Raman study of activated quasi-modes due to misorientation of ZnO nanowires

We present Raman scattering study of wurtzite ZnO nanowires deposited by metal–organic chemical vapor deposition (MOCVD) on (0001) sapphire. It is shown that the misorientation of the nanowires, i.e. the inclination with respect to the vertical direction, mixes A1 and E1 Raman modes, giving rise to new modes for which the propagation directions make various angles with the C-axis of ZnO nanowires. Two particular bands depending on the tilt of the nanowires are observed at 400 and 585 cm−1. They are attributed to TO and LO quasi-phonons, and explained using Loudon's model. Morphological information of the nanowires was extracted and an average orientation of nanowires is calculated.

Highlight
► The disorientation of the NWs mixes A1 and E1 Raman modes, giving rise to new modes.
► The new modes are attributed to TO and LO quasi phonons.
► A correlation between q-LO and q-TO modes on ZnO nanowires was done.
► An average orientation of NWs is calculated using Loudon's model.
► The effect of NWs disorder on the Raman mode at 331 cm−1 (E22–E21) is discussed.