Mechanism of Electron-Beam-Induced\nStructural Degradation\nin ZIF‑8 and its Electron Dose Tolerance

Zeolitic-imidazolate frameworks (ZIFs) are crystalline\nmicroporous\nmaterials with promising potential for gas adsorption and catalysis\napplication. Further research advances include studies on integrating\nZIFs into nanodevice concepts. In detail for the application, e.g.,\nelectron-beam-assisted structural modifications or patterning, there\nis a need to understand potential structural degradation processes\ncaused by such electron beams. Advanced transmission electron microscopy\n(TEM) has demonstrated its ability to study structures at the nanoscale.\nHere, we systematically investigated electron-beam-induced loss in\ncrystallinity in ZIF-8 under various experimental conditions, using\nas measure the attenuation of the relative intensity and the relative\ndisplacement of electron diffraction Bragg planes with increasing\ncumulative electron dose. The {110} Bragg planes reflect the overall\nstability of the ZIF-8 unit-cell structure, while the {431} Bragg\nplanes assess the stability of its micropore structure. We considered\na relative loss of Bragg plane intensity of 37% as the threshold for\ndetermining the critical electron dose, which varied for different\nBragg planes, with 35.6 ± 8.4 e<sup>–</sup>Å<sup>–2</sup> for {110} and 11.4 ± 3.0 e<sup>–</sup>Å<sup>–2</sup> for {431}. However, the critical dose\nper breakage of N–Zn bonds in a ZnN<sub>4</sub> tetrahedra\nper different Bragg plane was found to be ∼3 e<sup>–</sup>Å<sup>–2</sup>, which indicates continuous, simultaneous\nbreakage of N–Zn bonds throughout the crystal, confirming radiolysis\nas the dominant damage mechanism. In addition, we investigated the\neffects of TEM experiment parameters, including acceleration voltage,\nelectron dose rate, cryogenic sample temperature, in situ sample drying,\nand change in conductivity of the sample substrate (e.g., graphene).\nOur results unravel the degradation mechanisms in ZIF-8 and provide\nthreshold parameters for maximizing resolution in electron-beam-assisted\nexperiments and processes.