1. Condensed-Matter Physics & Materials Science Seminar

    "Low-dimensional Ordering in Nano-structured Materials"

    Presented by Professor Milan K. Sanyal, Saha Institute of Nuclear Physics, India

    Tuesday, November 5, 2013, 11 am
    Large Seminar Room, Bldg. 510

    Hosted by: Doon Gibbs and Peter Johnson

    Ordering of materials and associated structures of electrons can now be probed with desired accuracy to test theoretically predicted properties of one- and two- dimensional physics. We shall discuss here results of a series of synchrotron x-ray and electronic transport measurements of nano-structured materials to understand these ordering processes. Recently it was observed by electron microscopy studies that in Si-Ge superlattices at relatively low growth temperatures (<400°C), surprisingly large-length scale inter-diffusion of Ge occurs in Si layers provided the Ge layer thickness is kept in between 22 to 38…. This enigmatic inter-diffusion leads to the formation of Ge quantum-huts within Si sub-layer below the Ge wet-layer with apex pointing down towards Si substrate. We shall discuss here results of systematic anomalous x-ray scattering studies to develop an understanding of the growth process of these "quantum inverted huts" (QIH) structures embedded in silicon sub-layers of Si-Ge superlattice. The results presented here clearly show that the deposited Ge layer relaxes strain by uniform intermixing with the previously deposited lower Si layer to form a Si0.6Ge0.4 alloy wet-layer as in the low temperature growth(<400°C) in-plane diffusion is hindered. Our results also show that formation of zero-strain alloy by inter-diffusion over large-scale (>60…) below the wet-layer is the key-feature for the formation of QIH. Photo-conducting materials are of intense importance for the development of photo-detectors and photovoltaic cells. We shall discuss a new kind of photoconduction property of polypyrrole (PPy) when it forms nanowires. We shall also discuss characterization of these nanowires by XRD, SAXS, microscopy and photoemission techniques. At low temperature these nanowires show power-law behaviour current voltage (I-V) characteristics, resistance switching at relatively high bias, nega