Phase Transitions in Thin Block Copolymer Films
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in Thin Block Copolymer Films Edward J. Kramer
The following article is based on the Turnbull Lecture presented by Edward Kramer (University of California, Santa Barbara), recipient of the 2009 Materials Research Society David Turnbull Lectureship, at the 2009 MRS Fall Meeting on December 2 in Boston. Kramer was cited for “outstanding contributions in bringing insights and understanding to flux pinning in superconductors and to the fundamentals of fracture, diffusion, and interface phenomena in complex polymeric materials through research, teaching, mentoring, writing, and lecturing.”
students, and, in particular, I will discuss the work of Gila Stein, Vindhya Mishra, Rachel Segalman, Matt Hammond, and my colleague on the theoretical side, Glenn Fredrickson at the University of California, Santa Barbara, and his students and postdoctoral fellows. I will start by quoting a couple of pieces of wisdom from David Turnbull. He wrote: “As my students gained experience, their pace quickened to the point that they controlled their research and often took productive initiatives that I had not anticipated.” This truly applies to the particular research project I will discuss today. These students led me far away from my original intentions. He also wrote: “When very good students have their research well underway, the best policy for a research adviser is to ‘stay out of their way.’ ” I believe this is a very good policy indeed.
Phase Behavior of Block Polymers Abstract David Turnbull’s experiments and theoretical insights paved the way for much of our modern understanding of phase transitions in materials. In recognition of his contributions, this lecture will concentrate on phase transitions in a material system not considered by Turnbull, thin diblock copolymer films. Well-ordered block copolymer films are attracting increasing interest as we attempt to extend photolithography to smaller dimensions. In the case of diblock copolymer spheres, an ordered monolayer is hexagonal, but the ordered bulk is body-centered cubic (bcc). There is no hexagonal plane in the bcc structure, so a phase transition must occur as n, the number of layers of spheres in the film, increases. How this phase transition occurs with n and how it can be manipulated is the subject of the first part of my presentation. In the second part of the talk, I show that monolayers of diblock copolymer spheres and cylinders undergo order-to-disorder transitions that differ greatly from those of the bulk. These ordered 2D monolayers are susceptible to phonon-generated disorder as well as to thermal generation of defects, such as dislocations, which, while they are line defects in 3D, are point defects in 2D. The results are compared to the theories of melting of 2D crystals (spheres) and of 2D smectic liquid crystals (cylinders), a comparison that will allow us to understand most, but not all, of the features of these order-disorder transitions that occur as the temperature is increased.
Introduction It is a great pleasure for me to give this lecture, because
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