Selective Positioning and Density Control of Nanotubes within a Polymer Thin Film Emer Lahiff, † Chang Y. Ryu, ‡ Seamus Curran, | Andrew I. Minett,* ,† Werner J. Blau, † and Pulickel M. Ajayan § Department of Physics, Trinity College Dublin, Dublin 2, Ireland and Chemistry Department, Materials and Engineering Department, and Nanotechnology Center, Rensellaer Polytechnic Institute, Troy, New York 12180 Received May 1, 2003; Revised Manuscript Received July 9, 2003 ABSTRACT We introduce a completely new and innovative method of producing polymer/nanotube composites where the density and position of the nanotubes within the composite can be controlled. Carbon nanotubes are grown from organometallic micropatterns. These periodic nanotube arrays are then incorporated into a polymer matrix by depositing a curable polymer film on the as-grown tubes. This controlled method of producing free-standing nanotube/polymer composite films represents a more efficient method of combining these materials for potential flexible electronic applications in an inexpensive and scalable manner. Carbon nanotubes have captured the imagination of scientists and industrialists for the past decade. They appeared during initial investigations into fullerene research 1 and now stand on the brink of applicability in a number of noted directions. Both multiwalled and single-walled nanotubes have been studied for possible use in areas that would utilize their electrical, 2,3 mechanical, 4 and optical 5 properties. Potential applications encompass a diverse range of devices includ- ing: flat panel displays, 6 sensors, 7 electronic devices, 8,9 polymer composites, 10,11 quantum wires, 12 and actuators. 13 Before realizing their full potential, the issue of economic production of controlled nanotube arrays, either free-standing or in composites, must be overcome. Popular and successful methods of nanotube growth include chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD). Large quan- tities of nanotubes can be produced on a substrate simulta- neously, with a high degree of morphological control. In fact, in the past twelve months inventive methods have illustrated the possibility of control over growth, position, and direc- tionality of nanotubes. 14-18 The next step is to find a direct method of incorporating them into polymer composite systems. Various other groups have addressed this issue. 19 We report in this paper a controlled, efficient and cost- effective method of producing carbon nanotube arrays within a poly(dimethylsiloxane) polymer (PDMS) matrix. Carbon nanotubes were grown by chemical vapor deposition (CVD) on a pre-patterned template. From this, a mixture of base/ curing agent (weight ratio of 10:1) from a Sylgard 184 elastomer kit is deposited onto the patterned arrays of as- grown tubes. The mixture migrates into vacant areas on the nanotube film. The resultant cured (for 24 h at room temperature) PDMS composite is then simply peeled off the substrate giving a free-standing flexible film containing a controlled nanotube morphology. Our template for carbon nanotube growth is first prepared by soft lithography patterning, similar to previous reports. 20,21 Soft lithography can be used to rapidly pattern large areas under atmospheric conditions. The shape and dimensions of the molded elastomer, used to create the patterns, can be modified to create a variety of templates for CNT growth. Using an elastomer stamp, the organometallic polymer catalyst is patterned onto a silicon oxide substrate (Figure 1a-c). The micropattern feature sizes are dictated by the dimensions of the stamp. The height of the catalyst features can be controlled by varying the concentration of the polymer solution used to create the patterns. The organometallic polymer used was a poly(styrene-vinylferrocene) copolymer blend (PS-PVF). This PS-PVF was anionically synthesized in our lab. A combination of gel permeation chromatography and nuclear magnetic resonance revealed that the PS-PVF * Corresponding author. E-mail minetta@tcd.ie ² Trinity College Dublin. ‡ Chemistry Department, RPI. § Materials and Engineering Department, RPI. | Nanotechnology Center, RPI. NANO LETTERS 2003 Vol. 3, No. 10 1333-1337 10.1021/nl034273e CCC: $25.00 © 2003 American Chemical Society Published on Web 09/13/2003