title: Migration of Single Iridium Atoms and Tri-iridium Clusters on MgO Surfaces: Aberration-Corrected STEM Imaging and Ab Initio Calculations.
abstract: To address the challenge of fast, direct atomic-scale visualization of the migration of atoms and clusters on surfaces, we used aberration-corrected scanning transmission electron microscopy (STEM) with high scan speeds (as little as ∼0.1 s per frame) to visualize the migration of (1) a heavy atom (Ir) on the surface of a support consisting of light atoms, MgO(100), and (2) an Ir3 cluster on MgO(110). Sequential Z-contrast images elucidate the surface transport mechanisms. Density functional theory (DFT) calculations provided estimates of the migration energy barriers and binding energies of the iridium species to the surfaces. The results show how the combination of fast-scan STEM and DFT calculations allow visualization and fundamental understanding of surface migration phenomena pertaining to supported catalysts and other materials.
authors.affiliation: School of Materials Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Chang Wan
authors.initials: CW
authors.lastname: Han
authors.affiliation: Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Hakim
authors.initials: H
authors.lastname: Iddir
authors.affiliation: Department of Chemical and Biological Engineering, Koç University , Sariyer, Istanbul 34459, Turkey.
authors.forename: Alper
authors.initials: A
authors.lastname: Uzun
authors.affiliation: Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Larry A
authors.initials: LA
authors.lastname: Curtiss
authors.affiliation: Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States.
authors.forename: Nigel D
authors.initials: ND
authors.lastname: Browning
authors.affiliation: Department of Chemical Engineering & Materials Science, University of California , Davis, California 95616, United States.
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Gates
authors.affiliation: School of Materials Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Volkan
authors.initials: V
authors.lastname: Ortalan
keywords: density functional theory; heterogeneous catalysis; scanning transmission electron microscopy; supported catalysts; surface diffusion