Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University,...
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Transcript of Computational Nanoelectronics A. A. Farajian Institute for Materials Research, Tohoku University,...
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
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)
Nanotube molecular quantum wiresCredit: C. Dekker
Nanotube nanotransistor Credit: C. Dekker
Nanotube logic nanogate Credit: C. Dekker
Doped nanotube bundle Credit: R. Smalley
Doping with C60- and Cs+
Credit: G.-H. Jeong
2 nm
4 nm
(b)
(a)
Formation of junction between empty and Cs+ –doped parts
Credit: G.-H. Jeong
Conductance of a single benzene moleculeCredit: J.M. Tour
DNA conductance along axis D. Porath et al.
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
Doped nanotube junction
Negative differential resistance
Rectifying effect
Doped Nanotube Junctions
Ab initio calculation:inside doping is favored by ~ 0.2 eV
Ab initio calculation:energetics of light and heavy dopings
Ab initio calculation:band structures of light and heavy dopings
Ab initio calculation:density of states of light and heavy dopings
Junction and Bulk Geometries
Surface Green’s Function Matching
Screening charge pattern for doped metallic junction
(initial shifts of chemical potentials: 2.5 eV)
Screening charge pattern for doped semiconducting junction (initial shifts of chemical potentials: 2.5 eV)
Metallic nanotube doped by a charged dopant
Screening charge pattern of (5,5) for an external point charge 1.0 e
Bi line on Si(001): relatively stable
Bi line on Si(001): stable
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
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
Junction and Bulk Geometries
Conductance
2;,;
,
2
2
||),(S||)(2
),(T2
),(
nA
BAnnnB
nn
VEv
v
h
e
VEh
eVE
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
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
PT attached to gold contacts
PT in cross-linked Alpha CD
PT in Beta CD
Molecular wire:transport through shielded polythiophene
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
Density of States
Conductance
Spatial Extension of MOs (n~80; E~0.3)
LUMO
HOMO
LUMO+n
DNA conductance perpendicular to axis in collaboration with T.M. Briere
Au(111) STM Tip
Au(111) Substrate
AT Base Pair
CG Base Pair
Bulk Gold Contact
Density of States (Fermi energy ~ -0.1)
Conductance
AT: Spatial distribution of HOMO (E ~ -0.154)
AT: Spatial distribution of LUMO+n (E ~ 0.570)
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