High-resolution three-dimensional structural determination of unstained double-gyroid block copolymers through scanning transmission electron microscopy

Block copolymer-based multicomponent materials have garnered considerable attention because of tunable properties due to their various constituents. The use of electron tomography through transmission electron microscopy (TEM) for the three-dimensional (3D) imaging of stained block copolymers is an established approach for investigating structure-property relationships. Recently, scanning transmission electron microscopy (STEM) with an annular dark-field (ADF) detector has emerged as a method for the 3D structural analysis of unstained block copolymers. However, because of a lack of electron contrast, only a few low-resolution 3D reconstructions were reported for light elements. Herein, we report the first 3D structural analysis of a 200-nm-thick film composed of unstained double-gyroid block copolymers-polystyrene-b-poly(2-vinylpyridine) (PS-P2VP)-at a resolution of 8.6 nm through spherical aberration Cs-corrected STEM. At this resolution, P2VP molecules can be distinguished from PS molecules in z-contrast 3D reconstructions obtained both experimentally and theoretically. The 3D reconstructions revealed structural differences between stained and unstained specimens.

Automated summary

Block copolymer-based multicomponent materials have attracted attention due to their tunable properties. Electron tomography through TEM is an established method for the 3D imaging of stained block copolymers. STEM with an ADF detector has emerged as a method for the 3D structural analysis of unstained block copolymers. However, the lack of electron contrast has limited the resolution of 3D reconstructions for light elements. In this study, the first 3D structural analysis of unstained double-gyroid block copolymers was achieved using Cs-corrected STEM at a resolution of 8.6 nm.