When 10:30 AM - 11:30 AM Oct 26, 2018
Where 1571 G.G. Brown
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Tomographic AFM: 3-Dimensional Nanoscale Functional Materials Properties Nanoscale and Nano-Volumetric Properties of Functional Materials and Photovoltaics via High Speed and Tomographic AFM

Bryan D. Huey
Materials Science & Engineering, University of Connecticut

Nano- and meso- scale materials properties are crucial to the macroscopic performance of a wide range of functional and photovoltaic devices. To directly and efficiently investigate such systems with nanoscale aerial resolution, we previously developed High Speed Atomic Force Microscopy as well as several new variations of photoconductive AFM. With piezoelectrics, geometric strain relief is implemented to engineer the converse-piezoelectric coefficient (Keech et. al., Advanced Functional Materials, 2017). With ferroelectrics, movies of the domain switching process reveal nucleation and growth dynamics mediated by grain boundaries and other microstructural defects (Huey et. al., J.A.Cer.S. cover article, 2012), and notably stepwise polarization switching with multiferroics that is enabling for magnetoelectric devices (Heron et. al., Nature, 2014). For polycrystalline CdTe solar cells, novel photovoltaic performance maps reveal order-of-magnitude inter- and intra- granular heterogeneities (Atamanuk, Beilstein J. Nanotech, 2018). But ultimate device properties are sensitive or even controlled by sub-surface effects, often with profound thickness dependencies related to microstructure and concentration or field gradients. Therefore, we recently introduced Tomographic-AFM, achieving a 1,000,000x enhancement in resolution for direct volumetric materials property mapping. With CdTe, which already commands ~5% of the world’s solar cell market even though efficiency remains ~30-50% less than the theoretical limit, T-AFM uniquely reveals new proposed pathways to improve carrier separation (Luria et. al., Nature Energy, 2017). For BiFeO3, T-AFM confirms Kay-Dunn thickness scaling, LGD behavior with a minimum switchable thickness of <5 nm, and even 20 nm3domain and current tomography directly revealing the sub-surface domain structure and topological defects. 

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