Directional Migration and Rapid Coalescence of Au Nanoparticles on Anisotropic ReS2

Atomic-Scale Distribution and Evolution of Strain in Pt Nanoparticles Grown on MoS2 Nanosheet

Interface strain significantly affects the band structure and electronic states of metal-nanocrystal-2D-semiconductor heterostructures, impacting system performance. While transmission electron microscopy (TEM) is a powerful tool for studying interface strain, its accuracy may be compromised by sample overlap in high-resolution images due to the unique nature of the metal-nanocrystals-2D-semiconductors heterostructure. Utilizing digital dark-field technology, the substrate influence on metal atomic column contrasts is eliminated, improving the accuracy of quantitative analysis in high-resolution TEM images. Applying this method to investigate Pt on MoS2 surfaces reveals that the heterostructure introduces a tensile strain of ≈3% in Pt nanocrystal. The x-directional linear strain in Pt nanocrystals has a periodic distribution that matches the semi-coherent interface between Pt nanocrystals and MoS2, while the remaining strain components localize mainly on edge atomic steps. These results demonstrate an accurate and efficient method for studying interface strain and provide a theoretical foundation for precise heterostructure fabrication.

Directional growth and reconstruction of ultrafine uranium oxide nanorods within single-walled carbon nanotubes

Understanding the atomic structures and dynamic evolution of uranium oxides is crucial for the reliable operation of fission reactors. Among them, U4O9-as an important intermediate in the oxidation of UO2 to UO2+x -plays an important role in the nucleation and conversion of uranium oxides. Herein, we realize the confined assembly of uranyl within SWCNTs in liquid phase and reveal the directional growth and reconstruction of U4O9 nanorods in nanochannels, enabled by in situ scanning transmission electron microscopy (STEM) e-beam stimulation. The nucleation and crystallization of U4O9 nanorods in nanochannels obey the "non-classical nucleation" mechanism and exhibit remarkably higher growth rate compared to those grown outside. The rapid growth process is found to be accompanied by the formation and elimination of U atom vacancies and strain, aiming to achieve the minimum interfacial energy. Eventually, the segments of U4O9 nanorods in SWCNTs merge into single-crystal U4O9 nanorods via structural reconstruction at the interfaces, and 79% of them exhibit anisotropic growth along the specific 〈11̄0〉 direction. These findings pave the way for tailoring the atomic structures and interfaces of uranium oxides during the synthesis process to help improve the mechanical properties and stability of fission reactors.

Changes of phonon modes and electron transfer induced by interface interactions of Pd/MoS2 heterostructures

As functional materials and nano-catalysts, Pd nanoparticles (NPs) are often used to modify two-dimensional (2D) materials. In the heterostructures of metal NPs and 2D transition metal dichalcogenides, the interface atomic configuration and interface effect greatly affect material properties and stability. Therefore, the rational design of interface structures and in-depth analysis of interface interactions are of vital importance for the preparation of specific functional devices. In this work, Pd NPs were deposited on mechanically exfoliated MoS2 flakes and the epitaxial relationship between Pd and MoS2 was observed, accompanied by distinct moiré patterns. Raman spectra of the Pd NPs/MoS2 heterostructure showed an E12g' vibration mode indicative of the local strain in MoS2. A new vibration mode A'1g appeared in the higher-frequency direction compared with the pristine A1g peak. Combined with X-ray photoelectron spectra and density functional theory calculations, the new vibration mode can be attributed to the bonding between Pd and MoS2. Besides, graphene was inserted between Pd NPs and MoS2, and the decoupling of the interfacial effect by graphene was investigated. This study will help deepen our understanding on the interaction mechanism between metals and MoS2, thereby enabling the modulation of optoelectronic properties and the performance of these hybrid materials.

Atomic-Scale 3D Structure of a Supported Pd Nanoparticle Revealed by Electron Tomography with Convolution Neural Network-Based Image Inpainting

Electron tomography based on scanning transmission electron microscopy (STEM) is used to analyze 3D structures of metal nanoparticles on the atomic scale. However, in the case of supported metal nanoparticle catalysts, the supporting material may interfere with the 3D reconstruction of metal nanoparticles. In this study, a deep learning-based image inpainting method is applied to high-angle annular dark field (HAADF)-STEM images of a supported metal nanoparticle to predict and remove the background image of the support. The inpainting method can separate an 11 nm Pd nanoparticle from the θ-Al2O3 support in HAADF-STEM images of the θ-Al2O3-supported Pd catalyst. 3D reconstruction of the extracted images of the Pd nanoparticle reveals that the Pd nanoparticle adopts a deformed structure of the cuboctahedron model particle, resulting in high index surfaces, which account for the high catalytic activity for methane combustion. Using the xyz coordinate of each Pd atom, the local Pd-Pd bond distance and its variance in a real supported Pd nanoparticle are visualized, showing large strain and disorder at the Pd-Al2O3 interface. The results demonstrate that 3D atomic-scale analysis enables atomic structure-based understanding and design of supported metal catalysts.

Construction of the Heterostructure of NiPt Truncated Octahedral Nanoparticle/MoS2 and Its Interfacial Structure Evolution

Interfacial atomic configuration plays a vital role in the structural stability and functionality of nanocomposites composed of metal nanoparticles (NPs) and two-dimensional semiconductors. In situ transmission electron microscope (TEM) provides a real-time technique to observe the interface structure at atomic resolution. Herein, we loaded bimetallic NiPt truncated octahedral NPs (TONPs) on MoS₂ nanosheets and constructed a NiPt TONPs/MoS₂ heterostructure. The interfacial structure evolution of NiPt TONPs on MoS₂ was in situ investigated using aberration-corrected TEM. It was observed that some NiPt TONPs exhibited lattice matching with MoS₂ and displayed remarkable stability under electron beam irradiation. Intriguingly, the rotation of an individual NiPt TONP can be triggered by the electron beam to match the MoS₂ lattice underneath. Furthermore, the coalescence kinetics of NiPt TONPs can be quantitatively described by the relationship between neck radius (r) and time (t), expressed as rⁿ = Kt. Our work offers a detailed analysis of the lattice alignment relationship of NiPt TONPs on MoS₂, which may enlighten the design and preparation of stable bimetallic metal NPs/MoS₂ heterostructures.