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

Abstract

The structure and atomic ordering of Au-Ag nanoparticles grown in the gas phase are determined by a combination of HAADF-STEM, XPS and Refl-XAFS techniques as a function of composition. It is shown consistently from all the techniques that an inversion of chemical ordering takes place by going from Au-rich to Ag-rich compositions, with the minority element always occupying the nanoparticle core, and the majority element enriching the shell. With the aid of DFT calculations, this composition-tunable chemical arrangement is rationalized in terms of a four-step growth process in which the very first stage of cluster nucleation plays a crucial role. The four-step growth mechanism is based on mechanisms of a general character, likely to be applicable to a variety of binary systems besides Au-Ag.

Unraveling Structural Information of Turkevich Synthesized Plasmonic Gold–Silver Bimetallic Nanoparticles

“…It is therefore the first and foremost criterion that hints at alloy formation or shaping of domains of different composition, e.g., core–shell structures . It is a generally accepted idea that the appearance of a single plasmon band in the absorption spectrum hints at an alloy nanoparticle, while the appearance of two distinct plasmon bands indicates the coexistence of two separate metallic fractions (e.g., a core–shell structure) . Caution has to be taken, however, since one plasmon band can also indicate the appearance of a core–shell structure, in which the shell is thick enough to eliminate the optical effect of the core's plasmon resonance, or that the nanoparticle consists of a gradually altering alloy composition as will be shown later.…”

“…This method is based on the coreduction of metal precursors in the presence of a stabilizing agent, usually sodium citrate, in boiling water. Most studies report on the formation of alloy nanoparticles, although some researchers have also indicated the possible formation of core–shell structures . The assumption of a full alloy composition is mostly based on UV–vis absorption data, that only show one single plasmon band in the visible light range .…”

“…The assumption of a full alloy composition is mostly based on UV–vis absorption data, that only show one single plasmon band in the visible light range . Indeed, two separate plasmon bands are usually observed in the case of a core–shell structure . Hereby, it is important to note that according to Mie theory, the total extinction cross‐section scales with the volume of the nanoparticles .…”

Composition-Tuned Pt-Skinned PtNi Bimetallic Clusters as Highly Efficient Methanol Dehydrogenation Catalysts

“…Furthermore, the involvement of stabilizing chemicals in wet chemistry, such as ligand molecules, greatly alters the intrinsic properties of nanomaterials, making the understanding of their composition-and structure-dependent activity more complex. [35][36][37][38][39][40] Depositing preformed Pt-based bimetallic clusters/nanoparticles, with precisely-defined size, composition and surface coverages [41][42][43][44] on various oxide supports, using the Cluster Beam Deposition (CBD) technology could be one of the key solutions to design better fuel-cell catalysts. 45 Clusters are particles typically composed of less than a thousand atoms and have dimensions smaller than a few nanometres.…”

Relative Stability of Small Silver, Platinum, and Palladium Doped Gold Cluster Cations

“…In a gas phase experiment, clusters are produced and characterized as a function of size, composition, and charge state with atomic precision, and their inherent small size allows for direct comparison with detailed quantum chemical calculations. Many examples in the literature can be found in which small clusters are used to elucidate intrinsic properties of matter, such as the stability of alloy complexes [1,2], the reactivity and catalytic properties of metals [3,4], the optical responses of matter [5,6], and the magnetic coupling of different elements and their evolution from the atom to the bulk [7,8]. In particular, small gold clusters have been intensively studied over the past few decades due to their fascinating properties.…”