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MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 11

A Decade of Molecular Scale Transport

Mark ReedYale University

A Decade of Molecular Scale TransportA Decade of Molecular Scale Transport

Mark ReedMark ReedYale UniversityYale University

with: L. E. with: L. E. CalvetCalvet, J. Chen, M. , J. Chen, M. deJongdeJong, M. , M. DeshpandeDeshpande, J. , J. KlemicKlemic, I. , I. KretzschmarKretzschmar,, T. Lee, R. T. Lee, R. D. Lombardi, G. Martin, C. Muller, J. Su, W. Wang, C. Zhou, and D. Lombardi, G. Martin, C. Muller, J. Su, W. Wang, C. Zhou, and R. G. WheelerR. G. Wheeler

Collaborators: Pennsylvania State University, Rice University, UCollaborators: Pennsylvania State University, Rice University, U. Wisconsin . Wisconsin -- Milwaukee, Milwaukee, UCSB, Cornell NNF, MotorolaUCSB, Cornell NNF, Motorola


ET

+- +

+ELECTRON FLOWIVT

++

-

-+D+-σ-A-

-

-++

+

LUMO(A)

-

ET

-

HOMO(D)

--

++

Step 2

Fermi level (metal')

D-σ-A molecule

D0-σ-A0

-D0-σ-A0

-

Step 1 -

Forward bias: preferred direction of electron flow

S

S S

S

CNNC

CNNC

+

ETIVT

Fermi level (metal)

ET

D –σ–A

A. A. AviramAviram & M. A. & M. A. RatnerRatner,,Chem. Phys. Chem. Phys. LettLett. 29:277 (1974). 29:277 (1974)

0

0.0001

0.0002

0.0003

0.0004

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Cur

rent

/ m

A

Voltage / V

C CN

CNNC16H33

N

Results of Metzger et al., Results of Metzger et al., J. Am. J. Am. Chem. Soc.Chem. Soc. 119: 10455 (1997) 119: 10455 (1997) Al | 1LB CAl | 1LB C1616HH3333QQ--3CNQ | Al 3CNQ | Al

((HexadecylquinoliniumHexadecylquinoliniumTricyanoquinodimethanideTricyanoquinodimethanide))

water

LL--B approachB approach

A proposal ahead of it’s time:a unimolecular

zwitterionic rectifier

A proposal ahead of it’s time:A proposal ahead of it’s time:a a unimolecularunimolecular

zwitterioniczwitterionic rectifierrectifier


Early molecular junctionsEarly molecular junctionsMann and Kuhn,Mann and Kuhn, J. J. ApplAppl. Phys. . Phys. 4242, 4398 (1971) ; , 4398 (1971) ; PolymeropoulosPolymeropoulos and and SagivSagiv,, J. Chem. Phys. J. Chem. Phys. 6969, ,

1836 (1978)1836 (1978)

77 KFor C18

295 K

238 K

293 K

People lost People lost interest interest

because of because of inability to inability to characterize characterize the junctionsthe junctions


The 70s: The 70s: epiepi growth & growth & QWsQWs

The rise of mesoscopicsThe rise of mesoscopicsThe 80s: lateral confinement for low-d

• pattern/etch (problems with surface states (Si wires), critical dimension control, depletion layers)

• variant: etch-defined depletion

• gated low-d structures (2DEGs)

E quantization(Reed et al, PRL 1988;

Tarucha et al, PRL 1996)


L.P. L.P. Kouwenhoven Kouwenhoven et al. (1998)et al. (1998)


Coulomb blockadeCoulomb blockade

t(RCt(RC) = CR = C/G ; ) = CR = C/G ; t(RCt(RC) = ) = ħħ//δδEE

δδEE < < EcEc = e= e22/2C/2C

So G < eSo G < e22/2ħ ~ 2e/2ħ ~ 2e22/h/h


Excited states:

Coulomb diamondCoulomb diamond

A.K. Hüttel (2003)


Carbon nanotubesCarbon nanotubes

1/gap tE d∝New Materials

C60 inside nanotubes

armchair armchair θθ=30=3000

zigzag zigzag θθ=0=000

chiralchiral 0 < 0 < θθ < 30< 3000


H.W.C. Postma et al., Science 293, 76, 2001

J.B. Cui, Nano Lett. 2, 117, 2002

Carbon nanotube Coulomb blockade oscillations

20 nm


Conductance quantizationConductance quantizationConductance quantization

G = (2e2/h) ∑ tt†

n

Semiconductor point contactSemiconductor point contactSemiconductor point contact

λλFF ~ 100nm~ 100nmfor for llinelasticinelastic ~ ~ λλFF ~~ dd, ,

T must be ~ 10KT must be ~ 10K

Cambridge & Delft Cambridge & Delft groups, 1988groups, 1988

λλFF ~ .3nm~ .3nmfor for llinelasticinelastic ~ ~ λλFF ~~ dd, ,

T > 300KT > 300K

Metallic point contactMetallic point contactMetallic point contact

G (2

e2 /h)

