Volume 97, Issue 6, 15 March 2005
Index of content:
97(2005); http://dx.doi.org/10.1063/1.1861505View Description Hide Description
The propagation of a magnetic domain wall (DW) in a submicron magnetic wire consisting of a magnetic/nonmagnetic/magnetic trilayered structure with asymmetric notches was investigated by utilizing the giant magnetoresistanceeffect. The propagation direction of a DW was controlled by a pulsed local magnetic field, which nucleates the DW at one of the two ends of the wire. It was found that the depinning field of the DW from the notch depends on the propagation direction of the DW.
Field-effect transistors based on a polycyclic aromatic hydrocarbon core as a two-dimensional conductor97(2005); http://dx.doi.org/10.1063/1.1862757View Description Hide Description
Hexabenzocoronene (HBC) derivatives which are designed to self-assemble into a two-dimensional conductor have been synthesized. The derivatives were deposited by vacuum sublimation as an active layer in organic field-effect transistors. The dihexyl and tetrahexyl derivatives increased the field-effect mobilities and on∕off ratios by a factor of 10 or more as compared to the unsubstituted hexabenzocoronene and the hexahexyl derivative. This good performance could be explained by the self-assembly in a two-dimensional conductor of the HBC derivatives, i.e., the dihexyl and tetrahexyl derivatives, in contrast to the self-assembly in the one-dimensional conductor of the hexahexyl derivative and low self-assembling property of the unsubstituted HBC.
High electron concentration and mobility in Al-doped -ZnO epilayer achieved via dopant activation using rapid-thermal annealing97(2005); http://dx.doi.org/10.1063/1.1863416View Description Hide Description
We report on the growth of very high-quality Al-doped -type ZnO epilayers on sapphire substrates using a radio-frequency (rf) magnetron sputtering technique combined with a rapid-thermal annealing.Photoluminescence(PL) and Hall measurements show that both the optical and electrical properties of the ZnO layers are significantly improved with an increasing annealing temperature up to 900 °C. For example, the samples that are grown at 600 °C and a rf power of 100 W with an gas ratio of 1 give an electron concentration of and a mobility of , when annealed at 900 °C for 3 min in a nitrogen ambient. Furthermore, x-ray diffraction measurements show that both the as-grown and annealed samples are of excellent crystallinity.
97(2005); http://dx.doi.org/10.1063/1.1863415View Description Hide Description
Based on the nanothermodynamical approach, we performed the thermodynamical predictions of nanodiamonds synthesized by pulsed-laser ablation in liquid. The nanothermodynamical analyses showed that the formation of nanodiamonds with sizes of 3–5 nm would be preferable to that of large nanodiamonds in the pressure-temperature region of 10–15 GPa and 4000–5000 K created by pulsed-laser ablation of a graphite target in water in the carbon phase diagram. Meanwhile, the probabilities of the phase transition from graphite to diamond are calculated to be rather high, up to in the same pressure-temperature region. These theoretical results indicate that pulsed-laser ablation in liquid is expected to be an effective industrial route to synthesize ultrananocrystalline diamonds.
Effect of the valence electron concentration on the bulk modulus and chemical bonding in and (, , and )97(2005); http://dx.doi.org/10.1063/1.1861504View Description Hide Description
We have studied the effect of the valence electron concentration, on the bulk modulus and the chemical bonding in and (, , and ) by means of ab initio calculations. Our equilibrium volume and the hexagonal ratio agree well (within 2.7% and 1.2%, respectively) with previously published experimental data for . The bulk moduli of both and increase as is substituted with and by 13.1% and 20.1%, respectively. This can be understood since the substitution is associated with an increased valence electron concentration, resulting in band filling and an extensive increase in cohesion.