Substrate‐Restricted Asymmetric Evolution of Solid‐State Nanopores

Nanopore evolution theories predict symmetrical expansion or shrinkage by changing free surface energy. Here, a substrate‐restricted regime is uncovered where this criterion fails: in a substrate‐supported ultrathin film, nanopores shrink universally regardless of initial size. Through in situ annealing and cross‐sectional STEM characterization, asymmetric pore dynamics are revealed ‐ top expansion and bottom shrinkage, with a minimum aperture reduced and forming a conical geometry. Such inhomogeneous variation is proposed to be driven by substrate‐restricted molecular migration, following an energy potential gradient along the nanopore channel, distinct from the equilibrium evolution. A generalized kinetics model identifies substrate confinement as an independent variable, establishing a thickness‐dependent critical radius, validated across both single pores and pore arrays. This redefines nanopore evolution in confined systems, with broad avenues for tunable nanoscale interface design.