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One-dimensional lepidocrocite, 1DL, titania, TiO2, is a recently discovered form of this ubiquitous oxide that is of interest in a variety of applications ranging from photocatalysis to water purification, among others. The fundamental building blocks of these materials are snippets (30 nm long) of individual 1DLs that self-assemble into nanobundle, NB, structures. These NBs can then be driven to self-assemble into quasi-two-dimensional, 2D, sheets, films, or free-flowing mesoscopic particles. Here, we use analytical atomic-resolution scanning transmission electron microscopy (STEM) and first-principles density functional theory (DFT) calculations to demonstrate that the arrangement of the neighboring NFs can be altered through ion exchange with Li, Na, and tetramethylammonium hydroxide (TMA) cations. Moreover, using cryogenic electron energy-loss spectroscopy (EELS), we show that the introduction of different ion species results in a change in the local occupancy of the TiO2 t2g and eg orbitals. Both experimental findings are predicted by ground-state energy simulations of two-dimensional lepidocrocite TiO2. 

Electron imaging of biological samples stained with heavy metals has enabled visualization of nanoscale subcellular structures critical in chemical-, structural-, and neuro-biology. In particular, osmium tetroxide has been widely adopted for selective lipid imaging. Despite the ubiquity of its use, the osmium speciation in lipid membranes and the mechanism for image contrast in electron microscopy (EM) have continued to be open questions, limiting efforts to improve staining protocols and improve high-resolution imaging of biological samples. Following our recent success using photoemission electron microscopy (PEEM) to image mouse brain tissues with a subcellular resolution of 15 nm, we have used PEEM to determine the chemical contrast mechanism of Os staining in lipid membranes. Os (IV), in the form of OsO2, generates aggregates in lipid membranes, leading to a strong spatial variation in the electronic structure and electron density of states. OsO2 has a metallic electronic structure that drastically increases the electron density of states near the Fermi level. Depositing metallic OsO2 in lipid membranes allows for strongly enhanced EM signals of biological materials. This understanding of the membrane contrast mechanism of Os-stained biological specimens provides a new opportunity for the exploration and development of staining protocols for high-resolution, high-contrast EM imaging. 

Abstract Electron imaging of biological samples stained with heavy metals has enabled visualization of subcellular structures critical in chemical‐, structural‐, and neuro‐biology. In particular, osmium tetroxide (OsO₄) has been widely adopted for selective lipid imaging. Despite the ubiquity of its use, the osmium speciation in lipid membranes and the process for contrast generation in electron microscopy (EM) have continued to be open questions, limiting efforts to improve staining protocols and therefore high‐resolution nanoscale imaging of biological samples. Following our recent success using photoemission electron microscopy (PEEM) to image mouse brain tissues with synaptic resolution, we have used PEEM to determine the nanoscale electronic structure of Os‐stained biological samples. Os(IV), in the form of OsO₂, generates nanoaggregates in lipid membranes, leading to a strong spatial variation in the electronic structure and electron density of states. OsO₂has a metallic electronic structure that drastically increases the electron density of states near the Fermi level. Depositing metallic OsO₂in lipid membranes allows for strongly enhanced EM signals and conductivity of biological materials. The identification of the chemical species and understanding of the membrane contrast mechanism of Os‐stained biological specimens provides a new opportunity for the development of staining protocols for high‐resolution, high‐contrast EM imaging. 

Abstract While monazite (LaPO₄) does not flash sinter even at high fields of 1130 V/cm and temperatures of 1450°C, composite systems of 8YSZ–LaPO₄and Al₂O₃–LaPO₄have been found to more readily flash sinter. 8YSZ added to LaPO₄greatly lowered the furnace temperature for flash to 1100°C using a field of only 250 V/cm. In these experiments,‐Al₂O₃alone also did not flash sinter at 1450°C even with high fields of 1130 V/cm, but composites of Al₂O₃–LaPO₄powders flash sintered at 900‐1080 V/cm at 1450°C. Alumina–monazite (Al₂O₃–LaPO₄) composites with compositions ranging from 25 vol% to 75 vol% Al₂O₃were flash sintered with current limits from 2 to 25 mA/mm². Microstructures were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A eutectic microstructure was observed to form in all flash sintered Al₂O₃–LaPO₄composites. With higher power (higher current limits), eutectic structures with regular lamellar regions were found to coexist in the channeled region (where both the current and the temperature were the highest) with large hexagonal‐shaped‐Al₂O₃grains (up to 75 m) and large irregular LaPO₄grains. With lower power (lower current limits), an irregular eutectic microstructure was dominant, and there was minimal abnormal grain growth. These results indicate that Al₂O₃–LaPO₄is a eutectic‐forming system and the eutectic temperature was reached locally during flash sintering in regions. These eutectic microstructures with lamellar dimensions on the scale of 100 nm offer potential for improved mechanical properties.