Surface Zn enrichment induced by excimer laser annealing in ZnO nanorods

ZnO nanorods (NRs) play a crucial role in the manufacturing of electronic and optical devices and sensors. Using complementary techniques, we explore how their optical and conductive performances can be improved by Excimer Laser Annealing (ELA) at 75 and 100 mJ/cm2. Our data show that ELA induces the melting and re-crystallization of the NRs surface, resulting into the reduction of the average crystallite size and lattice parameter of the system and suggesting a partial transition towards metallic Zn. The increase of Zn and the removal of oxygen defects at the surface are compatible with photoelectron spectroscopies (UPS and XPS) data and explain the enhancement of the UV/visible emission ratio observed in photoluminescence. The ELA also affects the in-plane electrical conductivity: the carriers mobility improves up to 4 times depending on the laser energy density. Our results demonstrate that ELA is effective in tuning the surface properties of ZnO NRs affecting the Zn concentration at the surface and removing some oxygen defects. The combination of these two effects results into the improvement of the optical and electrical responses of the systems.