Liquid-cell transmission electron microscopy for tracking self-assembly of nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions. © 2017 Journal of Visualized Experiments101sciescopu

3-Dimensional Scanning of Entire Unit Cells in Single Nanoparticles.

Properties of nanomaterials such as optical, electrical, and chemical properties are strongly correlated with lattice symmetry, making characterization of lattice symmetry essential. We introduce a symmetry analysis method using 3D atomic coordinates obtained by Brownian one-particle 3D reconstruction. The method allows direct and quantitative analysis of symmetrical properties and delivers local structural characteristics of individual platinum (Pt) nanoparticles in unit-cell level. Local structural deformations of the Pt nanoparticles such as lattice distortion and internal symmetry breakage are demonstrated, revealing that the crystal structure of sub-3 nm Pt nanoparticles generally maintains FCC crystallinity and exhibits localized deviation from their bulk counterpart.11Nsciescopu

Designing a Safe Electrolyte Enabling Long‐Life Li/S Batteries

Lithium–sulfur (Li/S) batteries suffer from “shuttle” reactions in which soluble polysulfide species continuously migrate to and from the Li metal anode. As a consequence, the loss of active material and reactions at the surface of Li limit the practical applications of Li/S batteries. LiNO3 has been proposed as an electrolyte additive to reduce the shuttle reactions by aiding the formation of a stable solid electrolyte interphase (SEI) at the Li metal, limiting polysulfide shuttling. However, LiNO3 is continuously consumed during cycling, especially at low current rates. Therefore, the Li/S battery cycle life is limited by the LiNO3 concentration in the electrolyte. In this work, an ionic liquid (IL) [N-methyl-(n-butyl)pyrrolidinium bis(trifluoromethylsulfonyl)imide] was used as an additive to enable longer cycle life of Li/S batteries. By tuning the IL concentration, an enhanced stability of the SEI and lower flammability of the solutions were demonstrated, that is, higher safety of the battery. The Li/S cell built with a high sulfur mass loading (4 mg cm−2) and containing the IL-based electrolyte demonstrated a stable capacity of 600 mAh g−1 for more than double the number of cycles of a cell containing LiNO3 additive

Biomass-Derived Graphitic Carbon Encapsulated Fe/Fe3C Composite as an Anode Material for High-Performance Lithium Ion Batteries

Lithium ion (Li-ion) batteries have been widely applied to portable electronic devices and hybrid vehicles. In order to further enhance performance, the search for advanced anode materials to meet the growing demand for high-performance Li-ion batteries is significant. Fe3C as an anode material can contribute more capacity than its theoretical one due to the pseudocapacity on the interface. However, the traditional synthetic methods need harsh conditions, such as high temperature and hazardous and expensive chemical precursors. In this study, a graphitic carbon encapsulated Fe/Fe3C (denoted as Fe/Fe3C@GC) composite was synthesized as an anode active material for high-performance lithium ion batteries by a simple and cost-effective approach through co-pyrolysis of biomass and iron precursor. The graphitic carbon shell formed by the carbonization of sawdust can improve the electrical conductivity and accommodate volume expansion during discharging. The porous microstructure of the shell can also provide increased active sites for the redox reactions. The in-situ-formed Fe/Fe3C nanoparticles show pseudocapacitive behavior that increases the capacity. The composite exhibits a high reversible capacity and excellent rate performance. The composite delivered a high initial discharge capacity of 1027 mAh g−1 at 45 mA g−1 and maintained a reversible capacity of 302 mAh g−1 at 200 mA g−1 after 200 cycles. Even at the high current density of 5000 mA g−1, the Fe/Fe3C@GC cell also shows a stable cycling performance. Therefore, Fe/Fe3C@GC composite is considered as one of the potential anode materials for lithium ion batteries

Complex ligand adsorption on 3D atomic surfaces of synthesized nanoparticles investigated by machine-learning accelerated ab initio calculation

Nanoparticle surfaces are passivated by surface-bound ligands, and their adsorption on synthesized nanoparticles is complicated because of the intricate and low-symmetry surface structures. Thus, it is challenging to precisely investigate ligand adsorption on synthesized nanoparticles. Here, we applied machine-learning-accelerated ab initio calculation to experimentally resolved 3D atomic structures of Pt nanoparticles to analyze the complex adsorption behavior of polyvinylpyrrolidone (PVP) ligands on synthesized nanoparticles. Different angular configurations of large-sized ligands are thoroughly investigated to understand the adsorption behavior on various surface-exposed atoms with intrinsic low-symmetry. It is revealed that the ligand binding energy (E-ads) of the large-sized ligand shows a weak positive relationship with the generalized coordination number((CN)) . This is because the strong positive relationship of short-range direct bonding (E-bind) is attenuated by the negative relationship of long-range van der Waals interaction (E-vdW). In addition, it is demonstrated that the PVP ligands prefer to adsorb where the long-range vdW interaction with the surrounding surface structure is maximized. Our results highlight the significant contribution of vdW interactions and the importance of the local geometry of surface atoms to the adsorption behavior of large-sized ligands on synthesized nanoparticle surfaces.11Nscopu

Complex ligand adsorption on 3D atomic surfaces of synthesized nanoparticles investigated by machine-learning accelerated ab initio calculation

