Room-Temperature Imprinting Poly(acrylic acid)/Poly(allylamine hydrochloride) Multilayer Films by Using Polymer Molds Yingxi Lu, Xiaoling Chen, Wei Hu, Nan Lu, Junqi Sun,* and Jiacong Shen Key Lab of Supramolecular Structure and Materials, College of Chemistry, Jilin UniVersity, Changchun 130012, People’s Republic of China ReceiVed NoVember 8, 2006. In Final Form: December 15, 2006 Layer-by-layer assembled polyelectrolyte multilayer films of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) have been successfully patterned by room-temperature imprinting using a Norland Optical Adhesives (NOA 63) polymer mold. The proper amount of water in the PAA/PAH multilayer film can decrease the viscosity of the film and facilitate the imprinting. Many factors, such as imprinting pressure, length of imprinting time, and the structure and size of the patterns in the polymer mold, can produce an influence on the final imprinted pattern structures on multilayer films. A high imprinting pressure of 100 bar and elongated imprinting time of several hours is needed to achieve a patterned PAA/PAH multilayer film with a feature size of several tens of micrometers. With a twice imprinting, grid structures can be successfully produced when a NOA 63 mold having line structures is used. Room- temperature imprinting by using polymer NOA 63 mold provides a facile way to fabricate layered polymeric films with various kinds of pattern structures. Introduction Imprint lithography is a promising technology to fabricate pattern structures with a high-aspect ratio in the region of micro-/ nanometers. 1,2 Because of its low-cost, easy operation, and high- throughput, imprint technology has become one of the emerging technologies in fabricating optoelectronics, microelectric devices, nanofluidics, and so forth. Recently, researchers have developed many additive approaches beyond this method to resolve critical issues that need to be addressed for the further progress of this technology, such as room-temperature imprint lithography. 3-10 One of the important issues is the useful lifetime of the mold. In conventional imprinting technology, a hard mold typically made of Si, SiO 2 , and various metal materials is used to obtain certain hardness during the imprinting process. The problem encountered is that the conformal contact between the hard mold and the substrate is usually limited by the rigid nature of the mold material. Furthermore, cooling cycles and high pressure (50-130 bar) employed during imprinting produce stress and wear on the molds. 11 These issues would deteriorate the imprinted pattern fidelity. The use of the flexible polymer mold instead of the hard mold can provide better conformal contact with the substrate to be patterned and reduce the pressure needed during the imprinting step. 12,13 Therefore, the use of soft polymer mold in imprinting technology is an alternative to solve the problems encountered in using hard mold. To satisfy the application as a mold in imprinting technology, the polymer mold material must have a high modulus to withstand deformation of the mold during the imprinting. The composite poly(dimethylsiloxane) (PDMS) mold, which consists of a thin hard PDMS and a relatively thick soft PDMS, is a choice. 14 However, problems such as the brittleness of the hard PDMS and the thermal instability of the composite mold restrict the wide application of this kind of mold in nanofabrication. There are several reports about the fabrication of the soft polymer mold with high modulus in a relatively more easy way. Lee et al. reported the fabrication of amorphous fluoropolymer (Dupont Teflon AF 2400) mold with a feature size of sub-100 nm from a master mold of SiO 2 /Si wafer. The fluoropolymer has a tensile modulus of ∼1.6 GPa. Because of the high modulus, they successfully patterned densely populated features with a size as small as 80 nm and features with an aspect ratio up to 6:1 by using the fluoropolymer mold. 12,13 Norland Optical Adhesives (NOA 63) is a mercapto ester-type UV-curable prepolymer, which has outstanding optical and mechanical properties as well as a softening transition at mild temperatures. Kim et al. demonstrated that NOA 63 could be used as a promising material to manufacture polymer molds for transferring patterning nanostructures of high aspect ratio. 15 Hammond et al. used NOA 63 to make stamps for contact printing with a range of sub-micrometer to 80 nm features. 16 Polymer transfer printing of poly(acrylic acid) onto a polyelectrolyte multilayer platform has successfully resulted in chemically nanopatterned surfaces with well-defined structures and both positive and negative surface functionalities. UV-curable polyurethane acrylate is another choice for imprinting mold material because it has a Young’s modulus of ∼1.7 × 10 9 Nm -2 and the mold can be easily fabricated by replicating a preformed master. 17 These soft molds will open a wider application in * To whom correspondence should be addressed. Phone: 0086-431- 85168723. Fax: 0086-431-85193421. E-mail: sun_junqi@jlu.edu.cn. (1) Chou, S. Y.; Krauss, P. R.; Renstrom, P. J. Appl. Phys. Lett. 1995, 67, 3114. (2) Sotomayor Torres, C. M.; Zankovych, S.; Seekamp, J.; Kam, A. P.; Ceden ˜o, C. C.; Hoffmann, T.; Ahopelto, J.; Reuther, F.; Pfeiffer, K.; Bleidiessel, G.; Gruetzner, G.; Maximov, M. V.; Heidari, B. Mater. Sci. Eng., C 2003, 23, 23. (3) Xu, J. D.; Locascio, L.; Gaitan, M.; Lee, C. S. Anal. Chem. 2000, 72, 1930. (4) Lebib, A.; Chen, Y.; Cambril, E.; Youinou, P.; Studer, V.; Natali, M.; Pe ´pin, A.; Janssen, H. M.; Sijbesma, P. R. Microelectron. Eng. 2002, 61-62, 371. (5) Khang, D. Y.; Yoon, H.; Lee, H. H. AdV. Mater. 2001, 13, 749. (6) Khang, D. Y.; Lee, H. H. Appl. Phys. Lett. 2000, 76, 870. (7) Hong, P. S.; Lee, H. H. Appl. Phys. Lett. 2003, 83, 2441. (8) Pisignano, D.; Persano, L.; Raganato, M. F.; Visconti, P.; Cingolani, R.; Barbarella, G.; Favaretto, L.; Gigli, G. AdV. Mater. 2004, 16, 525. (9) Mele, E.; Di Benedetto, F.; Persano, L.; Cingolani, R.; Pisignano, D. Nano Lett. 2005, 5, 1915. (10) Behl Marc Seekamp, J.; Zankovych, S.; Sotomayor Torres, C. M.; Zentel, Rudolf Ahopelto, J. AdV. Mater. 2002, 14, 588. (11) Gates, B. D.; Xu, Q.; Stewart, M.; Ryan, D.; Willson, C. G.; Whitesides, G. M. Chem. ReV. 2005, 105, 1171. (12) Khang, D. Y.; Lee, H. H. Langmuir 2004, 20, 2445. (13) Khang, D. Y.; Kang, H.; Kim, T.; Lee, H. H. Nano Lett. 2004, 4, 633. (14) Odom, T. W.; Love, J. C.; Wolfe, D. B.; Paul, K. E.; Whitesides, G. M. Langmuir 2002, 18, 5314. (15) Kim, Y. S.; Lee, N. Y.; Lim, J. R.; Lee, M. J.; Park, S. Chem. Mater. 2005, 17, 5867. (16) Park, J.; Kim, Y. S.; Hammond, P. T. Nano Lett. 2005, 5, 1347. (17) Kim, Y. S.; Lee, H. H.; Hammond, P. T. Nanotechnology 2003, 14, 1140. 3254 Langmuir 2007, 23, 3254-3259 10.1021/la0632676 CCC: $37.00 © 2007 American Chemical Society Published on Web 02/02/2007