Abstract
Highly ordered TiO2 nanotube arrays (NTAs) on Si substrate possess broad applications due to its high surface-to-volume ratio and novel functionalities, however, there are still some challenges on facile synthesis. Here, we report a simple and cost-effective high-field (90–180 V) anodization method to grow highly ordered TiO2 NTAs on Si substrate, and investigate the effect of anodization time, voltage, and fluoride content on the formation of TiO2 NTAs. The current density–time curves, recorded during anodization processes, can be used to determine the optimum anodization time. It is found that the growth rate of TiO2 NTAs is improved significantly under high field, which is nearly 8 times faster than that under low fields (40–60 V). The length and growth rate of the nanotubes are further increased with the increase of fluoride content in the electrolyte.Graphical Highly ordered TiO2 nanotube arrays (NTAs) on Si substrate have been fabricated by high-field anodization method. A high voltage (90–180 V) leads to a high growth rate of TiO2 NTAs (35–47 nm s−1), which is nearly 8 times faster than the growth rate under low fields (40–60 V). Furthermore, the current density–time curves recorded during the anodization provide a facial method to determine the optimal anodization parameters, leading to an easy obtaining of the desired nanotubes.
Highlights
Based on a high-field anodization technique we previously developed [36, 37], a 938-nm-thick TiO2 nanotube arrays (NTAs) with high quality was achieved via anodizing titanium film on Si substrate at 120 V for 20 s, which is a significant improvement in growth rate
In order to remove the grains on the surface, the prepared samples were immersed into a 0.05 wt% hydrofluoride acid (HF) aqueous solution for 25 min, and the images of the immersed sample are presented in Fig. 2c, d
This may be due to the chemical dissolution of the fluoride-rich TiO2 layer between the TiO2 NTAs and substrate when exposed to HF aqueous solution for a long time [38,39,40]
Summary
Since the first report on the growth of highly ordered TiO2 nanotube arrays (NTAs) by a simple electrochemical anodization method in 1999 [1], TiO2 NTAs prepared by electrochemical anodization of titanium foil and alloys have attracted much attention in various applications, such as corrosion protection [2, 3], sensors [4,5,6], dye-sensitized solar cells [7], photocatalysis [8,9,10,11], biomedical [12, 13], and Li-ion batteries [14]. There are many reports about fabrication of TiO2 NTAs films on both conductive (ITO glass and Si) [29,30,31] and nonconductive (SiO2 and glass) substrates [27, 32,33,34] These nanotubular structures were fabricated by anodizing titanium film under low fields (10–60 V). Kim et al [27] prepared highly ordered TiO2 NTAs by anodization of as-prepared titanium films which were deposited on patterned Si substrate. Based on a high-field anodization technique we previously developed [36, 37], a 938-nm-thick TiO2 NTAs with high quality was achieved via anodizing titanium film on Si substrate at 120 V for 20 s, which is a significant improvement in growth rate. The effect of annealing temperatures on crystalline structure was examined
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