Photoluminescence and SERS investigation of plasma treated ZnO nanorods

Hydrothermally synthesized ZnO nanorods were treated with hydrogen and oxygen plasmas. We have found that the photoluminescence (PL) intensity of ZnO nanorods increases with hydrogen plasma treatment, but decreases after the subsequent treatment of oxygen plasma. There is no significant increase of PL intensity only by oxygen plasma treatment. By analyzing the components of the deep level emission band, we have concluded the plasma-induced PL intensity variation and band position shift are related to the existence of intrinsic defects in ZnO nanorods. H2 plasma reduces the concentration of oxygen vacancy or singly ionized oxygen vacancy, whereas O2 plasma increases the concentration of interstitial oxygen. The PL result is compared with surface-enhanced Raman scattering (SERS), X-ray power diffraction and scanning electron microscope characterization. We believe that plasma-induced defect formation in ZnO is also the reason responsible for the observed SERS intensity enhancement.