Size and shape of nanoclusters: single-shot imaging approach.

Y Han,D S He,Z Y Li,T Tsukuda,S Xie,Y Liu

doi:10.1002/smll.201102710

Abstract

A method of single-shot imaging via aberration-corrected scanning transmission electron microscopy equipped with high angle annular dark-field detector (STEM-HAADF) has been applied to size-selected gold model catalysts (Au(25) and Au(39) ) on hydroxyapatite. Through quantitative intensity analysis, the size, in terms of number of atoms as well as 3D shape of the clusters are obtained.

Highlights

Measuring size and shape of nanometer catalytic clusters is a challenging task
By optimizing imaging conditions of a scanning transmission electron microscopy (STEM) equipped with a high-angle annular dark-field (HAADF) detector, that the size and shape of the clusters can be obtained from the STEM-HAADF intensity profile through single-shot imaging
To determine the number of peaks (k) and the associated peak positions in each case, the Integrated Complete Likelihood (ICL) criterion was employed based on Gaussian distributions.[12]

Summary

Nanocluster Imaging

Gold nanoparticles on solid supports are of particular interest for their high catalytic activity for low-temperature CO oxidation.[1]. Real catalyst samples are often characterized by a distribution of size and shape. We apply this technique to size-selected model catalysts, Au25 and Au39 (clusters containing nominal 25 and 39 gold atoms, respectively). The histograms of the integrated intensities for the samples Au25 and Au39 are shown in Figure 2a,b, respectively. To assess distribution (full-width-half-maximum) in each case, 1.25 nm the microscopy conditions on quantification of mass of a for Au25 and 1.5 nm for Au39, with the mean diameter of cluster, two specimens, both containing single Au atoms sup- around 1.7–1.9 nm (See Figure 3). Further investigation is planned to see if these aggregated clusters, which have retained the memory of their initial sizes, still maintain their size-dependent catalytic performance

To gain insight of the bonding strength between clusters

Experimental Section