E. Scheer

Muller et al, PR B 1996Muller et al, PR B 1996


Cond

ucta

nce

(2e

/h)

2

Cond

ucta

nce

(2e

/h)

2

METALLIC QUANTUM POINT CONTACTS (QPC)

W ~ λF

Low electron densitymetals

λ >> a F 0

High electron density metals

λ ~ aF

0

G eh i

i

N=

=∑2 2

1τ

τ = 1, = ... = = 0 ττ1 N2

2DEGT = 600 mK

τ = ?i

v. Wees et al, 1988

0.0 -0.2 -0.4 -0.6 -0.802468

10

??????

T = 600 mKAluminium

Electrode distance (nm)-1.2 -0.8 -0.4 0.0

0

2

4

6

135

6≥8

Al

Courtesy E. Scheer


G = (2e2/h) ∑ tt†

n

Tune the transmission coefficientTune the transmission coefficient

Quantum point contact (T ~ 1)Quantum point contact (T ~ 1)Quantum point contact (T ~ 1) RTD ( T variable)RTD ( T variable)RTD ( T variable)


Emulation of the problem in the solid state: single electron occupancy of a single channelEmulation of the problem in the solid state: Emulation of the problem in the solid state:

single electron occupancy of a single channelsingle electron occupancy of a single channel∆∆E E CoulombCoulomb ~ 10 ~ 10 meVmeV∆∆EEexcitexcit > 10 > 10 meVmeV

⇒⇒ single esingle e-- occupancyoccupancyΓΓoutout , , ΓΓin in independently tunableindependently tunable


Critical test: Zeeman spin splitting

Critical test: Critical test: ZeemanZeeman spin splittingspin splitting

g* : E. L. g* : E. L. IvchencoIvchenco and A. A. and A. A. KiselevKiselev, , SovSov. . Phys. Phys. SemicondSemicond. . 2626, 827 (1992)., 827 (1992).

DeshpandeDeshpande et al.,et al., Phys. Rev. Phys. Rev. LettLett.. 7676, 1328 (1996), 1328 (1996)


vary temperature to verifyresult: coulomb frustration of spin degeneracy

vary temperature to verifyvary temperature to verifyresult: coulomb frustration of spin degeneracyresult: coulomb frustration of spin degeneracy

II11 = = pepeΓΓoutout II22 = (2p= (2p--pp22)e)eΓΓoutout

p = 0.6 = (p = 0.6 = (ΓΓinin / / ΓΓinin + + ΓΓoutout) ) ΓΓoutout = 650 MHz, = 650 MHz, ΓΓinin = 390 MHz= 390 MHz

M.R. M.R. DeshpandeDeshpande et. al, et. al, Phys. Rev.Phys. Rev. B62B62, 8240 (2000)., 8240 (2000).


L. E. L. E. CalvetCalvet et. al, J. et. al, J. ApplAppl. Phys.. Phys. 9191, 757 , 757 (2002); (2002); ApplAppl. Phys. . Phys. LettLett.. 8080, 1761 (2002)., 1761 (2002).

∆T

Measurement of “negative current” in a single atom contact

Measurement of “negative current” Measurement of “negative current” in a single atom contactin a single atom contact

Negative current?

current is the sum of current is the sum of electrical current electrical current (positive)(positive) and and thermoelectric current thermoelectric current

(negative)(negative)


Courtesy D. Ralph, CornellCourtesy D. Ralph, Cornell

Single Co impurity tunnelingSingle Co impurity tunneling(for 1(for 1stst (in (in SiSi), see ), see KopleyKopley, , McEuenMcEuen, & Wheeler, PRL, 1988), & Wheeler, PRL, 1988)


Fundamental role of contactsFundamental role of contactsFundamental role of contacts

The Good:The Good: principles of electron transport in principles of electron transport in mesoscopicsmesoscopics are essentially understood, because are essentially understood, because the contact technology existsthe contact technology exists

The Bad:The Bad: contacts have always been the contacts have always been the problem with every new device technology, and problem with every new device technology, and it has always been solved by alchemyit has always been solved by alchemy

The Ugly:The Ugly: in molecular systems, the device & in molecular systems, the device & contact contact

are difficult to characterize are difficult to characterize

are no longer separable (are no longer separable (mesoscopicsmesoscopicsconveniently sidesteps this due to length scales; conveniently sidesteps this due to length scales; i.e., the device is mostly depletion layer)i.e., the device is mostly depletion layer)

can dynamically changecan dynamically change


Single Molecule MeasurementsSingle Molecule MeasurementsSingle Molecule Measurements

Reed Reed et. alet. al, Science , Science 278278, 252 (1997), 252 (1997)

Cui Cui et. alet. al, Science , Science 294294, 571 (2001), 571 (2001)

Reichert Reichert et. alet. al, PRL 88, 176804 (2002), PRL 88, 176804 (2002)


experiment:experiment:M.A. Reed M.A. Reed et. alet. al, Science , Science 278278, 252 (1997), 252 (1997)

theory:theory:M.DiM.Di VentraVentra et. alet. al, , Phys. Phys. Rev. Rev. LettLett.. 84, 979 (2000).84, 979 (2000).

