Academic literature on the topic 'Multilayer Thin Films - Deposition'

Physics<br>Ph.D.<br>This thesis studies different Eu optical centers in MgS:Eu and CaS:Eu thin films produced by Chemically Controlled Pulse Laser Deposition (CCPLD) and evaluates their suitability for the development of spectral storage devices of the future. The produced thin films consist of one or more optically active layer(s), MgS:Eu, CaS:Eu or a similar material, and a corresponding ZnS capping layer that functions as a protecting barrier for the other layers and preserves their composition and integrity. Given that the synthesis of the materials used to produce the multilayer structures in this work proved a great challenge, careful attention was given to the optimization of all fabrication parameters. Mass Spectrometry was used during the deposition of the thin films and the data obtained resulted on improvements and optimization of the deposition process. Scanning electron microscopy studies of these thin films were conducted to study degradation upon long-term storage. Microscopy results show that the morphology of the produced thin films is correlated to the growth environment during deposition and deterioration of the deposited materials could be initiated by nano-gaps and cracks in the capping layer of the thin films. In addition to optical centers in MgS:Eu and CaS:Eu, new centers were created by changing the thin film growth environment inside a hi-vacuum chamber, modifying the composition of the ablation target material, or both. For example, introducing O2, or alternatively HCl, inside the CCPLD chamber while producing MgS:Eu thin films results in the formation of impurity associated centers across lattice sites throughout the deposited structures. In another method of impurity doping studied, Cl- and Na+ were introduced into the MgS:Eu and CaS:Eu lattices by mixing trace amounts of the impurity ions into these materials in polycrystalline form and making this mixture a deposition target by hi-pressure cold compression technique. The introduction of these impurity ions will alter the crystal field environment around the Eu ions thus creating new optical centers with a shift in energy of their characteristic Zero Phonon Line. After extensive characterization of the optical properties of the thin films produced, laser-induced fluorescence spectroscopy and absorption spectroscopy measurements confirm that they are suitable candidates to be used in conjunction with power-gated spectral holeburning technique and could potentially provide ultrahigh, terabits per square inch, storage densities.<br>Temple University--Theses

This thesis investigates the use of pulsed laser deposition (PLAD) for the preparation of metallic films and magnetic multilayers. Initial work focuses on the effects of the laser wavelength and the laser pulse temporal profile on the deposition rates of nickel and silver and the droplet numbers deposited on to films. The results show that the deposition of silver films is affected by the sputtering of material from the substrate by energetic ions in the plasma and that this leads to saturation of the deposition rate at high fluences. The saturation features are not as pronounced in nickel deposition rates. We see that droplet numbers are only weakly dependent upon the laser wavelength, with fewer being present at shorter wavelengths. The effect that the number of pulses has on droplet numbers is also investigated. In the case of the pulse profile study more droplets were observed on films deposited using the picosecond (ps) pulse profiles. As for the nanosecond (ns) pulse profile the saturation in the deposition rates was observed in silver but not in nickel. The results of the ps laser pulse profiles showed that the ns background was dominant in the ablation process. Two further investigations into reducing droplet numbers were performed. These showed that a uniform beam profile was not sufficient for eliminating droplets from the PLAD process and that the use of a tape target in conjunction with a ps pulse profile did not reduce droplet numbers either. The aims of the second section of this thesis were to assess the suitability of PLAD for depositing multilayers and obtain PylPt multilayers showing a sensitive giant magnetoresistance (GMR) effect at low applied magnetic field. Samples prepared by two PLAD systems and by RF sputtering were compared. An anisotropic magneto resistance effect was measured, however GMR was not. The multilayer structures were characterised using x-ray reflectivity and cross sectional transmission electron micrographs. The results showed greater uniformity in the layers deposited by sputtering than PLAD.