A representative SEM (Scanning Electron Microscope) image of TiO2 nanotube structure is shown Fig.1.  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.
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