Doctor of Philosophy (PhD)
Physics and Astronomy
Heteroepitaxial nanostructures have a diverse array of applications and show novel phenomena that arise from the exotic physics exhibited in reduced dimensions. We have investigated two nano-structured systems in order to gain insights into the dynamics of their nucleation, growth and have observed striking differences, due in part to a competition between lattice strain, surface and interfacial free energies. When Ag is deposited on clean, single-crystal Cu(110), it initially wets the surface with a (111) monolayer, and spontaneously nucleates nanowires as the coverage is increased. The nanowires nucleate at defects and step edges and grow aligned along the [1–10] direction. In the initial stages of growth, they extend from step edges onto the lower terrace but as their height increases they extend along on the upper terrace as well, growing ~10nm wide and ~2.5nm high. The growth rate for any particular nanowire is found to be nearly independent of its separation from nearby nanowires, indicating that surface diffusion is facile. At elevated temperature (T > ~700K) and in the absence of the Ag flux, the nanowires Ostwald ripen into larger nanobars with widths of 400-800nm where surface adatom diffusion results in the disappearance of smaller nanowires. Collective excitation of the electron gas within these nanowires reflects their distinct quasi-1D structural anisotropy. The dispersion of Ag plasmons has been obtained and along the nanowire axis we find that the plasmon dispersion is linear with momentum transfer and remains constant beyond 0.3/Å. No dispersion is found for the plasmon perpendicular to the nanowire axis, reminiscent of the localized Mie resonance found in clusters. In distinct contrast to Ag grown on Cu(110), where the surface free energy of Ag is smaller than that of the substrate, the structures formed when Co is grown on Ag(110) arise due to the larger surface free energy of the adsorbate. Co prefers to cluster, and grows in the form of nanodots ~0.6nm high and ~2.5nm wide, embedded in Ag to minimize its energy. Upon annealing the Co nanodots sinter and agglomerate and into super-clusters while a portion migrates into the Ag bulk.
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Senevirathne, Indrajith Chandima, "Growth and properties of metal-on-metal nanostructures: Ag on Cu(110) and Co on Ag(110)" (2008). LSU Doctoral Dissertations. 87.
Phillip P. Strunger