High-resolution imaging of organic two-dimensional (2D) materials is challenging despite advancements in transmission electron microscopes (TEM). This study reveals that selecting the incident electron energy is crucial for improving image resolution. Among various acceleration voltages (300 kV, 200 kV, 120 kV, and 80 kV), 120 kV yielded the highest resolution (1.9 Å) in HRTEM images of two imine-based 2D polymer thin films, revealing unexpected molecular interstitial defects. Quantum mechanical calculations identified the defects' structural nature, and the enhanced resolution and contrast at 120 kV facilitated the detection of functional groups at pore interfaces. This approach was also successful for an amorphous organic 2D material.

Baokun Liang, Yingying Zhang, Christopher Leist, Zhaowei Ou, Miroslav Položij, Zhiyong Wang, David Mücke, Renhao Dong, Zhikun Zheng, Thomas Heine, Xinliang Feng, Ute Kaiser, Haoyuan Qi