The channel electron mobility of a 1D nanowire due to scattering with interfacial phonon-plasmon modes arising from the high-k dielectric material under the presence of polysilicon or metal gate is studied in this manuscript. We solved the dispersion relationship of the coupled modes and the accompanying effective scattering potential for carrier relaxation in the channel. The resulting mobility was calculated for a series of geometrical configurations with polysilicon/metal as the gate material. We found that for the polysilicon gate case the mechanism gives rise to a significantly low mobility in the low to mid electrical field range, and that wires with smaller diameter suffer more heavily. Our simulation also reveals that metal gate effectively mitigates the effect through the suppression of effective scattering field. © 2011 IEEE.