Highly ordered TiO₂ nanotube (NT) arrays fabricated by electrochemical anodization have shown promising potential for photocatalystic applications ^[1]. Loading metallic nanoparticles has been introduced to enhance photocatalytic activity of the TiO₂ nanotubes. However, the applications are primarily focused on silver or gold due to their strong plasmonic behaviors at visible wavelength ^[2]. As a low cost alternative, nanoparticles Al exhibit strong plasmon resonances spanning much of visible region of the spectrum as well. In this paper, we fabricated nanoparticles Al on the wall of TiO₂nanotube arrays by magnetron sputtering technique and investigated their optical characteristics.

A representative SEM (Scanning Electron Microscope) image of TiO₂ nanotube structure is shown Fig.1. ^[3] The nanoparticles Al were deposited on TiO₂ nanotubes by a radio frequency (RF) reactive magnetron sputtering system (Sputter AJA 4050). The deposition parameters were kept at pressure (4.2 mTorr), power (120 W), gas (10 sccm), stable deposition rate (0.4Å/S). The nanoparticle thin films Al have been calibrated on glass substrates and TiO₂ with thickness from 0 to 20 nm, which can be well-controlled by the sputtering time, the photographs of various nanoparticles Al on glass (22 mm × 22 mm) and TiO₂ (10 mm × 20 mm) are shown in the Fig. 2. Compared with pure TiO₂ nanotubes, the absorbance spectra (400 - 850 nm) confirms that the absorption intensity of Al/TiO₂ NTs increases with increasing the thickness of Al NPs. The 10 nm Al/TiO₂ NTs sample exhibits a broad absorption peak centered close to 550 nm in the visible light region. The enhanced visible light absorption peak is ascribed to the enhancement of localized surface plasmon resonance of nanoparticle Al. These results indicate that the photo-response of TiO₂ NTs could be easily extended to the visible-light region through the aid of nanoparticles Al (Fig. 3).

In summary, well-dispersed distribution of nanoparticles Al have been assembled on the TiO₂ NTs by RF magnetron sputtering technique. The nanoparticles Al are readily controlled with thickness from 5 to 20 nm. The visible light absorption have been systematically studied. The optimized thickness is ~10 nm, which efficiently absorb light over a broad range of wavelength.

References

[1] Z. Endut, M. Hamdi, W.J. Basirun, Supercapacitance of bamboo-type anodic titania nanotube arrays, Surf. Coat. Tech. 215 (2013) 75–78.

[2] M.W. Knight, N.S. King, Lifei Liu, H.O Everitt, P. Nordlander and N.J. Halas, Aluminum for plasmonics. ACS Nano 8 (2013) 834-840.

[3] Kang Du, Guohua Liu, Xuyuan Chen, Kaiying Wang, PbS Quantum Dots Sensitized TiO2 Nanotubes for Photocurrent Enhancement, Journal of The Electrochemical Society,162(2015) E251-E257.