unimolecular devices

Laboratory of Molecular Electronics, Chemistry DepartmentUniversity of Alabama, Tuscaloosa, AL 35487-0336, USA

UNIMOLECULAR DEVICES

Robert M. MetzgerRobert M. Metzger

Laboratory for Molecular Electronics Laboratory for Molecular Electronics Department of Chemistry, The University of AlabamaDepartment of Chemistry, The University of Alabama

Tuscaloosa, AL 35487, USATuscaloosa, AL 35487, USAtel=1-205-348-5952, telefacsimile=1-205-348-9104tel=1-205-348-5952, telefacsimile=1-205-348-9104

[email protected][email protected]

NSF DMR-0095215

American Chemical Society -Petroleum Research Fund Workshop on the Chemistry of Information Technology”, University of Washington,. Seattle, WA, 18-25 June 2003


ALABAMA

TUSCALOOSA

GEOGRAPHY

In 1539, Chief Tuscaloosa (“Black Warrior” in Choctaw) fought and died in the only full battle between the Indians and the Spaniards (led by Hernando de Soto) at the village of Mauvilia (now lost) on one of the rivers of Alabama. The city of Mobile, AL is named after Mauvilia Hernando de Soto, in his exploration from Florida seeking gold, went on to the banks of the Mississippi river, where he died of syphilis in 1541.


UNIVERSITY OF ALABAMA QUAD, CAMPANILE, & CHERRY BLOSSOMS


ABSTRACT

Eight significant milestones in molecular-scale electronics, or

of unimolecular electronics (UE) will be discussed.


RATIONALEINORGANIC ELECTRONICS

Gordon E. Moore’s “Law”: At present, speed of computation doubles every 18 months Design rule of components (their distance) halves every 18 months. Now at 100 nm. What is the limit? Cost of fabrication laboratory increases exponentially with time (electron-beam or X-ray lithography) Field-effect transistors can be scaled down, until semiconductor or oxide fail (? 15 nm ?) Junction transistors can be scaled down, but not so far (? 50 nm?)

(UNI)MOLECULAR ELECTRONICS, or MOLECULAR-SCALE ELECTRONICS Molecular lines, spacers, alligator clips, tinkertoys, meccano components, resistors Molecular wires, antennas, conductors [conducting polymers, carotenes] Unimolecular rectifiers (Aviram-Ratner) and switches….negative differential resistance devices; diode logic Single-electron transistors & single-atom transistor (Coulomb blockade): no gain . Must reach out and touch molecules… STM, break junctions, macroscopic pads Molecules with gain? Unimolecular amplifier with gain? When and if all components exist, we can start to plan organic interconnects, instead of metal wires, and make the all-organic computer…..


RATIONALE

MOLECULAR ELECTRONICS (sensu lato) or MOLECULE-BASED ELECTRONICSo Organic metals [TTF TCNQ, 1973]

o Organic superconductors [TMTSF2PF6, 1979: Tc= 1 K, BEDT-TTF)2Cu(NCS)2, Tc = 13 K]

o Charge-transfer light-emitting diodes [Tang, 1987]o Charge-transfer polymers for electrostatic copiers [1967]

o Alkali fullerides [Cs2HC60, 1993, Tc ≈ 40 K]

o Conducting polymers [doped polyacetylene, 1977; polypyrrole, poly-p-phenylenevinylene, polythiophene]]o Organic polymeric light-emitting diodes [Friend, 1991]

(UNI)MOLECULAR ELECTRONICS (sensu stricto), or MOLECULAR-SCALE ELECTRONICSo Molecular lines, spacers, alligator clips, tinkertoys, meccano components, resistors

o Molecular wires, antennas, conductors [conducting polymers, carotenes]o Unimolecular rectifiers (Aviram-Ratner) and switches….negative differential resistance devices; diode logic

o Single-electron transistors & single-atom transistor (Coulomb blockade): no gain .o Must reach out and touch molecules… STM, break junctions, macroscopic pads

o Molecules with gain? Unimolecular “transistor” (molecular amplifier) with gain?o When and if all components exist, we can start to plan organic interconnects, instead of metal wires…


(From Dave Allara, Penn. State U.)


