ZnO monodispersed microspheres exhibiting only a c(þ)-plane on the surface were successfully synthesized by a novel soft-chemical solvothermal method with ethylene glycol (EG) and hexamethylenetetramine. The concentration of EG plays a critical role in the formation of these spherical particles. The spherical particles are dense and have hierarchical structure, where small crystallites are radially aligned along the c-axis. The polarity was determined using convergent-beam electron diffraction, and we established that the whole surface of the microspheres is a c(þ)-plane.
To establish an accurate determination technique for the polarity of InN by convergent-beam electron diffraction (CBED), we clarified the influence of the electron incidence direction, film thickness, and the temperature factor B on CBED patterns by simulation. The electron incidence direction of [11¯00] and a film thinner than 50nm were found to be preferable for easy and reliable polarity determination. Using an InN film grown on a (0001¯) GaN template on (0001) sapphire by metalorganic vapor-phase epitaxy, observation of the CBED pattern in the thin region of the film was confirmed from the simulation result. This InN film was clearly determined to have N polarity and the value of B was estimated to be less than 2.0Å2.
The applicability of transmission electron microscopy (TEM) to determine polarity was examined for GaN, ZnO, AlN and GaAs. The adopted methods are the TEM-EDS (energy dispersive X-ray spectroscopy) and the conventional convergent beam electron diffraction (CBED) methods. TEM observations and dynamical electron diffraction calculations were carried out. The results show that the CBED method is useful for ZnO and GaN, while the TEM-EDS method must be used for AlN and GaAs and can also be used for GaN and ZnO. It is clearly indicated that the TEM-EDS method is of use for the case where the difference in atomic scattering factor between the two constituent elements is small, while the CBED method is useful for the case where the difference is large.
Atomistic microstructures of long-period superstructures in Al-rich TiAl alloys were investigated by high-resolution transmission electron microscopy. The multi-slice image simulation revealed that Al-atoms in Ti-rich (002) layers of the superstructures are imaged as very bright dots under appropriate observing conditions. By enhancing the contrast of the very bright dots using an image processing technique, partially ordered long-period superstructures were clearly characterized. For the short-range order state, A4B, A2B and A3B type ordered-clusters are generated in the Ti-rich (002) layers. These ordered-clusters are in contact with each other, and form local microdomains of various superstructures, such as Al5Ti3, h-Al2Ti and so on. For the Al5Ti3 and h-Al2Ti ordered states, the ordered-clusters are tiled periodically to form the Al5Ti3 or h-Al2Ti domains and characteristic anti-phase boundary structures.
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