Directed Assembly of Polymer Blends Using Nanopatterned Templates By Ming Wei, Liang Fang, Jun Lee, Sivasubramanian Somu, Xugang Xiong, Carol Barry, Ahmed Busnaina, and Joey Mead* With the rapid advances in nanoscience, there is a need to develop simple and rapid fabrication techniques to create highly ordered functional nanostructures. [1–3] Block copolymers are of signifi- cant interest in this area because of their ability to self assemble into a variety of interesting and useful morphologies for application in nanolithography and assembly of nanodevices. [4–7] Obtaining long-range order in block copolymers has received much attention. [8–11] In particular, chemically modified surfaces have been used to prepare defect-free nanopatterns over large areas. [12] The difficulty in using block copolymers is that the size of the structure is dictated by the molecular structure of the polymer (e.g., block length). This restricts the range of accessible patterns and does not permit the preparation of nonuniform structures using block copolymers alone. In addition, to obtain more complex geometries, researchers have combined homo- polymers with block copolymers. However, this process requires significantly long annealing times to obtain nonuniform patterns. [13] Several groups have studied phase separation of polymer blends using self-assembled monolayers (SAMs) patterned by microcontact printing (mCP). [14–16] The smallest scale achieved so far is 2 mm, and the reported technology is limited by the difficulty in achieving high-resolution replication accuracy, due to the degradation of the elastomeric stamp and unbalanced contact pressure applied to the substrate. Ginger and coworkers reported phase separation into uniform geometries by patterned templates down to 150 nm by dip-pen nanolithography (DPN). [17,18] The disadvantage of DPN is that the sizes of templates that can be patterned are currently limited. To date, none of the published studies reported the preparation of complex, nonuniform patterns by directed assembly of polymer blends. Here, we report a method for the nanomanufacturing of highly ordered polymeric features in nonuniform geometries by directed assembly of polymer blends on chemically patterned surfaces. More specifically, alkanethiols with different chemical functionalities were patterned by combining electron-beam lithography and self-assembly of alkanethiol molecules, and these patterned alkanethiols were then used to direct the assembly of polystyrene (PS)/poly(acrylic acid) (PAA) blends. We also studied the effect of specific chemical interactions on the ability to form these patterns in a rapid fashion. The under- standing of this interaction provides the ability to control the site-specific deposition of polymer blends in a very short time. The advantage of this approach is that this selective assembly process can be accomplished in 30 s, without the need for the long annealing times (3–7 days) often required in the conventional assembly of block copolymers. [12] We have demonstrated that this method can be used to generate a variety of complex geometries, including 90 8 bends, T-junctions, and square and circle arrays, which have potential applications in the fabrication of integrated circuits in nanoelectronics. This technology provides a pathway for the preparation of nonuniform and complex patterns using readily available materials. In addition, the assembled polymeric structures can be patterned over a very large area and with high resolution, overcoming the constraint of limited areas and slow rates in the assembly of polymer blends by the DPN method and the low resolution of microncontact printing. The presented approach provides a path toward nanomanufacturing polymeric nanostructures at high rates and high volumes. These patterned polymeric structures with multiple surface functionalities can be used downstream for the fabrication of microphotonic arrays, biosensors, etc. [3] Electron-beam lithography (EBL) is a well-established pattern- ing technology capable of creating extremely fine patterns down to 10 nm, due to the very small spot size (2 nm) of the beam. [19] Here, taking advantage of the EBL capability of patterning polymethyl methacrylate (PMMA) resists on a gold substrate, we combine it with the self-assembly of thiol molecules to create patterned alkanethiols. Figure 1 shows the schematic diagram of patterning of hydrophilic/hydrophobic alkanethiols. To begin the process, an initial PMMA-resist layer around 150 nm was spin- coated on a gold substrate. Then, positive PMMA-resist line patterns were formed by EBL, followed by oxygen plasma treat- ment for 5 s. Afterwards, hydrophilic 11-amino-1-undecanethiol hydrochloride (MUAM) monolayers were assembled on the exposed gold surface at the bottom of the PMMA trenches, by immersing the template into a MUAM solution for 24 h. After thiolation, the remaining PMMA resist was removed by Soxhlet extraction of acetone for 24 h, to expose the gold surface. Finally, second hydrophobic 1-octadecanethiol (ODT) monolayers were assembled onto the exposed gold area, yielding a pattern with a different chemical functionality. COMMUNICATION www.advmat.de [*] Prof. J. Mead, Dr. M. Wei, L. Fang, Dr. J. Lee, Prof. C. Barry NSF Nanoscale Science and Engineering Center for High-Rate Nanomanufacturing Department of Plastics Engineering University of Massachusetts-Lowell One University Avenue, Lowell, MA 01854 (USA) E-mail: joey_mead@uml.edu Dr. S. Somu, Dr. X. Xiong, Prof. A. Busnaina NSF Nanoscale Science and Engineering Center for High-Rate Nanomanufacturing, Department of Mechanical and Industrial Engineering 467 Egan Center, Northeastern University 120 Forsyth Street, Boston, MA 02115 (USA) DOI: 10.1002/adma.200802052 794 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2009, 21, 794–798