•• reflective: T ~ 5 x 10reflective: T ~ 5 x 10--44

•• single? observe integer units (1,2,…)single? observe integer units (1,2,…)•• power dissipation?power dissipation?

•• J ~ 10J ~ 1088 A/cmA/cm2 2

•• P ~ 1P ~ 1µµW (1 molecule ?!)W (1 molecule ?!)•• T very contact geometry sensitiveT very contact geometry sensitive

MCB Measurement of benzene-1,4-dithiolMCB Measurement of benzeneMCB Measurement of benzene--1,41,4--dithioldithiol

KarlsruheKarlsruhe group, low Tgroup, low T


-2 0 2

Ratner group

Theory of MCB BDTTheory of MCB BDTTheory of MCB BDT


ComparisonComparison of of moleculesmolecules

Courtesy H. Weber


Molecular Measurements: which is best?Molecular Measurements: which is best?


Mercury junction Cross-wire junction

Rampi et al, CP (2002) Kushmerick et al, JACS (2002)

SiSi

Au

Au

SiN

Nanopore

Zhou et al, APL (1997)

Amlani et al, APL (2002)

Nanoparticle-trapped junction

Reed Group

Molecular Transport Characterization Testbeds II

Nanowire junction

Mbindyo et al, JACS (2002)


- Tip

• insulator (quartz) with square cross-section + Al-gate + insulator (SiO2) + metal electrodes

• self-assembly of various thiophenes

From N.B. Zhitenev et al., Nanotechnology 14, 254, 2003


MBE SelfMBE Self--AssemblyAssembly(Molecular Beaker (Molecular Beaker EpitaxyEpitaxy))

•• Single monolayer (& quality) Single monolayer (& quality) verified by electrochemistryverified by electrochemistry

•• ThiolThiol, , isonitrileisonitrile

•• Simplest case: Simplest case: alkanethiolalkanethiol

H. H. SchäferSchäfer et al., Adv. Mater. 10, 839, 1998et al., Adv. Mater. 10, 839, 1998


SAMs on Au(111)-STM Images

Poirier, Chem. Rev. 97, 1117 (1997)Octanethiol/Au(111)

Octanethiol

Yang et al, J. Phys. Chem. B 104, 9059 (2000)Arenethiol/Au(111)

SH

4-[4’-(phenylethynyl)-phenylethynyl]-benzenethiol


500 nm

Octanethiol (C8)Dodecanethiol (C12)Hexadecanethiol (C16)

SiSi

Au

Au

SiO2

Au

Si3N4

Au

Alkanethiol

Si3N4

50nm

YaleYale

NISTNIST

C8: 46 ± 2 nm; C12 & C16: 45 ± 2 nm

(99 % C.L.)

~50 nm~50 nmTEMTEM


Tunnelingno T-dependence

Thermal activationT-dependence

ConductionMechanism

CharacteristicBehavior

TemperatureDependence

VoltageDependence

DirectTunneling*

Fowler-NordheimTunneling

ThermionicEmission

HoppingConduction

none

none

TTJ 1~)ln( 2

VVJ 1~)ln( 2

21

~)ln( VJ

TVJ 1~)ln( VJ ~

VJ ~

)exp(~kTqVJ Φ

−

)4

exp(~ 2

kTdqVq

TJπε−Φ

−

)324exp(~

2/32

VqmdVJh

Φ−

)22exp(~ Φ− mdVJh

* only at low bias

Transport mechanisms (intrinsic)Transport mechanisms (intrinsic)


Alkane SAM MIM tunneling (non-ideal α factor)AlkaneAlkane SAM MIM tunneling (nonSAM MIM tunneling (non--ideal ideal αα factor)factor)

-1.0 -0.5 0.0 0.5 1.0

0.1

1

10

100

I (nA

)

V (V)

⎪⎩

⎪⎨⎧

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −Φ−⎟

⎠⎞

⎜⎝⎛ −Φ⎟⎟

⎠

⎞⎜⎜⎝

⎛= deVmeV

deJ BB

2/12/1

22 2)2(2exp

24α

π hh ⎪⎭

⎪⎬⎫

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ +Φ−⎟

⎠⎞

⎜⎝⎛ +Φ− deVmeV

BB

2/12/1

2)2(2exp

2α

h

C12

I(V,T)

(80-300K)

0.002 0.004 0.006 0.008 0.010 0.012 0.014

-22

-21

-20

-19

-18

-17

1.0 V0.9 V0.8 V0.7 V0.6 V0.5 V0.4 V0.3 V0.2 V0.1 V

ln I

1/T (1/K)