Nanoparticle surfaces are passivated by surface-bound ligands, and their adsorption on synthesized nanoparticles is complicated because of intricate and low-symmetry surface structures. Thus, it is challenging to precisely investigate ligand adsorption on synthesized nanoparticles. Here, we applied a machine-learning-accelerated ab-initio calculation into experimentally resolved 3D atomic structures of Pt nanoparticles to analyze the complex adsorption behavior of polyvinylpyrrolidone (PVP) ligands on synthesized nanoparticles. Different angular configurations of the large-sized ligands are thoroughly investigated to understand adsorption behaviors onto the various surface-exposed atoms with intrinsic low-symmetry. It is revealed that long-range van der Waals interaction (EvdW) shows weak negative relationship against generalized coordination number (-CN-), in contrast to the positive relationship in short-range direct bonding (Ebind), which attenuates the correlation between ligand binding energy (Eads) and -CN-. In addition, the PVP ligands favor to adsorb at which the long-range vdW interaction with surrounding surface structure is maximized. Our results highlight the significant contribution of vdW interactions and importance of local geometry of surface atoms to adsorption behavior of large-sized ligands on synthesized nanoparticle surfaces

A Large-Scale Array of Ordered Graphene-Sandwiched Chambers for Quantitative Liquid-Phase Transmission Electron Microscopy

© 2020 Wiley-VCH GmbH. Liquid-phase transmission electron microscopy (TEM) offers a real-time microscopic observation of the nanometer scale for understanding the underlying mechanisms of the growth, etching, and interactions of colloidal nanoparticles. Despite such unique capability and potential application in diverse fields of analytical chemistry, liquid-phase TEM studies rely on information obtained from the limited number of observed events. In this work, a novel liquid cell with a large-scale array of highly ordered nanochambers is constructed by sandwiching an anodic aluminum oxide membrane between graphene sheets. TEM analysis of colloidal gold nanoparticles dispersed in the liquid is conducted, employing the fabricated nanochamber array, to demonstrate the potential of the nanochamber array in quantitative liquid-phase TEM. The independent TEM observations in the multiple nanochambers confirm that the monomer attachment and coalescence processes universally govern the overall growth of nanoparticles, although individual nanoparticles follow different growth trajectories11sciescopu

SINGLE: Atomic-resolution structure identification of nanocrystals by graphene liquid cell EM.

Analysis of the three-dimensional (3D) structures of nanocrystals with solution-phase transmission electron microscopy is beginning to reveal their unique physiochemical properties. We developed a "one-particle Brownian 3D reconstruction method" based on imaging of ensembles of colloidal nanocrystals using graphene liquid cell electron microscopy. Projection images of differently rotated nanocrystals are acquired using a direct electron detector with high temporal (<2.5 ms) resolution and analyzed to obtain an ensemble of 3D reconstructions. Here, we introduce computational methods required for successful atomic-resolution 3D reconstruction: (i) tracking of the individual particles throughout the time series, (ii) subtraction of the interfering background of the graphene liquid cell, (iii) identification and rejection of low-quality images, and (iv) tailored strategies for 2D/3D alignment and averaging that differ from those used in biological cryo-electron microscopy. Our developments are made available through the open-source software package SINGLE

SINGLE: Atomic-resolution structure identification of nanocrystals by graphene liquid cell EM.

Analysis of the three-dimensional (3D) structures of nanocrystals with solution-phase transmission electron microscopy is beginning to reveal their unique physiochemical properties. We developed a "one-particle Brownian 3D reconstruction method" based on imaging of ensembles of colloidal nanocrystals using graphene liquid cell electron microscopy. Projection images of differently rotated nanocrystals are acquired using a direct electron detector with high temporal (<2.5 ms) resolution and analyzed to obtain an ensemble of 3D reconstructions. Here, we introduce computational methods required for successful atomic-resolution 3D reconstruction: (i) tracking of the individual particles throughout the time series, (ii) subtraction of the interfering background of the graphene liquid cell, (iii) identification and rejection of low-quality images, and (iv) tailored strategies for 2D/3D alignment and averaging that differ from those used in biological cryo-electron microscopy. Our developments are made available through the open-source software package SINGLE

A Large‐Scale Array of Ordered Graphene‐Sandwiched Chambers for Quantitative Liquid‐Phase Transmission Electron Microscopy

© 2020 Wiley-VCH GmbH. Liquid-phase transmission electron microscopy (TEM) offers a real-time microscopic observation of the nanometer scale for understanding the underlying mechanisms of the growth, etching, and interactions of colloidal nanoparticles. Despite such unique capability and potential application in diverse fields of analytical chemistry, liquid-phase TEM studies rely on information obtained from the limited number of observed events. In this work, a novel liquid cell with a large-scale array of highly ordered nanochambers is constructed by sandwiching an anodic aluminum oxide membrane between graphene sheets. TEM analysis of colloidal gold nanoparticles dispersed in the liquid is conducted, employing the fabricated nanochamber array, to demonstrate the potential of the nanochamber array in quantitative liquid-phase TEM. The independent TEM observations in the multiple nanochambers confirm that the monomer attachment and coalescence processes universally govern the overall growth of nanoparticles, although individual nanoparticles follow different growth trajectories11sciescopu