Shadow Nanosphere Lithography: Simulation and Experiment
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Shadow Nanosphere Lithography: Simulation and Experiment Michael Giersig Caesar Research Center Ludwig-Erhard-Allee 2 53175 Bonn Germany
ABSTRACT The creation of two dimensional large-areas of nanoparticles of different morphology and ordering is still a not fully solved problem. The presented paper shows new outstanding methods based on nanosphere lithography for controlling the mask morphology to improve fabrication of nanoscales perfectly ordered over some cm2 dots, rods and rings. An annealed mask with 30nm aperatures was used for the fabrication of ferromagnetic iron nanorings. These nanosystems are expected to find various unique applications. Our method permitted fabrication of nanostructured materials with unique morphology and properties. This field is expected to open new venues in science and technology. INTRODUCTON The basis of the nanosphere lithography (NSL)1-8 is the self-assembling of monodisperse latex spheres. Creation of large-areas of monolayer and their deposition of various materials are the first step following by evaporation of different materials on the way to well two dimensional organized nanostructures. It is known, that NSL can be used to make honeycomb lattices of triangularly-shaped islands on various substrates. The using of spheres with different diameters opens the possibility to change spacing and size of the periodically arranged islands. Controlled annealing the samples at the temperature of about 70% of the melting point of the bulk material, and allow the creation of spherical particles obtained.9 Van Duyne et. al. shown that nanooverlaps, nanogaps and nanochains can be obtained by multiple silver deposition at different deposition angles. They called this technique angle-resolved NSL.10 In this presentation we show, that the deposited structures can become much more complex, when the angle between the evaporation beam and the sample changes during the deposition process, and when the sample is simultaneously rotated during the process. We have developed computer simulations that predict the resulting structures. A variety of complex morphologies, ranging from cup-like structures to rods and wires, are possible using this technique. By the evaporation or sputtering of different materials through the latex particles mask it was possible to produce lattices of triangularly shaped islands on various substrates which are determined by the shape of the aperture between the spheres in the mask. It is obvious that the size of the aperture between the spheres depends on the size of the beads in the monolayer. To overcome that limitation we performed temperature treatment of the monolayer. Annealing was used to downsize the apertures in the mask from an initial 200 nm to 30 nm.
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EXPERIMENTAL DETAILS Details about nanosphere mask preparation can be found in our previous work [9]. In general on a square piece of silicon (up to some cm2) we have deposited well organized monolayers of latex particles. By using this method, it was possible to create crystals of about 2cm2,
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