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

2019; American Chemical Society; Volume: 123; Issue: 32 Linguagem: Inglês

10.1021/acs.jpcc.9b02901

1932-7455

M. Mozammel Hoque, Sandra Vergara, Partha Pratim Das, D. Ugarte, Ulises Santiago, Chanaka Kumara, Robert L. Whetten, Amala Dass, Arturo Ponce,

Gold and Silver Nanoparticles Synthesis and Applications

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.