Size dependence of electron-phonon coupling in ZnO nanowires

Raman spectra of ZnO powder and free-standing nanowires prepared by laser ablation have been studied. All observed vibrational modes in ZnO powder, both first order and higher order scattering, were assigned on the basis of group theoretical analysis. The size dependence of the coupling strength between electron and longitudinal optical (LO) phonon was experimentally estimated. It was found that the coupling strength determined by the ratio of second- to first-order Raman scattering cross sections diminishes with decreasing nanowire diameter, and the Frohlich interaction plays the main role in electron-phonon coupling in ZnO.