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Manganese oxides are good candidates of strongly correlated electron materials due to the uniqueness of electronic structure of manganese and the mobility of oxygen among lattice sites under external impacts. Here, we used electron beam as the excitation source to explore the structural evolution of YMnO3 and identified a new phase under the radiation of electron beam in the transmission electron microscope. Analyses of the electron energy-loss spectra reveal that this phase originates from ordered oxygen vacancy. We applied the first principles calculation to pick out the optimized stable structure with a lower polarization, and verified its correctness by electron diffraction and image simulations. Analyses of density of states indicate that weak Y–O covalence is favorable for the existence of ferroelectricity, supporting the electrostatic nature of ferroelectricity in the YMnO3.

The microstructures of the Bi0.4Ca0.6MnO3 (BCMO) and La0.67Ca0.33MnO3 (LCMO) epitaxial films are investigated by transmission electron microscopy in detail. BCMO epitaxial films (similar to 10 and similar to 40nm) exhibit an island growth mode whereas the LCMO films (similar to 6 and similar to 30nm) follow a layer by layer growth mode. Combined with the critical thickness models for the expected onset of the misfit dislocations in epitaxial films, an atomic collapse model is introduced to explain their mechanism of formation in manganite films. At the beginning of deposition, the strain caused by the lattice mismatch between the epitaxial film and substrate can be accommodated by elastic deformation. With the increase of film thickness, the strain becomes larger and larger. When the film thickness reaches the critical thickness, the strain can only be relaxed by the formation of misfit dislocations. Meanwhile, the atomic configuration of the epitaxial film will reorganize and some atoms begin to collapse, thus an island morphology will be formed. Once the collapse morphology is formed, maintenance of this wave-like morphology depends on atomic diffusion length of the deposited atoms. If the diffusion length of the deposited atoms is long, the island morphology will not be maintained. If the diffusion length of the deposited atoms is short, the island morphology will keep until the epitaxial film is thick enough. The results could shed light on the growth modes for other perovskite epitaxial films.

Composites containing carbon nanotubes (CNTs) in a poly(butyl methacrylate) (PBMA) have been prepared by in situ polymerization. Scanning electron microscopy and high-resolution transmission electron microscope showed that CNTs were well dispersed into PBMA matrix and wrapped with PBMA. The infrared spectrum illustrated that CNTs were covalently linked with PBMA through a CC bond. Owing to this covalent linkage, the composites had a better solubility in organic solvents and had higher thermal stability over pure PBMA. The direct shear testing showed strong mechanical behavior with up to 200% increase in Young's modulus. The possible strengthening mechanism was discussed. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

A big challenge in making a composite lies in achieving individual-nanotube dispersion of carbon nanotubes (CNTs) in a polymer matrix, without aggregation and entanglement and excellent interfacial adhesion between the CNTs and the polymers matrix. In this communication, using polyethylene glycol-200, we successfully prepared CNT-reinforced polyimide composites that exhibit individual-nanotube dispertion in the matrix at high-loading CNT's. The content of CNTs in a composite can reach 43 wt%. Copyright © 2007 John Wiley & Sons, Ltd.

Resistive switching processes in HfO2 are studied by electron holography and in situ energy-filtered imaging. The results show that oxygen vacancies are gradually generated in the oxide layer under ramped electrical bias, and finally form several conductive channels connecting the two electrodes. It also shows that the switching process occurs at the top interface of the hafnia layer.

The title nanoribbons are synthesized with large yields by solvothermal reaction of CuCl, BiCl3, CS2, and dodecylamine in toluene (autoclave, 200 °C, 30 h).