Despite the exceptional resolution in aberration-corrected high-resolution transmission electron microscope (AC-HRTEM) images of inorganic two-dimensional (2D) materials, achieving high-resolution imaging of organic 2D materials remains a daunting challenge due to their low electron resilience. Optimizing the critical dose (the electron exposure, the material can accept before it is noticeably damaged) is vital to mitigate this challenge. An understanding of electron resilience in porous crystalline 2D polymers including the effect of sample thickness has not been derived thus far. It is assumed, that additional layers of the sample form a cage around inner layers, which are preventing fragments from escaping into the vacuum and enabling recombination. In the literature this so called caging effect has been reported for perylene and pythalocyanine. In this work we determine the critical dose of a porous, triazine-based 2D polymer as function of the sample thickness. The results show that the caging effect should not be generalized to more sophisticated polymer systems. We argue that pore channels in the framework structure serve as escape routes for free fragments preventing the caging effect and thus showing surprisingly a thickness-independent critical dose. Moreover, we demonstrate that graphene encapsulation prevents fragment escape and results in an increase in the critical electron dose and unit-cell image resolution.

尽管无机二维（2D）材料的像差校正高分辨率透射电子显微镜（AC-HRTEM）图像具有出色的分辨率，但由于有机二维材料的电子弹性较低，实现有机二维材料的高分辨率成像仍然是一项艰巨的挑战。优化临界剂量（材料在明显损坏之前可以接受的电子暴露）对于缓解这一挑战至关重要。迄今为止，尚未得出对多孔结晶二维聚合物中的电子弹性（包括样品厚度的影响）的理解。据推测，样品的附加层在内层周围形成一个笼子，防止碎片逃逸到真空中并实现重组。文献中报道了苝和酞菁的这种所谓的笼蔽效应。在这项工作中，我们确定了多孔三嗪基二维聚合物的临界剂量作为样品厚度的函数。结果表明，笼蔽效应不应推广到更复杂的聚合物系统。我们认为，框架结构中的孔道可作为游离碎片的逃逸路线，防止笼罩效应，从而令人惊讶地显示出与厚度无关的临界剂量。此外，我们证明石墨烯封装可以防止碎片逃逸，并导致临界电子剂量和单位电池图像分辨率的增加。