Pushing the limits of high-resolution polymer microscopy using antioxidants

Abstract

High-resolution transmission electron microscopy (HRTEM) has been transformative to the field of polymer science, enabling the direct imaging of molecular structures. Although some materials have remarkable stability under electron beams, most HRTEM studies are limited by the electron dose the sample can handle. Beam damage of conjugated polymers is not yet fully understood, but it has been suggested that the diffusion of secondary reacting species may play a role. As such, we examine the effect of the addition of antioxidants to a series of solution-processable conjugated polymers as an approach to mitigating beam damage. Characterizing the effects of beam damage by calculating critical dose DC values from the decay of electron diffraction peaks shows that beam damage of conjugated polymers in the TEM can be minimized by using antioxidants at room temperature, even if the antioxidant does not alter or incorporate into polymer crystals. As a consequence, the addition of antioxidants pushes the resolution limit of polymer microscopy, enabling imaging of a 3.6 Å lattice spacing in 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).

Advanced Electron Microscopy of Nanophased Synthetic Polymers and Soft Complexes for Energy and Medicine Applications

“…In an example shown in Figure 14, the addition of organic small molecules in polymers serves the purpose of enhancing polymer characterization [115]. In another case, a ternary soft complex facilitates the formation of promising novel nanostructures for performance enhancement (Figure 15) [49].…”

Imaging 0.36 nm Lattice Planes in Conjugated Polymers by Minimizing Beam Damage

“…Indeed, recent work shows that blending PffBT4T-2OD, P3HT, or P3DDT with ca. 10 wt % of free-radical scavengers, such as butylated hydroxytoluene, leads to an increase in D C by a factor of about three . As the reacting species diffuses around, it causes further damage to the material in a cascading manner (Figure ).…”

Radiation Damage and Nanofabrication in TEM and STEM

“…Radiolysis in an organic specimen is reduced (by a factor of typically 2 to 20) by cooling to around 100 o K, supposedly by suppressing the diffusion of radiation-induced reaction products (single atoms, radicals, ionized species). Chemical scavengers such as antioxidants may also curtail structural damage at room temperature [2], but not at 100 o K where diffusion is already largely eliminated. Encapsulation in ice or between layers of carbon is found to reduce damage and is employed in cryo-EM (together with cooling) to permit structural measurements on proteins and other important biological molecules [3].…”