以原子力顯微術製作單一氧化鈦奈米線並應用於紫外光偵測

Fabrication of Single Titania Nanowires by Atomic Force Microscopy Nanomachining and its Application to Ultraviolet Light Detection

洪力揚(Li-Yang Hong)

指導教授 ： 林鶴南

國立清華大學/工學院/材料科學工程學系/碩士(2012年)

摘要

本文結合原子力顯微術奈米加工技術及光學微影技術，製作單一氧化鈦奈米線跨接於金電極的紫外光感測器。感測原理是由於氧化物半導體奈米線照射紫外光後，吸附於奈米線的表面的氧分子脫附，並造成接面蕭特基能障的降低，結果使得通過奈米線電流的上升，依此作為感測依據。
實驗中先製備長度為10微米，寬度約為100奈米，厚度50奈米的金屬鈦奈米線，並將其跨接於金電極的兩端，再以兩種不同的方式將其氧化成氧化鈦，一種是在大氣環境下加熱，另一種是利用原子力顯微術奈米氧化。之後單一氧化鈦奈米線紫外光感測器即製作完成。
紫外光感測方面，以254 nm、365 nm與白光這三種不同波長的光，分別照射感測元件，即時量測奈米線的電流在照光和未照光下的變化情況。實驗結果顯示，光響應與照射光的能量成正相關，且具有良好的波長選擇性，只對紫外光區的波長產生響應，可見光區則否，最佳的靈敏度於波長254 nm，功率3.3 mW cm-2的紫外光照射下可達12100 % 。
此研究成功以由上而下法取代一般由下而上成長的方法，製作單一氧化鈦奈米線的紫外光感測元件，克服了由下而上成長的氧化物奈米線隨機散佈無法準確定位的困難，期望以此方法也能製作其他種類的氧化物奈米線感測元件，並應用於氣體、化學和生醫感測等方面。

關鍵字

原子力顯微術 ； 奈米線 ； 紫外光偵測

並列摘要

We report on a method for the fabrication of a single titania nanowire (NW) connected with metal electrodes and its application to ultraviolet (UV) light detection. The detection mechanism is due to the desorption of oxygen molecules on the NW surface and the resultant decreasing of the Schottky barrier height at the NW/metal interface under UV illumination. Consequently, the current passing through the NW increases and can be utilized for detection.
A titanium NW with a width of around 100 nm, thickness of 50 nm and length of 10 m was first fabricated by atomic force microscopy nanomachining and lift-off, and contact electrodes were created by conventional photolithography. The NW was then oxidized by two methods: one was ambient heating and the other atomic force microscopy nano-oxidation. Then a titania NW UV photodetector was obtained.
The fabricated photodetectors were characterized by using light sources of white light and UV (254 and 365 nm at 3.3 mW cm-2) lamps. The results show that the devices do not respond to visible light and have good wavelength selectivity. The best sensitivity is around 12100% upon 254 nm light illumination.
The present work has successfully accomplished the fabrication of single titania NW UV photodetectors by a top-down approach instead of the commonly used bottom-up approaches, which have the main disadvantage of controlling the positions of the NWs. The present approach can be potentially applied to the construction of other oxide NW sensing devices.

參考文獻

2. Fan, S.-W.; Srivastava, A. K.; Dravid, V. P. Sensors and Actuators B-Chemical 2010, 144, (1), 159-163.

11. Lee, M. L.; Sheu, J. K.; Lai, W. C.; Su, Y. K.; Chang, S. J.; Kao, C. J.; Tun, C. J.; Chen, M. G.; Chang, W. H.; Chi, G. C.; Tsai, J. M. Journal of Applied Physics 2003, 94, (3), 1753-1757.

12. Chang, S. J.; Yu, C. L.; Chen, C. H.; Chang, P. C.; Huang, K. C. In Nitride-based ultraviolet metal-semiconductor-metal photodetectors with low-temperature GaN cap layers and Ir/Pt contact electrodes, 2006; AVS: 2006; pp 637-640.

17. He, J. H.; Lin, Y. H.; McConney, M. E.; Tsukruk, V. V.; Wang, Z. L.; Bao, G. Journal of Applied Physics 2007, 102, (8), 084303-4.

22. Soci, C.; Zhang, A.; Xiang, B.; Dayeh, S. A.; Aplin, D. P. R.; Park, J.; Bao, X. Y.; Lo, Y. H.; Wang, D. Nano Letters 2007, 7, (4), 1003-1009.