Structural Analysis of Ligand-Protected Smaller Metallic Nanocrystals by Atomic Pair Distribution Function under Precession Electron Diffraction

Abstract

Atomic pair distribution function (PDF) analysis has been widely used to investigate nanocrystalline and structurally disordered materials. Experimental PDFs retrieved from electron diffraction (ePDF) in transmission electron microscopy (TEM) represent an attractive alternative to traditional PDF obtained from synchrotron X-ray sources, particularly for studying minute samples. Nonetheless, the inelastic scattering produced by the large dynamical effects of electron diffraction may obscure the interpretation of ePDF. In the present work, precession electron diffraction (PED-TEM) has been employed to obtain the ePDF of two different sampleslipoic acid-and hexanethiolate-capped gold nanoparticles (∼4.5 and 4.2 nm, respectively)randomly oriented and measured at both liquid nitrogen and room temperatures. The electron diffraction data were processed to obtain ePDFs which were subsequently compared with the PDF of different ideal structure models. The results demonstrate that the PED-ePDF data are sensitive to different crystalline structures such as monocrystalline (truncated octahedra) and multiply twinned (decahedra, icosahedra) structures. The results indicate that PED reduces the residual from 46 to 29%; in addition, the combination of PED and low temperature further reduced the residual to 23%, which is comparable to X-ray PDF analysis. Furthermore, the inclusion of PED resulted in a better estimation of the coordination number from ePDF. To the best of our knowledge, the precessed electron-beam technique (PED) has not been previously applied to nanoparticles for analysis by the ePDF method.

Advances in the electron diffraction characterization of atomic clusters and nanoparticles

“…However, the use of precession electron diffraction and low temperatures (liquid nitrogen) reduces the dynamic contribution and the thermal scattering, respectively. The result of PED-ePDF improvement is the enhancement of the intensities for a higher scattering vector Q 56,57 . The example shown in HRTEM image of Fig.…”

“…PDF fit analysis in comparison with different structure models: (a') Ih, R w ~ 36%, (b') TOh, R w ~ 24%, and (c') Dh, R w ~ 22% (adapted from Ref. 56 with permission).…”

“…Cryogenic conditions (liquid N 2 ) resulted in the intensity profile that contains more signal at higher Q. Resolution damping (Q damp ) and the atomic displacement parameter are two quantities that improved from precession off to precession on 56 . The results obtained herein using the improved precession electron diffraction are comparable with the results obtained using high energy X-ray sources 67 .…”

Ligand‐Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?

“…Recently, atomically precise protected metal clusters have emerged as a promising class of well‐defined nanoclusters with enhanced catalytic activities and stabilities over polydisperse nanoparticles containing an uncertain number of atoms [8–14] . These clusters, consisting of well‐defined metal cores smaller than 2 nm in size and protected by ligands, have discrete electronic structures and therefore, exhibit various optical, catalytic, and magnetic properties different from those of bulk metals or nanoparticles larger than 3 nm [8–14] . Specifically, monodisperse metal nanoclusters allow for precise analysis of the underlying mechanism of their catalytic activity in various chemical reactions [15–17] .…”

New Evidence of the Bidentate Binding Mode in 3-MBA Protected Gold Clusters: Analysis of Aqueous 13–18 kDa Gold-Thiolate Clusters by HPLC-ESI-MS Reveals Special Compositions Aun(3-MBA)p, (n = 48–67, p = 26–30)

“…Such a proven structural uniformity of MPCs is essential to precision-intensive applications, as well as to all fundamental physicochemical understanding. The most compelling demonstrations are the cases of a total structure determination by single crystal X-ray [22] or electron diffraction methods [23], which for gold-thiolates have recently been extended to MPCs as large as Au 146 (pMBA) 57 (aqueous) [5] and Au 279 (TBBT) 84 (nonaqueous) [24].…”