Yan-Ru Lin

Highly sensitive ZnO nanowire ethanol sensor with Pd adsorption

The authors report the growth of high-density single crystalline ZnO nanowires on patterned ZnO:Ga∕SiO2∕Si templates, Pd adsorption on nanowire surfaces, and the fabrication of ZnO nanowire-based ethanol gas sensors. With Pd adsorption, it was found that measured sensitivities of the ethanol gas sensors increased from 18.5% to 44.5% at 170°C and increased from 36.0% to 61.5% at 230°C.

Highly Sensitive ZnO Nanowire Acetone Vapor Sensor With Au Adsorption

In this study, the growth of high-density single-crystalline ZnO nanowires on patterned ZnO:Ga/ SiO2/Si templates was reported. We also adsorbed Au onto nanowire surfaces and fabricated ZnO nanowire acetone vapor sensors. With 200-ppm acetone vapor concentration, it was found that we could enhance the device sensitivities at 300deg C from 18.5% to 82.5% by Au adsorption. It was also found that measured responses at 300degC were around 52%, 61%, 71%, 77%, and 82% when the accumulative acetone vapor concentration reached 5, 10, 50, 100, and 200 ppm, respectively, for the ZnO nanowire sensor with Au adsorption.

Vertical single-crystal ZnO nanowires grown on ZnO:Ga/glass templates

Vertical single-crystal ZnO nanowires with uniform diameter and uniform length were selectively grown on ZnO:Ga/glass templates at 600/spl deg/C by a self-catalyzed vapor-liquid-solid process without any metal catalyst. It was found that the ZnO nanowires are grown preferred oriented in the [002] direction with a small X-ray diffraction full-width half-maximum. Photoluminescence, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy measurements also confirmed good crystal quality of our ZnO nanowires. Field emitters using these ZnO nanowires were also fabricated. It was found that threshold field of the fabricated field emitters was 14 V//spl mu/m. With an applied electric field of 24 V//spl mu/m, it was found that the emission current density was around 0.1 mA/cm/sup 2/.

Well-Aligned, Vertically Al-Doped ZnO Nanowires Synthesized on ZnO : Ga ∕ Glass Templates

High-density, single-crystal, vertically aligned, Al-doped ZnO nanowires with an Al content of 1.05 atom % were synthesized on ZnO:Ga/glass templates at 550°C. Although introducing Al did not change the physical dimensions of the ZnO nanowires, the lattice constant increased by 0.25% and the optical properties of the ZnO nanowires were degraded. However, the experimental results also showed that the threshold emission field can be significantly decreased from 16 to 10 V/μm, and the work function, Φ, can also be reduced from 5.3 to 3.39 eV by introducing Al atoms into the ZnO nanowires.

ZnO Nanotube Ethanol Gas Sensors

This investigation reports on the growth of ZnO nanotubes on patterned Au/Al 2 O 3 /Au/RuO 2 templates by reactive evaporation and the fabrication of a ZnO nanotube ethanol gas sensor. The as-grown ZnO nanotubes were polycrystalline and had holes at their terminals and sidewalls. Injection of ethanol gas reduced the resistivity of the fabricated sensor. Introducing 100 ppm ethanol gas increased the measured sensitivities of the ethanol gas sensors from 34 to 87% as the temperature increased from 90 to 230°C. Additionally, the sensitivity of the sensor increased with the concentration of injected ethanol gas.

ZnO Nanowire-Based CO Sensors Prepared at Various Temperatures

/Sitemplates at various temperatures. It was found that the average length of the nanowires increased while the average diameter ofthe nanowires decreased as we increased the growth temperature from 600 to 700°C. It was also found that the nanowires becamesignificantly shorter as the growth temperature was increased. By measuring the resistivity change of the samples at 320°C, it wasfound that the sensor responses were of 3, 17, 57, 7.5, and 5% for the ZnO nanowires grown at 600, 650, 700, 750, and 800°C,respectively. Furthermore, it was found that the sensitivity of the sensor was relatively increased when the concentration ofinjected CO gas increased.© 2007 The Electrochemical Society. DOI: 10.1149/1.2789813 All rights reserved.Manuscript submitted June 25, 2007; revised manuscript received August 29, 2007. Available electronically October 9, 2007.

Indium-diffused ZnO nanowires synthesized on ITO-buffered Si substrate

We report the synthesis of well aligned, high density, vertical single-crystal ZnO nanowires on ITO-buffered Si substrate (ITO is indium tin oxide) at 550 ◦ Cf or 30 min. It was found that the average length and diameter of the ZnO nanowires were around 3.5 µ ma nd30 nm, respectively. It was also found that the ZnO nanowires were oriented in the (002) direction with extremely good crystal quality. Furthermore, it was found that In diffusion occurred at the bottom of the ZnO nanowires. (Some figures in this article are in colour only in the electronic version)

Crabwise ZnO Nanowire UV Photodetector Prepared on ZnO : Ga/Glass Template

Vertical well-aligned and crabwise ZnO nanowires were prepared on patterned ZnO:Ga/glass substrates by reactive evaporation method under different growth conditions. The average length and diameter of vertical well-aligned ZnO nanowires were around 1 mum and 50-100 nm, respectively. In contrast, the average length and diameter of crabwise ZnO nanowires were around 5 mum and 30 nm, respectively. Upon illumination with UV light (lambda = 362 nm), it was found that measured responsivities were 0.015 and 0.03 A/W for the crabwise ZnO nanowire photodetector biased at 10 and 15 V, respectively. Furthermore, a rejection ratio of approximately 10 was obtained for the crabwise ZnO nanowire photodetector with an applied bias of 10 V.

Growth and Characterization of Sparsely Dispersed ZnO Nanowires

This investigation describes the growth of sparsely dispersed vertical ZnO nanowires on sputtered-ZnO:Ga/sapphire templates by self-catalyzed vapor liquid solid method. Experimental results indicate that these ZnO nanowires grew with the preferred (002) orientation with good crystal quality. Conductive diamond-coated point probe forms Schottky contact on single ZnO nanowire with a sharp turn-on voltage of -2.5 V and a barrier height of approximately 0.38 eV.

Selective growth of vertical ZnO nanowires on ZnO:Ga∕Si3N4∕SiO2∕Si templates

High density vertical single crystal ZnO nanowires were selectively grown on ZnO:Ga∕Si3N4∕SiO2∕Si templates at various temperatures by a two-step oxygen injection process of self-catalyzed vapor-liquid-solid (VLS) technology. It was found that tips of the ZnO nanowires are hexagonal. It was also found that average length of the ZnO nanowires increased while the average tip diameter of the ZnO nanowires decreased as the growth temperature increased. Furthermore, it was found that the ZnO nanowires grown at 500°C were “tube-shaped” while the ZnO nanowires grown at 700°C were “cone-shaped.” Photoluminescence (PL), x-ray diffraction (XRD), and energy depersive x-ray (EDX) results all indicate that the quality of our ZnO nanowires is good.