Structural and Optical Characterizations of Electrochemically Grown Connected and Free-Standing TiO2 Nanotube Array

Abstract

A TiO2 nanotube array was grown electrochemically by using single and mixed electrolyte/s with 20 V constant potential at room temperature. Anodization was carried out for 120 min using five different electrolytes, e.g., H3PO4, NH4F, HF, NH4F with H3PO4 and HF with H3PO4. Structural characterizations of the grown titania nanotubes were conducted by using x-ray diffraction and field emission scanning electron microscopy. Optical properties of the grown nanotubes were investigated through photoluminescence (PL) spectroscopy. In the case of the 4 M H3PO4 electrolyte, no perceptible growth of nanotubes was observed. The individual electrolytes of 0.3 M NH4F and 1 M HF resulted into the formation of the wall-connected nanotubes. In contrast, the mixed electrolytes comprising the strong (NH4F, HF) and weak (H3PO4) electrolytes have been found to be efficient for the growth of wall-separated titania nanotubes. The results of the PL spectroscopy have demonstrated that the free-standing nanotubes offer low PL intensity compared to its connected counterpart owing to the lower carrier recombination rate of free-standing nanotubes.