Translating silk protein hierarchical structure into graphitic order by FIB-induced pyrolysis

Silk fibers are protein-based materials with a highly ordered hierarchical architecture extending from β-sheet-rich molecular domains and aligned polypeptide chains to nanofibrillar bundles and microscopic fibers, collectively giving rise to their exceptional mechanical performance. This intrinsic multiscale organization also offers a powerful, yet largely unexplored, platform for templating ordered carbon materials with programmable nanoscale anisotropy. During our nanoscale structural analysis, Bombyx mori (B. mori) silk fibers were unintentionally carbonized while being sectioned into thin lamellae using focused ion beam (FIB) milling. Subsequent scanning transmission electron microscopy (STEM) revealed the formation of distinct graphitic-like nanostructures whose spatial orientation and domain alignment were dictated by the pre-existing hierarchical organization of the native silk fiber. The observed graphitic-like ordering followed the directionality of silk molecular packing and fibrillar alignment, indicating that β-sheet stacking and chain orientation serve as structural templates guiding carbon nucleation and lattice organization during localized pyrolysis. Beyond advancing understanding of beam-induced protein carbonization, the results establish a new paradigm for using self-assembled protein fibers as bottom-up templates for structured carbon materials. Translating molecular organization into functional nanoscale carbon networks opens opportunities to engineer patterned, anisotropic graphitic materials for potential applications in nanoelectronics, sensing, energy storage, and advanced composite systems.