Axial Direction Of Nanowires Research Articles

Fabrication, structural and magnetic behavior of novel one-dimensional Fe2MnGa nanostructures

Well aligned Fe2MnGa nanowires (NWs) have been synthesized through low cost and versatile electrochemical deposition technique with constant stirring during the growth process in anodic aluminum oxide (AAO) templates. The average diameter is 50 nm and the lengths up to a few micrometers have been confirmed through morphological analysis. The NWs are found to be in body centered cubic structure with (220) preferred orientation. The magnetic behavior has been investigated at room temperature (RT) as well as at low temperatures. The dominant shape anisotropy compelled the preferable magnetization axis to be in axial direction of NWs. Angular dependence of coercivity shows coherent rotation of magnetic domain on reversal of external magnetic field due to the stronger interwire couplings. At lower temperatures, superparamagnetic contributions from very small nanoparticles in blocking state significantly improved saturation magnetization (Ms) from 0.101 to 0.205 emu and coercivity from 1354 to 1632 Oe. A mixed behavior of exchange bias has been manifested by the NWs at lower temperatures owing to the rearrangement of atoms between the interface of antiferromagnetic and ferromagnetic grains. This causes significant disturbance for pining effect resulting fluctuating exchange bias phenomenon.

Enhanced optical absorption of gradient-component Al[formula omitted]Ga[formula omitted]As nanowire arrays for solar cell applications

In this study, we numerically investigate the light capture performance of AlxGa1−xAs nanowires with gradient Al composition by utilizing COMSOL multiphysics based on finite element method (FEM). Different Al component ranges and sublayer thickness distributions along the axial direction of nanowire are considered. The simulation results show that the optical structure design of AlxGa1−xAs with a composition range varying from 0 to 0.4 show a better optical absorption ability compared with other composition range configurations. Besides, for AlxGa1−xAs nanowires with Al composition varying from 0 to 0.4 and 0 to 0.8, the absorptance of the structure with increasing sub-layer thickness from bottom to top is higher than that of the uniform thickness structure, while the structure with a decreasing thickness owns the worst performance. For AlxGa1−xAs nanowire arrays, the maximum optical absorption can be obtained when the incident light angle is 60°. The design principle proposed in this work would provide a reference for selecting appropriate parameters in the application of solar cells.

Determination of Crystal Growth Geometry Factors and Nucleation Site Densities of Electrodeposited Ferromagnetic Cobalt Nanowire Arrays

The time-dependence of electrochemical reduction current, which was observed during the one-dimensional (1-D) crystal growth of ferromagnetic cobalt nanowire arrays, was analyzed by Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. Textured hcp-Co nanowire arrays were synthesized by potentio-static electrochemical reduction of Co2+ ions in anodized aluminum oxide (AAO) nanochannel films. Crystal growth geometry factor n in the JMAK equation was determined to be ca. 1. Hence, the electrochemical crystal growth process of a numerical nanowires array can be explained by 1-D geometry. The crystal nucleation frequency factor, k in JMAK equation was estimated to be the range between 10−4 and 10−3. Our experimental results revealed that the crystal nucleation site density Nd increased up to 2.7 × 10−8 nm−3 when increasing the overpotential for cobalt electrodeposition by shifting the cathode potential down to −0.85 V vs. Ag/AgCl. The (002) crystal orientation of hcp-Co nanowire arrays was, remarkably, observed by decreasing Nd. Spontaneous magnetization behavior was observed in the axial direction of nanowires. By decreasing the overpotential for cobalt electrodeposition, the coercivity of the nanocomposite film increased and reached up to 1.88 kOe, with a squareness of ca. 0.9 at room temperature.

Stable plasmon excitations in quantum nanowires

Stable electrostatic plasmon excitations due to propagation of Gaussian electron pulses are studied in a cylindrical nanowire of radius “a” and length “L”. For this purpose, we consider conduction electrons that follow the quantum hydrodynamical model to account for quantum statistics, quantum diffraction, and exchange-correlation effects in the presence of classical static ions. The use of the well-known Fourier transform technique and the Trivelpiece-Gould configuration leads to the generalized dispersion for plasmons with finite mode quantization effects via the radial and azimuthal mode indices, as well with quantum settings. The excitations of plasmon wakefield appear when the electron beam propagates with a constant velocity along the axial direction of nanowires. The stability conditions are also analyzed for the existence of wakefield excitations by solving three important inequalities using typical parameters of gold nanowires. The results may prove useful for understanding the plasmon excitations in quantum nanowires, where electrons can be trapped and accelerated in the wakefield to emit radiation in the extreme-ultraviolet range.

