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1. Recent advances in liquid phase transmission electron microscopy of nanoparticle growth and self-assembly

   https://doi.org/10.1557/s43577-024-00702-z  

   Kim, Joodeok; Kang, Sungsu; Cheng, Fanrui; Wang, Yi; Ye, Xingchen; Park, Jungwon (April 2024, MRS Bulletin)

   Chen, Qian; Zhang, Xin (Ed.)

   Abstract Over the last several decades, colloidal nanoparticles have evolved into a prominent class of building blocks for materials design. Important advances include the synthesis of uniform nanoparticles with tailored compositions and properties, and the precision construction of intricate, higher-level structures from nanoparticles via self-assembly. Grasping the modern complexity of nanoparticles and their superstructures requires fundamental understandings of the processes of nanoparticle growth and self-assembly.In situliquid phase transmission electron microscopy (TEM) has significantly advanced our understanding of these dynamic processes by allowing direct observation of how individual atoms and nanoparticles interact in real time, in their native phases. In this article, we highlight diverse nucleation and growth pathways of nanoparticles in solution that could be elucidated by thein situliquid phase TEM. Furthermore, we showcasein situliquid phase TEM studies of nanoparticle self-assembly pathways, highlighting the complex interplay among nanoparticles, ligands, and solvents. The mechanistic insights gained fromin situliquid phase TEM investigation could inform the design and synthesis of novel nanomaterials for various applications such as catalysis, energy conversion, and optoelectronic devices. Graphical abstract 

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2. Carving growing nanocrystals: coupling seed-mediated growth with oxidative etching

   https://doi.org/10.1039/c8nr06895j  

   Villarreal, Esteban; Li, Guangfang Grace; Wang, Hui (October 2018, Nanoscale)

   This work presents multiple experimental evidences coherently showing that the versatile structural evolution of Au nanocrystals during seed-mediated growth under the guidance of foreign metal ions and halide-containing surfactants is essentially dictated by the dynamic interplay between oxidative etching and nanocrystal growth. Coupling nanocrystal growth with oxidative etching under kinetically controlled conditions enables the in situ surface carving of the growing nanocrystals, through which the surface topography of shape-controlled nanocrystals can be deliberately tailored on the nanometer length-scale. 

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3. Advances in Graphene‐Based Liquid Cell Electron Microscopy: Working Principles, Opportunities, and Challenges

   https://doi.org/10.1002/smtd.201900026  

   Ghodsi, Seyed Mohammadreza; Megaridis, Constantine M.; Shahbazian‐Yassar, Reza; Shokuhfar, Tolou (February 2019, Small Methods)

   Abstract Imaging materials and biological structures in a liquid environment pose a significant challenge for conventional transmission electron microscopy (TEM) due to stringent requirement of ultrahigh vacuum design in the microscope column. The most recent liquid‐cell TEM technique, graphene liquid‐cell (GLC) microscopy, employs only layers of graphene to encapsulate liquid specimens. Recent efforts with GLC–TEM have demonstrated superior imaging resolution of beam‐sensitive specimens. Herein, the parameters that affect the quality of GLC analysis, including the graphene transfer onto TEM grids, are reviewed. Several important factors that affect the in situ TEM imaging of specimens, including the variations in GLC geometries and capillary pressure are discussed. The interaction between the electron beam and the liquid along with the possibility for artifacts or the formation of radical ions is also highlighted in this review. The scientific discoveries enabled by GLC–TEM in the areas of nucleation and growth of crystals, corrosion, battery science, as well as high‐resolution imaging of organelles and proteins are also briefly discussed. Finally, possible future research directions of GLC–TEM and the associated challenges are discussed. The synergistic effort to accomplish the proposed research directions has the potential to yield new discoveries in both materials and life sciences. 

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4. Shape Transformation via Etching and Regrowth: A Systematic Study of Pd Nanocrystals with Different Shapes and Twin Structures

   https://doi.org/10.1002/chem.202301465  

   Lv, Tian; Liu, Maochang; Zhou, Siyu; Xia, Younan (August 2023, Chemistry – A European Journal)

   Abstract This article describes a systematic study of the oxidative etching and regrowth behaviors of Pd nanocrystals, including single‐crystal cubes bounded by {100} facets, single‐crystal octahedra and tetrahedra enclosed by {111} facets; and multiple‐twinned icosahedra covered by {111} facets and twin boundaries. During etching, Pd atoms are preferentially oxidized and removed from the corners regardless of the type of nanocrystal, and the resultant Pd²⁺ions are then reduced back to elemental Pd. For cubes and icosahedra, the newly formed Pd atoms are deposited on the {100} facets and twin boundaries, respectively, due to their relatively higher energies. For octahedra and tetrahedra, the Pd atoms self‐nucleate in the solution phase, followed by their growth into small particles. We can control the regrowth rate relative to etching rate by varying the concentration of HCl in the reaction solution. As the concentration of HCl is increased, 18‐nm Pd cubes are transformed into octahedra of 23, 18, and 13 nm, respectively, in edge length. Due to the absence of regrowth, however, Pd octahedra are transformed into truncated octahedra, cuboctahedra, and spheres with decreasing sizes whereas Pd tetrahedra evolve into truncated tetrahedra and spheres. In contrast, Pd icosahedra with twin boundaries on the surface are converted to asymmetric icosahedra, flower‐like icosahedra, and spheres. This work not only advances the understanding of etching and growth behaviors of metal nanocrystals with various shapes and twin structures but also offers an alternative method for controlling their shape and size. 

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5. Cu2S Nanocrystals and Their Superlattices

   https://doi.org/10.3390/cryst15050387  

   Fuentes, Samuel; Hart, Ryan; Ramirez, Juan; Mulgaonkar, Aditi; Luo, Rainie; Killham, Brady; Debnath, Sashi; Wang, Yunfeng; Sun, Xiankai; Jiang, Jiechao; et al (May 2025, Crystals)

   We report the successful synthesis of monodispersed Cu2S nanocrystals and the subsequent formation of highly ordered nanocrystal superlattices. The synthesis is performed under ambient air conditions using simple experimental setups, making the process both accessible and scalable. By systematically tuning the reaction temperature and duration, we demonstrate precise control over the nanocrystal size, which is crucial in achieving uniformity and monodispersity. Furthermore, we uncover a previously unidentified nanocrystal growth mechanism that plays a key role in producing highly monodisperse Cu2S nanocrystals. This insight into the growth process enhances our fundamental understanding of nanocrystal formation and could be extended to the synthesis of other semiconductor nanomaterials. The self-assembly of these nanocrystals into superlattices is carefully examined using electron diffraction techniques, revealing the presence of pseudo-crystalline structures. The ordered arrangement of nanocrystals within these superlattices suggests strong interparticle interactions and opens up new possibilities to tailor their collective optical, electronic, and mechanical properties for potential applications in optoelectronics, nanomedicine, and energy storage. 

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