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Cerium oxide nanoparticles (CNPs) are of significant interest to the scientific community due to their widespread applications in a variety of fields. It is proposed that size-dependent variations in the extent of Ce3+ and Ce4+ oxidation states of cerium in CNPs determine the performance of CNPs in application environments. To obtain greater molecular and structural understanding of chemical state transformations previously reported for ceria of ≈3 nm nanoparticles (CNPs) in response to changing ambient conditions, micro-XRD and Raman measurements were carried out for various solution conditions. The particles were observed to undergo a reversible transformation from a defective ceria structure to a non-ceria amorphous oxyhydroxide/peroxide phase in response to the addition of 30% hydrogen peroxide. For CNPs made up of ∼8 nm crystallites, a partial transformation was observed, and no transformation was observed for CNPs made up of ∼40 nm crystallites. This observation of differences in size-dependent transition behavior may help explain the benefits of using smaller CNPs in applications requiring regenerative property.
Amorphous zinc tin oxide (ZTO) was investigated to determine the effect of deposition and postannealing conditions on film structure, composition, surface contamination, and thin-film transistor (TFT) performance. X-ray diffraction results indicated that the ZTO films remain amorphous even after annealing to 600 °C. Rutherford backscattering spectrometry indicated that the bulk Zn:Sn ratio of the sputter-deposited films were slightly tin rich compared to the composition of the ceramic sputter target. X-ray photoelectron spectroscopy indicated that residual surface contamination depended strongly on the sample postannealing conditions where water, carbonate, and hydroxyl species were adsorbed to the surface. Electrical characterization of ZTO TFTs indicated that the best devices had mobilities of 17 cm2/Vs, threshold voltages of −1.5 V, subthreshold slopes of 0.9 V/dec, turn-on voltages of −12 V, and on-to-off ratio of >107. Annealing ZTO in vacuum assisted in the removal of adsorbed species, which may reduce defects in the films and improve device performance.
A new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ∼50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ∼2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states.
Transmission electron microscopy (TEM) and spectroscopy have been evolved to a stage such that they can be routinely used to probe the structure and composition of the materials with the resolution of a single atomic column. However, a direct in situ TEM observation of structural evolution of the materials in a lithium ion battery during dynamic operation of the battery has never been reported. In this paper, we report the results of exploring the in situ TEM techniques for observation of interfaces in the lithium ion battery during the operation of the battery. A miniature battery was fabricated using a single nanowire and an ionic liquid electrolyte. The structure and composition of the interface across the anode and the electrolyte was studied using TEM imaging, electron diffraction, and electron energy-loss spectroscopy. In addition, we also explored the possibilities of carrying out in situ TEM studies of lithium ion batteries with a solid state electrolyte.