Recently, evidence was presented that certain single-walled carbon nanotubes (SWNTs) possess helical defective traces, exhibiting distinct cleaved lines, yet their mechanical characterization remains a challenge. On the basis of the spiral growth model of SWNTs, here we present atomic details of helical defects and investigate how the tensile behaviors of SWNTs change with their presence using molecular dynamics simulations. SWNTs have exhibited substantially lower tensile strength and strain than theoretical results obtained from a seamless tubular structure, whose physical origin cannot be explained either by any known SWNT defects so far. We find that this long-lasting puzzle could be explained by assuming helical defects in SWNTs, exhibiting excellent agreement with experimental observation. The mechanism of this tensile process is elucidated by analyzing atomic stress distribution and evolution, and the effects of the chirality and diameter of SWNTs on this phenomenon are examined based on linear elastic fracture mechanics. This work contributes significantly to our understanding of the growth mechanism, defect hierarchies, and mechanical properties of SWNTs.

We exploited the practical sonochemical route for preparing silicon nanocrystals at room temperature and ambient pressure. This synthesis provided the very fast reaction within a few hours and the useful modification for the surface of silicon nanoparticles. The average size of prepared nanocrystals was 2.8 nm and confirmed by TEM images. The chlorine-capped nanoparticles were characterized by FT-IR spectroscopy. The luminescence of silicon colloid was observed in the wide range between 340 nm and near 700 nm and showed white color with commercial low-intensity UV-lamp exposure. This synthetic strategy is potentially applicable for illuminating devices such as white light emitting diodes.

Transparent and low resistance amorphous ZnO-doped In 2 O 3 ͑IZO͒ anode films were grown by radio-frequency ͑rf͒ sputtering on an organic passivated polyethersulfone ͑PES͒ substrate for use in flexible organic light-emitting diodes ͑OLEDs͒. Under optimized growth conditions, a sheet resistance of 15.2 ⍀/ᮀ, average transmittance above 89% in the green range, and a root mean square roughness of 0.375 nm were obtained, even for the IZO anode film grown in a pure Ar ambient without the addition of oxygen as a reactive gas. All of the IZO anode films had an amorphous structure regardless of the rf power and the working pressure due to the low substrate temperature of 50°C and the structural stability of the amorphous IZO films. In addition, an X-ray photoelectron spectroscopy depth profile obtained for the IZO/PES showed no obvious evidence of interfacial reactions between the IZO anode and the PES substrate, except for some indiffusion of oxygen atoms from the IZO anode. Furthermore, the current-voltageluminance of the flexible OLEDs fabricated on IZO anode was found to be critically dependent on the sheet resistance of the IZO anode.

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Polycrystalline BaTiO3 thin films with thickness ranging from 2100 to 20 000 Å were prepared on platinum substrates using off-axis radio-frequency magnetron sputtering. The variation in room temperature permittivity of the films was investigated with respect to thickness using x-ray diffraction and transmission electron microscopy. All films were ferroelectric and their room temperature permittivity, which was significantly higher than previously reported values, showed a strong dependence on film thickness. Higher permittivity was attributed primarily to the presence of ferroelectric domains. The room temperature permittivity of the thin films showed large variations with grain size, as in the case of BaTiO3 ceramics. The increase in permittivity with increasing film thickness was attributed to the decrease in defect concentration with grain growth. The 20 000 Å film showed an abrupt decrease in permittivity and the presence of an intergranular phase having titanium-excess composition; these phenomena are discussed in terms of domain boundary pinning and recrystallization.