Polymer-on-Polymer Stamping on Micro- and Nano-Scales
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Polymer-on-Polymer Stamping on Micro- and Nano-Scales Shoshana Gourdin1, Travis Crites2, Seth Coe3, Vladimir Bulovic3, and Paula Hammond 1* Massachusetts Institute of Technology, Department of Chemical Engineering, Cambridge, Massachusetts 02139 2 West Virginia University, Department of Chemical Engineering, Morgantown, West Virginia 26506 3 M assachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, Cambridge, Massachusetts 02139 1
ABSTRACT The goal of the project was to determine whether PDAC (poly (diallyldimethylammonium chloride), also abbreviated PDADMAC) could be printed reproducibly to create patterns with a sub-micron resolution. PDAC was stamped onto bare silicon using PDMS stamps having features only about 150 nm wide. A variety of aqueous PDAC inks were tried, to study the effect of concentration and ionic strength on the pattern produced. In order to get good prints, new stamping techniques were also required. A rigid stamping apparatus was built to ensure steady placement, and the stamps were spin coated with a different ink solution to produce thin, even coats of ink. [1] Using these methods, the pattern transferred.
INTRODUCTION We produced 150 nm features by microcontact printing the polycation PDAC (poly (diallyldimethylammonium chloride), also abbreviated PDADMAC) onto a silicon substrate. Previously, microcontact printing had been limited to small molecules that chemically adhered to the substrate. Polymers could be more useful than such molecules in building nanometer scale devices because polymers can be printed on a wider variety of substrates and can include more than one type of monomer, which makes it easy to tailor a polymer to a specific application. With an increased demand for device miniaturization comes an increased need for the requisite processing techniques. Traditional photolithography is reliable and produces excellent small-scale patterns, but it is not suitable for all applications. It requires a flat surface so that the light is not distorted. Specialized materials are required, substrates must withstand harsh processing, and the apparatus needed is expensive. In contrast, electronics, photonics, and biomedical implants require patterning techniques applicable to a wide variety of materials and production conditions. Cost is also a factor. For any consumer product, lower manufacturing costs permit cheaper products and higher profits, and expand the range of applications for which the product is appropriate. What is needed, then, is a flexible and inexpensive patterning method that can reproduce micro- and nanoscopic patterns. Soft lithography encompasses a wide variety of techniques, including micromolding, in which the material of interest is cast from a patterned mold, and dip-pen nanolithography, which uses a stylus to draw a pattern. [2, 3] Micro contact printing is a popular technique that uses a stamp to transfer patterns. In a key early paper, Whitesides and Kumar introduced the use of polydimethylsiloxane (PDMS) stamps m
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