1.0 1.2 1.4 1.6 1.8 2.0-17.8

-17.7

-17.6

-17.5

-17.4

-17.3

-17.2

lnI /

V2

1/V (1/V)

290K240K190K140K90K

F-N

ArrheniusW. Wang W. Wang et alet al, PRB 68, 035416 (2003), PRB 68, 035416 (2003)


LB Alkane defect-mediated transportLB Alkane defect-mediated transport

Mann and Kuhn,Mann and Kuhn, J. J. ApplAppl. Phys. . Phys. 4242, 4398 (1971) ; , 4398 (1971) ; PolymeropoulosPolymeropoulos and and SagivSagiv,, J. Chem. Phys. J. Chem. Phys. 6969, 1836 (1978);, 1836 (1978);Stewart et al., Stewart et al., NanoLettersNanoLetters 20032003

77 KFor C18

295 K

238 K

293 K


Filamentary conductionFilamentary conduction

2.0x10-6

1.5

1.0

0.5

0.0

Cur

rent

(A)

1.51.00.50.0Applied Voltage (V)

50403020100Time (min)

1st IV sweep from 0 to 1 volt 2nd IV sweep from 0 to 1 volt v = .1v and hold (offset 3.5 min) v = .5v and hold (offset 17 min) v = .9v and hold (offset 30 min)

Commonly observed in our

large area devices


RedoxRedox Mechanism in Mechanism in CatenanesCatenanes

SS

S S

OO

OO

O

OOOO

O

NN

NN

++

++

e-_

+ e-

M. Asakawa, P.R. Ashton, V. Balzani, A. Credi, C. Hamers, G. Mattersteig,M. Montalti, A.N. Shipway, N. Spencer, J.F. Stoddart, M.S. Tolley,

M. Venturi, A.J.P. White, D.J. Williams, Angew. Chem. Int. Ed., 1998, 37, 333

Catenane at 0 V

Catenaneat –0.4 V

Catenaneat +0.4 V

Electrochromic Properties:A “RGB” System


EChem Hysteresis in [2]Rotaxane (SAM) Monolayer (“½ device”)

-20

20

40

0

0 200 400 600 800 1000

Current density

µA/cm2

mVolts

Metastable state

Au

Au

Ground State

( )τt

NNN

groundmeta

meta −=+

exp

1st cv

2nd cv

H.-R. Tseng, Stoddart GroupCourtesy J. Heath


Planar “conventional” sandwiches (1,4Planar “conventional” sandwiches (1,4--phenylene phenylene diisocyanidediisocyanide))

Conductivity and current at 4 K for 3 different devices

C. Dupraz et al. (2003)


Determining ΦΒ and αDetermining Determining ΦΦΒΒ and and αα

⎪⎩

⎪⎨⎧

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −Φ−⎟

⎠⎞

⎜⎝⎛ −Φ⎟⎟

⎠

⎞⎜⎜⎝

⎛= deVmeV

deJ BB

2/12/1

22 2)2(2exp

24α

π hh ⎪⎭

⎪⎬⎫

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ +Φ−⎟

⎠⎞

⎜⎝⎛ +Φ− deVmeV

BB

2/12/1

2)2(2exp

2α

h

Minimized fits (nonlinear LSQ) Minimized fits (nonlinear LSQ)

to I(V) gives to I(V) gives ΦΦ,,α,∆α,∆

-1.0 -0.5 0.0 0.5 1.0-40

-20

0

20

40

Measured ΦB = 1.42 eV, α = 0.65 ΦB = 0.65 eV, α = 1

I (nA

)

V (V)0.5 0.6 0.7 0.8 0.9 1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

α

ΦB (e

V)

1E-95E-91E-85E-81E-75E-71E-65E-6

ΦΒ = 1.42 eV, α = 0.65


Determining ΦΒ and αDetermining Determining ΦΦΒΒ and and αα

Minimized fits (nonlinear LSQ) Minimized fits (nonlinear LSQ)

to Simmons I(V) gives to Simmons I(V) gives ΦΦ,,α,∆α,∆

-1.0 -0.5 0.0 0.5 1.0-40

-20

0

20

40

Measured ΦB = 1.42 eV, α = 0.65 ΦB = 0.65 eV, α = 1

I (nA

)

V (V)

0.5 0.6 0.7 0.8 0.9 1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

α

ΦB (e

V)

1E-95E-91E-85E-81E-75E-71E-65E-6

ΦΒ = 1.42 eV, α = 0.65

β0 = 0.79 Å-1


Length dependenceLength dependenceLength dependence

2/12/1

2)2(2

⎟⎠⎞

⎜⎝⎛ −Φ=

eVmBαβ

h

Low V approximationLow V approximation

dd ededI ββ −−−− ∝∝ 21 ;

