Jung-Hsien Yen

Fabrication and Characterization of Cu2O Nanorod Arrays and Their Electrochemical Performance in Li-Ion Batteries

This study is an investigation of the electrochemical performance of Cu 2 O nanorods in Li ion battery application. The templatemediated electroplating was applied to fabricate Cu 2 O nanorod arrays. The morphological observation shows that the nanorods with 60 nm diam and 450 nm length were grown perpendicularly to the substrate. The cyclic voltammetry sweeping indicates a reversible electrochemical reactivity between Cu 2 O nanorods and Li, and cycling tests show that the nanorod arrays exhibit a capacity of 330 mAh/g after 100 cycles. The high capacity and good cycle retention imply that Cu 2 O nanorods are a candidate anode material for rechargeable power source.

Preparation of Ni Nanodot and Nanowire Arrays Using Porous Alumina on Silicon as a Template Without a Conductive Interlayer

Recently, various technologies have been developed to create nanoscale structures over a large area at low cost. 1-3 One way to this goal is the template-mediated process. Many nanostructures have been fabricated using porous materials as a mask or a template. 4-6 Porous anodic alumina ~PAA! is now a most popular material for the fabrication of nanometer-sized structures due to its controllable pore characteristics and simplicity of production. One-dimensional nanostructures may be obtained by depositing materials into the PAA through many methods, such as chemical vapor deposition, 7 electrodeposition, 8 electroless deposition, 9 and sol-gel deposition. 10 Among these methods, electrodeposition is a powerful tool for the fabrication of nanostructures with a high aspect ratio due to fieldassisted migration of ions into channels of the template membranes. Conventionally, a conductive layer, such as Ag and Au, must be deposited on one side of the PAA as the cathode for electrodeposition. 11,12 In this study, a simple process was presented for the preparation of Ni nanodots and nanowires. A conductive layer was not necessary for the fabrication of Ni nanostructures into the PAA on the Si substrate. The dots and wires may be obtained over a large area with high efficiency and good reproducibility. Moreover, some findings regarding the electrodeposition process and the formation mechanism for these nanostructures are reported. The Ni nanostructures can be used as the magnetic storage media in the recording devices and as the mold for the nanoimprinting process. 13,14 Moreover, Ni nanostructures may also be used as nanoelectrode ensembles for investigating an electrochemistry and redox process that is difficult to measure using conventional macroscopic electrodes. 15,16

Sheath-dependent orientation control of carbon nanofibres and carbon nanotubes during plasma-enhanced chemical vapour deposition

The aligned growth of carbon nanofibres (CNFs) and carbon nanotubes (CNTs) via a simple sheath-dependent technique for orientation control is demonstrated. Significant difference in the alignment behaviour of CNFs/CNTs, involving the transition of sheath-dependent electric fields, is found to depend on the relation between the sheath width and the sample dimension. The electric field within the plasma sheath contributes to the aligned growth of CNFs/CNTs with an absolute orientation, and can be used to direct the assembly of CNFs/CNTs in a predetermined manner relative to the substrate by tilting the sample in a sheath region. The consequent application for synthesis of kinked carbon nanostructures by altering the alignment angle to the substrate during growth is also achieved.

Density Control for Carbon Nanotube Arrays Synthesized by ICP-CVD Using AAO/Si as a Nanotemplate

Carbon nanotubes (CNTs) with tunable density have been grown directly by inductively coupled plasma chemical vapor deposition (ICP-CVD) using anodic aluminum oxide (AAO) on silicon as a substrate. The density of CNTs (10 6 to 10 9 CNTs/cm 2 ) can be controlled by changing the length of catalytic Ni nanowires embedded in AAO. The one-dimensional CNTs-Ni nanowire heterojunction without observable defects by transmission electron microscopy characterization ensures good contact between the CNT and the Ni nanowire. The realization of combining AAO on silicon and controlling the density of carbon nanotubes by a plasma process is significant for application of CNTs as field emitters and nanoelectronic devices.

Fabrication of Various Nickel Nanostructures by Manipulating the One-Step Electrodeposition Process

By employing colloidal crystal templates with different colloid diameters, nickel well-ordered macroporous structures (inverse opal) with different void diameters can be fabricated via a template-mediated electrodeposition process. It was found that the different degrees of filling colloidal crystal template produces different nickel nanostructures during the electrodeposition process. Moreover, the filling behavior for electrodeposition of nickel into the template can be characterized in terms of the current transients recorded. Because of preferential nickel-filling into the interstitial spaces among the colloids, fabrication of well-ordered nickel nanorod and monolayer porous arrays are manipulated by controlling electrodeposition times accurately at 5 and 10 s, respectively. However, the macroporous structure covered with hollow sphere arrays on the surface can be formed in 120 s due to preferential nickel-coating around the colloidal surface. Therefore, various kinds of nickel-based structures derived from colloidal crystals can be constructed via a one-step, template-mediated electrodeposition process.

Spatially oriented carbon nanofibres manipulated by a hollow cathode discharge process

The ability to manipulate the orientation of nanoscale materials is of great importance for applications in advanced devices. Here, we describe the controlled growth of aligned carbon nanofibres (CNFs) in a hollow cathode discharge (HCD) set-up. Instead of vertical alignment well demonstrated in other plasma-based chemical vapour deposition, CNFs with specific and symmetrically aligned configurations are grown on a flat surface during HCD. Experimental evidence shows that the alignment is not the result of the edge or flow effect, but results from a unique electric field distribution imposed on the substrate surface in the HCD environment. Due to the field reversal characteristic of the HCD, two alignment trends simultaneously occur. For the transverse direction of the channel, the grown CNFs on the substrate appear in a convergent manner, while those along the longitudinal direction exhibit a radiative arrangement. These results will open up the possibility of both tuning the electric fields on the basis of plasma design and tailoring the spatial orientations of CNFs using HCDs.