Synthesis of SiO 2 Nanowires and CdS/SiO 2 Composite Nanowires and Investigation of Their Electron Field Emission Proper
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Synthesis of SiO2 Nanowires and CdS/SiO2 Composite Nanowires and Investigation of Their Electron Field Emission Properties Jun Jiao, Lifeng Dong, David W. Tuggle, Jeremy Petty, Logan Love, and Michael Coulter* Physics Department, Portland State University, Portland, Oregon 97207 *Oregon Episcopal School, Portland, Oregon 97223 ABSTRACT A thermal evaporation method was used to obtain SiO2 and CdS/SiO2 nanowires by heating Si substrates coated with a gold thin film in a quartz tube furnace. During growth, pure CdS powder was placed at the heating zone in the furnace, serving as the CdS source for the CdS/SiO2 composite nanowires. It was found that both non-porous and porous Si substrates served as the Si source for the growth of SiO2 nanowires and the CdS/SiO2 composite nanowires. It was also found that the effect of the temperature gradient in the reaction chamber plays an important role in the density distribution of different nanowires (SiO2 or CdS/SiO2 nanowires). The electron field emission properties of these nanowires were investigated using an electron field emission microscope equipped with a Faraday cup. INTRODUCTION Due to quantum confinement effect, nanostructural semiconductors are expected to show optical and electronic properties distinctive from bulk materials. Nanowires, one-dimensional nanostructures, have shown great potential for nanoscaled electronic and optoelectronic devices [1-3]. However, because of the difficulties of fabricating these nanoscale materials with controlled structural configurations, the realization of these technological promises is still a distant goal. In an effort aimed at tailoring nanowires to designed specifications, we have systematically investigated the effects of preparation parameters on the formation of ZnO nanowires [4], SiO2 nanowires, and CdS nanowires. We also studied the electron field emission properties of these nanowires in relation to their nanostructural morphologies. In this paper, we demonstrate the growth of SiO2 and CdS/ SiO2 composite nanowires by a thermal evaporation method and the investigation of their electron field emission properties. A comparison of the field emission properties between nanowires and carbon nanotubes is also discussed. EXPERIMENTAL (1) Growth of SiO2 and CdS/SiO2 Nanowires –Silicon (Si) wafer pieces were used as substrates for the growth of the nanowires. A piece of Si wafer was cut into small rectangles, which were then cleaned ultrasonically in acetone. Some of those pieces were made porous by electrochemical etching. In a 1:1 in volume of HF (48%) and ethanol solution, the Si pieces were etched for approximately 3-4 minutes with a current density of approximately 15 mA/cm2 and then cleaned thoroughly with distilled water. Both nonporous and porous Si pieces were then sputter coated with a gold thin film approximately 40 nm thick using an SEM sputter coater equipped with a gold target. The thickness of the gold thin film was controlled by the deposition time. Pure CdS powder was put on to a ceramic plate. The plate w
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