ZnO nanostructures formed by off-axis pulsed laser deposition

ZnO nanostructures were formed on a Si substrate by an off-axis pulsed laser deposition (PLD) system in which a substrate plane was tilted toward the plume propagation direction. Atomic force microscopy (AFM) showed islands of 20–40 nm in width. An x-ray diffraction (XRD) pattern that exhibited only the (002) ZnO peak showed that the islands observed in AFM image were well crystallized. Expansion of the optical bandgap from 3.26 to 3.47 eV at room temperature and from 3.37 to 3.57 eV at 13 K, respectively, was observed by photoluminescence (PL); the expansion is suggested to be due to the quantum size effect of the ZnO nanostructures.