| AVS 63rd International Symposium & Exhibition | |
| Electronic Materials and Photonics | Wednesday Sessions |
| Session EM+NS+SP+SS-WeA |
| Session: | Nanoscale Imaging of Metals and Compound Semiconductor based Nanostructures, Surfaces and Interfaces |
| Presenter: | Christian Kisielowski, Molecular Foundry, Lawrence Berkeley National Laboratory |
| Authors: | C. Kisielowski, Molecular Foundry, Lawrence Berkeley National Laboratory P. Specht, University of California Berkeley |
| Correspondent: | Click to Email |
As heterogeneous materials scale below 10 nm, a suitable combination of single digit nanocrystals with their rich variety of tunable surfaces and interfaces allows tailoring unprecedented materials with novel structure-function relationships. The design of new catalysts [1], investigations of polymers at atomic resolution [2] or analyses of deviations from a random doping distributions at atomic resolution [3] may serve as examples. This contribution describes research that aims at exploiting the emerging ability to analyze and understand such materials by directly determining their atom arrangement in three-dimensions using aberration-corrected transmission electron microscopy [4]. Attempts to unravel the atomic structure of such nanoscale composites in this manner must explicitly address their pronounced sensitivity to the probing radiation that can unintentionally alter their pristine structure, often beyond recognition. We address this challenge by applying low dose-rate in-line holography [5], which allows operating electron microscopes with dose rates as low as 5-10 e/Å2s that help maintaining structural integrity at atomic resolution to an unexplored end. The approach mimics best practices in biological research but achieves atomic resolution with single atom sensitivity by the acquisition of large image series. We observe a variety of previously unknown atom configurations in surface proximity of CoOx nanocrystals and coatings that are hidden behind unusually broadened diffraction patterns but become visible in real space images because the phase problem is solved. The observed structures are drastically altered by an exposure of the material to water vapor or other gases, which is investigated at atomic resolution in environmental electron microscopy. It is shown for Rh/W catalysts that electron beam-induced atom dynamics can be entirely suppressed even for atom clusters made from less than 10 atoms. Resultantly, chemical compositions can be determined by contrast measurements alone and functional processes can be triggered and tracked in real time at atomic resolution.[6]
[1] J. A. Haber et al., Advanced Energy Materials 5 (2015) 1402307
[2] D. Lolla et al., Nanoscale 8 (2016) 120 - 128
[3] P. Specht, C. Kisielowski, On the chemical homogeneity of InxGa1-xN alloys - Electron microscopy at the edge of technical limits, submitted (2016)
[4] F.R. Chen et al., Nature Commun. 7:10603 doi: 10.1038/ ncomms10603 (2016)
[5] C. Kisielowski, Advanced Materials 27 (2015) 5838-5844
[6] The Molecular Foundry, which is supported by the Office of Science, the Office of Basic Energy Sciences, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231