Synthesis and Characterization of ZnO Nanostructures Templated Using Diblock Copolymers Robert F. Mulligan, 1 Agis A. Iliadis, 2 Peter Kofinas 3 1 Department of Materials and Nuclear Engineering, University of Maryland, College Park, Maryland 20742 2 Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland 20742 3 Department of Chemical Engineering, University of Maryland, College Park, Maryland 20742-2111 Received 29 May 2002; accepted 3 October 2002 ABSTRACT: The development of self-assembled ZnO nanoparticles within a diblock copolymer matrix using wet chemical processing specific to ZnO is reported. Diblock copolymers consisting of polynorbornene and poly(nor- bornene– dicarboxcylic acid) (NOR/NORCOOH) were syn- thesized with a block repeat unit ratio of 400 for the first block and 50 for the second block, to obtain spherical mi- crophase separation. The block copolymer self-assembly was used to template the growth of ZnO nanoparticles by introducing a ZnCl 2 precursor into the second polymer (NORCOOH) block at room temperature and processing the copolymer by wet chemical methods to substitute the chlo- rine atoms with oxygen. X-ray photoemission spectroscopy (XPS) verified the conversion of ZnCl 2 to ZnO by monitoring the disappearance of the Cl 1s peak and the shift in the binding energy of the Zn 2p 3 peak in the high-resolution spectra. The substitution of Cl by O was found to be a highly preferential process, whereby only one approach using a weak base (NH 4 OH) succeeded in effectively replacing Cl with O to result in spherical ZnO nanoparticles having a size ranging from 7 to 15 nm, as determined by transmission electron microscopy. The development of such block copol- ymer-templated ZnO nanoparticles% is important in en- abling the functionalization of large-area nanodevice tech- nologies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1058 –1061, 2003 Key words: block copolymers; templates; nanocomposites INTRODUCTION The formation of self-assembled nanostructures has recently attracted significant interest, as it presents a very promising approach to the development of func- tional nanodevices. One approach to the growth of nanoparticles is the microphase separation observed in diblock copolymers. The synthesis of nanoparticles within microphase-separated diblock copolymers based on diffusing the doping agent (metal or semi- conductor) into the copolymer matrix in the solid phase has been extensively reported. 1–11 In the present work, a novel synthetic approach tailored to the spe- cific production of zinc oxide within the copolymer is reported. Having both metal and polymer constitu- ents of the nanocomposite dissolved in a common solvent allows rapid diffusion of the metal to the functional groups of the block copolymer and results in more uniformly dispersed ZnO nanostructures, which are produced using a wet chemical processing at room temperature. The templating strategy used in our experiments is similar to the “universal” approach to synthesizing metal nanoparticles within diblock co- polymers as proposed by Clay and Cohen, 12 but has been modified for the specific templating of ZnO nanoparticles. ZnO is of significant importance due to its electronic and optical properties. It is a wide band gap (E g = 3.3 eV) metal oxide semiconductor with piezoelectric and optical properties in the UV range. 13 It crystallizes in the wurtzite structure and displays piezoelectric properties when its c-axis is oriented per- pendicular to a substrate. For this reason, it is found in many electroacoustic applications such as sound sen- sors, SONAR emitters and detectors, and pressure transducers. ZnO is used as the clear top electrode in solar cells 13 and has potential in the area of informa- tion storage as a piezoelectric memory device. Fur- thermore, new and enhanced properties are expected due to confinement in nanoscale dimensions when controlled nanocrystalline forms of this system are developed. The development of ZnO in its nanocrys- talline and/or nanocomposite form and its successful integration into current and future device technolo- gies is one of the goals of our research. EXPERIMENTAL Monomer and polymer synthesis Norbornene (NOR), ethyl vinyl ether, and dichlo- romethane (CH 2 Cl 2 ) were purchased from Aldrich Correspondence to: P. Kofinas (kofinas@eng.umd.edu). Contract grant sponsor: National Science Foundation; contract grant number: ECS-9980794. Journal of Applied Polymer Science, Vol. 89, 1058 –1061 (2003) © 2003 Wiley Periodicals, Inc.