Direct Imaging of the Atomic Mechanisms Governing the Growth and Shape of Bimetallic Pt–Pd Nanocrystals by In Situ Liquid Cell STEM

Abstract

Understanding the atomic mechanisms governing the growth of bimetallic nanoalloys is of great interest for scientists. As a promising material for photocatalysis applications, Pt–Pd bimetallic nanoparticles (NPs) have been in the spotlight for many years due to their catalytic performance, which is typically superior to that of pure Pt NPs. In this work, we use in situ liquid cell scanning transmission electron microscopy to track the exact atomic mechanisms governing the formation of bimetallic Pt–Pd NPs. We find that the formation process of the bimetallic Pt–Pd is divided into three stages. First, the nucleation and growth of ultrasmall primary nanoclusters are formed by the agglomeration of Pt and Pd atoms. Second, the primary nanoclusters are involved in a coalescence process to form two types of bigger agglomerates, namely, amorphous (a-NC) and crystalline (c-NC) nanoclusters. In the third stage, these clusters undergo a coalescence process leading to the formation of Pt–Pd NPs, while, in parallel, monomer attachment continues. We found that the third stage contains three types of coalescence processes, a-NC–a-NC, a-NC–c-NC, and c-NC–c-NC coalescence, which eventually give rise to crystalline bimetallic alloys. However, each type of coalescence gave distinct NPs in terms of shape and defects. Our results thus reveal the exact growth mechanisms of bimetallic alloys on the atomic scale, unravel the origin of their structure, and overall are of key interest to tailor the structure of bimetallic NPs.

Nonclassical Nucleation and Growth of Pd Nanocrystals from Aqueous Solution Studied by In Situ Liquid Transmission Electron Microscopy

“…In respect to the rather small liquid volume we probe by the electron beam and considering the overall reactive environment formed during nearly continuous electron irradiation, this explanation does not seem to be appropriate. Hence, based on our observation, it seems more likely that an instantaneous nucleation event is not a realistic description of a nucleation reaction, at least for the system investigated here and for the systems we investigated in the recent past. ,, Moreover, in LaMer’s model, the number of nuclei reflects the number of formed nanoparticles. Another aspect where our experimental data contradicts LaMer’s model concerns the growth of the clusters and nanoparticles.…”

“…Hence, based on our observation, it seems more likely that an instantaneous nucleation event is not a realistic description of a nucleation reaction, at least for the system investigated here and for the systems we investigated in the recent past. 25,29,39 Moreover, in LaMer's model, the number of nuclei reflects the number of formed nanoparticles. Another aspect where our experimental data contradicts LaMer's model concerns the growth of the clusters and nanoparticles.…”

In Situ Observation of Chemically Induced Protein Denaturation at Solvated Interfaces

“…To address the question of whether the formation of ferritin nanorings is influenced by the DLC-coated Si AFM probe, we performed STEM measurements (see Supporting Information Section S4 for details on the STEM setup and imaging protocols) on ferritin proteins confined in micrometer-sized GLCs (see Figure a). This GLC-STEM approach was demonstrated to be suitable for in situ observation of various phenomena, such as biomineralization of ferritins and nanocrystal growth . A low-magnification STEM image of a GLC pocket containing ferritin proteins is shown on the right side of Figure a (see Figure S12 for details on the GLC sample preparation).…”

Sudden collective atomic rearrangements trigger the growth of defect-free silver icosahedra

“…The conditions allowing LBL growth have been deeply studied and understood. 1 Obtaining such regular growth for nanoscale objects, such as nanoparticles, [2][3][4][5] introduces new challenges. In fact nanoparticles present inequivalent adsorption sites (e.g.…”