9707975 Martin This research project will investigate the microstructure and macroscopic properties of specific grain boundary defects in crystalline, semiconducting polymer materials. The long-term goal of this work is to isolate individual grain boundaries so that their microstructure and influence on macroscopic properties can be determined unambiguously. "Polymer bicrystals" make it possible to examine the mechanical and electrical properties of these materials as a function of defect geometry. Measurements of the mechanical strength and photocurrent transport both decrease with increasing misorientation between component grains. These properties measurements are corroborated by structural investigations using opticalmicroscopy, scanning electron microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and white-beam synchrotron X-ray topography (WBSXT). The current research project will involve (1) investigations of new materials of current interest for device applications, (2) processing schemes for introducing defects into crystalline organic semiconductors in a controlled manner, (3) structural characterization by transmission electron microscopy, electron diffraction, and WBSXT, and (4) measurements of macroscopic properties by mechanical and electrical testing. Of particular scientific and technological interest is the manner in which carrier transport and mechanical deformation is accommodated across individual grain boundaries. The manner in which slip deformation is accommodated across the engineered grain boundary interfaces as a function of tilt and twist misorientation angle will be investigated. From these results we will learn about the manner in which planes of oriented polymer molecules laterally translate by what are expected to be dislocatio n-mediated mechanisms of slip. %%% This research should provide an insight into the defect- limited behavior of ordered polymer and organic solids. These efforts will provide fundamental information about the relationship between microstructure and macroscopic properties of these materials in the solid-state. Optoelectrically active polymers are of considerable interest for devices such as thin film transistors, flat panel displays, chemical sensors, and injection lasers. Recent publications have identified the critical role of grain boundary defects in limiting the performance of these flexible, organic-based electronic devices for low cost, large scale applications. ***
