Structure of Gold–Silver Nanoparticles

Abstract

Nanoparticles with nominal structures of Au@Ag (core@shell) and Au@Ag@Au (core@shell@shell) were prepared using the sequential citrate reduction technique and characterized using routine characterization techniques, including transmission electron microscopy. X-ray absorption spectroscopy was then carried out on the samples, and extended X-ray absorption fine structure (EXAFS) analysis was used to determine the structure of the systems. The results of the routine techniques and the X-ray absorption spectroscopy were then compared. EXAFS analysis of the nanoparticles with the Au@Ag structure revealed very limited bimetallic interactions, supporting the assignment of a core@shell structure. EXAFS analysis of the nanoparticles with Au@Ag@Au structure showed an increased proportion of bimetallic interactions. Based on the colloid composition, the other characterization techniques and the chemistry of the system, these nanoparticles were interpreted as having an Au@Au/Ag-alloy structure. The EXAFS analyses corroborated the other characterization techniques and enabled the determination of the average-structure of the entire sample.

Unravelling the nucleation mechanism of bimetallic nanoparticles with composition-tunable core–shell arrangement

“…Unlike XRD and conventional TEM, XAFS can detect alloying in a few-atom size Au-Ag bimetallic system and even when the interatomic distances of the alloy and the pure metal are very similar. 40 The interference between Ag and Au phase shifts indeed generates a characteristic beat in the XAFS that appears as a doublet in the Fourier transform. 40 Moreover, analysis of the X-ray Absorption Near-edge Structure (XANES) can provide valuable information on the electronic properties of the BNPs and in particular on the electron transfer that is likely to occur between Au and Ag atoms.…”

“…40 The interference between Ag and Au phase shifts indeed generates a characteristic beat in the XAFS that appears as a doublet in the Fourier transform. 40 Moreover, analysis of the X-ray Absorption Near-edge Structure (XANES) can provide valuable information on the electronic properties of the BNPs and in particular on the electron transfer that is likely to occur between Au and Ag atoms. 50 The XAFS technique is also complementary to electron microscopy since it allows, as a bulk technique, the investigation of a more representative amount of clusters.…”

Deposition of Ag and Ag–Au nanocrystalline films with tunable conductivity at the water–toluene interface

“…However, we believe that further studies based on techniques such as X-ray absorption spectroscopy and related techniques are required to establish the veracity of alloying in these deposits. 37 As alluded to earlier, in all cases, the lms consist of hierarchical structure whereby nanocrystals with diameters of z10 nm form higher order aggregates. The persistence of this organization across the composition range suggests that structural control lies in factors extrinsic to the reaction.…”

Determination of the 3D Atomic Structures of Nanoparticles

“…The classification methodology needs to be improved, such that the atomic structures of important alloy particles with smaller atomic weight differences, such as Ag/Au nanoparticles, can be resolved. [ 75,76 ] Further development of 3D reconstruction methodologies will allow identification of the atomic structures of various types of materials, such as metal oxides, sulfides, selenides, and phosphides, and more complex materials, such as core–shell structures, doping materials, Janus structures, and alloy materials.…”