Abstract
Along with hydrogen, carbon, nitrogen and oxygen are the arguably mostimportant elements for organic chemistry. Due to their rich variety of possiblebonding configurations, they can form a staggering number of compounds. Here, wepresent a detailed analysis of nitrogen and oxygen bonding configurations in adefective carbon (graphene) lattice. Using aberration-corrected scanningtransmission electron microscopy and single-atom electron energy loss spectroscopy,we directly imaged oxygen atoms in graphene oxide, as well as nitrogen atomsimplanted into graphene. The collected data allows us to compare nitrogen and oxygenbonding configurations, showing clear differences between the two elements. Asexpected, nitrogen forms either two or three bonds with neighboring carbon atoms,with three bonds being the preferred configuration. Oxygen, by contrast, tends tobind with only two carbon atoms. Remarkably, however, triple-coordinated oxygen withthree carbon neighbors is also observed, a configuration that is exceedingly rare inorganic compounds.
Highlights
Along with hydrogen, carbon, nitrogen and oxygen are the arguably most important elements for organic chemistry
In scanning transmission electron microscopy (STEM)[1], the contrast mechanism behind annular dark field images allows the identification of light elements (e.g. B, C, N, O) despite their very similar atomic number[2]
In aberrationcorrected high-resolution transmission electron microscopy (HRTEM), these elements have an almost-identical contrast and their discrimination becomes difficult in particular when they are incorporated into irregular structures such as defects[3,4]
Summary
Carbon, nitrogen and oxygen are the arguably most important elements for organic chemistry Due to their rich variety of possible bonding configurations, they can form a staggering number of compounds. In scanning transmission electron microscopy (STEM)[1], the contrast mechanism behind annular dark field images allows the identification of light elements (e.g. B, C, N, O) despite their very similar atomic number[2]. Few HRTEM studies have revealed disorder and defects in graphene oxide[16,17,18,19], a direct visualization of oxygen atoms that includes their unambiguous chemical identification (e.g., via contrast in STEM or via electron energy loss spectroscopy, EELS) along with their bonding with a carbon matrix has not been achieved yet. We describe the dynamics of reduction observed under the electron beam for the case of oxygen
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