Molecular

Electronics

Metal/Molecule/Metal (M3)Switching & Memory

Single “Molecule”Logic Devices-I• nanotubes

n-Rod-Molecule-

n-Rod junctions

n-Particle-Molecule Bridges

(From Dave Allara, PSU)


gate

DS

3-Terminal Memory: Molecule-Coated

Semiconductor n-Rod

M3 Junctions with Field Gates

Park et al, Nature (2002)

Molecular

Electronics

Crossbar Devices• M3 - nanowires• nano-mechanical (nanotubes)

From Dave Allara, PSU


Molecular

ElectronicsMolecular Q-Dot

Cellular Automata Computers

Molecular Q-Dot Quantum Computers

eN

V-

V+

Single MoleculeLogic Devices-II• large molecules

Molecule-n-ParticleLogic Blocks


EIGHT SIGNIFICANT MILESTONES IN UNIMOLECULAR ELECTRONICS1) STS: currents across alkanethiols on Au (111) << STS currents through aromatic

thiols on Au(111) [L. A. Bumm, et al., Science 271, 1705 (1996)].2) Break junction: resistance between two Au shards with a single 1,4-benzenedithiol

bonded to them is several M. [M. A. Reed, et al., Science 278, 252 (1997)]3) Molecules of 2’-amino-4-ethynylphenyl-4’-ethynylphenyl-2’-nitro-benzene-1-thiolate,

attached to Au on one side and topped by a Ti electrode on the other, exhibit negative differential resistance [J. Chen, et al., Science 286, 1550 (1999)].

4) The Landauer quantum of resistance, 12.9 k was measured at 300 K between a single-walled carbon nanotube, glued to a conducting atomic force microscope (AFM) tip, and a pool of liquid Hg [S. Frank, et al., Science 280, 1744 (1999)].

5) FET behavior was observed for a single-walled carbon nanotube curled over parallel Au lines, with the STM acting as a gate electrode; the power gain was 0.33. [S. J. Tans, et al., Nature 386, 474 (1997)].

6) For an LB monolayer of a bistable [3]catenane closed-loop molecule, with a naphthalene group as one ”station”, and TTF as the second “station”, and a tetracationic catenane hexafluorophospate salt traveling on the catenane, like a “train” on a closed track, deposited on poly-silicon, and topped by a 5 nm Ti layer, then Al, the current-voltage plot is asymmetric as a function of bias (which moves the train on the track),as the train stops in different stations [C. P. Collier et al., Science 289, 1172 (2000)].

7) The organometallic equivalent of a single-electron transistor has been realized at 0.1 K with a Co(II) tris-bipyridyl: this structure has no power gain, but can be ascribed to the redox behavior (Co(II) <--> Co(III)) [J. Park, et al., Nature 417, 722 (2002)].

8) Unimolecular rectification…



thiols on Au(111) [L. A. Bumm, et al., Science 271, 1705 (1996)].2) Break junction: resistance between two Au shards with a single 1,4-

benzenedithiol bonded to them is several M. [M. A. Reed, et al., Science 278, 252 (1997)]

3) Molecules of 2’-amino-4-ethynylphenyl-4’-ethynylphenyl-2’-nitro-benzene-1-thiolate, attached to Au on one side and topped by a Ti electrode on the other, exhibit negative differential resistance [J. Chen, et al., Science 286, 1550 (1999)].







