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Spring 2008 Seminar Series
Thursday, April 24, at 3:30 p.m.
Room 264 MacQuigg Labs
K. Andre Mkhoyan
Cornell University
Ithaca, NY
Quantitative Electron Microscopy and Spectroscopy at Atomic-Scale
Abstract
Scanning transmission electron microscopes (STEM) equipped with electron energy loss spectrometers (EELS) are powerful experimental tools to study the new phenomena in nano-scale materials with atomic-level precision. With current advances in sub-Å resolution, it is now possible to image local crystal structures of materials where dramatically different atoms are separated from each other at distances of less than 1 Å. In one case, implementation of annular dark field (ADF) imaging in an aberration-corrected STEM allowed direct imaging of atomic columns of light nitrogen atoms in close proximity to columns of aluminum in wurtzite aluminum nitride and, as a result, provided direct determination of the local lattice polarity. In another case, by employing EELS capabilities of STEM an unusual complete recovery of extensive electron-beam-induced damage in CaO-Al2O3-SiO2 glass was discovered. Nano-scale EELS measurements showed that the glass may return to its original compositional and structural state. EELS measurements also provided detail understanding of the atomic processes that taking place during damage and recovery. The combination of ADF imaging and energy loss spectroscopy, in the case of III-V nitride heterostructures, allowed in-depth atomic-scale characterization of the system and, therefore, provided better quantification of the critical electronic properties of these systems.
Bio
Andre Mkhoyan was born in Yerevan, 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 a B.S. and M.S. in Physics in 1996 with honors specializing in Solid State Physics. From Feb. 1998 he was working as a researcher at Bell Laboratories of Lucent Technologies in Murray Hill, NJ. He entered the Graduate School at Cornell University in a fall of 1999 in School of Applied and Engineering Physics and join the research group of Prof. John Silcox. He received the M.S. in May 2003 and Ph.D. in January 2004, both in Applied Physics. Now he is Postdoctoral Research Associate at Cornell and Visiting Scientist at T.J. Watson Lab of IBM working with Dr. Phil Batson.
Please join our speaker for light refreshments in 479 Watts Hall following the talk.
