Preparation and characterization of Tin Oxide Nanowires for gas sensing
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Preparation and characterization of Tin Oxide Nanowires for gas sensing Daihua Zhang, Zuqin Liu, Chao Li, and Chongwu Zhou1 Department of Electrical Engineering - Electrophysics University of Southern California Los Angeles, California 90089, U. S. A ABSTRACT Efficient and reliable laser-ablation approaches for large-scale synthesis of SnO2 nanowires are reported. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to confirm the crystal structure of the nanowires. The results show that these nanowires had uniform diameters around 20 nm and lengths in the order of 10 µm. In addition, field effect transistors have been constructed based on individual SnO2 nanowires. Excellent n-type transistor characteristics have been observed for SnO2 nanowire transistors. Detailed analysis revealed threshold voltages ~ -50V with on/off ratios as high as 103 at room temperature. These nanowire transistors were further demonstrated to work as sensitive UV detectors and gas sensors. INTRODUCTION Transparent conductive oxides such as In2O3, ZnO, SnO2, CdO, and Ga2O3 are interesting materials that are both electrically conductive and visually transparent [1, 2]. SnO2 and ZnO in the nanowire form have enormous potential to work as building blocks for nanoelectronics, and are also expected to offer superior chemical sensing performance due to the enhanced surface-tovolume ratios. Despite the utmost importance, only a relatively small effort has been directed toward the synthesis of SnO2 and ZnO whiskers, nanorods and more recently nanobelts [3-5]. Much is left to be explored, especially for the synthesis of high-quality, single-crystalline SnO2 with precisely controlled diameters below 30 nm, as required for high-performance field-effect nanowire transistors. In this paper, we report an efficient and reliable laser-ablation approach for large-scale synthesis of SnO2 nanowires. Precise control over the nanowire diameters has been achieved by using monodispersed gold clusters as the catalyst. Detailed material analysis such as transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to confirm the single-crystalline nature of our nanowires. In addition, field effect transistors (FETs) have been constructed based on individual SnO2 nanowire with on/off ratios up to 103. These nanowire transistors were further demonstrated to work as sensitive UV light detectors. EXPREIMENTAL DETAILS Tin oxide nanowires were prepared by using a pulsed Nd:YAG laser with a repetition rate of 10 Hz and a pulse power of 1.0 W. A pure Sn (Alfa Aeser, 99.995%) target were mounted at the upper-stream of a quartz tube furnace and then ablated to supply the vapor, which was carried downstream by diluted oxygen in argon. SiO2/Si substrates coated with Au nanoparticles
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were placed at the downstream of the tube furnace with the Au particles serving as the catalyst for growth. The reaction was typically carried out around 900˚C for ten to thirty minutes with 100 sccm Ar/O2 mixture flowing. The chamber press
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