High-aspect-ratio TiO2 nanotubes by anodization of titanium
High-aspect-ratio TiO2 nanotubes by anodization of titanium
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DOI：
10.1002/anie.200462459
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Schmuki, P
中科院分区：
文献类型：
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作者：
Macák, JM;Tsuchiya, H;Schmuki, P
近年来，通过在铝[1,2]和硅[3,4]等材料上电化学形成自组织多孔结构而产生的纳米管材料表面引起了人们的极大兴趣。虽然科学推力通常指向阐明自组织现象的原理，但技术努力的目标是基于直接使用高表面积的应用，例如，用于传感[5,6]或受控催化，[7]利用光子晶体，[8]波导，[9]或3D排列布拉格堆叠类型反射器的光学特性高度组织化的结构可以间接用作模板[11]，用于沉积其他材料，如金属、半导体、[13]或聚合物在过去的几年里，通过电化学阳极氧化钛也形成了纳米多孔TiO2结构。[15-17]虽然已经提出了几种应用[18,19]，但由于这些层只能生长到几百纳米的极限厚度，这些结构的广泛影响受到了阻碍。在这里，我们首次展示了如何通过调整钛阳极化过程中的电化学条件来生长高光谱、自组织的TiO2薄膜。图1显示了在含有0.5 wt.% NH4F的1m (NH4) 2SO4电解质中形成厚度约2.5 μm的自组织多孔氧化钛的扫描电镜（SEM）图像。从SEM图像中可以看出，自组织的规则孔结构由均匀孔径约为100 nm，平均间距为150 nm的孔阵列组成。同样清楚的是，孔口在层的顶部是打开的，而在结构的底部，由于存在约50纳米厚的TiO2阻挡层，管是关闭的。实现高宽高比生长的关键是通过在孔底进行局部酸化来调节TiO2的溶解速率，同时在孔壁和孔口处保持保护环境。在我们之前对HF和NaF溶液的研究中[15,20]，我们确定了多孔层的厚度本质上是TiO2在孔底的电化学形成与TiO2在含有FÀ离子的溶液中的化学溶解之间平衡的结果（图2）。TiO2在
Nanotubular material surfaces produced by the electrochemical formation of self-organized porous structures on materials such as aluminum [1, 2] and silicon [3, 4] have attracted significant interest in recent years. While scientific thrust is often directed towards the elucidation of the principles of the self-organization phenomena, technological efforts target applications based on the direct use of the high surface area, for example, for sensing [5, 6] or controlled catalysis,[7] exploit the optical properties in photonic crystals,[8] waveguides,[9] or in 3D arranged Bragg-stack type of reflectors.[10] The highly organized structures may be used indirectly as templates [11] for the deposition of other materials such as metals,[12] semiconductors,[13] or polymers.[14] Over the past few years, nanoporous TiO2 structures have also been formed by electrochemical anodization of titanium.[15–17] Although several applications have been proposed,[18, 19] a wider impact of these structures has been hampered by the fact that the layers could only been grown to a limiting thickness of a few hundreds of nanometers.Herein we demonstrate for the first time how high-aspectratio, self-organized, TiO2 films can be grown by tailoring the electrochemical conditions during titanium anodization. Figure1 shows scanning electron microscope (SEM) images of self-organized porous titanium oxide formed to a thickness of approximately 2.5 μm in 1m (NH4) 2SO4 electrolyte containing 0.5 wt.% NH4F. From the SEM images it is evident that the self-organized regular porous structure consists of pore arrays with a uniform pore diameter of approximately 100 nm and an average spacing of 150 nm. It is also clear that pore mouths are open on the top of the layer while on the bottom of the structure the tubes are closed by presence of an about 50-nm thick barrier layer of TiO2. The key to achieve high-aspect-ratio growth is to adjust the dissolution rate of TiO2 by localized acidification at the pore bottom while a protective environment is maintained along the pore walls and at the pore mouth. In our previous work in HF and NaF solutions [15, 20] it was established that the thickness of the porous layer is essentially the result of an equilibrium between electrochemical formation of TiO2 at the pore bottom and the chemical dissolution of this TiO2 in an FÀ ion containing solution (Figure 2). The solubility of TiO2 in