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Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan In collaboration with K. Esfarjani, K. Sasaki, T.M. Briere, R.V. Belosludov, H. Mizuseki, M. Mikami, Y.Kawazoe, and B.I. Yakobson

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Overview: Molecular electronics insertion strategy; Active atom wire interconnects Keeping the initial target application simple, cheap and unsophisticated: passive interconnects Initial products will be silicon complements with response time of the order of second: sensors Moving on to active devices, with novel function, form, or cost advantage Finally; introducing entirely new generation of products: commercial delivery time of more than one decade Molecular Electronics J.M. Tour, World Scientific (2003)

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Nanotube molecular quantum wires Credit: C. Dekker

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Nanotube nanotransistor Credit: C. Dekker

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Nanotube logic nanogate Credit: C. Dekker

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Doped nanotube bundle Credit: R. Smalley

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Doping with C 60 - and Cs + Credit: G.-H. Jeong 2 nm 4 nm (b) (a)

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Formation of junction between empty and Cs + –doped parts Credit: G.-H. Jeong

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Conductance of a single benzene molecule Credit: J.M. Tour

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DNA conductance along axis D. Porath et al.

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Specific systems within the prescribed scheme: Shielded, passive/active, molecular wires: polythiophene/polyaniline inside cyclodextrines Building upon the existing silicon base: Bi line on Si surface Active (rectifying) device: doped nanotube junction How good is DNA? Cheking DNA’s transport

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Doped nanotube junction

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Negative differential resistance

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Rectifying effect

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Doped Nanotube Junctions

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Ab initio calculation: inside doping is favored by ~ 0.2 eV

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Ab initio calculation: energetics of light and heavy dopings

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Ab initio calculation: band structures of light and heavy dopings

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Ab initio calculation: density of states of light and heavy dopings

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Junction and Bulk Geometries

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Surface Green’s Function Matching

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Screening charge pattern for doped metallic junction (initial shifts of chemical potentials: 2.5 eV)

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Screening charge pattern for doped semiconducting junction ( initial shifts of chemical potentials: 2.5 eV)

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Metallic nanotube doped by a charged dopant

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Screening charge pattern of (5,5) for an external point charge 1.0 e

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Bi line on Si(001): relatively stable

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Bi line on Si(001): stable

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Hamiltonian and overlap Using the above-mentioned basis, the Hamiltonian of the system is obtained using Gaussian 98 program Moreover, as the basis is non-orthogonal, the overlap matrix is also obtained The Hamiltonian and overlap matrices are then used in calculating the conductance of the system using the Green’s function approach

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Reflected and Transmitted Amplitudes; Transmission Matrix

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Junction and Bulk Geometries

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Conductance

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Conductance, alternative derivation Conductance [2e 2 /h]: With Being the Green’s function of the molecule (junction part of the system)

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Surface Green’s functions And With Σ 1(2) being the surface terms describing the semi-infinite parts attached to the junction part Finally

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PT attached to gold contacts

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PT in cross-linked Alpha CD

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PT in Beta CD

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Molecular wire: transport through shielded polythiophene

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HOMO-LUMO energies(Hartree) PT in ACD non- interacting PT in BCD interacting PT in BCD non- interacting PT LUMO-0.1288-0.1355-0.1273-0.1290 HOMO-0.1366-0.1431-0.1378-0.1381

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Density of States

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Conductance

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Spatial Extension of MOs (n~80; E~0.3) LUMO HOMO LUMO+n

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DNA conductance perpendicular to axis in collaboration with T.M. Briere Au(111) STM Tip Au(111) Substrate

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AT Base Pair

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CG Base Pair

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Bulk Gold Contact

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Density of States (Fermi energy ~ -0.1)

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Conductance

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AT: Spatial distribution of HOMO (E ~ -0.154)

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AT: Spatial distribution of LUMO+n (E ~ 0.570)

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Conclusions: Two stable positions for Cs along diagonal direction Rectifying effect New nearly flat bands via doping Alignment of Frmi energy and van Hofe singularity: possibility of superconductivity In DNA transport, dominant current-carrying states are localized on the hydrogen bonds A high density of states does not necesserarily mean high conductance AT and CG have different conductance due to differently localized states

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