ZnO nanowire growth based on the VS mechanism (left) and by adding ionic liquids (right). Most of the non-polar ZnO NWs are a-oriented mixed with other non-polar oriented ZnO NWs.
Normalized PL spectra from (a) polar and (b) non-polar ZnO NWs averaged over a large number of nanowires. The red lines show the samples after annealing at 500 °C for 1 h in the air. The defect emission of c-oriented NWs was decreased, while the defect emission of a-oriented NWs was increased. (Please note that the peak at 440 nm and 590 nm is an artifact from the measurement setup.)
The GE and NBE recombination mechanism of (a) normal ZnO surface (b) modified surface passivated by residues of the ionic liquid. (c) The formation of an oxygen defect during the growth. The defect forms at the surface during the growth process, and later becomes an internal lattice oxygen vacancy. (d) Small ZnO NWs grown in Zn-polar c-orientation, and (e) grown in a-orientation.
(a) Image of the sensor head. CO sensing measurement result of (b) non-polar ZnO NW, and (c) polar ZnO NW. (d) CO sensitivity as a function of the CO concentration. The polar NWs have a good room temperature CO response, while non-polar ZnO NWs have no response to the change in CO concentration.
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