Diameter-dependent thermal transport in individual ZnO nanowires and its correlation with surface coating and defects.

A systematic study of the thermal transport properties of individual single-crystal zinc oxide (ZnO) nanowires (NWs) with diameters in the range of ∼50-210 nm is presented. The thermal conductivity of the NWs is found to be dramatically reduced by at least an order of magnitude compared to bulk values, due to enhanced phonon-boundary scattering with a reduction in sample size. While the conventional phonon transport model can qualitatively explain the temperature dependence, it fails to account for the diameter dependence. An empirical relationship for assessing diameter-dependent thermal properties is observed, which shows an approximately linear dependence of the thermal conductivity on the cross-sectional area of the NWs in the measured diameter range. Furthermore, it is found that an amorphous-carbon layer coating on the NWs does not perturb the thermal properties of the NW cores, whereas 30 keV Ga(+) ion irradiation at low dose (∼4 × 10(14) cm(-2)) leads to a remarkable reduction of the thermal conductivity of the ZnO NWs.