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Growth of Single-Crystalline Wurtzite Aluminum Nitride Nanotips with a Self-Selective Apex Angle


  • The authors gratefully acknowledge the financial supports for this project from the National Science Council (NSC) and the Ministry of Education (MOE) in Taiwan. The authors also thank Prof. Guang-Yu Guo and Chung-Huai Chang in the Department of Physics, National Taiwan University, for technical support.


Single-crystalline, hexagonal aluminum nitride nanotips are fabricated using a vapor-transport and condensation process (VTCP) on silicon substrates with or without a catalyst layer. The resultant tips have very sharp nanoscale apexes (∼1 nm), while their bases and lengths are up to hundreds of nanometers wide and several micrometers long, respectively. It has been demonstrated that the thickness of the gold-catalyst layer plays a critical role in controlling the size of the tip; in addition, a catalyst-free growth mode has been observed, which results in lesser control over the nanotip morphology. Nevertheless, a remarkably narrow distribution of the apex angle of the nanotips, regardless of whether or not a catalyst was used in the VTCP, has been obtained. Compared with the commonly observed ridge and pyramid structures, the nanotips produced by VTCP have higher angles (∼81°) between the tilted (221) and the basal (001) planes that encase it. A mechanism for this self-selective apex angle in aluminum nitride nanotip growth is proposed.

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