12 14 16 18 20 22 2410-8

10-6

10-4

10-2

100

0.4V0.3V0.2V0.1V

Jd2 (A

)

Jd (A

/cm

)

Length (Å)

10-15

10-13

10-11

10-91.0V0.9V0.8V0.7V0.6V0.5V

C8

C12

C16

0.0 0.2 0.4 0.6 0.8 1.00.2

0.4

0.6

0.8

1.0

1.2

β (Å

-1)

V (V)

0.5 0.6 0.7 0.8 0.9 1.00.1

0.2

0.3

0.4

0.5

0.6

0.7

β v2 (Å-2)

V (V)

correct β(V,T) dependence


DithioalkaneDithioalkane calculations withcalculations withTransiestaTransiesta code (DFT + NEGF)code (DFT + NEGF)

Carbon atoms

ln J(1V)

6 8 10

AngstromrJJ

/63.0)(exp0

=−=

ββ

Expt. 0.60/Angstrom

RatnerRatner groupgroup


band parametersband parametersband parameters

ΦB = 1.39 ± 0.01 eV (1σΜ), α = 0.65 ± 0.01 (1σΜ)(β0 = 0.79 ± 0.01 Å-1)

0.4

0.8

1.2

1.6

βv2

FittingC16

FittingC12

Fitting

ΦB (e

V)

0.6

0.8

1.0

1.2

α

ΦΒ

α

monothiolmonothiol 0.79 1500 1.4 0.79 1500 1.4 MM--II--M M Wang et al, PR B 68, 035416 (2003)Wang et al, PR B 68, 035416 (2003)

((bilayerbilayer) ) monothiolmonothiol 0.87 130 2.1 Hg0.87 130 2.1 Hg--junction junction HolmlinHolmlin et al, JACS 123, 5075 (2001)et al, JACS 123, 5075 (2001)

JunctionJunction ββ (Å(Å--11)) J @1V (A/cmJ @1V (A/cm22) ) ΦΦBB ((eVeV) Technique) Technique Ref.Ref.

monothiolmonothiol 0.730.73--0.95 1100 2.20.95 1100 2.2 CAFM CAFM Wold et al, JACS 123, 5549 (2001)Wold et al, JACS 123, 5549 (2001)

Hg-ju

nctio

nSo

lid M

-I-M

STM

Hg-ju

nctio

n

STM

CAFM

CAFM

Tuni

ng fo

rk A

FMEl

ectro

chem

ical

Theo

ry

Elec

troch

emica

lEl

ectro

chem

ical

Theo

ryTh

eory

0.0

0.5

1.0

1.5

2.0monothiolbilayer monothioldithiol

β (Å

-1)

0.8 Å-1

Nanopore


Hg-ju

nctio

nSo

lid M

-I-M

STM

Hg-ju

nctio

n

STM

CAFM

CAFM

Tuni

ng fo

rk A

FMEl

ectro

chem

ical

Theo

ry

Elec

troch

emica

lEl

ectro

chem

ical

Theo

ryTh

eory

10-1

100

101

102

103

104

105

106

107

Extrapolated for C12monothiolbilayer monothioldithiol

J (A

/cm

2 )

Alkanethiol parametersAlkanethiol parametersββ (decay coefficient)(decay coefficient) J (current density)J (current density)

•• G G ∝∝ exp(exp(--ββdd), ), ββ tunneling decay coefficienttunneling decay coefficient• • ββ = 2.2 Å= 2.2 Å--11 for Aufor Au--vacuumvacuum--Au tunnelingAu tunneling• no error range reported• no error range reported

• J (A/cm• J (A/cm22) extrapolated for C12 @ 1 Volt ) extrapolated for C12 @ 1 Volt from published results for other lengthfrom published results for other lengthmolecules by using G molecules by using G ∝∝ exp(exp(--ββdd))• Only included when • Only included when ββ is reportedis reported

Hg-ju

nctio

n

Solid

M-I-

M

Hg-ju

nctio

n

STM

CAFM

CAFM

0.0

0.5

1.0

1.5

2.0monothiolbilayer monothioldithiol

β (Å

-1)

0.8 Å-1

Nanopore

Nanopore


Junction β (Å-1) J (A/cm2)at 1 V

ΦB (eV) Technique Ref.

