Nanomechanical properties of self-structured azopolymer defects [Invited]

Light-driven structuring has emerged as a powerful tool for nanoscale material patterning. Azopolymers, in particular, undergo mass migration when exposed to light, forming nanoscale surface patterns. However, self-structuring via single-beam illumination inherently gives rise to topographical defects due to nonlinear mass transport. While their optical and morphological properties are well studied, their mechanical characteristics, especially those of the defects, remain poorly understood. Using bimodal atomic force microscopy, we reveal azimuthal variations in the out-of-plane Young’s modulus, indicating residual stress anisotropy imprinted by light-induced mass transport. This stress-mediated mechanical patterning links optical structuring to mechanical response, enabling tunable stiffness gradients at the nanoscale. Our findings open new pathways for engineering polymeric surfaces for flexible photonics, nano-imprinting, and responsive materials.