Current Profiles of Molecular Nanowires; DFT Green Function Representation

The Liouville-space Green function formalism is used to compute the current density profile across a single molecule attached to electrodes. Time ordering is maintained in real, physical, time, avoiding the use of artificial time loops and backward propagations. Closed expressions for molecular currents, which only require DFT calculations for the isolated molecule, are derived to fourth order in the molecule/electrode coupling.Comment: 21 page

Sign-reversal of drag in bilayer systems with in-plane periodic potential modulation

We develop a theory for describing frictional drag in bilayer systems with in-plane periodic potential modulations, and use it to investigate the drag between bilayer systems in which one of the layers is modulated in one direction. At low temperatures, as the density of carriers in the modulated layer is changed, we show that the transresistivity component in the direction of modulation can change its sign. We also give a physical explanation for this behavior.Comment: 4 pages, 4 figure

Letter to Nature. Growth of nanowire superlattice structures for nanoscale photonics and electronics

The assembly of semiconductor nanowires and carbon nanotubes into nanoscale devices and circuits could enable diverse applications in nanoelectronics and photonics1. Individual semiconducting nanowires have already been configured as field-effect transistors2, photodetectors3 and bio/chemical sensors4. More sophisticated light-emitting diodes5 (LEDs) and complementary and diode logic6-8 devices have been realized using both n- and p-type semiconducting nanowires or nanotubes. The n- and p-type materials have been incorporated in these latter devices either by crossing p- and n-type nanowires2, 5, 6, 9 or by lithographically defining distinct p- and n-type regions in nanotubes8, 10, although both strategies limit device complexity. In the planar semiconductor industry, intricate n- and p-type and more generally compositionally modulated (that is, superlattice) structures are used to enable versatile electronic and photonic functions. Here we demonstrate the synthesis of semiconductor nanowire superlattices from group III–V and group IV materials. (The superlattices are created within the nanowires by repeated modulation of the vapour-phase semiconductor reactants during growth of the wires.) Compositionally modulated superlattices consisting of 2 to 21 layers of GaAs and GaP have been prepared. Furthermore, n-Si/p-Si and n-InP/p-InP modulation doped nanowires have been synthesized. Single-nanowire photoluminescence, electrical transport and electroluminescence measurements show the unique photonic and electronic properties of these nanowire superlattices, and suggest potential applications ranging from nano-barcodes to polarized nanoscale LEDs

Lattice dynamics investigations of SiGe core-shell nanowires

61.46.-w Nanoscale materials, 61.48.De Structure of carbon nanotubes, boron nanotubes, and closely related graphitelike systems (for structure of hollow nanowires, see 61.46.Np), 65.40.-b Thermal properties of crystalline solids,

Structural phase transition and the related electronic and optical properties of MgZnO nanowires

We theoretically investigate the stabilities and electronic structures of MgZnO nanowires with different compositions of Mg. It is found that with increasing composition of Mg, wurzite MgZnO nanowires become less stable, and cubic MgZnO nanowires are energetically favored. The phase transition from wurzite to cubic structure occurs, when the composition of Mg in the Mg x Zn 1- x O nanowire reaches about 0.65. Furthermore, our calculations show that the band gaps can be effectively modulated by composition of Mg for either wurzite or cubic nanowires. This is reflected in the calculated absorption spectra, where the absorption edges shift with variation of the compositions of Mg. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011