-dimensional nanometer scale components11, or they can be based on a)
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