• Admin
    UC Research Repository
    View Item 
       
    • UC Home
    • Library
    • UC Research Repository
    • College of Science
    • Science: Theses and Dissertations
    • View Item
       
    • UC Home
    • Library
    • UC Research Repository
    • College of Science
    • Science: Theses and Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of the RepositoryCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

    Statistics

    View Usage Statistics

    Studies of Alloy Nanoclusters and Their Influence on Growth of Carbon Nanotubes

    Thumbnail
    View/Open
    Thesis_fulltext.pdf (14.83Mb)
    Author
    Belic, Domagoj
    Date
    2012
    Permanent Link
    http://hdl.handle.net/10092/6401
    Thesis Discipline
    Physics
    Degree Grantor
    University of Canterbury
    Degree Level
    Doctoral
    Degree Name
    Doctor of Philosophy

    In this work we examine Ag-Au and Ni-Cu nanoclusters: their structural,compositional, and morphological characteristics are investigated in detail. The clusters are produced by the inert gas aggregation (IGA) method from magnetron sputtered alloy targets, in an UHV compatible system. The design of the system is optimized for production and deposition of the clusters with size in the range 5 nm < D < 10 nm. In order to increase the flux of sub-5 nm clusters in the system, we conducted modeling and experimental studies of cluster motion: the simulations showed that skimmers with wider internal angles might significantly improve the flux of smaller nanoclusters; however, the experimental study revealed a major influence of the background gas on scattering of such nanoclusters which consequently led to the loss of their flux. A comprehensive study of Ag0:85Au0:15 nanoclusters was conducted over a period of more than 2 years. Nanoclusters with sizes in the range 3 nm < D < 10 nm were deposited onto a-C films at various surface coverages and systematically investigated by transmission electron microscopy. We found that Ag-Au nanoclusters initially exhibited icosahedral and decahedral structural motifs, with a very small fraction of face centered cubic nanoclusters present. This may suggest that the source conditions used in the experiments (primarily Ar flow) left Ag-Au nanoclusters kinetically trapped in structures which correspond to local thermodynamic minima, rather than global energetically favoured atomic configurations. When left exposed to ambient conditions, over time Ag-Au nanoclusters exhibited structural, morphological, and compositional changes: core-shell and Janus nanoclusters were observed in aged samples, as well as fragmentation of bigger particles. We attribute these changes to oxidation of the Ag component and increased diffusion of Ag₂O over the substrates. The final morphology of aged nanocluster-based thin films is governed by a combination of diffusion, Ostwald ripening, and the Plateau-Rayleigh instability. High resolution transmission electron microscopy confirmed the presence of fivefold symmetric structures in Ni-Cu nanoclusters; however, their higher oxidation rate may have influenced the structures from the outset. In addition, when these nanoclusters were exposed to the electron beam, crystalline artifacts (nanochimneys)started to grown on them, with a structure corresponding to the NiO structure. Ni-Cu nanoclusters are subsequently used as catalysts in a pilot study of carbon nanotube synthesis which confirmed that such alloy nanoclusters are catalytically active for single-wall and multi-wall carbon nanotube growth.

    Subjects
    nanocluster
     
    nanoalloy
     
    nanotube
     
    AgAu
     
    NiCu
    Collections
    • Science: Theses and Dissertations [3449]
    Rights
    https://canterbury.libguides.com/rights/theses

    UC Research Repository
    University Library
    University of Canterbury
    Private Bag 4800
    Christchurch 8140

    Phone
    364 2987 ext 8718

    Email
    ucresearchrepository@canterbury.ac.nz

    Follow us
    FacebookTwitterYoutube

    © University of Canterbury Library
    Send Feedback | Contact Us