1. Reorientation of Nanoscale Block Copolymer Domains by Shear (DMR 0819860)IRG-C: A. Marencic, D. Adamson (Univ. of Connecticut), P. Chaikin (NYU), and R. Register Block copolymer thin films are attractive templates for covering large areas with nanoscale features– such as parallel metal nanowires 20 nm across and 20 nm apart, covering the surface of a 12” silicon wafer [1]. But for such wires to be useful, we need to control where they go: in other words, to direct the orientation of these wires at various places on the wafer. Mechanical shear can realign the nanocylinders in block copolymer films– the precursors to the nanowires– but up until now, we have not known how much stress is required to budge the cylinders. PCCM researchers have recently developed a model for this shear-alignment process, and tested it by shearing a film and examining its structure by atomic force microscopy (AFM) [2]. To obtain the maximum possible data from the minimum number of experiments, they designed a “combinatorial” shear where different stresses and reorientation angles were applied to different parts of the film. The figure at right shows that agreement between the model and experiment is excellent– we now know precisely what is required to “write” complex patterns of aligned cylinders into these films. The “double-shear” experiment. Circles represent the 25-mm-diameter sheared regions (rotational shear axis at center of circle). The dashed circle at right is the outline of the “first shear” region and the solid circle at left corresponds to the “second shear”. In the lozenge-shaped intersection of the two regions, the block copolymer film is first sheared one way, then another. The color map in the background is the model prediction for the orientational order parameter in the film after the second shear (color scale at right). The circles represent the actual order parameter measured locally in various points in the film by AFM; agreement between the model and data, particularly in the location of the realignment zone (where the color goes from blue to red), is excellent. References: [1]A.P. Marencic and R.A. Register, “Controlling Order in Block Copolymer Thin Films for Nanopatterning Applications”, Ann. Rev. Chem. Biomol. Eng., 1, 277-297 (2010). [2] A.P. Marencic, D.H. Adamson, P.M. Chaikin, and R.A. Register, “Shear Alignment and Realignment of Sphere-Forming and Cylinder-Forming Block Copolymer Thin Films”, Phys. Rev. E, 81, 011503 (2010).