Now showing items 1-20 of 22

    • Muffin Tins, Green's Functions, and more! 

      Stewart, Derek (2006-06-05)
      This presentation was originally presented as part of the 2005 Cornell Nanoscale Facility Fall Workshop, "Modeling the Nanoscale World". An overview of multiple scattering theory and how it relates to electronic structure ...
    • Properties of short channel ballistic carbon nanotube transistors with ohmic contacts 

      Leonard, Francois; Stewart, Derek (Institute of Physics, 2006-08-30)
      We present self-consistent, non-equilibrium Green's function calculations of the characteristics of short channel carbon nanotube transistors, focusing on the regime of ballistic transport with ohmic contacts. We first ...
    • Magnetism in Coaxial Palladium Nanowires 

      Stewart, Derek (American Institute of Physics, 2007-03-21)
      While bulk palladium is non-magnetic, several recent studies have shown that magnetism can occur in hcp Pd films, fcc twinned Pd nanoparticles, and Pd atomic strands. These studies show that small changes in Pd atomic ...
    • Intrinsic lattice thermal conductivity of semiconductors from first principles 

      Broido, David; Malorny, Michael; Birner, Gerd; Mingo, Natalio; Stewart, Derek (American Institute of Physics, 2007-12-07)
      We present an ab initio theoretical approach to accurately describe phonon thermal transport in semiconductors and insulators free of adjustable parameters. This technique combines a Boltzmann transport formalism with ...
    • Phonon transmission through defects in carbon nanotubes from first principles 

      Mingo, Natalio; Stewart, Derek A; Broido, David A; Srivastava, Deepak (American Physical Society, 2008-01-30)
      We compute the effect of different isolated defects on the phonon transmission through carbon nanotubes, using an ab initio density functional approach. The problem of translational and rotational invariance fulfillment in ...
    • Ab initio investigation of phonon dispersion and anomalies in palladium 

      Stewart, Derek (IOP Publishing Ltd and Deutsch Physikalische Gesellschaft, 2008-04-14)
      In recent years, palladium has proven to be a crucial component for devices ranging from nanotube field effect transistors to advanced hydrogen storage devices. In this work, I examine the phonon dispersion of fcc Pd using ...
    • Ab-initio study of polarizability and induced charge densities in multilayer graphene films 

      Yu, Eric; Stewart, Derek; Tiwari, Sandip (American Physical Society, 2008-05-06)
      We present an ab initio analysis of polarization of multilayer graphene systems under applied electric fields. The effects of applied electric fields are calculated using a Berry phase approach within a plane-wave ...
    • Phonon Transport in Isotope-Disordered Carbon and Boron-Nitride Nanotubes: Is Localization Observable? 

      Savic, Ivana; Mingo, Natalio; Stewart, Derek (American Physical Society, 2008-10-13)
      We present an ab initio study which identifies dominant effects leading to thermal conductivity reductions in carbon and boron-nitride nanotubes with isotope disorder. Our analysis reveals that, contrary to previous ...
    • Thermal conduction mechanisms in boron nitride nanotubes: Few-shell versus all-shell conduction 

      Savic, Ivana; Stewart, Derek; Mingo, Natalio (American Physical Society, 2008-12-29)
      It has been argued that the experimentally observed limitation of heat transport through boron nitride nanotubes is due to intershell scattering rather than to inefficient heat transfer to inner shells. Using an atomistic ...
    • Contribution of d-band electrons to ballistic transport and scattering during electron-phonon nonequilibrium in nanoscale Au films using an ab initio density of states 

      Hopkins, Patrick; Stewart, Derek (American Institute of Physics (AIP), 2009-09-08)
      Electron-interface scattering during electron-phonon nonequilibrium in thin films creates another pathway for electron system energy loss as characteristic lengths of thin films continue to decrease. As power densities ...
    • Ab initio theory of the lattice thermal conductivity in diamond 

      Ward, Alistair; Broido, David; Stewart, Derek; Deinzer, Gernot (American Physical Society, 2009-09-16)
      We present a first-principles theoretical approach to calculate the lattice thermal conductivity of diamond based on an exact solution of the Boltzmann transport equation. Density-functional perturbation theory is employed ...
    • Cluster scattering effects on phonon conduction in graphene 

