Abstract
Material properties are sensitive to atomistic structure defects such as vacancies or impurities, and it is therefore important to determine not only the local atomic configuration but also their chemical bonding state. Annular dark-field scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy has been utilized to investigate the local electronic structures of such defects down to the level of single atoms. However, it is still challenging to two-dimensionally map the local bonding states, because the electronic fine-structure signal from a single atom is extremely weak. Here, we show that atomic-resolution differential phase-contrast STEM imaging can directly visualize the anisotropy of single Si atomic electric fields in monolayer graphene. We also visualize the atomic electric fields of Stone–Wales defects and nanopores in graphene. Our results open the way to directly examine the local chemistry of the defective structures in materials at atomistic dimensions.
Highlights
Material properties are sensitive to atomistic structure defects such as vacancies or impurities, and it is important to determine the local atomic configuration and their chemical bonding state
We show atomic-resolution electric field imaging at dopants and topological defects in graphene by using differential phase-contrast (DPC)–scanning transmission electron microscopy (STEM) recorded with a second-generation segmented annular all-field detector (SAAF, 16 segment elements)[10,14], operating the microscope at 80 kV (JEOL ARM300CF installed at the University of Tokyo)[15]
In DPC–STEM, the segmented detectors are set in the bright-field region[10,12] and permit direct visualization of the local electric fields at atomic dimensions, where the electric field is detected as the variation of the center of mass (CoM) in the diffraction pattern for each probe position[11,17]
Summary
Material properties are sensitive to atomistic structure defects such as vacancies or impurities, and it is important to determine the local atomic configuration and their chemical bonding state. Pure graphene consists of sp[2] hybridized carbon atoms arranged in a honeycomb lattice, but synthesis inevitably introduces a wide variety of atomistic structure defects including impurity dopants, vacancies, nonhexagonal polygons, edges, and nanopores[5]. We show atomic-resolution electric field imaging at dopants and topological defects in graphene by using DPC–STEM recorded with a second-generation segmented annular all-field detector (SAAF, 16 segment elements)[10,14], operating the microscope at 80 kV (JEOL ARM300CF installed at the University of Tokyo)[15]. We identify the local enhancement or suppression of electric fields of topological defects such as Stone–Wales defects and nanopores in graphene This result opens a new capability to investigate the local chemistry of atomistic defects in materials and might shed light on our understanding of material properties at the level of single atoms
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