SCANNING TUNNELING SPECTROSCOPY (STS): THE STS CURRENTS ACROSS ALKANETHIOLS ON AU (111) <<<< STS CURRENTS THROUGH AROMATIC THIOLS ON AU(111)

L. A. Bumm, J. J. Arnold, M. T. Cygan, T. D. Dunbar, T. P. Burgin, L. Jones II, D. L. Allara, J. M. Tour, and P. S. Weiss, “Are Single Molecular Wires Conducting?” Science 271, 1705 (1996)

Abstract Molecular wire candidates inserted into ``nonconducting'' n-dodecanethiol self-assembled monolayers on Au{111} were probed by scanning tunneling microscopy (STM) and microwave frequency alternating current STM at high tunnel junction impedance (100 G) to assess their electrical properties. The inserted conjugated molecules, which were 4,4-di(phenylene-ethynylene)-benzenethiolate derivatives, formed single molecular wires that extended from the Au{111} substrate to about 7 angstroms above and had very high conductivity, as compared with that of the alkanethiolate.(Cf. Henry Taube in the 1950s and 1960s)

Au (111)

SSSSS S S S S


40 x 40 nm

STM: * Guest ~0.7 nm above host lattice at constant current* Enhanced conductivity

S

Guest molecule

C12H25S- Host lattice on Au{111}

Bumm, Arnold, Cygan, Dunbar, Burgin, Jones, Allara, Tour, & Weiss, Science, 271: 1705 (1996); Cygan, Dunbar, Arnold, Bumm, Shedlock, Burgin, Jones, Allara, Tour, & Weiss JACS 120, 2721(1998)

(H)

Conductance of a Single Molecule via STM


BREAK JUNCTION: RESISTANCE BETWEEN TWO Au SHARDS WITH A SINGLE 1,4-BENZENEDITHIOL BONDED TO THEM IS 22 M.

M. A. Reed, C. Zhou, C. J. Muller, T. P. Burgin, and J. M. Tour, “ Conductance of a Molecular Junction", Science 278: 252-254 (1997).

1 mMsolution

a b c d

e

fGold wire

Gold wire

A

D

C

B

Add THF and benzene-1,4-dithiol

SAM

SAM

Wire stretched until breakage,resulting in tip formation

Solvent evaporates, th en tipsbrought to gether unti l the onsetof conductance

Goldelectrode

Goldelectrode

Goldelectrode

Goldelectrode


BREAK JUNCTION: RESISTANCE BETWEEN TWO Au SHARDS WITH A SINGLE 1,4-BENZENEDITHIOL BONDED TO THEM IS 22 M.

M. A. Reed, C. Zhou, C. J. Muller, T. P. Burgin, and J. M. Tour, “ Conductance of a Molecular Junction", Science 278: 252-254 (1997)

.

S S

SSX

S

SX

S

SH

SH

S

SXS

S

HS

S

HS

SXS

SHS

S

HS

SSX

SH

S

8.46 Å

Current

Goldelectrode

Goldelectrode

.

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0

0.05

0.1

-4 -2 0 2 4Voltage (V)

Current (µA)

Conductance (µS)(A)

0

0.05

0.1

0 1 2 3 4 5Voltage (V)

Conductance (µS)

(B)

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0

0.125

0.25

-4 -2 0 2 4Voltage (V)

Current (µA)

Conductance (µS)(C)


MOLECULES OF BiPHENYL-THIOLATE, ATTACHED TO Au ON ONE SIDE AND TOPPED BY A Ti ELECTRODE ON THE OTHER,

(Nanopore) RECTIFY (due to different Schottky barriers at Au and Ti interfaces)

Au

TiAu

top electrode

SS S SS

O

bottom electrode

SiSiN

SiNSi

SiO 2

SiN

top electrode

bottom electrode

TiAu

Au

(a)

(b)

(c)

C. Zhou, M. R. Deshpande, and M. A. Reed, “Nanoscale Metal/Self-Assembled Monolayer/Metal Heterostructures”,

Appl. Phys. Lett. 71: 611-613 (1997).


