| Summary: | 碩士 === 國立中山大學 === 電機工程學系研究所 === 103 === In this thesis, the PNPN heterojunctions with three-dimensional nanodendrite structure were developed for ethanol sensing applications. Firstly, the p-type silicon substrates were etched into nanorods structure by immersing in a mixture of chemical solution. The solution is composed of silver nitrate (AgNO3) and hydrofluoric acid (HF). Next, a zinc oxide (ZnO) film was deposited on the Si nanorods as a seed layer by RF sputtering system. Hydrothermal method was used immediately for growing ZnO nanowires. Copper oxide (CuO) and ZnO thin film were deposited sequentially also by sputtering on the surface of the ZnO nanowires. Once again, a second hydrothermal method was utilized to produce more branches of ZnO nanowires. Finally, the aluminum (Al) electrodes were deposited on the top and the bottom of the Si-NR/ZnO-NW/CuO/ZnO-NW (PNPN) heterojunctions to complete the sensing devices.
Nanodendrite structure has a larger response area, which can enhance the sensing ability. These structures were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM) for the crystallinity, morphology and thickness. The characteristics of the materials were analyzed and discussed for the optimal device parameters. Different etching times and different seed layer sputtering times were investigated for comparing their sensing performances.
According to the experimental results, the all planar device Si/ZnO/CuO/ZnO has only 25% of sensitivity. On the other hand, the device with nanodendrite structure is effectively raised to 90%. The response and recovery times are shortened to 16 s and 40 s, respectively. The large surface to volume ratio of the nanostructure enhances the sensing ability of the device to ethanol gas. It has a great potential for applying into industrial security and prevention of drunk driving.
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