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Open AccessArticle

In Situ Raman Investigation of TiO2 Nanotube Array-Based Ultraviolet Photodetectors: Effects of Nanotube Length

1
School of Chemistry and Life Science, Advanced Institute of Materials Science, Changchun University of Technology, Changchun 130012, China
2
College of Chemical Engineering, Changchun University of Technology, Changchun 130012, China
3
Jilin Provincial Center for Disease Control and Prevention, Changchun 130062, China
*
Author to whom correspondence should be addressed.
Academic Editors: Gavino Sanna and Barbara Bonelli
Molecules 2020, 25(8), 1854; https://doi.org/10.3390/molecules25081854
Received: 20 March 2020 / Revised: 8 April 2020 / Accepted: 15 April 2020 / Published: 17 April 2020
TiO2 nanotube arrays (TNAs) with tube lengths of 4, 6, and 7 μm were prepared via two-step anodization. Thereafter, ultraviolet (UV) photodetectors (PDs) with Au/TiO2/Au structures were prepared using these TNAs with different tube lengths. The effects of TNA length and device area on the performance of the device were investigated using in situ Raman spectroscopy. The maximum laser/dark current ratio was achieved by using a TNA with a size of 1 × 1 cm2 and a length of 7 μm, under a 532 nm laser. In addition, when the device was irradiated with a higher energy laser (325 nm), the UV Raman spectrum was found to be more sensitive than the visible Raman spectrum. At 325 nm, the laser/dark current ratio was nearly 24 times higher than that under a 532 nm laser. Six phonon modes of anatase TNAs were observed, at 144, 199, 395, 514, and 635 cm−1, which were assigned to the Eg(1), Eg(2), B1g(1), A1g/B1g(2), and Eg(3) modes, respectively. The strong low-frequency band at 144 cm−1 was caused by the O-Ti-O bending vibration and is a characteristic band of anatase. The results show that the performance of TNA-based PDs is length-dependent. Surface-enhanced Raman scattering signals of 4-mercaptobenzoic acid (4-MBA) molecules were also observed on the TNA surface. This result indicates that the length-dependent performance may be derived from an increase in the specific surface area of the TNA. In addition, the strong absorption of UV light by the TNAs caused a blueshift of the Eg(1) mode. View Full-Text
Keywords: TiO2 nanotube arrays; UV photodetector; Raman spectroscopy; Surface-enhanced Raman scattering; SERS TiO2 nanotube arrays; UV photodetector; Raman spectroscopy; Surface-enhanced Raman scattering; SERS
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MDPI and ACS Style

Ren, Y.; Shi, X.; Xia, P.; Li, S.; Lv, M.; Wang, Y.; Mao, Z. In Situ Raman Investigation of TiO2 Nanotube Array-Based Ultraviolet Photodetectors: Effects of Nanotube Length. Molecules 2020, 25, 1854.

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