Figure 1

Crystal structures of ZnO.

(a), Schematics of different growth modes and structural models of the polar and the non-polar surfaces without and with Ga atoms replacing surface Zn atoms. The red, blue and yellow-brown spheres indicate O, Zn and Ga atoms, respectively. (b), Optical microscope images of ultra-long ZnO wires grown by using ZnO powder mixed with a GaAs wafer as a source material. (c, d,) The SAED pattern (c) and EDS elemental mapping (d) taken from the same sample, which confirm that the wire is the wurtzite structured ZnO. (e–g), High-magnification SEM images of representative ZnO wires grown by changing the weight ratio of ZnO to GaAs sources with 20 (e), 5 (f) and 2 (g), respectively. (h), Micro-Raman spectra of a single ZnO wire with the non-polar growth direction. Additional local vibration modes, derived essentially from host lattice defects induced by dopants, were clearly observed. This indicated that Ga atoms are indicated into ZnO wires. i, FE-AES survey spectra obtained from the near surface (rectangular region marked as “A”) and centre (rectangular region marked as “B”) with a single wire.