Surface optical phonions in gallium phosphide nanowires

Raman scattering studies of crystalline GaP nanowires reveal a strong additional peak in the first order spectrum that can be clearly assigned to surface optical (SO) phonons. The frequency of this SO peak is found to be sensitive to the dielectric constant of the surrounding medium in which the nanowire is embedded. A theory for the SO phonons in cylindrical wires is presented, the SO mode dispersion omega(q) and the experimental peak frequency are then used to predict the wavelength of the dominant Fourier component of the surface potential responsible for activating the SO mode. Interestingly, this SO phonon wavelength is found to agree with the wavelength of diameter modulation observed for some nanowires.