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Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan In collaboration with K. Esfarjani,

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Presentation on theme: "Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan In collaboration with K. Esfarjani,"— Presentation transcript:

1 Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University, Sendai , 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 wires Credit: C. Dekker

4 Nanotube nanotransistor Credit: C. Dekker

5 Nanotube logic nanogate Credit: C. Dekker

6 Doped nanotube bundle Credit: R. Smalley

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

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

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

10 DNA conductance along axis D. 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 [2e 2 /h]:  With  Being the Green’s function of the molecule (junction part of the system)

33 Surface Green’s functions  And  With Σ 1(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) PT in ACD non- interacting PT in BCD interacting PT in BCD non- interacting PT LUMO HOMO

39 Density of States

40 Conductance

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

42 DNA conductance perpendicular to axis in 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 ~ )

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

50 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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