Amorphous Ta–O nanotubes (NTs) prepared by anodization in a sulfuric-acid-based solution have been found to contain considerable amounts of extra oxygen and sulfur. Their structural and thermal stability has been studied by combining x-ray diffractometry, transmission electron microscopy, and thermal analysis. The amorphous Ta–O, whose composition was estimated to be Ta2O6.6S0.7, crystallizes into orthorhombic β-Ta2O5 at temperatures around 1073 K by an endothermic reaction, at which excess oxygen and impurity sulfur are released. The amorphous NTs were found to be thermally more stable than stoichiometric amorphous Ta2O5, whose crystallization temperature is around 973 K. Excess oxygen and impurity sulfur, which form chemical bonds with Ta atoms in the amorphous solid, must be the origin of the stability. The crystallization follows the out-diffusion of oxygen and sulfur from the solid at temperatures where the mobility of atoms is high enough, indicating that the crystallization is kinetically arrested.

Chemical disorder in ion-irradiated SiC and GaN has been examined by means of transmission electron microscopy. Radial distribution functions obtained by a quantitative analysis of electron diffraction intensities revealed that homonuclear bonds, which do not exist in the crystalline state, are formed in both ion-irradiated specimens. The origin of the homonuclear bonds is quite different between SiC and GaN. The constitute elements mix on the atomic-scale in amorphous SiC, while phase separation induced by irradiation is attributed to the formation of self-bonded Ga atomic pairs in amorphous/nanocrystalline GaN.

We have proposed spin quantum cross (SQC) devices, in which organic materials are sandwiched between two edges of magnetic thin films whose edges are crossed, towards the realization of novel beyond-CMOS switching devices. In SQC devices, nanometer-size junctions can be produced since the junction area is determined by the film thickness. In this study, we have fabricated Ni SQC devices with poly-3-hexylthiophene (P3HT): 6, 6-phenyl C61-butyric acid methyl ester (PCBM) organic materials and investigated the current-voltage (I-V) characteristics experimentally and theoretically. As a result of I-V measurements, ohmic I-V characteristics have been obtained at room temperature for Ni SQC devices with P3HT:PCBM organic materials, where the junction area is as small as 16 nm × 16 nm. This experimental result shows quantitative agreement with the theoretical calculation results performed within the framework of the Anderson model under the strong coupling limit. Our calculation also shows that a high on/off ratio beyond 10000:1 can be obtained in Ni SQC devices with P3HT:PCBM organic materials under the weak coupling condition.

Electron-beam-induced effects in preamorphized Sr2Nd8(SiO4)6O2 were investigated in situ using transmission electron microscopy with 200-keV electrons at temperatures ranging from 380 to 780 K. Within the electron-irradiated area, epitaxial recrystallization was observed from the amorphous/crystalline interface toward the surface, with the rate of recrystallization increasing as temperature increased from 380 to 580 K. Structural contrast features (i.e., O deficient amorphous material), as well as recrystallization, were observed outside of the irradiation area at temperatures from 680 to 780 K. Ionization-induced processes and local nonstoichiometry induced by oxygen migration and desorption are possible mechanisms for the electron-beam- induced recrystallization and for the formation of the structural contrast features, respectively.

Amorphous silicon carbides (a-SiC) fabricated by Xe+ ion implantation into 6H-SiC (0001) to fluences of 1015 and 1016/cm2 have been annealed at 850 °C for 1 hour. Transmission electron microscopy (TEM) observations revealed that the 1015 Xe+/cm2 implanted sample was completely recrystallized, while most of the a-SiC remains in the 1016 Xe+/cm2 implanted sample. Pair-distribution function analyses of both of the as-implanted samples show that the peak intensity of Si-C heteronuclear bonds is higher and the peak intensities of Si-Si and C-C homonuclear bonds are lower in the 1015 Xe+/cm2 implanted sample, indicating that the atomistic structure of the 1015 Xe+/cm2 implanted sample is more chemically ordered than that of the 1016 Xe+/cm2 implanted sample. This result suggests that more chemically ordered atomistic structure of 1015 Xe+/cm2 implanted a-SiC leads to complete recrystallization during thermal annealing.

Atomistic structures of amorphous silicon carbide generated by energetic particles were examined by electron diffraction techniques in combination with imaging plates. Atomic pair distribution functions revealed that not only heteronuclear (silicon-carbon) bonds but also homonuclear (silicon-silicon and carbon-carbon) bonds exist in the first coordination shell of amorphous silicon carbide induced by ion- or electron-beam-irradiation. Structural changes from amorphous silicon carbide to amorphous silicon were observed under the electron irradiation.

Molecular dynamics calculations have been performed to simulate crystal growth from melted silicon (Si) and defect formation processes based on the ordinary Langevin equation employing the Tersoff interatomic potential. The findings of this investigation are as follows: (i) The [110] bonds at the solid-liquid interface induce the eclipsed configurations or hexagonal Si structures which stabilize microfacets composed of the {111} planes. (ii) Defect formation during crystal growth processes is due to misorientations at the {111} interfaces which result in an “elementary” grown-in defect structure including five- and seven-member rings. (iii) The “elementary” grown-in defect migrates in c-Si by bond-switching motions during further crystal pulling or annealing.