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J. Phys. Chem. C 2007, 111, 17254-17259
Fabrication of Three-Dimensional ZnO-Carbon Nanotube (CNT) Hybrids Using Self-Assembled CNT Micropatterns as Framework Xing-bin Yan,* Beng-kang Tay, Yi Yang, and Wendy Yung Ka Po School of Electrical and Electronic Engineering, Nanyang Technological UniVersity, Nanyang AVenue, Singapore 639798, Singapore ReceiVed: July 31, 2007; In Final Form: September 10, 2007
Large-scale pyramid-like micropatterns were prepared via capillarity-driven self-assembly during the evaporation of water from aligned carbon nanotubes (ACNTs) wrapped by a polyelectrolyte, poly (sodium 4-styrenesulfonate) (PSS). PSS wrapping results in providing negative charges on every tube, which makes it possible to balance the capillary force and to form uniformed pyramid-like architecture. By using such regular threedimensional CNT patterns as an idea candidate for the framework/template, two complex architectures consisting of ZnO nanorods and CNT patterns were successfully fabricated, which show revisable surface wettability properties.
Introduction Future devices consisting of well-defined configurations and various functional materials with exciting properties will be built from nanoscale building blocks,1-3 such as nanotubes, nanowires, nanofibers, and nanorods, etc. Among the various forms of the nanomaterials, carbon nanotubes (CNTs) are currently the subject of intense research because of their interesting physicochemical properties and molecular symmetries, and many approaches have been developed for their fabrication.4 However, better control is still needed over the building and organization of CNT-based architectures. Thus far, vertically and horizontal aligned CNTs (ACNTs) have been fabricated on prepatterned substrates or prepatterned catalysts by chemical vapor deposition (CVD).5-12 Self-assembly is an efficient and often preferred process to build micro- and nanoparticles into ordered macroscopic structures.13 Recently, some studies showed that after being immersed into a liquid and dried, the pristine ACNTs would self-assembled bundle together to form a cellular network structure,14-18 while other studies discovered that this selfassembly process occurred during the spreading of a liquid droplet.19-20 Concretely, Chakrapani et al.14 observed the formation of cellular network after immersing and drying long ACNT arrays (∼50 µm), and they found that the cellular network was formed during the evaporation process through freeze-dried experiment and in situ optical microscope observation. Liu et al.19 also observed the cellular network formation on long ACNT arrays (∼19 µm) through the water-spreading effect. Correa-Duarte et al.15 also found that for short CNTs (∼3 µm), a pyramid-like CNT cluster was formed during the drying process when they attempted to culture cells on the ordered cellular patterns formed by self-assembly of long ACNTs (∼50 µm). A similar pyramid-like CNT cluster was observed by Nguyen et al. during the short ACNTs purification process.16 Lau et al.18 found that the bundling of ACNTs (
