Browsing by Author "Assadi, MHN"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Enhancement of co substitution induced by Eu codoping in ZnO-based diluted magnetic semiconducting thin films
    (American Institute of Physics, 2010-02) Photongkam, P; Zhang, YB; Assadi, MHN; Li, S; Yu, DH; Ionescu, M; Pan, AV
    To avoid the occurrence of doped magnetic ion clustering is a challenge in fabrication of diluted magnetic semiconductors (DMSs). In this work, we report the intrinsic ferromagnetic behavior in Co-doped ZnO DMSs induced by Eu codoping. Both structural parameters and magnetic properties demonstrate the existence of an interaction between Co and Eu ions. The observation of multiplet structures for the localized Co 3d states in x-ray absorption and x-ray magnetic circular dichroism characterization evidences that the codoped Eu plays an important role in facilitating the Co substitution of Zn, leading to intrinsic ferromagnetism. © 2010, American Institute of Physics
  • No Thumbnail Available
    Item
    Immobilization of Na ions for substantial power factor enhancement: site-specific defect engineering in Na0.8CoO2
    (American Chemical Society, 2012-02-16) Tsai, PH; Assadi, MHN; Zhang, T; Ulrich, C; Tan, TT; Donelson, R; Li, S
    Simultaneous enhancement of the interdependent Seebeck coefficient and electrical conductivity has been achieved through defect engineering by doping Mg into specific sites of Na0.8CoO2. Results from thermoelectric measurement demonstrate that the power factor was substantially increased by 50% at ambient. Experimental and theoretical analyses show that the occupation of divalent Mg in the disordered Na layer immobilizes the Na ions and thus induces a long-range ordering of Na ions. This phenomenon improves the carrier mobility significantly, giving rise to the observed exotic thermoelectric performance. Moreover, it is predicted that other electronically closed-shell dopants in sodium cobaltate play a similar role in enhancing the thermoelectric conversion efficiency. © 2012, American Chemical Society.