Fei-Yi Hung

Fabrication and Characterization of Coaxial p-Copper Oxide/n-ZnO Nanowire Photodiodes

The deposition of copper oxide onto vertically well-aligned n-ZnO nanowires by sputtering and the fabrication of p-copper oxide/n-ZnO coaxial nanowire photodiodes are reported. It was found that we could change the copper oxidation number to obtain Cu₂O/ZnO nanowire photodiode, Cu₄O₃/ZnO nanowire photodiode and CuO/ZnO nanowire photodiode by simply changing the O flow rate during deposition. It was also found that noise equivalent powers were 6.1 × 10^-11, 3.8 × 10^-10, and 7.2 × 10^-8 W while normalized detectivities were 6.35 × 10⁹, 1.02 × 10⁹, and 5.37 × 10⁶ cmHz^0.5 W^-1 for the fabricated Cu₂O/ZnO nanowire photodiode, Cu₄O₃ /ZnO nanowire photodiode and CuO/ZnO nanowire photodiode, respectively.

Simple Fabrication Process for 2D ZnO Nanowalls and Their Potential Application as a Methane Sensor

Two-dimensional (2D) ZnO nanowalls were prepared on a glass substrate by a low-temperature thermal evaporation method, in which the fabrication process did not use a metal catalyst or the pre-deposition of a ZnO seed layer on the substrate. The nanowalls were characterized for their surface morphology, and the structural and optical properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL). The fabricated ZnO nanowalls have many advantages, such as low growth temperature and good crystal quality, while being fast, low cost, and easy to fabricate. Methane sensor measurements of the ZnO nanowalls show a high sensitivity to methane gas, and rapid response and recovery times. These unique characteristics are attributed to the high surface-to-volume ratio of the ZnO nanowalls. Thus, the ZnO nanowall methane sensor is a potential gas sensor candidate owing to its good performance.

Si Nanowire-Based Humidity Sensors Prepared on Glass Substrate

The authors report the growth of Si nanowires on glass substrate by low-temperature vapor-liquid-solid process and the fabrication of Si nanowire-based humidity sensors. It was found that average length of Si nanowires decreased from 1.6 to 1 μm while the diameter of Si nanowires increased from 90 to 490 nm as we increased the initial Au catalytic layer thickness from 5 nm to 15 nm. It was also found that current measured from these Si nanowires decreased monotonically with RH. Furthermore, it was found that samples with a thinner Au layer thickness could provide a larger sensor response.

The Crystallized Mechanism and Optical Properties of Sol–Gel Synthesized ZnO Nanowires

ZnO nanowires were successfully prepared on a silica glass substrate using the sol-gel method. The ZnO nanowires grew from ZnO grains or ZnO grain boundaries, and the length increased with an increment in crystallized temperature. Diffused zinc ions combined with injected oxygen and gradually formed the ZnO nanowires. According to the diffusion mechanism and the law of conservation of mass, the bottom film of ZnO decreased but ZnO nanowires grew. The 650°C film not only possessed better crystallization, but also had the efficacy of nanowires that enhanced optical characteristics.

A Flexible ZnO Nanowire-Based Humidity Sensor

In this paper, the authors report the direct growth of ZnO nanowires (NWs) on a flexible substrate by the hydrothermal process and the fabrication of ZnO NW-based humidity sensor. It was found that average length and diameter of the ZnO NWs were 0.6 μm and 50 nm, respectively. It was also found that resistance of the ZnO NWs decreased by 45% as we increased the relative humidity from 52% to 90%. Furthermore, it was found that measured resistance was very stable with negligible fluctuation after 16 days continuous testing.

CuO-Nanowire Field Emitter Prepared on Glass Substrate

This study reports the growth of CuO nanowires (NWs) on glass substrate, and the fabrication of CuO-NW field emitter. Using CuO as the adhesion layer, we successfully grew CuO NWs of 2.5 μ m average length and 70 nm average diameter by thermal annealing at 450 °C for 5 h in air. It was found that turn-ON field of the fabricated field emitters was 4.5 V/μm. It was also found that the field enhancement factor β of the fabricated CuO-NW field emitter was 1610.