(bilayer)monothiol

0.87 130a) 2.1e) Hg-junction Holmlin et al, JACS 123, 5075 (2001)

(bilayer)monothiol

0.71 5a) Hg-junction Slowinski et al, JACS 121, 7257 (1999)

monothiol 0.79 1500b) 1.4e) Solid M-I-M Wang et al, PR B 68, 035416 (2003)

monothiol 1.2f) STM Bumm et al, JPC B 103, 8122 (1999)

dithiol 0.8 4 × 105 c) 5 ± 2f) STM Xu et al, Science 301, 1221 (2003)

monothiol 0.73-0.95 1100d) 2.2e) CAFM Wold et al, JACS 123, 5549 (2001)

monothiol 0.64-0.8 50d) 2.3e) CAFM Cui et al, NT 13, 5 (2002)

dithiol 0.46 5 × 105 c) 1.3-1.5e)

CAFM Cui et al, JPCB 106, 8609 (2002)

monothiol 1.37f) 1.8f) Tuning forkAFM

Fan et al, JACS 124, 5550 (2002)

monothiol 0.96 Electrochemical

Smalley et al, JPC 99, 13141 (1995)

0.85 Electrochemical

Weber et al, JPCB 101, 8286 (1997)

0.91 Electrochemical

Slowinski et al, JACS 119, 11901 (1997)

monothiol 0.76 2 × 104 (at0.1 V)

1.3 or3.4g)

Theory Kaun et al, Nano Lett. in press

monothiol 0.76 Theory Piccinin et al, JCP 119, 6729 (2003)

monothiol 0.79 Theory Tomfohr et al, PR B 65, 245105 (2002)

• Some decay coefficients β were converted into the unit of Å-1 from the unit of per methylene.• The junction areas were estimated by optical microscopea), SEMb), assuming single moleculec), and Hertzian contact theoryd). • Current densities (J) for C12 monothiol or dithiol at 1 V are extrapolated from published results for other length molecules byusing conductance ∝ exp(-β d) relationship.• Barrier height ΦB values were obtained from Simmons equatione), bias-dependence of βf), and a theoretical calculationg).


Franz 2-band modelFranz 2Franz 2--band modelband model

0.20 0.15 0.10 0.05 0.00-8

-6

-4

-2

0

Hole tunneling

Electron tunneling

E (e

V)

-k2 (Å-2)

LUMO

HOMO

ΦB

ΦB

best fit with ΦB = 1.55 ± 0.59 eVm* = 0.38 ± 0.20 m

(α = 0.62)

∇T can determine which

∇T can determine which


dithioldithiol vsvs monothiolmonothiol

-1.0 -0.5 0.0 0.5 1.0

10

100

1000

I (nA

)

V (V)

C8 dithiol

C8 mono-thiol

C8 C8 dithioldithiol, J = 1.1 , J = 1.1 ×× 101055 A/cmA/cm22

C8 C8 monithiolmonithiol, J = 3.8 , J = 3.8 ×× 101044 A/cmA/cm22 (@ 1 V)(@ 1 V)

Consistent with theory (Consistent with theory (KaunKaun and and GuoGuo, , NanolettersNanoletters 2003; 2003; NEGF + DFT gives NEGF + DFT gives didi/mono = 16) & CAFM data/mono = 16) & CAFM data

C8 C8 dithioldithiol C8 C8 monothiolmonothiol

15.1Å15.1Å 13.3Å13.3Å

0.0 0.1 0.2 0.3 0.4 0.5

10n

100n

1µ

T = 4K T = 50K T = 100K T = 150K T = 200K T = 250K T = 290K

I (A

)V (V)


Inelastic Electron Tunneling Spectroscopy (IETS)Tunneling electrons couple with vibrational modes of molecule

Elastic tunnelingeV < hν

Inelastic tunnelingeV > hν

σ = σe + σie

- hνhν

dG/dV = d2I/dV2

- hν hν

G = dI/dV

- hν

hν

I

V

V

V

σe

σe

σie


Inelastic electron tunneling spectroscopy on Inelastic electron tunneling spectroscopy on SAMsSAMs

Scissoring Rocking

WaggingStretching

0.0 0.1 0.2 0.3 0.4 0.5

dI2 /d

V2 (

Arb

. uni

t)

V (V)

0 1000 2000 3000 4000 cm-1

Au-S stretching (33 meV) C-C stretching (133 meV)

CH2 wagging (158 meV)

CH2 stretching (360 meV)CH2 rocking (107 meV)

S-C stretching (80 meV)

CH2 scissoring (186 meV)

2ω @ T = 4 K

Si-H

C-C-C

SiO-H

AuS-H

Wang Wang et. al,et. al, NanoLettersNanoLetters (in press)(in press)


Correct temperature and modulation dependencies

0.0 0.1 0.2 0.3 0.4 0.5

T = 80K T = 65K T = 50K T = 35K T = 20K T = 4K

d2 I/dV

2 (Arb

. uni

t)

V (V)

CC--C stretch intrinsic C stretch intrinsic linewidthlinewidth~4meV~4meV

1 2 3 4 5 6 7 8 9 10 11 120

5

10

15

20

FWH

M (m

V)

AC modulation (RMS value) (mV)

theory

experimental

intrinsic


Correct temperature and modulation dependencies

intrinsic intrinsic linewidthlinewidth ~4meV~4meV

1 2 3 4 5 6 7 8 9 10 11 120

5

10

15

20

FWH

M (m

V)

