Effect of Single-Layer Graphene Substrate on Mitigating the Electron Beam Induced Damage in ZIF-8 Metal-Organic-Framework (MOF)

Description

Characterizing materials at the atomic level is essential for understanding structure-property relationships at the nanometer scale. Typically, high-resolution scanning/transmission electron microscopy (HR-S/TEM) is employed for this purpose, utilizing high-energy electrons. However, when studying delicate soft matter, the use of an electron beam as a probe can be intrusive, potentially altering the original structure [1]. Therefore, it's important to investigate and comprehend how atomic-scale experiments affect the sample's structure. By controlling electron-sample interactions, including adjusting high tension, total electron dose, and electron dose rate, structural damage during experiments can be minimized [2][3].
Zeolitic imidazolate frameworks-8 (ZIF-8) are a subclass of MOFs characterized by a cubic crystal structure (space group I4 ̅3m) with pore sizes of 11.6 Å connected with pore aperture of 3.4 Å [4]. Due to its chemically stable crystalline structure and large pore size, ZIF-8 finds applications in gas separation and catalysis. This non-conducting crystalline structure is difficult to characterize using high energy electrons using HR-S/TEM due to radiolysis damage, charging and heating. It has been shown [5] that in PbPc organic materials, beam effects can be reduced by using graphene as support to quench the electronic excitation and thus improve the total allowable critical dose.
This study investigates the impact of a conductive substrate, such as single-layer graphene, on electron beam damage tolerance of ZIF-8 MOF. One approach to assess beam effects and associated structural changes is to quantify the decrease in the intensity of specific Bragg spots in electron diffraction (ED) patterns [1]. Experimental data were collected using a FEI Tecnai G2 microscope (LaB6, 200 keV), recording time-series ED patterns until all Bragg diffraction rings faded out. The dose rate was kept constant at 1 e- A-2 sec-1 with exposure time of 1 sec was used for acquiring single ED pattern. The bright field TEM image of the ZIF-8 nanoparticles on the amorphous holey carbon and single-layer graphene support are shown in fig. 1a and 1b, respectively, and the corresponding ED patterns at time (t = 1sec) are shown in fig. 1c and 1d, respectively. The last ED pattern is considered as background in the dataset.
Fig. 1e shows the background subtracted radially averaged intensity profiles of Bragg rings of ED pattern at time (t = 1sec) on amorphous carbon support, seen in fig. 1c. Fig. 1f shows the fading of the relative intensity of 431 Bragg rings (interplanar spacing of 3.4 Å) vs. cumulative electron dose in the time series.
The effect of using graphene as a substrate on attenuating electron beam damage to ZIF-8 is investigated using the measured critical dose and compared to beam effects on ZIF-8 on amorphous holey carbon. [6].

Period	2024
Event title	Microscopy and Microanalysis
Event type	Conference
Conference number	Volume 30, Issue Supplement_1
Location	Cleveland, United States, OhioShow on map
Degree of Recognition	International