Non-equilibrium processing of block copolymer (BCP) thin films via thermal zone-annealing promises to overcome significant challenges of traditional thermodynamic approaches to create defect free and long-range ordered functional films for high-tech applications. Thermal zone annealing involves passing a moving thermal temperature gradient across the plane of the film to locally melt and solidify the film. Recently a low temperature "cold zone annealing" or CZA version was demonstrated with promising results. Since most block copolymers will degrade at significantly high temperatures above melt point, CZA is broadly applicable to many block copolymer systems. Results for CZA on glassy cylinder forming PS-PMMA block copolymer films indicate up to an order of magnitude in enhanced ordering kinetics and alignment. Based on these promising results, key molecular mechanisms underlying the CZA driven ordering phenomena for BCPs will be examined at a fundamental level. This research will investigate these fundamental aspects of CZA using different block copolymers systems to illuminate general governing principles of CZA induced ordering of block copolymer thin film systems. An important component of the research plan relies on an Activation Energy analysis of ordering of block copolymer in CZA from grain size growth or correlation length development as a function of CZA parameters of velocity, maximum temperature, and gradient magnitude and the BCP molecular weight and block-block interaction parameter. In addition, the origin and mechanism of orientational alignment will be elucidated using both patterned and non-patterned substrates.
NON-TECHNICAL SUMMARY:
Block copolymer materials have been the focus over the last decade as potential solutions to a wide range of emerging nanotechnology needs from functional photonic materials to terabit density data storage devices. The major limitation to the use of these materials, however, is the presence of defects. This proposal will seek to understand the fundamentals of a new annealing platform that significantly reduces the barrier to defect removal. These fundamentals could lead to new processing techniques allowing advances in many industrially relevant fields. The PI's students will get experience at the Advanced Photon Source at Argonne National Lab allowing for exposure and training at national research facilities. An active component of the research is aimed at involving students at adjacent high-schools through the Akron Early College High School program as well the Post Secondary Distance Learning Opportunities and through a new program between St. Vincent St. Mary's High School in Akron and the College of Polymer Science and Engineering involving both students and teachers. In addition, the research will involve minority and women participation in their research program and both the University of Akron and University of Arkansas at Little Rock are both well known for their high ratio of minorities and women in research programs. In addition, this research project at UALR would incorporate secondary high school science teachers during the summer through a program known as STRIVE. The exposure of the teachers to this research including synthesis and nanocharacterization would improve their science skills as well as their understanding of the field making them better educators.
The major objective of this project was to better understand the fundamentals of cold zone annealing. This work was performed as a collaborative effort between the University of Arkansas at Little Rock (UALR) and the University of Akron (UA). This Project Outcomes Report will focus on the contributions of UALR. For more information regarding the outcomes of this project, please see the University of Akron’s Project Outcomes Report. During the course of this project, there have been two major findings that have contributed to the broader understanding of block copolymer ordering during the zone annealing process. Firstly, it was discovered that film thickness significantly affects the ordering of these systems. As film thickness decreases, the orientation order of these systems also decreases due to pinning at the substrate. Secondly, it was discovered that CZA is an effective means of orienting BCP nanostructures perpendicular to the substrate. Traditionally, this has been accomplished through chemical or physical modification of the substrate. However, at particular noncommensurate film thicknesses, it was shown that BCP systems annealed via CZA oriented vertically. For CZA with sharp gradients (CZA-S, see UA’s report), vertical orientation could be obtained with all film thicknesses. This is particularly relevant for applications requiring nanosize features such as high density memory storage in which the BCP is used as a sacrificial template with which to pattern the substrate. In addition to the intellectual merit of this project, 2 graduate and 2 undergraduate students have been trained in a variety of techniques such as thin film preparation, zone annealing, Labview programming, NR fitting, elipsometry, AFM, SEM, TEM, as well as many synthesis techniques including anionic polymerization, ATRP, and click reactions. These skills will benefit these students greatly as they continue their careers as scientists and educators.
