Surface Morphology Of Nanowires Research Articles

Molecular Beam Epitaxial Growth and Device Characterization of AlGaN Nanowire Ultraviolet-B Light-Emitting Diodes

We report on the design and fabrication of high performance AlxGa1−xN nanowire ultraviolet (UV) light-emitting diodes (LEDs) on silicon substrate by molecular beam epitaxy. The emission wavelength and surface morphology of nanowires can be controlled by varying the growth parameters that include substrate temperatures and/or Aluminum/Gallium flux ratios. The devices exhibit excellent current-voltage characteristics with relatively low resistance. Such nanowire LEDs generate strong emission in the UV-B band tuning from 290 nm to 330 nm. The electroluminescence spectra show virtually invariant blue-shift under injection current from 50 mA to 400 mA, suggesting the presence of a negligible quantum-confined Stark effect. Moreover, we have shown that, the AlGaN nanowire LEDs using periodic structures, can achieve high light extraction efficiency of ~ 89% and 92% for emissions at 290nm and 320nm, respectively. The randomly arranged nanowire 290 nm UV LEDs exhibit light extraction efficiency of ~ 56% which is higher compared to current AlGaN based thin-film UV LEDs.

I-V Characteristics of NiO Nanowire Based Resistive Change Memory

1. Introduction Resistive switching random access memory (ReRAM) has been expected to a next generation memory due to high-speed response, non-volatility, low power consumption [1]. However, poor reproducibility of a switching voltage hinders the practical application. According to a filament model, many kinds and number of filaments made at the soft breakdown of an insulator are thought to be the origin. In our previous studies, we employed anodic porous alumina (APA) with ordered nanoholes as the insulator of ReRAM because nanoholes are expected to inhibit the growth of conductive filaments spacially. In the result, we succeeded in suppression of the switching voltage variation [2].Looking at the top view of SEM image of APA (Fig. 1), we notice no restriction along the dashed lines. It means that there exist a division indicating a bulk property. In this study, a nanowire based insulator has been focused on to confine the filaments omnidirectionally. 2. Experiment Nickel nanowires were buried into nanoholes of APA using electroplating method, where nickel sulfate was used as an electrolyte solution. The exposed Ni nanowires were obtained by chemical etching the alumina layer. The nanowires were oxidized by oxygen plasma for 1, 3, 5 min. The surface morphology of nanowires was investigated by a field emission scanning electron microscope (FE-SEM). For a contact preparation, Indium solder was used against the top electrode. The bottom electrode was a residual aluminum substrate. The I-Vcharacteristics of NiO nanowires were measured by a standard two-probe method at room temperature, where the current was limited to 1 mA in a SET process guard the device from a complete dielectric breakdown. 3. Results Figure 2 (a) ~ (c) shows the cross-sectional SEM images of NiO nanowires. The typical diameter and the length were about 40 nm and 600 nm, respectively. Significant oxidation time dependence was not found in the shape. We can see clear switching behaviors for all samples. In case of 1 min oxidation, a relatively wide distribution of the switching voltage was measured. The distribution width became smaller in 3 min oxidation and widens again in 5 min oxidation. The relatively high current found in the RESET process in case of 3 min oxidation. It might be due to poor crystallinity of the NiO thin film because oxygen plasma is expected to make the film amorphous by the high kinetic energy of oxygen plasma. Longer oxidation time might help to formation of many filaments. So, this leads to widen the switching voltage distribution again in 5 min oxidation.

Nickel Oxide Nanowires Growth by VLS Technique for Gas Sensing Application

In this work, nickel oxide (NiO) nanowires have been synthesized on alumina substrate by vapor-liquid-solid (VLS) technique and were tested for alcohol sensing. RF magnetron sputtered gold particles were used as catalyst for the growth of NiO nanowires. Nanowire surface morphology was analyzed by using scanning electron microscopy (FE-SEM). Afterwards, a set of conductromertric sensing devices were prepared and mounted on TO packages using electro-soldered gold wires. The response of prepared sensors towards different gases such as acetone and ethanol was measured. The dynamic sensing phenomena and the calibration curves of NiO nanowire sensors exposed towards these gases were also studied in detail. The optimal working temperature of the sensors were found to be 500°C for both the gases.

Nickel Alloying Effect on Formation of Cobalt Nanoparticles and Nanowires via Electroless Deposition under a Magnetic Field

Co-Ni nanowires 40–100 nm in diameter with several dozen μm of length were prepared via electroless deposition under a magnetic field. The formation of Co-Ni nanowires was investigated by an in-situ mixed potential measurement and a cyclic voltammetry combined with a quartz crystal microbalance electrode. These electrochemical measurements revealed that the deposition rate of nickel on nickel is lower than that of cobalt on cobalt. Nickel works as an inhibitor in a growth process of Co-Ni alloys. Thus, the thickness of Co-Ni alloy nanowires is drastically reduced by the addition of Ni(II) in solution. The morphology of Co-Ni nanowires is also strongly affected by the magnetization of Co-Ni alloy nanoparticles which are precursors in the formation of nanowires. Both the magnetization and the deposition rate in Co-Ni alloys are the key parameters to control the aspect ratio and surface morphology of nanowires.

Synthesis and Investigation of Electrodeposited Half-Metallic Fe3O4 Thin Films and Nanowires

Thin films and nanowires of Fe3O4 have potentiostatically been electrodeposited on ITO coated glass and employing templates in a conventional three-electrode cell using two different baths. Appropriate potential windows, suitable for films and nanowires, were estimated from cyclic voltametry. Structural property of Fe3O4 films was studied by X-ray diffraction. A large (−3.35%, at 2.3 kOe) longitudinal magnetoresistance (MR) was observed at room temperature, and the shape of MR curves showed a reduced hysteresis loop for Fe3O4 films with low coercivity. Room-temperature magnetic properties of Fe3O4 films were studied by vibrating sample magnetometer (VSM). Surface morphology of nanowires was studied by scanning electron microscope (SEM). The nonlinear I–V characteristic of nanowires was observed at room temperature. An attempt has been made to understand the conduction mechanism.