Microscopy and Microanalysis | 2021
Atomic-resolution and Atomic-scale Imaging of Small Organic Molecules
Abstract
The ability to image atomic arrangements in small organic molecules via transmission electron microscopy (TEM) offers a promising avenue for structural determination. Yet, attempts to image small-molecule crystals [1-4] or individual small molecules [5-8] at or even near atomic-resolution have had limited success because of their weak electron scattering and extreme beam sensitivity. [9,10]. For example, the critical dose of organic molecules typically ranges from 0.5-1000 e-/Å2, several orders of magnitude lower than the doses required to image single carbon atoms in graphene [10]. As a result, developing new methods that can achieve high resolution at low dose is a key goal for enabling the study of small molecules and soft materials in the electron microscope. Here, we combine low-dose aberration-corrected annular dark-field scanning TEM (ADF-STEM) with advanced image processing methods from electron crystallography and single-particle analysis. We demonstrate that our approach can produce elementally sensitive images in atomically-thin 2D metallated porphyrin and phthalocyanine crystals with an effective resolution up to 1.3 Å – sufficient to distinguish individual carbon and nitrogen atoms. To our knowledge, this is the highest resolution image ever reported of an individual small organic molecule using electron microscopy.