Impact of swift heavy ion-induced point defects on nanoscale thermal transport in ZnO

Near-surface nanoscale thermal conductivity (k) variation of ion-irradiated single-crystalline ZnO was studied by time-domain thermoreflectance. ZnO was irradiated by 710 MeV Bi swift heavy ions (SHI) in the 1010-1013 ion/cm2 fluence range to investigate the progression of radiation damage both from single ion impacts and ion path overlapping regimes. Structural characterization using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy indicated the absence of amorphization. The degradation in k was attributed primarily due to phonon scattering on point defects. The results of measured k were used to validate several models including the semi-analytical Klemens-Callaway model, and a novel hybrid modeling approach based on the Monte-Carlo code TREKIS coupled with molecular dynamics simulations which captures the effects of single ion and ion path overlapping regimes, respectively. The findings promote a novel approach to developing radiation-controlled thermally functional materials.