Self-gating effect induced large performance improvement of ZnO nanocomb gas sensors.

Much greater surface-to-volume ratio of hierarchical nanostructures renders them with promising potential for high performance chemical sensing. In this work, crystalline nanocombs were synthesized via chemical vapor deposition and fabricated into resistive gas sensors. Particularly, NO2 sensing performance of these devices has been systematically characterized, showing higher sensitivity as compared to their nanobelt counterparts. Through device simulation, it was discovered that the teeth part of a nanocomb could serve as a "negative-potential gate" after accumulating electrons captured by surface adsorbed NO2 molecules. This self-gating effect eventually results in a greater reduction of nanocomb device channel conductance upon NO2 exposure, as compared to a nanobelt device, leading to a much higher NO2 detection sensitivity. This study not only sheds light on the mechanism of performance enhancement with hierarchical nanostructures, but also proposes a rational approach and a simulation platform to design nanostructure based chemical sensors with desirable performance.