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The structures of Ge nanowires are studied by means of geometry optimization method in this paper. As the radii of carbon nanotubes increase, the structures of the Ge nanowires transform from a monoatomic chain to helical and multishell coaxial cylinders. The physical properties, such as density of states, transmission functions, current-voltage (I-V) characteristics, and conductance spectra (G-V) of optimized nanowires sandwiched between two gold contacts are also obtained. The transport properties of a carbon-coated Ge atomic chain are significantly different from those of Ge single atomic chain. Furthermore, some nonequilibrium properties of Ge nanowires are compared with those of Sn and Si nanowires. [ABSTRACT FROM AUTHOR]

Five kinds of nanowires and a nanochain that is embedded in a carbon nanotube have been optimized by density function theory, and the electronic transport properties through these nanowires and nanochain are studied. Our results indicate that the transmission spectra exhibit size-dependent oscillations. We observe and study the nonlinear contribution to the I-V characteristic (current-voltage) curves that is due to the quantum size effect. The I-V curve of the single chain is different from that when the chain is embedded in a carbon nanotube. The results provide valuable information on the correlation between the transport properties of nanowires and their microstructures. [ABSTRACT FROM AUTHOR]

Co/Cu multilayer nanowires fabricated in an array using anodized aluminium oxide (AAO) template has been investigated. Experimental conditions are optimized to fabricate Co/Cu multilayer systems with fixed Cu and variable Co layer thicknesses. Magnetization reversal mode is found to depend on the Co layer thickness. A transition occurs from coherent rotation to a combination of coherent and curling rotation at around t(Co) = 60 nm with increasing t(Co). The reversal modes have been investigated using the magnetic hysteresis loops measured at room temperature for Co/Cu nanowires placed at various angles between the directions of the nanowire axis and external fields using a vibrating sample magnetometer. The magnetic easy axis changes from the direction perpendicular to nanowires to that parallel to the nanowires at around t(Co) = 60 nm, indicating a change in the magnetization reversal mode. The reversal mode for the nanowires with thin disk-shaped Co layers is of a coherent rotation type, while that for long rod-shaped Co layers can be explained by a combination of coherent rotation and a curling mode. [ABSTRACT FROM AUTHOR]

Well-ordered single, double/four parallel, three/four-strands helical chains, and five-strand helical chain with a single atom chain at the center of Si nanowires (NWs) inside single-walled carbon nanotubes (Sin@SWCNTs) are obtained by means of molecular dynamics. On the basis of these optimized structures, the structural evolution of Sin@SWCNTs subjected to axial stress at low temperature is also investigated. Interestingly, the double parallel chains depart at the center and transform into two perpendicular parts, the helical shell transformed into chain, and the strand number of Si NWs increases during the stress load. Through analyzis of pair correlation function (PCF), the density of states (DOS), and the z-axis polarized absorption spectra of Sin@SWCNTs, we find that the behavior of Sin@SWCNTs under stress strongly depends on SWCNTs' symmetry, diameter, as well as the shape of NWs, which provide valuable information for potential application in high pressure cases such as seabed cable. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

The magnetic field (MF) annealing of dc electrodeposited ferromagnetic nanowire arrays of compositions Co94 Fe06, Co91 Fe07B2 was done in the direction of their easy axis of magnetization (in plane) at 265°C under 800 Oe applied magnetic field for 2 h. An induced magnetic anisotropy (MA) and a large increase in saturation magnetization (Ms) were manifested by the changes in hysteresis loops of the nanowire samples before and after the annealing process. The structural changes were investigated using X-ray diffraction and transmission electron microscopy (TEM). The shape of nanowires, the predicted natural texture with c-axis in the plane of membrane (because of high concentration of cobalt) and diffusional pair ordering of unlike atoms along the direction of external applied field were thought to be the causes of induced MA. The reannealing of samples in absence of MF at 400 °C and 600 °C produced no significant changes in hysteresis loops instead of removing the MA but with evolution of crystalline phase in both the samples. Therefore, the shape of nanowire was concluded to play the major role in persistence of induced MA in nanowire samples after high temperature annealing. [ABSTRACT FROM AUTHOR]

Helical and nonhelical shell structures of Fe−Al alloy nanowires are obtained using molecular dynamics (MD) and density functional theory (DFT) calculations. The electrical transport properties of alloy nanowires are investigated and compared with those of pure metallic aluminum and iron nanowires. The calculations indicate that the conductance of the Fe−Al alloy nanowire is less than that of the pure Al or Fe nanowires. The results show that the conductance of a carbon-coated Fe−Al alloy nanowire (28,7) is significantly larger than that of Fe−Al alloy nanowire. The difference in the electrical behavior of the Fe−Al alloy nanowire and the carbon-coated structure can be attributed to the two interfering pathways between the CNT and the alloy nanowire. The nonlinear feature of the current−voltage (I−V) for all alloy nanowires suggests that it does not follow the Ohmic pattern. [ABSTRACT FROM AUTHOR]