AC modulation (RMS value) (mV)

theory

experimental

intrinsic

0 10 20 30 40 50 60 70 80 9010

15

20

25

30

35

40

45

50

55 Theoretical calculation Experimental result: V

AC = 8.7 mV

FWH

M (m

V)

Temperature (K)


Au

Au

Interesting case: nitro-amine redox centerInteresting case: nitroInteresting case: nitro--amine amine redoxredox centercenter

2'2'--aminoamino--44--ethynylphenylethynylphenyl--4'4'--ethynylphenylethynylphenyl--5'5'--nitronitro--11--benzenethiolbenzenethiol

0.0 0.5 1.0 1.5 2.0 2.5

0.0

400.0p

800.0p

1.2n

Ivalley= 1 pA

Ipeak= 1.03 nA

T= 60 K

I (A

)

V

J = 53 A/cm2

NDR = -380 µΩ-cm2

J. Chen J. Chen et. alet. al, , ScienceScience 286286, 1550, 1550--1552 (1999)1552 (1999)

J ~ 50 A/cmJ ~ 50 A/cm22

NDR ~ NDR ~ --380 380 µΩµΩ--cmcm22


measurement dispersion in molecular structures

measurement dispersion in molecular structures

0.0 0.5 1.0 1.5 2.0 2.50.0

100.0p

200.0p

300.0p

400.0pT = 300 K

Curre

nt (A

)

Voltage (V)

NO2

nanoporemonothiol

nanoparticle bridgedithiols

nanowiremonothiol

0.0 0.5 1.0 1.5 2.0 2.5

0.0

400.0p

800.0p

1.2n

Ivalley= 1 pA

Ipeak= 1.03 nA

T= 60 K

I (A

)

V

J = 53 A/cm2

NDR = -380 µΩ-cm2

CAFMdithiol

CAFMxbarmonothiol

other similarother similar

nanoporenitroamine

Hgdrop

bilayer

II. . Amlani Amlani et alet al., ., APLAPL 8080, 2761 (2002), 2761 (2002)

J. J. ChenChen et et alal., ., ScienceScience, , 286286, 1550 (1999), 1550 (1999)

J. D. Le, J. D. Le, ApplAppl. Phys. . Phys. Lett. Lett. in in presspress

WalzerWalzer et al., JACS, ja06771v (2004)et al., JACS, ja06771v (2004)

J. J. ChenChen et et alal., ., APLAPL 7777, 1224 (2000), 1224 (2000)

I. Kratochvilova I. Kratochvilova et alet al., ., J. Mat. Chem.J. Mat. Chem. 1212, 2927 (2002), 2927 (2002)

C. Li C. Li et et alal., ., APLAPL 8282, 645 (2003), 645 (2003)

A. M. Rawlett A. M. Rawlett et et alal., ., APL APL 8181, 3043 (2002), 3043 (2002)

A. M. Rawlett A. M. Rawlett et et alal.., , NTNT 1414, 377 (2003), 377 (2003)

STM(done correctly)


2.5 3.0 3.5 4.0

0.0

1.0n

2.0n

3.0n

I (A

)

VFluctuation ~ 1% in peak position and ~ 6% in peak intensity

-2 0 2 4 60.0

1.0n

2.0n

3.0n 1st +sweep 1st -sweep 2nd +sweep 2nd -sweep 3rd +sweep

T = 60K

I (A

)

V

Stability & RepeatabilityStability & RepeatabilityStability & Repeatability

0 2 4 60.0

1.0n

2.0n

3.0n

T = 60 K

Curre

nt (A

)

V

1

23

Fabrication repeatability

Device stability

(as good as T)

(NDR drop ~ 6meV wide, stable)


0

50

100

150

0.0

1.0x10-9

2.0x10-9

3.0x10-9

4.0x10-9

5.0x10-9

0 1 2 3 4 5

0

4.5nACurre

nt (A

)

Voltage (V)

Tem

pera

ture

(K)

-5E-10-4.45E-10-3.9E-10-3.35E-10-2.8E-10-2.25E-10-1.7E-10-1.15E-10-6E-11-5E-125E-111.05E-101.6E-102.15E-102.7E-103.25E-103.8E-104.35E-104.9E-105.45E-106E-106.55E-107.1E-107.65E-108.2E-108.75E-109.3E-109.85E-101.04E-91.095E-91.15E-91.205E-91.26E-91.315E-91.37E-91.425E-91.48E-91.535E-91.59E-91.645E-91.7E-91.755E-91.81E-91.865E-91.92E-91.975E-92.03E-92.085E-92.14E-92.195E-92.25E-92.305E-92.36E-92.415E-92.47E-92.525E-92.58E-92.635E-92.69E-92.745E-92.8E-92.855E-92.91E-92.965E-93.02E-93.075E-93.13E-93.185E-93.24E-93.295E-93.35E-93.405E-93.46E-93.515E-93.57E-93.625E-93.68E-93.735E-93.79E-93.845E-93.9E-93.955E-94.01E-94.065E-94.12E-94.175E-94.23E-94.285E-94.34E-94.395E-94.45E-94.505E-94.56E-94.615E-94.67E-94.725E-94.78E-94.835E-94.89E-94.945E-95E-9

