Title: Complex oscillatory decrease with size in diffusivity of {100}-epitaxially supported 3D fcc metal nanoclusters

Abstract

Diffusion and coalescence of supported 3D metal nanoclusters (NCs) leads to Smoluchowski Ripening (SR), a key pathway for catalyst degradation. Variation of the NC diffusion coefficient, $$D_N$$, with size $N$ (in atoms) controls SR kinetics. Traditionally, a form $$D_N ~ N^{-β}$$ was assumed consistent with mean-field analysis. However, KMC simulation of a stochastic model for diffusion of {100}-epitaxially supported fcc NCs mediated by surface diffusion reveals instead a complex oscillatory decrease of $$D_N$$ with $N$. Barriers for surface diffusion of metal atoms across and between facets, along step edges, etc., in this model are selected to accurately capture behavior for fcc metals. (This contrasts standard bond-breaking prescriptions which fail dramatically.) For strong adhesion, equilibrated NCs are truncated pyramids (TP). Local minima of DN sometimes but not always correspond to sizes, $N$_TP, where these have a closed-shell structure. Local maxima generally correspond to $N ≈ N$_TP + 3 for $N$ = O(10²). For weak adhesion, equilibrated NCs are truncated octahedra (TO), and local minima of $$D_N$$ occur for sizes close or equal to those of just a subset of closed-shell structures. Analytic characterization of energetics along the NC diffusion pathway (which involves dissolving and reforming outer layers of facets) provides fundamental insight into the behavior of $$D_N$$, including the strong variation with $N$ of the effective NC diffusion barrier.

Authors:

Lai, King C.  ^[1];

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Evans, James W.  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-5806-3720"
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+ Show Author Affiliations

1. Division of Chemical & Biological Sciences, Ames Laboratory, USDOE and Department of Physics & Astronomy, Iowa State University, Ames IA 50011

Publication Date:

2019-09-26

Research Org.:

Ames Lab., Ames, IA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1562571

Alternate Identifier(s):

OSTI ID: 1569740

Report Number(s):

IS-J 9974
Journal ID: ISSN 2040-3364; NANOHL

Grant/Contract Number:  

AC02-07CH11358

Resource Type:

Published Article

Journal Name:

Nanoscale

Additional Journal Information:

Journal Name: Nanoscale Journal Volume: 11 Journal Issue: 37; Journal ID: ISSN 2040-3364

Publisher:

Royal Society of Chemistry (RSC)

Country of Publication:

United Kingdom

Language:

English

Subject:

77 NANOSCIENCE AND NANOTECHNOLOGY