Quantifying the Protection Factor of Graphene Substrates for Atomic-scale Imaging of Organic Crystals

Abstract

Graphene substrates have been proposed as ultra-thin supports for dose-sensitive samples, where they increase dose resistance as a result of high thermal and electrical conductivity. For example, a single layer of graphene has provided a 9-fold protection factor when imaging single-layer MoS2 [1]. Unlike for inorganic crystals, graphene's protection factor for organic molecular crystals has yet to be systematically quantified. Here we use selected area electron diffraction (SAED) to measure the critical dose of both bulk and 2D bilayer organic crystals on either amorphous carbon (a-C) or single-layer graphene substrates. We find that the single layer of graphene offers a 2-7-fold improvement in the dose resistance. This improvement is significant: for example, increasing the critical dose by a factor of four should double the dose limited resolution for organic molecules [2]. Importantly, by comparing the improvement in critical dose for different d-spacings, we find that the protection factor provided by graphene is higher for higherorder diffraction spots. Our results indicate that graphene is especially useful for enabling near atomicresolution imaging of dose-sensitive samples, which we demonstrate by using aberration-corrected scanning transmission electron microscopy (ADF-STEM) to acquire images of cobalt(II) meso-tetrakis(4methoxyphenyl) porphyrin (CoTMPP).

Liquid phase electron microscopy of bacterial ultrastructure

“…However, D.radiodurans is known to tolerate fluences at least tenfold greater in magnitude than E.coli, suggesting an LF50 of D.radiodurans under the same circumstances of approximately 100 e -/nm 2 . This fluence limit is further increased by the 2-7x protection factor afforded by graphene encapsulation [48][49][50] , potentially leading the way for low fluence live-cell imaging in LP-STEM. Our observations of proteins at ~24 nm and other biomolecules within these bacterial cells suggest that even at cumulative fluences significantly higher than the putative LF50 of D.radiodurans, it may still be more favorable to monitor protein dynamics and interactions in situ than in purified protein solutions, with beam-related damage potentially mitigated by the native reactive oxygen defense system of D.radiodurans.…”

High-Resolution Imaging of Unstained Polymer Materials

“…22,23,48−51 Aromatic polymers show higher tolerance of electron dose relative to aliphatic polymers due to the delocalization of electrons. 37,52−54 In addition, the tolerance of radiation damage of aromatic polymers can be increased by using a graphene supporting film 55 or adding an antioxidant. 45 More details about the dependence of radiation damage on temperature, dose rate, acceleration voltage, and the specificity of damage to different polymers can be found elsewhere.…”

“…An example of such a reaction is formation of hydrogen gas in hydrocarbon polymers. To prevent radiation damage in typical aliphatic polymers, the accumulated electron dose deposited on the field of view, where an image is acquired, must be between 5 and 30 e /Å 2 . ,,− Aromatic polymers show higher tolerance of electron dose relative to aliphatic polymers due to the delocalization of electrons. ,− In addition, the tolerance of radiation damage of aromatic polymers can be increased by using a graphene supporting film or adding an antioxidant . More details about the dependence of radiation damage on temperature, dose rate, acceleration voltage, and the specificity of damage to different polymers can be found elsewhere. ,, Nevertheless, some form of beam damage must be endured if larger doses are used in an attempt to increase the signal-to-noise ratio.…”