Annealing experiments on albite powders, thin sections, and TEM specimens have been performed utilizing an optical microscope heating stage. Sample orientations were determined by optical microscope and XRD, and then confirmed by TEM diffraction patterns. Partial melting of samples occurred at -l2 hr for powder, but at -12 hr for TEM specimen. It is difficult to get TEM images of albite microstructures above this temperature due to thickening and the amorphous phase of the melted part. Correlative studies between optical microscopy and TEM indicated that the -12 hr annealing in ambient condition was most adequate to observe tweed microstructures in albite through TEM. In situ TEM heating experiments for direct observation of tweed microstructures in albite may require annealing at slightly higher temperatures than considering the high vacuum condition inside TEM.
We report a simple technique for the fabrication of dots-on-spheres (DoS) structures in which conjugated polymer dots (CPdots) are immobilized on the surface of silica spheres via charged interaction. Red-, green-, and blue-emissive conjugated polymers were synthesized and employed to validate the feasibility of an approach to develop a DoS system with emission across the visible range. The robust binding of CPdots to silica particles provides a buffer resistance and good stability to photoirradiation and mechanical agitation. Further bioconjugation of the DoS system is achieved by the introduction of polyarginine and neu antibody that is specific for the HER2 receptor, leading to their successful application to targeted imaging of SKBR-3 breast cancer cells overexpressing HER2. Moreover, DoS with simultaneous multicolor emissions of red, green, and blue can be easily synthesized and used to demonstrate the versatility of this strategy for multicolor cellular imaging based upon a single excitation source. We believe that this hybrid DoS strategy and the easy fabrication of organic polymer nanoparticles with silica substrates will facilitate their effective integration of organic and inorganic materials into versatile applications.
With the application of the scanning transmission electron microscopy (STEM) detector, transmitted electron images similar to transmission electron microscopy (TEM) can be obtained from scanning electron microscopy (SEM), which is referred to STEM-in-SEM imaging. Compared to TEM-energy dispersive spectroscopy (EDS), SEM-EDS is expected to be more efficient and reliable for chemical analysis of TEM specimens due to the larger sample space in SEM and the higher take-off angle of the SEM-EDS detector. Unfortunately, this advantage is not well applied to TEM specimens in practice, mainly because of fault signals generated from the commercial grid holders used in SEM and STEM-in-SEM. This study is designed to solve this problem by modifying the commercial holders and to test them through EDS analysis of apatite phases. We first changed the way of assembling parts of the commercial multi-grid holder for SEM. This new assembly was capable of producing a thinner upper cover part, resulting in the reduction of the EDS fault signals generated from the holder. Furthermore, the thin upper part allowed us to get images in shorter working distances, that is, at higher magnifications. This design concept was also applied to the commercial single-grid holder for STEM-in-SEM, producing a new multi-grid holder to be used for loading multiple samples. We confirmed that the new holders produced reliable chemical data from apatite phases. In case of oxygen analysis, despite of low electron brightness from the tungsten source, 5 kV provided more stable acquisition and signal yields than 15 kV. We expect that these modified holders facilitate more efficient EDS analysis for multiple samples under the same analytical conditions in SEM and STEM-in-SEM.
The structure of hydroxyapatite (HA) nanopowder has been determined by theta-scan precession electron diffraction (TS-PED) and Rietveld analysis. To evaluate the usefulness of the TS-PED technique, this result was compared with that of the Rietveld analysis using conventional electron diffraction (ED) and normal precession electron diffraction (PED). The intensity ratios of the (002) to (121) reflections (I002/I121) obtained by both PED data were in better agreement with the reference X-ray diffraction (XRD) data than that obtained by the conventional ED data. Although the lattice parameters of HA determined by the TS-PED data were slightly deviated from the reference XRD data, the a/c-axis ratio had the best agreement with the reference XRD data. The reliability factors (Rp, Rwp and χ2) of TS-PED refinement results were substantially improved, when compared with the values obtained by the conventional ED data. These results demonstrate that TS-PED technique could be a useful analytical method for structure determination of nanopowder.
On the basis of Pauling's first rule for ionic bonding, the coordination number of cations with oxygen anions can be determined by comparison of their relative ionic size ratio. In contrast to simple oxides, various site occupancies by multicomponent cations with similar sizes usually occur in complex oxides, resulting in distinct physical properties. Through an unprecedented combination of in situ high-temperature high-resolution electron microscopy, crystallographic image processing, geometric phase analysis, and neutron powder diffraction, we directly demonstrate that while the initial crystallites after nucleation during crystallization have a very high degree of ordering, significant local cation disordering is induced by rapid crystal growth in Li-intercalation metal-phosphate nanocrystals. The findings in this study show that control of subsequent crystal growth during coarsening is of great importance to attain a high degree of cation ordering, emphasizing the significance of atomic-level visualization in real time.
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