Solving Structurally Complex Materials
  • 1:25 p.m. Nov. 21, 2017
  • B-75 Amundson Hall
  • Paul M. Voyles
  • Department of Materials Science and Engineering
  • University of Wisconsin - Madison

Crystallography offers tremendously powerful approaches based on diffraction for solving structures with translation symmetry and a limited number of degrees of freedom. Nanostructures with a large fraction of surface atoms, interfaces, and glasses have much higher structural complexity – up to 3N degrees of freedom for a glass of N atoms – and require different approaches, often including experimental data from microscopy. This seminar will discuss our recent efforts combining electron microscopy data with tools from data science to solve the structure of complex materials. We have used non-rigid image registration to create highly-quantitative, sub-picometer precision high-resolution STEM images [1]. We have used those images to study surface distortion on Pt nanocatalysts [1] and combined them with structural modeling by DFT to image single La vacancies in LaMnO3 with sub-unit cell resolution in three dimensions. Chemically sensitive imaging using STEM EELS, combined with DFT calculations, has been used to solve Co2MnSi / GaAs interfaces designed with different interface terminations. For more complex structures not uniquely constrained by experimental data alone, we have developed structure refinement methods that combine microscopy data with simulated system energies and applied them to Au nanoparticles [2] and metallic glasses [3]. Structural models derived from automatic optimization or by-hand modeling can be interrogated to develop abstract structural characteristics of the material or used as the starting point for additional simulations to uncover structure-property relationships, such as the spin transport properties of Co2MnSi / GaAs interfaces.

[1] A. B. Yankovich et al., Picometre-precision analysis of scanning transmission electron microscopy images of platinum nanocatalysts. Nat. Commun. 5, 4155 (2014).

[2] M. Yu, A. B. Yankovich, A. Kaczmarowski, D. Morgan, P. M. Voyles, Integrated Computational and Experimental Structure Refinement for Nanoparticles. ACS Nano. 10, 4031 (2016).

[3] J. Hwang et al., Nanoscale Structure and Structural Relaxation in Zr50Cu45Al5 Bulk Metallic Glass. Phys. Rev. Lett. 108, 195505 (2012).

Seminars are open to alumni, friends of the Department, and the general public.

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