In Situ High-Resolution Transmission Electron Microscopy (TEM) Observation of Sn Nanoparticles on SnO2 Nanotubes Under Lithiation

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

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.

Multi-step atomic mechanism of platinum nanocrystals nucleation and growth revealed by in-situ liquid cell STEM

The understanding of crystal growth mechanisms has broadened substantially. One significant advancement is based in the conception that the interaction between particles plays an important role in the growth of nanomaterials. This is in contrast to the classical model, which neglects this process. Direct imaging of such processes at atomic-level in liquid-phase is essential for establishing new theoretical models that encompass the full complexity of realistic scenarios and eventually allow for tailoring nanoparticle growth. Here, we investigate at atomic-scale the exact growth mechanisms of platinum nanocrystals from single atom to final crystals by in-situ liquid phase scanning transmission electron microscopy. We show that, after nucleation, the nanocrystals grow via two main stages: atomic attachment in the first stage, where the particles initially grow by attachment of the atoms until depletion of the surrounding zone. Thereafter, follows the second stage of growth, which is based on particle attachment by different atomic pathways to finally form mature nanoparticles. The atomic mechanisms underlying these growth pathways are distinctly different and have different driving forces and kinetics as evidenced by our experimental observations.

Atomic Mechanisms of Nanocrystallization via Cluster-Clouds in Solution Studied by Liquid-Phase Scanning Transmission Electron Microscopy

The formation of nanocrystals is at the heart of various scientific disciplines, but the atomic mechanisms underlying the early stages of crystallization from supersaturated solutions are still rather unclear. Here, we used in situ liquid-phase scanning transmission electron microscopy to study at the atomic level the very early stages of gold nanocrystal growth, and the evolution of its crystallinity. We found that the nucleation is initiated by the formation of poorly crystalline nanoparticles. These are transformed into monocrystals via nanocrystallization governed by a complex process of multiple out-and-in exchanges of matter between a crystalline-core and a disordered-shell, referred to as the cluster-cloud. Our observations at the crystal/cluster-cloud interface during growth demonstrate that the initially formed nanocrystals expel the poorly crystallized phases as nanoclusters into the cluster-cloud, then readsorb it by two distinct pathways, namely, by (i) monomer attachments and (ii) nanocluster coalescence. This growth process eventually leads to the formation of monocrystalline nanoparticles.

Live Cell Electron Microscopy Using Graphene Veils

As a promising tool over the optical resolution limits, liquid electron microscopy is practically utilized to visualize the structural information on wet biological specimens, such as cells, proteins, and nucleic acids. However, the functionality of biomolecules during their observation is still controversial. Here we show the feasibility of live-cell electron microscopy using graphene veils. We demonstrate that the electron dose resistivity of live bacterial cells increases to 100-fold in graphene veils, and thus they maintain their structures and functions after electron microscopy experiments. Our results provide the guidelines and show possibilities for the electron microscopy imaging of live cells and functional biomolecules.

Graphene Liquid Cell Electron Microscopy of Initial Lithiation in Co3O4 Nanoparticles

As it governs the overall performance of lithium-ion batteries, understanding the reaction pathway of lithiation is highly desired. For Co₃O₄ nanoparticles as anode material, here, we report an initial conversion reaction pathway during lithiation. Using graphene liquid cell electron microscopy (GLC-EM), we reveal a CoO phase of the initial conversion product as well as morphological dynamics during Co₃O₄ lithiation. In accordance with the in situ TEM observation, we confirmed that the Co₃O₄ to CoO conversion is a thermodynamically favorable process by calculating the theoretical average voltage based on density functional theory. Our observation will provide a useful insight into the oxide electrode that undergoes conversion reaction.