Effect of aspect ratio and temperature on magnetic properties of permalloy nanowires.

Arrays of permalloy nanowires (NWs) were fabricated into the pores of self-engineered Anodic Aluminium Oxide (AAO) templates by a simple electrodeposition technique (EDT) with a diameter -200 nm. By varying the length of the nanowires from 1.5 to 7.5 microm, got corresponding changes in aspect ratio from 7.5 to 37.5. We studied the growth and structural properties of permalloy nanowires using scanning electron microscopy, X-ray diffraction spectra and transmission electron microscopy. We performed the magnetic measurements of permalloy nanowires using vibrating sample magnetometer. The coercivity (H(c)) and anisotropy field (H(an)) observed considerably higher when the applied magnetic field was perpendicular to the nanowires axial direction (In-Plane) compare to the applied magnetic field was parallel to the nanowire axial direction (Out-of-plane). Reverse trend was observed for the maximum remanent ratio (M(r)/M(s)). So we concluded that the magnetic easy axis of the permalloy nanowires are along the axial direction of the nanowires and magnetic hardness of the nanowires higher in transverse direction compare to the axial direction of nanowires. For the first time temperature (80 K < or = T < or = 300 K) and aspect ratio dependence magnetic properties of the permalloy nanowires have been studied in detail.

Investigation on Epitaxial Lateral Overgrowth of InGaN/GaN Multi-Quantum-Well Nanowires

To achieve semipolar InGaN/GaN multi-quantum-well (MQW) structure, we fabricate InGaN/GaN MQW nanowires by using a combination of selectively epitaxial lateral overgrowth and patterned GaN/sapphire substrate techniques. Basing on the SEM observations, the nanowires along different crystal orientation of GaN substrate have various surface morphologies. Furthermore, cathodoluminescence measurements exhibit the dependence of the emission peaks of InGaN quantum wells on the axial direction of nanowires, being mainly attributed to the change of the morphology situation of the side facet. The shift of the peaks is larger than 30 nm as the axial direction of a nanowire varies between [1120] and [1100].

Transformation of silicon nanowires to nanocoils by annealing in reducing atmosphere

Silicon nanocoils were synthesized by annealing silicon nanowires with an outer oxide layer in reducing atmosphere. The high resolution transmission electron microscopy revealed that the reduction rate of the oxide layer was non-uniform; more precisely the cross-section of the interface of SiO x /Si was not straight but sinusoidal along the axial direction of nanowires. As a result, if the oxide layer was thicker, the diameter of the core silicon was smaller and vice versa. This non-uniformity would produce alternating tensile and compressive stresses, which were believed to cause the nanowires to get coiled.

A multistep ac electrodeposition method to prepare Co nanowires with high coercivity

It is known that the ac electrodeposition method with low current density can grow compact metal nanowires, but the length of those nanowires is very short. In contrast, the ac electrodeposition method with high current density can grow long metal nanowires. However these long nanowires are not compact and contain lots of defects. In this paper, we describe a multistep ac electrodeposition method to fabricate long metal nanowires with compact structure uniformly filled upon a porous anodic aluminum oxide template. Using this method, Co nanowires with high coercivity (Hc∥) and remnant ratio (Mr/Ms) have been prepared under relatively low deposition current density. The Co nanowires exhibited obvious magnetic anisotropy with the easy axis along the axial direction of nanowires. The maximal Hc∥ (2900 Oe) and Mr/Ms (0.95) were optimal for the perpendicular magnetic recording materials. The magnetic microstructure of Co nanowires is also discussed in this paper.

Ferroelectric and piezoelectric behaviors of individual single crystalline BaTiO3 nanowire under direct axial electric biasing

A method, which is especially useful for the study of ferroelectric nanowire with piezoresponse force microscopy (PFM), was developed. In this method electric bias is directly applied on the axial direction of nanowire. The axial poling and switching of single crystalline BaTiO3 nanowire were realized, and hysteresis loop and shear piezoresponse were acquired with PFM operated in lateral mode. The study demonstrated the ferroelectric nature of the nanowire and the need of a significantly higher poling electric field to reach polarization saturation in nanowire than that in bulk BaTiO3 crystal.

Long-range magnetostatic interactions in arrays of nanowires

Experimental measurements and micromagnetic simulations of the hysteresis loops of arrays of cobalt nanowires are compared here. Arrays of cobalt nanowires (200 nm in diameter) were electrodeposited into the pores of alumina membranes (thickness 60 μm). Their hysteresis loops along the axial direction of nanowires were measured using vibrating sample magnetometry. Micromagnetic simulations were performed considering dipolar interaction between nanowires leading to similar hysteresis loops as those obtained experimentally.