MOLECULES OF 2’-AMINO-4-ETHYNYLPHENYL-4’-ETHYNYLPHENYL-2’-NITRO-BENZENE-1-THIOLATE, ATTACHED TO Au ON ONE SIDE AND TOPPED BY Au ELECTRODE ON THE OTHER, EXHIBIT NEGATIVE DIFFERENTIAL RESISTANCE

J. Chen, M. A. Reed, A. M. Rawlett, and J. M. Tour, "Large On-Off Ratios and Negative Differential Resistance in a Molecular Electronic Device", Science 286:

1550 (1999).

S

NH2

O2N

Au

Au (111)






4) The Landauer quantum of resistance, 12.9 k was measured at 300 K between a multiple-walled carbon nanotube, glued to a conducting atomic force microscope (AFM) tip, and a pool of liquid Hg [S. Frank, et al., Science 280, 1744 (1999)].






For a single mode of a molecule linked to macroscopic metal electrodes, Landauer showed that the [24] current I as a function of the bias V is:

I(V) = (e / h) E=- E= (E,V) p(E,V) dE (1)

e = electronic charge, h = Planck's constantp(E,V) = difference in the Fermi-Dirac occupation factors of the levels at energy

E in the electrodes on the two sides, (E,V) = transmission factor. If (E,V) = 1 (it is usually less than that), the molecule can be considered to be a nanowire. This condition yields the Landauer quantum of conductance

G = (e2 / h) = 38.8 µS. For a spin-degenerate pair of modes, this corresponds to a resistance

R = (h / 2 e2) = 12.9 k. When the nanowire has several modes, whose propagating energy range straddles the Fermi level, each one contributes 38.8 µS to the total conductance.

THE LANDAUER QUANTUM OF RESISTANCE

R. Landauer, "Spatial Variation of Currents and Fields due to Localized Scatterers in Metallic Conduction", IBM

J. Res. Dev. 1: 223-231 (1957).


THE LANDAUER QUANTUM OF RESISTANCE, 12.9 K WAS MEASURED AT 300 K BETWEEN A MULTIPLE-WALLED CARBON

NANOTUBE, GLUED TO A CONDUCTING ATOMIC FORCE MICROSCOPE (AFM) TIP, AND A POOL OF LIQUID HG

S. Frank, P. Poncharal, Z. L. Wang, and W. A. de Heer, “Carbon Nanotube Quantum Resistors” Science 280, 1744-1746 (1998).

The conductance of multiwalled nanotubes (MWNTs) was found to be quantized, by measuring the conductance of nanotubes by replacing the tip of a scanning probe microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber.

The conductance of arc-produced MWNTs is one unit of the conductance quantum G0.

The nanotubes conduct current ballistically and do not dissipate heat.

The nanotubes, which are typically 15 nm wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors.

Extremely high stable current densities have been attained.


FET BEHAVIOR WAS OBSERVED FOR A SINGLE-WALLED CARBON NANOTUBE CURLED OVER PARALLEL AU LINES, WITH THE STM ACTING AS A GATE ELECTRODE; THE POWER GAIN WAS 0.33.

S. J. Tans, M. H. Devoret, H. Dai, A. Thess, R. E. Smalley, L. J. Greelings, and C. Dekker, Nature 386, 474 (1997).


V. Derycke, R. Martel, J. Appenzeller, and Ph. Avouris, “Carbon Nanotube Inter- and Intramolecular Logic Gates” Nanoletters 1, 455 (2001).

Single wall carbon nanotubes (SWCNTs) have been used as the active channels of field effect transistors (FET).

The next development step involves the integration of CNTFETs to form logic gates; the basic units of computers. For this we need to have both p- and n-type CNTFETs. Without special treatment, CNTFETs are always p-type: the current carriers are holes and the devices are ON for negative gate bias.

Here we show that n-type CNTFETs can be prepared not only by doping but also by annealing SWNT-based p-FETs in a vacuum.

p- and n-type nanotube transistors were used to build the first nanotube-based logic gates: voltage inverters.

