Imaging 0.36 nm Lattice Planes in Conjugated Polymers by Minimizing Beam Damage
Brooke Kuei, Carol M. Bator, Enrique D. Gomez
Abstract
Transmission electron microscopy can resolve the atomic structure of materials with 0.5 Å resolution. High-resolution transmission electron microscopy (HRTEM) of soft materials, however, is limited by beam damage. We characterized damage in a series of conjugated polymers comprising poly(3-hexylthiophene-2,5-diyl) (P3HT), poly(3-dodecylthiophene-2,5-diyl) (P3DDT), and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″’-di(2-octyldodecyl)-2,2′;5′,2″;5″,2″’-quaterthiophene-5,5″’-diyl)] (PffBT4T-2OD) by monitoring the decay of electron diffraction peaks as a function of dose rate, beam blanking, and temperature. We also measured the decay of low-loss electron energy-loss spectra as a function of dose rate. These damage experiments suggest that the dominant mechanism of beam damage in conjugated polymers is the diffusion of a reacting species generated from ionization, likely of side chains. Elucidating a mechanistic description of radiation effects leads to imaging protocols that can minimize damage, which enables the direct imaging of 3.6 Å π–π stacking in a solution-processed conjugated polymer (PffBT4T-2OD), improving state-of-the-art resolution of this class of materials by an order of magnitude.