An Algorithm for Tailoring of Nanoparticles by Double Angle Resolved Nanosphere Lithography
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An Algorithm for Tailoring of Nanoparticles by Double Angle Resolved Nanosphere Lithography Christoph Brodehl1,2, Siegmund Greulich-Weber1,2 and Jörg K. N. Lindner1,2 1 University of Paderborn, Dept. of Physics, Warburger Str. 100, 33098 Paderborn, Germany. 2 Center for Optoelectronics and Photonics Paderborn (CeOPP), 33098 Paderborn, Germany. ABSTRACT Nanosphere lithography (NSL) is a technique capable of creating large-area arrays of small objects with tailor-made shapes. Here we present an algorithm, which simulates the shape and morphology of nanoparticles produced via NSL in combination with physical vapor deposition from variable angles. The key idea is based on a ray-tracing technique. Mask clogging effects have a major influence on the shape of resulting nanoobjects and are therefore taken into account. In addition, we implemented a metaball concept for the precise description of thermally modified masks. The calculated results are compared exemplarily with atomic force microscopy (AFM) data of experimentally fabricated nanostructures. INTRODUCTION Nanostructures show novel and interesting effects due to a variety of reasons, including quantum effects, surface-to-volume effects and the subwavelength size of objects compared to the wavelength of visible light. In order to take profit from these effects, one has to carefully design and arrange nanostructures with respect to each other. Conventional optical lithography would be the technique of choice to fabricate regularly patterned large-area surface but is limited in resolution due to diffraction effects. Direct writing techniques such as electron beam lithography can easily deal with nanometer structures, but are too slow and cost-intensive for large area samples. Self-organization based processes like NSL are cheap and applicable on large areas but typically limited to very elementary motives [1, 2]. These motives are usually the vertical projections of the nanomasks openings. It has already been demonstrated that using tilted geometries during the deposition of materials through such self-organized nanomasks, simple other motive shapes can be generated on the substrate [3-5]. As we will show here, the motives can be tailored into almost any desired shape by continuously varying the deposition angles during the deposition process. However, the prediction of motive shapes obtained at non-vertical deposition geometries is not straight forward since the three-dimensional shape of the nanomasks must be taken into account. In addition, the shape and size of mask openings continuously changes during the deposition process due mask clogging. Therefore, we developed algorithms to simulate the fabrication of nanopatterns and to speed up the design of nanomotives. THEORY Nano Sphere Lithography NSL is a shadow mask lithography technique where the mask consists of a self-arranged hexagonally close-packed mono- or bilayer of colloidal spheres on a substrate. The free space in between each triple of mutually touching spheres in a plane forms a triangular aperture, whic
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