University of Minnesota
Institute of Technology
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Electrical and Computer Engineering

Imaging 'Invisible' Dopant Atoms

Dr. Andre Mkhoyan
University of Minnesota - CEMS

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. We combine electron energy loss spectroscopy with annular dark-field scanning transmission electron microscopy (ADF-STEM) to image individual Mn impurities inside ZnSe nanocrystals. While Mn is invisible to conventional ADF-STEM in this host, our experiments and detailed simulations show consistent detection of Mn. Thus, a general path is demonstrated for atomic-scale imaging and identification of individual dopants in a variety of semiconductor nanostructures.

Prof. Mkhoyan is native of Armenia. In 1991 he graduated with honors from the Physics and Mathematics oriented high school in Yerevan and enrolled into Yerevan State University. There he received B.S. and M.S. in Physics in 1996 with honors specializing in Solid State Physics. Then he spent couple of years working as a researcher at Bell Laboratories of Lucent Technologies. He then received the M.S. in 2003 and Ph.D. in 2004 from School of Applied and Engineering Physics at Cornell University. From 2004 to 2008 he was Postdoctoral Research Associate at Cornell and Visiting Scientist at T.J. Watson Lab of IBM. He joined Department of Chemical Engineering and Materials Science in August of 2008 as Assistant professor.