Zhan-Shuo Hu

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.

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.

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.

Optoelectronic Properties of Thermally Evaporated ZnO Films with Nanowalls on Glass Substrates

Zinc oxide (ZnO) films with two-dimensional (2D) vertically aligned nanowalls, denoted by nanowalls-films, are successfully prepared on glass substrates at a low growth temperature of 450 °C without using metal catalysts. The morphology and optical properties of the nanowalls-film are characterized by scanning electron microscopy, X-ray diffraction analysis, transmission electron microscopy, energy dispersive X-ray spectroscopy, and photoluminescence measurement. The ZnO nanowalls-film show a strong UV emission and a preferred c-axis orientation with a hexagonal structure. The UV sensor measurement of the ZnO nanowalls-film shows a high sensitivity to UV light, rapid rise and decay times, and a good UV-to-visible rejection ratio.

The low-temperature crystallization and interface characteristics of ZnInSnO/in films using a bias-crystallization mechanism

This study presents a successful bias crystallization mechanism (BCM) based on an indium/glass substrate and applies it to fabrication of ZnInSnO (ZITO) transparent conductive oxide (TCO) films. The effects of bias-crystallization on electrical and structural properties of ZITO/In structure indicate that the current-induced Joule heating and interface diffusion were critical factors for low-temperature crystallization. With biases of 4V and 0.1 A, the resistivity of the ZITO film was reduced from 3.08 × 10-4 Ω*cm to 6.3 × 10-5 Ω*cm. This reduction was attributed to the bias-induced energy, which caused indium atoms to diffuse into the ZITO matrix. This effectuated crystallizing the amorphous ZITO (a-ZITO) matrix at a lower temperature (approximately 170°C) for a short period (≤20 min) during a bias test. The low-temperature BCM developed for this study obtained an efficient conventional annealed treatment (higher temperature), possessed energy-saving and speed advantages, and can be considered a candidate for application in photoelectric industries.

Align Ag nanorods via oxidation reduction growth using RF-sputtering

Silver nanorod arrays grew on the individual metallic silver particles after the thermal decomposition of the silver oxides. The formation of silver oxide came from the input of oxygen during sputtering. The subsequent growth of the Ag nanorods started from the single silver grain that originated from the decomposition caused by thermal reduction. This method for oxidation reduction growth used no catalysts and improved the interface effect for the lattice match. Photoluminescence of Ag nanorods was detected at 2.17 eV.

The crystallization characteristics and photoluminescence properties of ZnO/Ag nanoflower arrays

Three dimensional (3D) zinc oxide (ZnO) nanoflowers have been successfully synthesized on oxidized silver clusters using a vapor transportation method on a 50nm Ag layer. One dimensional (1D) ZnO nanorods can be fabricated on even the thinner Ag layers (2nm and 10nm). During the heating process, with a trace amount of oxygen present, the Ag layer (50nm) melted and agglomerated forming silver oxide until the temperature reached the melting point of the zinc powder. Initially, the oxygen-rich phase ZnO formed and the zinc atoms diffused from the ZnO shell forming pistils and after an increase in time formed the zinc-rich ZnO nanoflowers. The ultraviolet (UV) emission (3.28eV) from ZnO nanoflowers and nanorods revealed useful properties relating to the recombination of free excitons and the formation of zinc interstitials or zinc antisites was evidenced by the broad visible peak in the 50nm Ag layer spectra.

High temperature characteristics of ZnO-based MOS-FETs with photochemical vapor deposition SiO 2 gate oxide

ZnO-based MOSFETs were fabricated in this study. The I-V curve of the source-drain ohmic contacts shows in figure 1. We can get the good ohmic performance by using the Ti/Al/Ti/Au metals and annealing at 525 °C, 3 minutes. Then, we deposited the SiO2 layer by using photo-CVD system and the schematic diagram of photo-CVD system shows in figure 2.

Structures and opto-electrical characteristics of ZITO thin films

Transparent conductive oxide (TCO) thin film has received extensive attention all the time due to its potential applications in various opto-electronic devices [1–2]. Among various TCO films, indium-doped ZnO (IZO) and indium tin oxide (ITO) thin films have been widely investigated due to their particular optical and electrical properties [3–4]. Regardless of ZnO-based or ITO films, the studies were focused on the doping effects and crystallized mechanisms on materials characteristics were rarely explored. To achieve better conductivity, the multi-compound films were deposited by sputtering, such as ZnO-SnO2-In2O3, In2O3-ZnO and In2O3-SnO2 films etc [5–6]. However, the investigation of sol-gel derived multi-compound ZITO (ZnO combined ITO) film has never been studied. For these reasons, the ZITO films were synthesized to investigate the effects of ITO contents and the effect of temperature on structural characteristics, the optical transmittance and electrical properties. To obtain the aqueous solution of ZITO, ZnO and ITO solutions were firstly prepared by sol-gel method, respectively. All clear solutions were mixed with various volume ratios (ZnO : ITO = 1:1 and 2:1). Hereafter, the films will be designated according to volume ratio of ZnO and ITO as Z1ITO and Z2ITO. Subsequently, this resultant solution was deposited onto the silica-glass substrates using a spin coating. After that, the samples were dried at 200 ºC to evaporate the solvent and remove organic residuals (non-stop until to desired thickness of 150 nm). Finally, the samples were performed at 600~700 ºC for 1 hour under O2 atmosphere.

Advanced Transparent Conductive ZnO/ITO/ZnO multilayer thin films

Institute of Microelectronics & Department of Electrical Engineering; Center for Micro/Nano Science and Technology National Cheng Kung University, Tainan 701, TAIWAN Institute of Nanotechnology and Microsystems Engineering; Center for Micro/Nano Science and Technology National Cheng Kung University, Tainan 701, TAIWAN Institute of Electro-Optical Science and Engineering, Center for Micro/Nano Science and Technology National Cheng Kung University, Tainan 701, TAIWAN