Mapping Nanoscale Heterogeneity in Soft Materials With Modified Tapping-Mode AFM

Atomic force microscopy (AFM) in tapping mode is widely used to image soft materials with minimal damage, but its brief tip-sample contact limits sensitivity to local mechanical response. Here, we introduce a modified tapping regime in which the tip maintains weak continuous contact during scanning, enhancing the detection of local deformation, relaxation, and energy dissipation that cannot be resolved by conventional tapping. We demonstrate this approach by imaging soft insulin aggregates as a representative biological soft-matter system, revealing finer internal heterogeneity and localized nanodomain-scale dissipation-linked features referenced to a sub-k_BT noise-equivalent baseline. This method improves phase and reconstructed energy-dissipation contrast, enabling mapping of mechanical heterogeneity at the nanoscale while preserving the overall topographic scaffold. Incorporating this method into tapping-mode AFM will be useful for investigating soft and biological interfaces where morphology alone does not capture important local response variations.