dc.description.abstract | In the present study, we have demonstrated that large-area, length-tunable arrays of vertically aligned Si nanowire were successfully produced on (001)Si and (111)Si substrates by using the PS nanosphere lithography combined with the Au-assisted selective chemical etching process. The diameter of the Si nanowire produced was very uniform and observed to be approximately 120 nm. Based on the analyses of the TEM image and the corresponding SAED patterns, it can be concluded that the Si nanowires produced have single-crystalline nature and form along the [001] and/or [111] directions. In order to further modulate the morphologies of the Si nanowires, a post wet etching process with a dilute KOH solution was developed. In this work, the tapering process was performed at 20℃ for various etching time. The length and width of Si nanowires can be controlled and reduced by adjusting the KOH etching duration. After appropriate KOH etching, the diameter of the Si nanowire tips can be reduced from 120 nm to about 12 nm. Field emission measurements showed that the KOH-etched Si nanowires exhibited significantly improved field emission properties compared to the as-produced Si nanowires. In the study, a low turn-on field of 1.21 V/μm was obtained, and the corresponding field enhancement factor, β value, was greatly enhanced to as high as 8127.
For the gas sensing experiments, three kinds of samples, blank-Si wafer, Si nanowires, and porous Si nanowires, were prepared and used as the gas sensing in this study. Their gas sensing properties towards water vapor, ethanol, and acetone were investigated at room temperature. The measurement results clearly show that the response magnitudes of the three kinds of sensors improved significantly with increasing the gas concentrations. Whether exposed to water vapor, ethanol, or acetone, the sensitivity of the porous Si nanowires sensor is much higher than that of the blank-Si and Si nanowires sensors. In this work, the sensitivity of the porous Si nanowires sensor reaches as high as 9.7% for 11 ppm acetone. The enhanced sensing performances of the porous Si nanowires sensor can be attributed to its high surface-to-volume ratio.
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