Imaging Negative Charge around Single Vanadium Dopant Atoms in Monolayer Tungsten Diselenide Using 4D Scanning Transmission Electron Microscopy.

There has been extensive activity exploring the doping of semiconducting two-dimensional (2D) transition metal dichalcogenides in order to tune their electronic and magnetic properties. The outcome of doping depends on various factors, including the intrinsic properties of the host material, the nature of the dopants used, their spatial distribution, as well as their interactions with other types of defects. A thorough atomic-level analysis is essential to fully understand these mechanisms. In this work, the vanadium-doped WSe2 monolayer grown by molecular beam epitaxy is investigated using four-dimensional scanning transmission electron microscopy (4D-STEM). Through center-of-mass-based reconstruction, atomic-scale maps are produced, allowing the visualization of both the electric field and the electrostatic potential around individual V atoms. To provide quantitative insights, these results are successfully compared to multislice image simulations based on ab initio calculations, accounting for lens aberrations. Finally, a negative charge around the V dopants is detected as a drop in the electrostatic potential, unambiguously demonstrating that 4D-STEM can be used to detect and to accurately analyze single-dopant charge states in semiconducting 2D materials.

Practice of electron microscopy on nanoparticles sensitive to radiation damage: CsPbBr3 nanocrystals as a case study.

In-depth and reliable characterization of advanced nanoparticles is crucial for revealing the origin of their unique features and for designing novel functional materials with tailored properties. Due to their small size, characterization beyond nanometric resolution, notably, by transmission electron microscopy (TEM) and associated techniques, is essential to provide meaningful information. Nevertheless, nanoparticles, especially those containing volatile elements or organic components, are sensitive to radiation damage. Here, using CsPbBr3 perovskite nanocrystals as an example, strategies to preserve the native structure of radiation-sensitive nanocrystals in high-resolution electron microscopy studies are presented. Atomic-resolution images obtained using graphene support films allow for a clear comparison with simulation results, showing that most CsPbBr3 nanocrystals are orthorhombic. Low-dose TEM reveals faceted nanocrystals with no in situ formed Pb crystallites, a feature observed in previous TEM studies that has been attributed to radiation damage. Cryo-electron microscopy further delays observable effects of radiation damage. Powder electron diffraction with a hybrid pixel direct electron detector confirms the domination of orthorhombic crystals. These results emphasize the importance of optimizing TEM grid preparation and of exploiting data collection strategies that impart minimum electron dose for revealing the true structure of radiation-sensitive nanocrystals.

Low temperature, easy scaling up method for development of smart nanostructure hybrid lipid capsules for drug delivery application.

Lipid Nanocapsules (LNCs) have been used for drug delivery in cells and animal models for several years. LNCs with unique physicochemical properties for favorable biorecognition, biocompatibility and stimuli responsive (pH/temperature etc.) properties i.e., smart-LNCs, are most promising for future nanomedicine applications. However, conventional phase inversion temperature (PIT) method of LNCs preparation may not be suitable for the fabrication of thermally labile drug loaded LNCs and smart-LNCs. Herein, we report for the first time, a novel low temperature (LT) method for the preparation of LNCs (including smart-LNCs of size 25-150 nm), hereafter, named as nanostructure hybrid lipid capsules (nHLCs), comprising safe excipients such as oil (Labrafac™ PG), surfactant (Kolliphor® HS 15, Brij® S100), and lipid (Lipoid S-75, Lipoid S PC-3, Lipoid PE 18:1/18:1, Lipoid PC 16:0/16:0 etc.). Effects of process parameters on the physicochemical properties of nHLCs were probed to optimize the process. Ternary phase diagram shows that our method allows for great flexibility in the formation of nHLCs with tailored size and composition. This method resulted in drug loaded (regorafenib used as model drug) nHLCs with 95 % encapsulation efficiency and sustained release profile at 37 °C. The drug loaded nHLCs (as prepared or in lyophilized form) has excellent storage stability at 4 °C (for more than one month) as well as biocompatibility similar to that of LNCs prepared by PIT method. Our novel LT method of LNCs (i.e. nHLCs) preparation is a generic method for the development of drug loaded (including thermally labile) and smart-LNCs for future nanomedicine applications.