The final public oral examination of Mingshaw Wu will take place on Friday, June 24, 2005 at 5:00 p.m. in Room 202. The examining committee will consist of Professors Paul Chaikin, Richard Register, Suzanne Staggs and Duncan Haldane. Any other members of the University wishing to attend the examination may do so.

The thesis of Mingshaw Wu entitled " Progresses in Block Copolymer Lithography" has been placed on deposit.

Any member of the University wishing to read the thesis may do so. Any objections should be submitted to me in writing. The principal advisor for this work was Professor Paul Chaikin. The abstract is below:

ABSTRACT

The versatility and self-assembling properties of block copolymers have potential applications in nanometer-scale lithography. The feature size and spacing of the structures produced with block copolymer lithography are a few tens of nanometers - a length scale largely inaccessible to currently available lithographic methods. In addition to the immediate possible applications, block copolymers thin films are also a model system for study ordering in two-dimensional systems.

In the first part of this thesis, we use several block copolymer lithographic techniques to fabricate electronic structures. We combine standard techniques in polymer chemistry and microelectronics lithography. The geometry of the device to be fabricated determines the methods used. Specifically, we fabricate arrays of metallic dots, anti-dots, and wires, which potentially have novel electronic properties.

In the second part, we present a study of shear-induced alignment of thin films of a sphere morphology diblock copolymer which forms hexagonal packed planes. Two-dimensional systems cannot have long range translational order; however, long range order can be produced using an alignment field. In the present case, the dynamic field is the shear stress. We use a stress-controlled rheometer to apply the shear stress through a viscous fluid several orders of magnitude thicker than the polymer thin film. To study the alignment under certain shearing conditions as a function of shear stress, we image ex situ the top layer of the spheres using atomic force microscopy. Below the order-disorder temperature and above the glass-transition temperature, a threshold stress for the alignment exists. Above this threshold, the close-packed direction aligns in the shear direction. Below, the alignment decays continuously to a polygranular morphology (unaligned) at zero stress. We observe alignment only in film thicknesses greater than a monolayer of spheres, which suggests an alignment mechanism similar to that found in uncharged colloids and granular materials. The alignment of our block copolymer thin films using shear stress is a process related to dynamical phase transitions

Daniel Marlow
Chair, Dept. of Physics