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Quantifying the Nucleation and Growth Kinetics of Electron Beam Nanochemistry with Liquid Cell Scanning Transmission Electron Microscopy

preprint
submitted on 18.07.2018 and posted on 19.07.2018 by Mei Wang, Chiwoo Park, Taylor Woehl
In this article, we report on complex nanochemistry and transport phenomena associated with nanocrystal formation by electron beam induced growth and liquid cell electron microscopy (LCEM). We synthesized silver nanocrystals using scanning transmission electron microscopy (STEM) electron beam induced synthesis and systematically varied the electron dose rate, a parameter solely thought to regulate nanocrystal formation kinetics via the rate of metal precursor reduction. Rationally modifying the solution chemistry with tertiary butanol to scavenge radical oxidizing species established a strongly reducing environment and enabled repeatable LCEM experiments. Interestingly, nanocrystal growth rate decreased with increasing electron dose rate despite the predicted increase in reductant concentration. We present evidence that this counterintuitive trend stems from increased oxidizing radical concentration and radical recombination at high magnifications, which together decrease rate of precursor reduction. Nucleation rate was proportional only to imaging magnification, which we rationalized based on local radical accumulation at high magnification causing increased supersaturation and fast nucleation. Radiation chemistry and reactant diffusion scaling models yielded new scaling laws that quantitatively explained the observed effects of electron dose rate on nucleation and growth kinetics. Finally, we introduce a new reaction kinetic model that enables unraveling nucleation and growth kinetics to probe nucleation kinetics occurring at sub-nanometer length scales, which are typically not accessible with LCEM. Our systematic investigation of nanocrystal formation kinetics with LCEM indicates that the intricacies of radiation chemistry and reactant transport must be accounted for to effectively harness radical scavengers and electron beam induced growth to systematically probe nanocrystal formation kinetics. We expect the empirical trends, scaling laws, and reaction kinetic model presented here will be indispensable tools for in situ electron microscopists and materials chemists alike when designing, analyzing, and interpreting LCEM nanocrystal formation data.

Funding

ORAU #17061851; AFOSR #FA9550-18-1-0144

History

Email Address of Submitting Author

tjwoehl@umd.edu

Institution

University of Maryland, College Park

Country

United States

ORCID For Submitting Author

0000-0002-4000-8280

Declaration of Conflict of Interest

no conflict of interest

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