Schottky nanocontacts on ZnO nanorod arrays

We report on fabrication and electrical characteristics of ZnO nanorod Schottky diode arrays. High quality ZnO nanorods were grown for the fabrication of the Schottky diodes using noncatalytic metalorganic vapor phase epitaxy and Au was evaporated on the tips of the vertically well-aligned ZnO nanorods. I-V characteristics of both bare ZnO and Au/ZnO heterostructure nanorod arrays were measured using current-sensing atomic force microscopy. Although both nanorods exhibited nonlinear and asymmetric I-V characteristic curves, Au/ZnO heterostructure nanorods demonstrated much improved electrical characteristics: the reverse-bias breakdown voltage was improved from -3 to -8 V by capping a Au layer on the nanorod tips. The origin of the enhanced electrical characteristics for the heterostructure nanorods is suggested. (C) 2003 American Institute of Physics.X11326sciescopu

Time-resolved photoluminescence of the size-controlled ZnO nanorods

Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 mum. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results. (C) 2003 American Institute of Physics.X11100sciescopu

Fabrication and electrical characteristics of high-performance ZnO nanorod field-effect transistors

We report on fabrication and electrical characteristics of high-mobility field-effect transistors (FETs) using ZnO nanorods. For FET fabrications, single-crystal ZnO nanorods were prepared using catalyst-free metalorganic vapor phase epitaxy. Although typical ZnO nanorod FETs exhibited good electrical characteristics, with a transconductance of similar to140 nS and a mobility of 75 cm(2)/V s, the device characteristics were significantly improved by coating a polyimide thin layer on the nanorod surface, exhibiting a large turn-ON/OFF ratio of 10(4)-10(5), a high transconductance of 1.9 muS, and high electron mobility above 1000 cm(2)/V s. The role of the polymer coating in the enhancement of the devices is also discussed. (C) 2004 American Institute of Physics.X11333sciescopu

Dry etching of ZnO films and plasma-induced damage to optical properties

To study the effects of plasma chemistries on etch characteristics. and plasma-induced damage to the optical properties, dry etching of ZnO films has been carried out using inductively coupled plasmas of Cl-2 /Ar, Cl-2 /H-2 /Ar, and CH4 /H-2 /Ar. The CH4 /H-2 /Ar chemistry showed a faster etch rate and a better surface morphology than the Cl-2-based chemistries. Etched samples in all chemistries showed a substantial decrease in the PL intensity of band-edge luminescence mainly due to the plasma-induced damage. The CH4 /H-2 /Ar chemistry showed the least degradation of the optical properties. (C) 2003 American Vacuum Society. [DOI: 10.1116/1.1563252].open1139sciescopu

Electrical and optical characteristics of hydrogen-plasma treated ZnO nanoneedles

We report on optical characteristics as well as electron emission of hydrogen-plasma treated ZnO nanoneedle arrays. The nanoneedle arrays were vertically grown on Si substrates using catalyst-free metalorganic chemical vapor deposition and subsequently treated by hydrogen plasma at room temperature. After hydrogen plasma treatment, the field emission characteristic curves of nanoneedle arrays exhibited significantly reduced turn-on field and increased emission current density, and the electrical conductivity was increased. In addition, low temperature photoluminesence (PL) measurements indicate that a neutral-donor bound exciton PL peak intensity was increased by the hydrogen- plasma treatment. These effects of the plasma treatment on the physical properties may be explained in terms of hydrogen doping effect. (c) 2005 American Vacuum Society.open112224sciescopu

Excitonic emissions observed in ZnO single crystal nanorods

We report on the photoluminescent characteristics of ZnO single crystal nanorods grown by catalyst-free metalorganic vapor phase epitaxy. From photoluminescence (PL) spectra of the nanorods at 10 K, several PL peaks were observed at 3.376, 3.364, 3.360, and 3.359 eV. The PL peak at 3.376 eV is attributed to a free exciton peak while the other peaks are ascribed to neutral donor bound exciton peaks. The observation of the free exciton peak at 10 K indicates that ZnO nanorods prepared by the catalyst-free method are of high optical quality. (C) 2003 American Institute of Physics.open11374393sciescopu

Enhanced light output of GaN-based light-emitting diodes with ZnO nanorod arrays

We report enhanced light output of GaN-based light-emitting diodes (LEDs) with vertically aligned ZnO nanorod arrays. The ZnO nanorod arrays were prepared on the top layer of GaN LEDs using catalyst-free metalorganic vapor phase epitaxy. Compared to conventional GaN LEDs, light output of GaN LEDs with the ZnO nanorod arrays increased up to 50% and 100% at applied currents of 20 and 50 mA, respectively. The source of the enhanced light output is also discussed. (C) 2008 American Institute of Physics.open11132146sciescopu

An Automated WSDL Generation and Enhanced SOAP Message Processing System for Mobile Web Services

Web services are key applications in business-to-business, business-to-customer, and enterprise applications integration solutions. As the mobile Internet becomes one of the main methods for information delivery, mobile Web Services are regarded as a critical aspect of e-business architecture. In this paper, we proposed a mobile Web Services middleware that converts conventional Internet services into mobile Web services. We implemented a WSDL (Web Service Description Language) builder that converts HTML/XML into WSDL and a SAOP (Simple Object Access Protocol) message processor. The former minimizes the overhead cost of rebuilding mobile Web Services and enables seamless services between wired and wireless Internet services. The latter enhances SOAP processing performance by eliminating the Servlet container (Tomcat), a required component of typical Web services implementation. Our system can completely support standard Web Services protocol, minimizing communication overhead, message processing time, and server overload. Finally we compare our empirical results with those of typical Web Service

Metalorganic vapor-phase epitaxial growth of vertically well-aligned ZnO nanorods

We report metalorganic vapor-phase epitaxial growth and structural and photoluminescent characteristics of ZnO nanorods. The nanorods were grown on Al2O3(00.1) substrates at 400 degreesC without employing any metal catalysts usually needed in other methods. Electron microscopy revealed that nanorods with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates. The mean diameter of the nanorods is as narrow as 25 nm. In addition, x-ray diffraction measurements clearly show that ZnO nanorods were grown epitaxially with homogeneous in-plane alignment as well as a c-axis orientation. More importantly, from photoluminescence spectra of the nanorods strong and narrow excitonic emission and extremely weak deep level emission were observed, indicating that the nanorods are of high optical quality. (C) 2002 American Institute of Physics.open1110681105sciescopu