Robust Local Thickness Estimation of Sub-Micrometer Specimen by 4D-STEM

Subchronic Inhalation of TiO2 Nanoparticles Leads to Deposition in the Lung and Alterations in Erythrocyte Morphology in Mice

TiO2 nanoparticles (NPs) are extensively used in various applications, highlighting the importance of ongoing research into their effects. This work belongs among rare whole-body inhalation studies investigating the effects of TiO2 NPs on mice. Unlike previous studies, the concentration of TiO2 NPs in the inhalation chamber (130.8 μg/m3) was significantly lower. This 11-week study on mice confirmed in vivo the presence of TiO2 NPs in lung macrophages and type II pneumocytes including their intracellular localization by using the electron microscopy and the state-of-the-art methods detecting NPs' chemical identity/crystal structure, such as the energy-dispersed X-ray spectroscopy (EDX), cathodoluminescence (CL), and detailed diffraction pattern analysis using powder nanobeam diffraction (PNBD). For the first time in inhalation study in vivo, the alterations in erythrocyte morphology with evidence of echinocytes and stomatocytes, accompanied by iron accumulation in spleen, liver, and kidney, are reported following NP's exposure. Together with the histopathological evidence of hyperaemia in the spleen and kidney, and haemosiderin presence in the spleen, the finding of NPs containing iron might suggest the increased decomposition of damaged erythrocytes. The detection of TiO2 NPs on erythrocytes through CL analysis confirmed their potential systemic availability. On the contrary, TiO2 NPs were not confirmed in other organs (spleen, liver, and kidney); Ti was detected only in the kidney near the detection limit.

Thickness- and quality-controlled fabrication of fluorescence-targeted frozen-hydrated lamellae

Cryogenic focused ion beam (FIB) milling is essential for fabricating thin lamella-shaped samples out of frozen-hydrated cells for high-resolution structure determination. Structural information can only be resolved at high resolution if the lamella thickness is between 100 and 200 nm. While the lamella fabrication workflow has improved significantly since its conception, quantitative, live feedback on lamella thickness, quality, and biological target inclusion remains lacking. Using coincident light microscopy integrated into the FIB scanning electron microscope (FIB-SEM), we present three strategies that enable accurate, live control during lamella fabrication. First, we combine four-dimensional (4D) STEM with fluorescence microscopy (FM) targeting to determine lamella thickness. Second, with reflected light microscopy (RLM), we screen target sites for ice contamination and monitor lamella thickness and protective Pt coating integrity during FIB milling. Third, we exploit thin-film interference for fine-grained feedback on thickness uniformity below 500 nm. Finally, we present a fluorescence-targeted, quality-controlled workflow for frozen-hydrated lamellae, benchmarked with excellent agreement with energy-filtered transmission electron microscopy (EFTEM) measurements and tomograms from electron cryotomography.

Robust Preparation of Sub-20-nm-Thin Lamellae for Aberration-Corrected Electron Microscopy

Aberration-corrected scanning transmission electron microscopy (STEM) has been advancing resolution, sensitivity, and microanalysis due to the intense demands of atomic-level microstructural investigations. Recent STEM technologies require preparing a thin lamella whose thickness is ideally below 20 nm. Although focused-ion-beam/scanning-electron-microscopy (FIB/SEM) is an established method to prepare a high-quality lamella, nanometer-level controllability of lamella thickness remains a fundamental problem. Here, the robust preparation of a sub-20-nm-thin lamella is demonstrated by FIB/SEM with real-time feedback from thickness quantification. The lamella thickness is quantified by back-scattered-electron SEM imaging in a thickness range between 0 and 100 nm without any reference to numerical simulation. Using real-time feedback from the thickness quantification, the FIB/SEM terminates thinning a lamella at a targeted thickness. The real-time feedback system eventually provides 1-nm-level controllability of the lamella thickness. As a proof-of-concept, a near-10-nm-thin lamella is prepared from a SrTiO3 crystal by our methodology. Moreover, the lamella thickness is controllable at a target heterointerface. Thus, a sub-20-nm-thin lamella is prepared from a LaAlO3/SrTiO3 heterointerface. The methodology offers a robust and operator-independent platform to prepare a sub-20-nm-thin lamella from various materials. This platform will broadly impact aberration-corrected STEM studies in materials science and the semiconductor industry.