FETs OF SINGLE-WALLED CARBON NANOTUBES PUT INTO A VOLTAGE INVERTER CIRCUIT


(a) AFM: intramolecular logic gate. One nanotube bundle is put over the Au electrodes to produce two p-type CNTFETs in series. The device is covered by PMMA; a Window, opened by e-beam lithography, exposes part of the nanotube. K is then evaporated through this window to produce an n-CNTFET, while the other CNTFET remains p-type. (b) Characteristics of the resulting intramolecular voltage inverter. Open red circles are raw data for five different measurements on the same device (V = ±2 V). The blue line is the average of these five measurements. The thin straight line corresponds to an output/input gain of one.



A. Bachtold, P. Hadley, T. Nakanishi, and C. Dekker, “Logic circuits with Carbon nanotube transistors” Science 294: 1317 (2001).

Logic circuits were demonstrated in single carbon naotubeFETs, which by strong coupling with the gate area (Si covered by AL2O3) could be doped electrostatically n-type or p-type at room temperature. Gains higher than 10, and on/off ratios of 100,000 were seen. These FETs could be arrranged in logic circuits (inverter, logical NOR, RAM memory, AC ring oscillator)

SINGLE-WALLED NANOTUBE TRANSISTORS


FOR AN LB MONOLAYER OF A BISTABLE [3]CATENANE CLOSED-LOOP MOLECULE, WITH A NAPHTHALENE GROUP AS ONE ”STATION”, AND TTF AS THE SECOND “STATION”, AND A

TETRACATIONIC CATENANE HEXAFLUOROPHOSPATE SALT TRAVELING ON THE CATENANE, LIKE A “TRAIN” ON A CLOSED

TRACK, DEPOSITED ON POLY-SILICON, AND TOPPED BY A 5 NM TI LAYER, THEN AL, THE CURRENT-VOLTAGE PLOT IS ASYMMETRIC

AS A FUNCTION OF BIAS (WHICH MOVES THE TRAIN ON THE TRACK),AS THE TRAIN STOPS IN DIFFERENT STATIONS

C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K. Beverly, J. Sampaio, F. M. Raymo, J. F. Stoddart,and J. R. Heath, “A [2]-Catenane-Based Solid State Electronically Reconfigurable Switch”, Science 289, 1172 (2000).


C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K. Beverly, J. Sampaio, F. M. Raymo, J. F. Stoddart,and J. R. Heath, “A [2]-Catenane-Based Solid State Electronically Reconfigurable Switch”, Science 289, 1172 (2000).

THE TRAIN STATIONS


C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K. Beverly, J. Sampaio, F. M. Raymo, J. F. Stoddart,and J. R. Heath, “A [2]-Catenane-Based Solid State Electroniically Reconfigurable Switch”, Science 289, 1172 (2000).

THE CURRENT ACROSS AN LB MONOLAYER BETWEEN Si AND Ti ELECTRODES AT 291 K, DUE TO MOTION IN THE CATENANE, AND REPRODUCIBILITY


THE ORGANOMETALLIC EQUIVALENT OF A SINGLE-ELECTRON TRANSISTOR HAS BEEN REALIZED AT 0.1 K WITH A CO(II) BIS-TRIPYRIDYL: THIS STRUCTURE HAS NO POWER GAIN, BUT ITS COULOMB BLOCKADE CHANGES WITH GATE

VOLTAGE CAN BE ASCRIBED TO THE REDOX BEHAVIOR (CO(II) <--> CO(III))

J. Park, A. N. Pasupathy, J. I. Goldsmith, C. Chang, Y. Yaish, J. R. Petta, M. Rinkoski, J. P. Sethna, H. D. Abruña, P. L. McEuen, and D. C. Ralph, “Coulomb Blockade and the Kondo Effect in Single-Atom Transistors”, Nature 417, 722 (2002).

N

N

HS

N

N

N

HS

N

Co

Si

SiO2

Au Au

Au Au

Co


J. Park, et al., Nature 417, 722 (2002).

SINGLE-ELECTRON TRANSISTOR OF CO(II) BIS-TRIPYRIDYL










8) Unimolecular rectification

unimolecular devices

Documents