University of Wisconsin-Madison
Materials Science and Engineering
Find All the Atoms! High-Resolution, High-Precision STEM Characterization of Nanostructures
Location: EB1 Room 1011
Friday, November 7th 2014 - 11:00 am
Aberration-corrected scanning transmission electron microscopy (STEM) at sub-Ångstrom spatial resolution can reveal the position and element of almost every atom in many crystalline materials. I will discuss two applications of STEM imaging. In the first, I will explain the structural origins of stable, reproducible, p-type conductivity in ZnO nanowires . Most ZnO is n-type, but nanowires can be rendered p-type by doping with Sb. We have shown that the Sb in confined to inversion domain boundary defects, which, combined with a pattern of associated internal voids, effectively co-dope the materials with Sb and O, rendering it p-type. In the second example, I will discuss a new STEM technique capable of measuring the position of atoms to better than 1 pm, and its application to characterizing the surface structure of a Pt nanocatalyst . We find that flat sides of the particle bulge outwards from the particle center, but corners contract substantially. Such under-coordinated, strained surface atoms may play a large role in the catalytic activity of small particles.
 "Stable p-type conduction from Sb-decorated head-to-head basal plane inversion domain boundaries in ZnO nanowires", A. B. Yankovich, B. Puchala, Fei Wang, Jung-Hun Seo, D. Morgan, Xudong Wang, Z. Ma, A. V. Kvit, and P. M. Voyles Nano Letters 12, 1311-1316 (2012).
 "Picometre-precision analysis of scanning transmission electron microscopy images of platinum nanocatalysts." Andrew B. Yankovich, Benjamin Berkels, W. Dahmen, P. Binev, S. I. Sanchez, S. A. Bradley and P. M. Voyles Nat. Commun. 5, 4155 (2014).
Sb-decorated inversion domain boundary in a ZnO nanowire .
Picometer-scale displacements of surface atoms on a Pt nanocatalyst .