The microstructures and growth mechanism of Fe 2 O 3 nanowires (NWs) synthesized by thermal oxidation of iron are studied in detail by transmission electron microscopy. Three different structures, single-crystalline, bicrystalline, and tricrystalline, are observed in the NWs. It is found that single-crystalline Fe 2 O 3 NWs have a hexagonal structure while bicrystalline and tricrystalline NWs possess a cubic one. The differences in the electronic structures of the three Fe 2 O 3 NWs are examined by electron energy-loss spectroscopy. A modulated structure with a periodicity of 1.53 nm is observed in single-crystalline Fe 2 O 3 NWs, but not in bicrystalline or tricrystalline Fe 2 O 3 NWs. The formation of the modulated structure in single-crystalline NWs is attributed to the periodical appearance of stacking faults, because of the shear stress occurred during the growth process. NWs possessing a cubic c-Fe 2 O 3 structure tend to coalesce into the bicrystalline or tricrystalline NWs whereas NWs with the hexagonal a-Fe 2 O 3 structure prefer to grow as single-crystalline NWs. The formation mechanism of Fe 2 O 3 NWs with the different morphologies is discussed.
The charge ordering (CO) behaviors of Pr 0.5 Ca 0.35 Sr 0.15 MnO 3 films grown on STO(100), STO(110) and LAO(100) are systematically investigated by transport measurements and transmission electron microscopy (TEM) examinations. From the transport measurements, the CO transition temperatures of all the three films are much higher than those of the bulk materials, showing that the film strain could enhance the CO transition. From TEM observations, many superlattice spots appear in the electron diffraction patterns taken from the films, indicating the appearance of the CO modulation structures at room temperature. The modulation vectors are determined to be (1/2, 0, 0) for STO (100), (1/2, 1/2, 1/2) for STO (110), and both (0, 1/2, 0) and (1/2, 1/2, 0) for LAO (100). It is shown that both the substrate orientation and the film strain have a great effect on the CO modulation structures. The CO state is much easier to appear in the compressive strain direction which is due to the Mn-O-Mn angle tilting. V C 2015 AIP Publishing LLC. [http://dx.
CdTe 0.67 Se 0.33 nanocrystals were synthesized using a typical organic route. Two major morphologies are observed from transmission electron microscopy (TEM) images, one being a tripod, and the other being a tripod-like with a black dot in the center of the nanocrystal. The nanocrystals have two distinct geometrical shapes, one being a tripod, and the other being a tetrapod. High-resolution TEM (HRTEM) examinations show that the tetrapod nanocrystals consist of a zinc-blende nucleus and four wurtzite arms connected through a common facet, whereas the tripod nanocrystals result from the coalescence of three zinc-blende nanorods. These results are helpful to interpret the growth process of other II-VI semiconductor NCs.
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