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![Page 1: Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan In collaboration with K. Esfarjani,](https://reader035.fdocuments.net/reader035/viewer/2022062620/551b594a5503465c7e8b5e99/html5/thumbnails/1.jpg)
Computational Nanoelectronics
A. A. FarajianInstitute 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 ElectronicsJ.M. Tour, World Scientific (2003)
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Nanotube molecular quantum wiresCredit: 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 C60- 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 moleculeCredit: 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
1,;,
;1
,;,1;11
1,;
;1
,;,1;11
1,;
),(S
)(
nnAnABA
nB
BAnn
nAnnAnAABABnBtn
nBnnBnBBBBBBnBrn
GSTVE
GGG
GGG
G
GGG
GGGG
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Junction and Bulk Geometries
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Conductance
2;,;
,
2
2
||),(S||)(2
),(T2
),(
nA
BAnnnB
nn
VEv
v
h
e
VEh
eVE
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Conductance, alternative derivation
Conductance [2e2/h]:
With
Being the Green’s function of the molecule (junction part of the system)
)(Tr ),( 12 GGVE MOLMOL
)( 211
HESG MOLMOL
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Surface Green’s functions
And
With Σ1(2) being the surface terms describing the semi-infinite parts attached to the junction part
Finally)]()()[,()( 12 EfEfVEdEVI
)(i 2)1()2(1)2(1
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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