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Computational Nanoelectronics

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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Computational Nanoelectronics

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  1. 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

  2. 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)

  3. Nanotube molecular quantum wiresCredit: C. Dekker

  4. Nanotube nanotransistorCredit: C. Dekker

  5. Nanotube logic nanogateCredit: C. Dekker

  6. Doped nanotube bundle Credit: R. Smalley

  7. (a) 4 nm (b) 2 nm Doping with C60- and Cs+Credit: G.-H. Jeong

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

  9. Conductance of a single benzene moleculeCredit: J.M. Tour

  10. DNA conductance along axisD. Porath et al.

  11. 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

  12. Doped nanotube junction

  13. Negative differential resistance

  14. Rectifying effect

  15. Doped Nanotube Junctions

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

  17. Ab initio calculation:energetics of light and heavy dopings

  18. Ab initio calculation:band structures of light and heavy dopings

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

  20. Junction and Bulk Geometries

  21. Surface Green’s Function Matching

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

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

  24. Metallic nanotube doped by a charged dopant

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

  26. Bi line on Si(001): relatively stable

  27. Bi line on Si(001): stable

  28. 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

  29. Reflected and Transmitted Amplitudes; Transmission Matrix

  30. Junction and Bulk Geometries

  31. Conductance

  32. Conductance, alternative derivation • Conductance [2e2/h]: • With • Being the Green’s function of the molecule (junction part of the system)

  33. Surface Green’s functions • And • With Σ1(2) being the surface terms describing the semi-infinite parts attached to the junction part • Finally

  34. PT attached to gold contacts

  35. PT in cross-linked Alpha CD

  36. PT in Beta CD

  37. Molecular wire:transport through shielded polythiophene

  38. HOMO-LUMO energies(Hartree)

  39. Density of States

  40. Conductance

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

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

  43. AT Base Pair

  44. CG Base Pair

  45. Bulk Gold Contact

  46. Density of States(Fermi energy ~ -0.1)

  47. Conductance

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

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

  50. 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 Conclusions:

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