Synergistically enhanced ultraviolet emission of Yb doped ZnO films by using a capping of ultrathin Al and SiO2 microspheres.

We studied the enhancement effects of ultraviolet (UV) emission from rare earth ytterbium (Yb) doped ZnO films, by using capping layers of Al and SiO2 micro-spheres. The films were deposited on Si substrates with magnetron sputtering followed by high temperature (∼1000°C) heat treatment, and then capped with a nanoscale ultrathin aluminum (Al) layer and/or SiO2 micro-spheres on the surface of the films. The photoluminescence (PL) results indicate that compared to the case without any capping, the UV emission is enhanced by a factor ranging from several to dozens times, the films capped with 2.0 nm Al layer and 5.0 µm SiO2 microspheres have the longest highest PL intensity among the samples. The PL enhancements are discussed in terms of increased optical (or electrical) fields around the surface of the films combined with defect passivation after the capping. Our work has proposed a strategy to enhance the UV emissions of ZnO, which will broaden the application potential of ZnO in UV photonics.

Evolution of vibrational modes of SiO2 during the formation of Ge and Si nanocrystals by ion implantation and magnetron sputtering.

Structural variations of SiOx matrix have been studied with Fourier Transform Infrared Spectroscopy (FTIR) during the formation of Si and Ge nanocrystal. Two frequently used methods, magnetron sputtering and ion implantation have been employed to form SiOx matrix containing excess Si and Ge. The Si-O-Si stretching mode has been deconvoluted to monitor the evolution of SiOx films during the annealing process. The integrated area and the shift in the SiOx peak positions are found to be well correlated with the change of the film stoichiometry and nanocrystal formation. It is shown that the nonstoichiometric SiOx matrix turns into stoichiometric SiO2 as the excess Si and Ge atoms precipitate to form nanocrystals. This process takes place at much lower temperatures for Ge than Si for both ion implantation and magnetron sputtering. FTIR technique is shown to be useful to study the matrix hosting nanocrystals to monitor nanocrystal formation.

Structural and optical properties of ge nanocrystals embedded in Al2O3.

Ge nanocrystals (NCs) embedded in aluminum oxide were grown by RF-magnetron sputtering. Raman, high resolution transmission electron microscopy (HRTEM), selected area diffraction (SAD), and X-ray diffraction (XRD) techniques confirmed good cristallinity of the NCs from samples annealed at 800 degrees C. The average NC size was estimated to be around 7 nm. Photoluminescence (PL) measurements show an emission related to the NCs. The temperature dependence of the PL confirms the confinement phenomenon in the Ge NCs.