The role of barrier layer temperature in the formation of long and small-diameter TiO 2 nanotube arrays
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The role of barrier layer temperature in the formation of long and small‑diameter TiO2 nanotube arrays Vajihe Asgari1 · Mohammad Noormohammadi1 · Abdolali Ramazani1,2 · Mohammad Almasi Kashi1,2
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Small-diameter TiO2 nanotubes (TNTs) are fabricated at a fast growth rate by developing an effective anodization method in an organic electrolyte. Two different temperatures are applied to both sides of sample in order to increase the current density during the anodization process. Here, we use a high temperature for the backside of the sample (direct heating of the barrier oxide layer) in order to increase the current density while keeping the electrolyte at a low temperature to decrease the chemical etching at top of the TNT arrays. Increasing the backside temperature up to 55 °C leads to the formation of longest TNTs with an average diameter of about 17 nm at high-speed TNT growth of about 2000 nm/h under 20 V. Based on the high-field theory and accurate estimation of the barrier layer (BL) temperature, the incremental effect of increasing the BL temperature on the anodization current is also investigated. Keywords TiO2 nanotube arrays · Anodization · Growth rate · Barrier layer · High-field theory Abbreviations TNT TiO2 nanotube BL Barrier layer FE-SEM Field-emission scanning electron microscopy
1 Introduction In recent years, a great deal of attention has been attracted to self-ordered TiO2 nanotube (TNT) arrays with a high surface-to-volume ratio fabricated by titanium anodization due to their large number of applications in sensors [1], solar cells [2, 3] photocatalytic activities [4–6], and environmental purification [7]. The Ti foil anodization has been demonstrated to be a precisely controllable and facile process for synthesizing TNTs in fluoride-based baths [8, 9]. The TNT geometrical features depend strongly on anodization parameters such as electrolyte concentration, anodization voltage and electrolyte temperature [10–13].
* Mohammad Noormohammadi [email protected] 1
Department of Physics, University of Kashan, Kashan 87317−51167, Iran
Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan 87317−51167, Iran
2
It is well known that the functionality of TNTs strongly depends on their thickness and diameter. For several applications, it is more efficient to apply TNTs with small diameter due to their large specific surface area [14–16]. In general, TNTs with small diameters can be obtained at a low voltage. Lan et al. showed that TNTs with diameters between 10 and 100 nm can be generated by controlling anodization voltage [17]. However, the major problem regarding the TNTs prepared at low voltages is their limited length due to chemical dissolution effects [18]. There have been few reports regarding the improvement of the TNT growth rate at low voltages. Notably, Zhu et al. fabricated TNTs with a pore diameter of 30 ± 4 nm at 20 V, while the tube thickness was only 5.7 μm after 70 h (i.e
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