Synthesis of Periodically Structured Titania Nanotube Films and Their Potential for Photonic Applications

Abstract

Nanoscience and nanotechnology have attracted much interest in recent years because materials exhibit novel properties when structured at nanometer dimensions. In particular, titania (TiO 2 ) nanotubes, a unique functional material combined with directionality and dimension, have been regarded as having unlimited potential. Although many successes have already been achieved, for instance, as solar-energy materials, [1][2][3][4][5] for use in batteries, [6][7][8] and as a tool for sensing, [9][10][11] signifi cantly less research has focused on the potential of such structures for manipulating photons in terms of an optical material-"photonic crystals" (PCs)-which can open a new range of possibilities for fl exible materials synthesis and new phenomena generation.Three-dimensional (3D) PCs, which have enormous omnidirectional bandgaps, became an emerging fi eld in the 1990s, since when various synthesis approaches have been proposed and demonstrated, such as self-assembly, [12][13][14][15][16] lithography, [17][18][19] and direct laser writing. [20][21][22] However, most of these methods bear inherent limitations that may hinder their practical deployment, for instance, complicated and costly micromanipulation techniques, the limited tunability of the stop band, and the diffi culty of integration. Herein, we present a material assembly route that can bridge the gap between TiO 2 nanotubes and photonics. The main benefi t of this method for 3D PC manufacture is its high effi ciency, good quality, and continuous production, thereby promoting a new application of TiO 2 nanotubes for photon manipulation.To fabricate nanostructured TiO 2 arrays, anodization is a simple, straightforward, and self-driven approach among several synthesis strategies, [23][24][25] both on Ti foils and Ti thin fi lms. [ 26 , 27 ] For years, scientists in the realm of anodization predominantly focused on the investigation of tube synthesis under potentiostatic conditions. Anodization at a certain voltage leads to an ordered oxide layer consisting of smooth or irregular corrugated tubes in different electrolytes, [ 9 , 28 ] and such corrugated stacks show defi ned interference patterns. Proposals of the potential application of nanopores and nanotubes in 2D PCs fi rstly emerged due to their periodically aligned nature in two dimensions. [29][30][31][32][33] Recently, 3D structural TiO 2 nanotubes were made available under specifi c alternating-voltage conditions, with the attempt to create bamboo-type or multilayer nanotubes, [ 32 , 34 , 35 ] for example, for optimizing solar-cell effi ciencies. However, the complex architectures fabricated with the aid of periodic voltages are erratic, and lack the quality that PCs demand. Ordered 3D pore structures were only developed in alumina (Al 2 O 3 ) in combined mild and hard anodization processes with periodic changes in diameters in specifi c electrolyte solutions. [36][37][38] Cyclic anodizing voltages [ 39 , 40 ] have also been utilized to create periodically and partially branched Al 2 O 3 p...

TiO2 nanotube structures for the enhancement of photon utilization in sensitized solar cells

“…Chen et al first reported in 2011 the work on the potential capability of periodically structured TiO 2 NTs for photonic applications (or the so-called 1D anodic TiO 2 NT PC) [228].…”

Large-scale preparation of nanoporous TiO2 film on titanium substrate with improved photoelectrochemical performance

“…By treating the H 2 O 2 pre-oxidized Ti plate in TiCl 3 , the film displays a large-scale irregular porous structure, as shown in Figure 1E,F. Moreover, the appearance of NP-TiO 2 film is red color (as inset in Figure 1F), which is different from the normal appearance of most anodic TiO 2 nanorod or nanotube films [22]. The pores are in the sizes of 50 to 100 nm on the surface and about 20 nm inside; the walls of the pores are in the sizes of 10 nm and show continuous connections.…”

“…They possibly originated from the periodic irregular nanoporous structure. Such nanoporous structure is favorable to increase the photoresponsible performance, because the incident light that entered the porous structure would extend the interaction of light with TiO 2 and result in an enhanced absorption performance, which can be observed in other nanotube or photonic crystal structural TiO 2 films [22,23]. …”

Direct and Seamless Coupling of TiO2 Nanotube Photonic Crystal to Dye‐Sensitized Solar Cell: A Single‐Step Approach

“…A similar method using constant current pulses to obtain a periodic structure has been reported. [ 27 ] Cho Tung Yip Direct and Seamless Coupling of TiO 2 Nanotube Photonic Crystal to Dye-Sensitized Solar Cell: A Single-Step Approach normal incidence of unpolarized light, a broad peak centered at around 430 nm (purple sample in air) was observed, with maximum refl ectance of around 60% and additional features at longer wavelengths. The refl ectance spectra were strongly affected by the refractive index contrast.…”