ZnO Nanotapered Arrays With Successively Modulated Sharpness Via a Supersaturation-Controlled Hydrothermal Reaction for Efficient Field Emitters

ZnO nanotapered arrays (NTAs) with successively modulated sharpness have been successfully demonstrated by a novel supersaturation-controlled hydrothermal method in zinc-NH3 center dot H2O system. The filament-like, needle-like, sword-like, and pagoda-like ZnO NTAs with cone angle ranging from similar to 0 degrees, 4.9 similar to 1.5 degrees, 20.4 +/- 3.7 degrees to 63.7 +/- 2.5 degrees can be obtained in an early supersaturated solution with different supersaturation level. The field emitter based on the sharper ZnO NTAs exhibits more excellent field emission (FE) performance. The sword- like emitter with cone angle of about 20 degrees presents the most excellent FE performance with low turn-on electric field of 1.5 V.mu m(-1), low threshold voltage of 3.0 V.mu m(-1), a field enhancement factor of up to 9656 and stability for 60 min. The emitter with the smallest cone angle of about 4.9 degrees shows abnormal performance degradation due to joule heating generated tip-melting phenomenon. Accordingly, the field emitter with proper sharpness is beneficial to FE devices for high efficiency. Our study provides an effective method and throws new light for performance optimization in flat panel displays and electronic devices.