      Mingo, Natalio; Esfarjani, Keivan; Broido, David; Stewart, Derek (American Physical Society, 2010-01-13)
      The phonon-scattering cross section associated with isotopic clusters is evaluated from first principles and used to estimate the reduction in thermal conductance of wide graphene samples. A strong sensitivity of the ...
    • Ultrafast thermoelectric properties of gold under conditions of strong electron-phonon nonequilibrium 

      Hopkins, Patrick; Bauer, Matthew; Duda, John; Smoyer, Justin; English, Timothy; Norris, Pamela; Beechem, Thomas; Stewart, Derek (American Institute of Physics (AIP), 2010-11-23)
      The electronic scattering rates in metals after ultrashort pulsed laser heating can be drastically different than those predicted from free electron theory. The large electron temperature achieved after ultrashort pulsed ...
    • Band Gap and Electronic structure of an Epitaxial, Semiconducting Cr0.80Al0.20 Thin Film 

      Boekelheide, Z.; Gray, A. X.; Papp, C.; Balke, B.; Stewart, D. A.; Ueda, S.; Kobayashi, K.; Hellman, F.; Fadley, C. S. (American Physical Society, 2010-12-03)
      Cr(1-x)Alx exhibits semiconducting behavior for x=0.15-0.26. This Letter uses hard x-ray photoemission spectroscopy and density functional theory to further understand the semiconducting behavior. Photoemission measurements ...
    • Thermal conductivity of indium arsenide nanowires with wurtzite and zinc blende phases 

      Zhou, Feng; Moore, Arden; Bolinsson, Jessica; Persson, Ann; Froberg, Linus; Pettes, Michael; Kong, Huijun; Rabenberg, Lew; Caroff, Philippe; Stewart, Derek; Mingo, Natalio; Dick, Kimberly; Samuelson, Lars; Linke, Heiner; Shi, Li (American Physical Society, 2011-05-19)
      The thermal conductivity of wurtzite and zinc blende indium arsenide nanowires was measured using a microfabricated device, with the crystal structure of each sample controlled during growth and determined by transmission ...
    • Role of light and heavy embedded nanoparticles on the thermal conductivity of SiGe alloys 

      Kundu, Anupam; Mingo, Natalio; Broido, David; Stewart, Derek (American Physical Society, 2011-09-09)
      We have used an atomistic ab initio approach with no adjustable parameters to compute the lattice thermal conductivity of Si0.5Ge0.5 with a low concentration of embedded Si or Ge nanoparticles of diameters up to 4.4 nm. ...
    • Antiferromagnetism in Cr3Al and relation to semiconducting behavior 

      Boekelheide, Zoe; Saerbeck, Thomas; Stampfl, Anton; Robinson, Robert; Stewart, Derek; Hellman, Frances (American Physical Society, 2012-03-09)
      Antiferromagnetism and chemical ordering have both been previously suggested as causes of the observed semiconductorlike behavior in Cr3Al. Two films of Cr3Al(001)/MgO(001) were grown under different conditions to achieve ...
    • Thermal conductivity of diamond nanowires from first principles 

      Li, Wu; Mingo, Natalio; Lindsay, Lucas; Broido, David; Stewart, Derek; Katcho, Nebil (American Physical Society, 2012-05-17)
      Using ab initio calculations we have investigated the thermal conductivity (k) of diamond nanowires, unveiling unusual features unique to this system. In sharp contrast with Si, k(T) of diamond nanowires as thick as 400 ...
    • Chemical ordering in Cr3Al and relation to semiconducting behavior 

      Boekelheide, Zoe; Stewart, Derek; Hellman, Frances (American Physical Society, 2012-08-15)
      Cr3Al shows semiconductor-like behavior which has been attributed to a combination of antiferromagnetism and chemical ordering of the Cr and Al atoms on the bcc sublattice. This article presents a detailed theoretical and ...
    • Thermal conductivity of bulk and nanowire Mg2Si_{x}Sn_{1-x} alloys from first principles 

      Li, Wu; Lindsay, Lucas; David, Broido; Stewart, Derek; Mingo, Natalio (American Physical Society, 2012-11-29)
      The lattice thermal conductivity (κ) of the thermoelectric materials, Mg2Si, Mg2Sn, and their alloys, are calculated for bulk and nanowires, without adjustable parameters. We find good agreement with bulk experimental ...