Optical properties of TiO2 nanotube arrays fabricated by the electrochemical anodization method

Ngoc Tai Ly, Van Chien Nguyen, Thi Hoa Dao, Le Hong Hoang To, Duy Long Pham, Hung Manh Do, Dinh Lam Vu and Van Hong Le

Abstract

Perpendicularly self-aligned TiO₂ nanotube samples of size of 3 × 5 cm² were fabricated by the electrochemical anodization method using a solution containing NH₄F. Influences of the technological conditions such as NH₄F concentration and anodization voltage were studied. It was found that NH₄F concentration in the solution and anodization voltage significantly affect the diameter and length of a TiO₂ nanotube. The diameter and the length of a TiO₂ nanotube were observed and estimated by using scanning electron microscopy. It has shown that the largest diameter and the longest length of about 80 nm and 20 μm, respectively, were obtained for the sample anodized in a solution containing 0.4% of NH₄F, under a voltage of 48 V. Photoluminescence spectra excited by laser lights having wavelengths of 325 and 442 nm (having energies higher and lower than the band gap energy of TiO₂) was recorded at room temperature for the TiO₂ nanotube arrays. An abnormal luminescence result was observed. It is experimental evidence that the manufactured TiO₂ nanotube array is an expected material for hydrogen splitting from water by photochemical effect under sunlight as well as for the nano solar cells