Heat treatment mechanism and biodegradable characteristics of ZAX1330 Mg alloy

Heat treatments are key processes in the development of biodegradable magnesium implants. The aim of this study is to investigate the factors of microstructures and metallurgical segregation on the functionality of biodegradable magnesium alloy. The solid solution heat treatment and strain induced melting activation heat treatment were employed to alter the microstructures of ZAX1330 alloy in this study. Heat treatments caused a significant change on grain size and distribution of secondary phases. The fine-grained microstructure enhanced the mechanical strength, corrosion resistance and achieved the lowest degradation rate in simulated body fluid solution. In coarse-grained microstructure systems, grain growth followed liquid phase formation. The corrosion rate increased due to a larger cathodic region. The status of micro-alloyed calcium (in solid solution or segregated) influenced the microstructural evolution mechanisms, mechanical strength, and degradation properties. A cytotoxicity test and a live/dead assay showed that ZAX1330 had good cytocompatibility, which varied with heat treatment, and no cell toxicity. The results suggest that heat treatment should be controlled precisely in order to improve the cytocompatibility of magnesium alloys for application in orthopedic implants.

An investigation into the crystallization and electric flame-off characteristics of 20 μm copper wires

Copper wires are used in electronic packaging, however the workability and reliability still need to be improved. This work investigates the microstructural characteristics and mechanical properties of annealed wires and un-annealed wires. In addition, the interface bonding characteristics of Al pads are also studied. Experimental results indicate that at the two annealing conditions of 610 °C/0.02 s and 510 °C/0.4 s, 20 μm copper wires possessed a fully annealed structure. Compared with the un-annealed wire, the annealed tensile strength and the annealed hardness decreased, and the annealed elongation increased. Through thermal crystallization, the matrix structure transformed from long, thin grains to equiaxed grains and a few annealed twins. The microstructure of the free air ball (FAB) after an EFO process consisted of column-like grains, and grew from the heat-affected zone (HAZ) to the Cu ball. As for bonding testing, the pull strength of the bonded samples increased with increasing the Al film thickness (from 76 nm to 800 nm).

Intermetallic Phase on the Interface of Ag-Au-Pd/Al Structure

Three wires, Au, Cu, and Ag-Au-Pd, were bonded on an Al pad, inducing IMC growth by a 155 hr high temperature storage (HTS) so that the electrical resistance was increased and critical fusing current density (CFCD) decreased. Observations of the Ag-Au-Pd wire after HTS (0–1000 hr) indicated that IMC between the Ag-Au-Pd wire and Al Pad was divided into three layers: Ag2Al layers above and below the bonding interface and a polycrystal thin layer above the total IMC. A high percentage of Pd and Au existed in this 200 nm thin layer, and could suppress Al diffusion into the Ag matrix to inhibit IMC growth. After PCT-1000 hr, a noncontinuous structure still remained between the IMC layer and interface, and the main phase of IMC was (Ag, Au, Pd)2Al with a hexagonal structure.

Noise Properties of ZnO Nanowalls Deposited Using Rapid Thermal Evaporation Technology

ZnO nanowalls are rapidly grown on a glass substrate using a low-temperature thermal evaporation method, without the use of a catalyst and the pre-deposition of a ZnO seed layer on the substrate. Most of the ZnO nanowalls are grown vertically and are about 70-200-nm thick and 2-μm long. The room-temperature photoluminescence spectra show a strong intrinsic ultraviolet (UV) emission and a weak defect-related orange emission. The ZnO nanowall UV sensor is highly sensitive to UV light, with an excellent UV-to-visible ratio and good flicker noise characteristics. This shows the strong potential of ZnO nanowalls for use in UV sensors. At an applied bias of 2 V, the noise equivalent power and the normalized detectivity of the ZnO nanowall UV sensor are 1.87 × 10-10 W and 3.38 × 109 cm·Hz0.5·W-1, respectively.