TiO₂ nanotubes have emerged as potential building blocks in nanostructured solar cells and photocatalytic devices, but the improvement of their crystalline quality and morphological control still requires further development. We report an original fabrication process to form open-ended TiO₂ nanotubes in the framework of the positive template-assisted growth using ZnO nanowires. The process involves the combination of atomic layer deposition with a postdeposition thermal treatment in air at a moderate temperature to crystallize an amorphous TiO_x layer into a soluble, cubic-Zn₂TiO₄ shell on the top face of ZnO nanowires and an insoluble, anatase-TiO₂ shell with large-sized domains on their sidewalls. The differential crystallization process originates from the differential reactivity on the polar c-plane and nonpolar m-plane surfaces of ZnO nanowires, further enhanced by the different thickness of the amorphous TiO_x layer. Following chemical etching, open-ended TiO₂ nanotubes exhibit a hexagonal shape and high crystalline quality with sharp, well-oriented walls. These findings open the way for integrating high-quality open-ended TiO₂ nanotubes with tunable length and wall thickness on a wide range of substrates. The present approach can further be developed to form other types of nanotubes and original nanowire heterostructures with highly localized, distinct phases for the shell using one simple thermal treatment.

中文翻译：

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使用原子层沉积法进行模板辅助生长的六角形开口式TiO ₂纳米管

TiO ₂纳米管已成为纳米结构太阳能电池和光催化装置中潜在的构建基块，但是其晶体质量和形态控制的改善仍需要进一步发展。我们报告的原始制造工艺，以使用ZnO纳米线在正模板辅助生长的框架内形成开放式TiO ₂纳米管。该工艺涉及在室温下在空气中进行原子层沉积与沉积后热处理的组合，以将无定形TiO _x层结晶成ZnO纳米线顶面上的可溶立方体Zn ₂ TiO ₄壳和不溶锐钛矿。 -TiO ₂壳在侧壁上具有大尺寸畴。差异结晶过程源于ZnO纳米线的极性c平面和非极性m平面上的差异反应性，并通过不同厚度的非晶TiO _x层进一步增强。经过化学蚀刻后，开放式TiO ₂纳米管呈现出六边形的形状，并具有清晰，定向良好的壁，具有较高的晶体质量。这些发现为整合高质量开放式TiO ₂开辟了道路在各种基材上具有可调长度和壁厚的纳米管。使用一种简单的热处理，可以进一步发展本方法以形成具有高度局部化，不同相的壳的其他类型的纳米管和原始纳米线异质结构。