Ordered block copolymer films are of great interest for lithographic applications with nanometer length scales, e.g. as templates for production of quantum dot arrays. Diblock copolymers, consisting of two immiscible chains (blocks) joined end to end, self-assemble to form a variety of nanoscale structures. If the two blocks are very different in size, nanometer scale spheres are formed.

Achieving long range positional order and orientation of these structures, i.e. epitaxy, has been elusive, however. We have recently demonstrated a graphoepitaxial strategy that is not only simple, but can create epitaxial single crystal films of block copolymers of high perfection over large areas of a substrate. In this process, a thin film overlayer is placed on a substrate with a topographical relief which forces the overlayer to reduce its interfacial energy by organizing preferentially with the edges of the relief.

In the case of a polymer overlayer, this effect is achieved due to the preferential attraction of one of the blocks to the surfaces. This attraction can induce the arrangement of spheres in the direction away from the surface.

Schematic of a confinement edge

Thus, a confined stripe of copolymer can be ordered in a single crystalline, close packed structure with hexagonal symmetry for stripe widths as wide as 10 microns. Such control may prove useful in lithographic applications of block copolymer films. Further, we are currently using this technique to observe the impact of grain defect evolution, surface effects, and thermodynamics on the crystalline order in this diblock copolymer sphere system.

AFM of a well ordered, confined array

2-D Fast Fourier Transform of a well ordered array

To Learn more about the Research of the Kramer Group please visit: Prof. Edward J. Kramer

Rachel A. Segalman Graduate Student Department of Chemical Engineering University of California, Santa Barbara e-mail: segalman@mrl.ucsb.edu Rachel Segalman's Webpage

copyright 2001 R.A. Segalman