Rapid Estimation of Catalyst Nanoparticle Morphology and Atomic-Coordination by High-Resolution Z-Contrast Electron Microscopy

Abstract

Heterogeneous nanoparticle catalyst development relies on an understanding of their structure-property relationships, ideally at atomic resolution and in three-dimensions. Current transmission electron microscopy techniques such as discrete tomography can provide this but require multiple images of each nanoparticle and are incompatible with samples that change under electron irradiation or with surveying large numbers of particles to gain significant statistics. Here, we make use of recent advances in quantitative dark-field scanning transmission electron microscopy to count the number atoms in each atomic column of a single image from a platinum nanoparticle. These atom-counts, along with the prior knowledge of the face-centered cubic geometry, are used to create atomistic models. An energy minimization is then used to relax the nanoparticle's 3D structure. This rapid approach enables high-throughput statistical studies or the analysis of dynamic processes such as facet-restructuring or particle damage.

Optimal ADF STEM imaging parameters for tilt-robust image quantification

“…ADF STEM quantification treats these images as numerical datasets for either comparison with careful simulation or statistical interpretation methods to reveal more information about material structures [2][3][4][5][6][7]. Early attempts to quantify particle size and therefore size-distributions of small metallic nanoparticles [8,9] assumed that the total intensity of the particles scaled linearly with the number of atoms they contain.…”

A coarse-grained Monte Carlo approach to diffusion processes in metallic nanoparticles

“…This well-known feature holds as long as no saturation effects occur, i.e. for metallic particles with diameters of only a few nanometers, and is commonly used to obtain additional morphology and composition information in high-angle annular dark-field (HAADF) scanning transmission electron microscopy [55][56][57]. A fit of this simplified model to the real TEM data for small Ni, Pd and Au nanoparticles is shown in Figure 4, together with the corresponding images.…”

Development of Quantitative STEM for a Conventional S/TEM and Real-Time Current Calibration for Performing QSTEM with a Cold Field Emission Gun

“…From these values, the scattering cross-section for each NP was calculated and the number of atoms determined, c.f., Figure 1. More recently, the introduction of aberration-correctors enabled the development of atomic-resolution QSTEM, wherein by normalizing the intensities of an atomically resolved HAADF-STEM micrograph into units of fractional incident beam current, the number of atoms in each atomic column can be calculated through comparison with image simulations [4]. In combination with energy minimization computations, estimations of the particle's 3D morphology and atomic coordination can be reconstructed [5]. In this presentation we will discuss our development of a QSTEM technique on the aberration-corrected Hitachi HD2700-C STEM at Brookhaven National Laboratory.…”