pH-Responsive One-Dimensional Periodic Relief Grating of Polymer Brush-Gold Nanoassemblies on Silicon Surface Jem-Kun Chen,* ,† Ping-Chun Pai, † Jia-Yaw Chang, ‡ and Shih-Kang Fan § † Department of Materials Science and Engineering and ‡ Department of Chemical Enigneering, National Taiwan University of Science and Technology, 43, Sec 4, Keelung Rd, Taipei, 106, Taiwan, Republic of China § Department of Materials Science and Engineering, National Chiao Tung University, 1001 University Road, Hsinchu, Taiwan 300, Republic of China ABSTRACT: In this work, we focus on the fabrication of the nanoassemblies consisting of the poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes and gold nanoparticles (AuNPs). The employed process involves grafting of the PDMAEMA chains on an underlying substrate in a brush conformation followed by the immobilization of surface function- alized AuNPs by means of physical interaction (electrostatic attraction, entanglement, and hydrogen bonding). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy have been employed to characterize the prepared PDMAEMA-AuNP nanoassemblies. Polymer brushes possessing various thicknesses have been found to suppress the nanoparticles’ aggregation and, hence, facilitate the surface coverage. Furthermore, we patterned the PDMAEMA-AuNP nanoassemblies as an one-dimensional periodic relief grating (OPRG). The subwavelength structure of OPRG has the optical features including artificial refractive index, form birefringence and resonance and band gap effects. A mean refractive index of the PDMAEMA-AuNP nanoassemblies can be controlled by the filling factors of the OPRG structure, so that a desired distribution of refractive index of the polymer brushes-gold OPRG under various stimuli can be realized. The employed approach is simple and highly versatile for the modification of surfaces with a wide range of NPs. KEYWORDS: PDMAEMA brush, nanolithography, gold nanoparticles, binary grating ■ INTRODUCTION Metal nanoparticles (NPs) represent a special class of the materials, which has recently attracted much attention of the researchers because of their fascinating properties and potential applications in a wide range of areas including in the fabrication of nanosensors, electronics and optical devices. 1 A great deal of the research efforts have been devoted to the gold (Au) NPs because of their unique properties. 2,3 In addition, many attempts have been made for the immobilization of AuNPs on macroscopic surfaces in order to improve the accessibility of their unusual optical properties. In comparison to the stabilization with gels or other 3D matrixes, one can access a relatively higher surface area of the NPs by means of their immobilization over macroscopic surfaces, as in the previous case NPs remain partly or wholly inside the gels. 4 Due to the high surface energy, they tend to aggregate, and aggregation limits their use in above-mentioned applications. A great deal of effort has been devoted to the stabilization of NPs by exploiting a wide range of stabilizers such as self-assembled monolayers, 5 polymer brushes, 6 block copolymers, 7 latex particles, 8 micro- gels, 9 and so on. 10 Among these systems, polymer brushes have been found to offer an easy and effective way for the stabilization of NPs on macroscopic surfaces. Stable polymer brushes can provide excellent mechanical and chemical protection to a substrate, alter the electrochemical character- istics of an interface, and provide new pathways for the functionalization of Si surfaces. 11,12 One particular advantage that polymer brushes have over spin-coated polymer layers is their stability against solvents, resulting from their covalent bonding to the substrates. In addition, polymer brushes are the assemblies of macromolecules that are tethered by one end to the underlined substrate in such a way that the distance between two grafted chains is lower than that of the radius of the gyration of a polymer chain. 12 Earlier studies demonstrate that polymer brushes serve as a perfect template for the preparation, stabilization, and application of NPs on the account of their nanometer dimensions, well-defined structure, and ability to control assembly of NPs over multiple length scales, superior precision over template architecture, and the availability of a greater variety of functional groups. 13,14 Fabrication of ordered arrays of nanoparticles is of significance for both fundamental science associated with low- Received: November 22, 2011 Accepted: March 16, 2012 Published: March 16, 2012 Research Article www.acsami.org © 2012 American Chemical Society 1935 dx.doi.org/10.1021/am201632e | ACS Appl. Mater. Interfaces 2012, 4, 1935-1947