STEM - Internal Home
 
 

Atom-by-atom analysis

Ondrej L. Krivanek1, Matthew F. Chisholm2, Valeria Nicolosi3, Timothy J. Pennycook2,4, George J. Corbin1, Niklas Dellby1, Matthew F. Murfitt1, Christopher S. Own1, Zoltan S. Szilagyi1, Mark P. Oxley2,4, Sokrates T. Pantelides2,4, and Stephen J. Pennycook2,4


Annular dark-field STEM image of monolayer boron nitride. a) As recorded. b) Corrected for distortion, smoothed, and deconvolved to remove probe tail contributions to nearest neighbours. c) Line profiles through (b) identifying C and O atoms based on intensity. The insert in the upper right corner of (a) shows the Fourier transform of an image area away from the thicker regions. Its two arrows point to (11 0) and (20 0) reflections of the hexagonal BN that correspond to recorded spacings of 1.26 and 1.09 Å.

Atoms with low atomic number (Z), such as carbon, oxygen, nitrogen and boron, are important components in new materials for energy technologies such as batteries and organic solar cells. Until now, it has not been possible to image and identify individual low Z atoms with scanning transmission electron microscopy (STEM). For the first time individual atoms of boron, carbon, nitrogen and oxygen have been resolved, identified and located in single-layer boron nitride using aberration-corrected STEM. A number of new defect configurations were identified, and the deduced structures were confirmed by total-energy density functional calculations. The new level of sensitivity is made possible by Z-contrast imaging that distinguishes atoms of different Z values by their different scattering power. The new microscope, a Nion UltraSTEM100 provides the smallest beam so far achieved at an energy of 60 kV, which is low enough to avoid most of the atomic displacements caused by higher voltages. Some defects were still induced by the beam, which may open a new route to atomic-precision lithographic doping in single-layer boron nitride and graphene.


 Oak Ridge National Laboratory