Multi-Scale Grafted Polymeric Nanostructures Patterned Bottom-Up by Colloidal Lithography and Initiated Chemical Vapor D
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Multi-Scale Grafted Polymeric Nanostructures Patterned Bottom-Up by Colloidal Lithography and Initiated Chemical Vapor Deposition (iCVD) Nathan J. Trujillo, Salmaan H. Baxamusa and Karen K. Gleason Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave. 66-419, Cambridge, MA 02139, U.S.A.
ABSTRACT Colloidal lithography is a popular, non-conventional process that uses two– dimensional self-assembled monolayer arrays of colloidal nanoparticles as masks for techniques such as etching or sputtering. Initiated Chemical Vapor Deposition (iCVD) is a surface controlled process which offers unprecedented opportunity for producing polymeric layers grafted to substrates with dangling vinyl bonds and patterned through a colloidal template. We demonstrate a generic “bottom-up” process as an inexpensive and simple technique for creating well-ordered arrays of functional patterned polymeric nanostructures. These patterns were produced from thin polymer films of p(butyl acrylate) and p(hydroxyethyl methacrylate), and are robustly tethered to the underlying substrate, as demonstrated by their ability to withstand aggressive solvents. Furthermore, using capillary force lithography, we created topographical templates for large-scale orientation of the nanoparticle assembly. Through this “top-down” approach, for assisting the bottom-up assembly, we present a process for multi-scale patterning of functional polymeric materials, without the need for expensive lithography tools. INTRODUCTION Materials patterning through non-conventional lithography can reduce the cost of patterning fine structures when compared to traditional nanofabrication techniques such as photolithography [1]. Liftoff techniques form patterns on a wafer surface by an additive process. A negative pattern is formed by first depositing a stencil layer, which exposes the substrate in specific locations. A film is subsequently deposited over the stencil and exposed substrate. The stencil is removed by dissolution in solvent, leaving behind a patterned film. We report on a variation of this liftoff technique; one that uses a self-assembled monolayer of colloidal particles as the stencil. Monodisperse colloidal particles can self-assemble into 2-D hexagonal arrays when deposited onto various substrates. By controlling the drying process, solution cast colloidal particles will selfassemble into a hexagonally closed packed monolayer. The ordered void array in the particle intersticies has been used as a patterning mask for over 25 years [2]. These 2-D patterns have been used to pattern carbon nanotubes [3], ZnO nanorods [4], nickel and gold dots [5, 6]. Several experimental techniques for creating monolayers using commercially available latex spheres have been described [4, 5, 7, 8]. Nanopatterns of p(acrylic acid) domes have been created from top down patterning [9], however, this method requires the use of a hydrophilic polymer and a reactive ion etch, which can destroy the delicate polymer functionality.
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In 2007,
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