Transparent highly ordered TiO2 nanotube arrays via anodization of titanium thin films
Transparent highly ordered TiO2 nanotube arrays via anodization of titanium thin films
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DOI：
10.1002/adfm.200500096
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发表时间：
2005-08-01
影响因子：
19
通讯作者：
Grimes, CA
中科院分区：
文献类型：
--
作者：
Mor, GK;Varghese, OK;Grimes, CA
通过射频 (rf) 溅射沉积制备的 400 nm 至 1000 nm 厚的钛薄膜在含有乙酸和氢氟酸的电解液中进行阳极氧化，形成高度有序的二氧化钛纳米管阵列的光学透明薄膜。在固定电位下实时监测阳极氧化电流，可在不干扰结构的情况下可控地消除氧化钛纳米管阵列下方的钛层。对于实现透明纳米管阵列薄膜至关重要的制造变量包括阳极氧化的初始非晶纳米管阵列的退火温度和钛薄膜溅射沉积变量，包括速率、薄膜厚度和基板温度。对透明纳米管阵列的结构研究表明，即使在 500 摄氏度退火后，也仅存在锐钛矿相。相比之下，在纳米管下方具有金属层并在高于 430 摄氏度的氧气环境中退火的薄膜中观察到金红石相和锐钛矿相。随着退火过程中发生金属氧化，金红石生长发生在纳米管-金属界面处。透明纳米管阵列薄膜在紫外-可见光范围内的平均折射率为1.66，计算孔隙率为67%；带隙确定为 3.34 eV，带隙尾延伸至 2.4 eV。
Titanium thin films, 400 nm to 1000 nm thick, fabricated by radio frequency (rf) sputter deposition are anodized in an electrolyte containing acetic acid and hydrofluoric acid to form optically transparent films of highly ordered titania nanotube arrays. Real-time monitoring of the anodization current, at a fixed potential, is used to controllably eliminate the Ti layer underneath the titanium oxide nanotube array without disturbing the architecture. Fabrication variables critical to achieving the transparent nanotube-array film include annealing temperature of the anodized, initially amorphous nanotube array and Ti-film sputter deposition variables, including rate, film thickness, and substrate temperature. Structural investigations on the transparent nanotube arrays reveal only the presence of the anatase phase even after annealing at 500 degrees C. In contrast, both rutile and anatase phases were observed in films with a metal layer underneath the nanotubes and annealed in an oxygen ambient above 430 degrees C. Rutile growth occurs at the nanotube-metal interface as metal oxidation takes place during annealing. The average refractive index of the transparent nanotube-array film is found to be 1.66 in the UV-vis range, with a calculated porosity of 67 %; the bandgap is determined as 3.34 eV, with a bandgap tail extending to 2.4 eV.