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Imaging 'Invisible' Dopant Atoms
Nanometer-scale semiconductors that contain a few intentionally added impurity atoms can provide new opportunities for controlling electronic properties. However, since the physics of these materials depends strongly on the exact arrangement of the impurities, or dopants, inside the structure, and many impurities of interest cannot be observed with currently available imaging techniques, new methods are needed to determine their location.
Mkhoyan group in collaboration with David Norris's group from ETH Zurich combined electron energy loss spectroscopy with annular dark-field scanning transmission electron microscopy (ADF-STEM) to image individual Mn impurities inside ZnSe nanocrystals. Thus, a general path is demonstrated for atomic-scale imaging and identification of individual dopants in a variety of semiconductor nano structures. The paper was published in Nano Letters ( A.A. Gunawan et al., Nano Lett. 11, 5553 (2011) ) and highlighted in February 2012 issue of Nature Chemistry.