Voltage (V)

Cur

rent

(A)

Tem

pera

ture

(K)

0 50 100 150 2000

1

2

3

Vpe

ak

Temperature (K)

Ea ~ 34 meV

0341

17 VkTmeV

epeakV +

−+

=

Ea

Energetics: 2 state modelEnergeticsEnergetics: 2 state model: 2 state model


Observing NDR in STM experimentsObserving NDR in STM experimentsObserving NDR in STM experiments

Z. J. Donhauser Z. J. Donhauser et al.,et al., unpublished (Weiss group)unpublished (Weiss group)

GGsamplesample > > GGcontrolcontrol, smaller V drop , smaller V drop ⇒⇒ VVbiasbias < < VVthresholdthreshold

0.0 0.5 1.0 1.5 2.0 2.50.0

100.0p

200.0p

300.0p

400.0pT = 300 K

Curre

nt (A

)

Voltage (V)

0.00 0.25 0.50 0.75 1.00

0.0

300.0n

600.0n

T = 60 K

First trace Second trace

T = 295 K

I (A

)

V

~0.9V

i ~ ÷2

~0.95V

i ~ ÷5

(1)(1) Using sample/control current ratio,Using sample/control current ratio,VV””biasbias”” = V= VSTM STM ((iisamplesample/i/icontrolcontrol) ) –– VVvacvac gapgapVVmaxmax, STM, STM < 0.25V to 0.65V< 0.25V to 0.65V

(2) using (less accurate) absolute current (2) using (less accurate) absolute current density, real density, real VmaxVmax, STM ~ 0.2V , STM ~ 0.2V

Max voltage < 0.65 (max)

WalzerWalzer et al., JACS, et al., JACS, ja06771v (2004)ja06771v (2004)


Conformational ChangeConformational ChangeJ. Gaudioso et al., Phys. Rev. Lett. 85, 1918 (2000);

P. Weiss et al., Science 292, 2303 (2001)


DOS of the moleculeDOS of the moleculeDOS of the molecule

20 nm × 20 nm, -2 V, 0.1 nA

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

-6.0 -4.0 -2.0 0.0 2.0 4.0 6.0

V (Volts)

I (n

A)

II--V Curve of Individual TEMPOV Curve of Individual TEMPOMolecule on Clean Si(100)Molecule on Clean Si(100) Hersam, NanoLetters 2003


2-terminal memory cell22--terminal terminal

memory cellmemory cell

Input

Output

write write

erase erase

read read

t (s)200

Vol

tag e

(5V

/ di v

)

0 2 4 6

0.0

50.0p

100.0p

150.0p

"0" "1"

T = 60K

Curre

nt (A

)

Voltage (V)

1.00 1.25 1.50 1.75 2.00

0.0

200.0p

400.0p

600.0p

800.0p T = 300 K "0" "1"

Curre

nt (A

)

Voltage (V)

0 1500 3000 4500 6000

-29

-28

-27

-26

-25

-24 T = 300 Kτ = 910 s

ln(I-

I 0)

t (s)

Appl. Phy. Lett. 78, 3735 (2001).


Is “microelectronics” an adequate justification?Is “microelectronics” an adequate justification?Honestly compare your favorite Honestly compare your favorite nanonano--device (confined device (confined semiconductor, molecular, nanotube, spin, etc.) on the basis ofsemiconductor, molecular, nanotube, spin, etc.) on the basis of

DensityDensityPower dissipationPower dissipationReliabilityReliabilityIntegrationIntegrationSpeedSpeedCostCost

Microelectronics is not a silicon technology

-it’s a lithography technology(*if the devices are good enough)


Fundamental Limits of Transistors

(Zhirnov, et al., Proc. IEEE, Nov. 2003)

Eb

ES

τ = L υ

EbEd

Lmin

off on

ES min= ln(2) kBT

Lmin ≈h 2mEmin =1.5nm(300K)

τ min ≈h ES min

= 0.40 fs (300K)

Limits 2016 ITRS

ES ≈ 735ES min

L ≈ 6Lmin

τ ≈ 4τ min


Why should we care about devices anymore?Why should we care about devices anymore?Honestly compare your favorite Honestly compare your favorite nanonano--device (confined device (confined semiconductor, molecular, nanotube, spin, etc.) on the basis ofsemiconductor, molecular, nanotube, spin, etc.) on the basis of


Y. Chen Y. Chen et al.et al., Nanotechnology , Nanotechnology 1414, 462 (2003), 462 (2003)“…“… (a density) more than 10 times (a density) more than 10 times

greater than today’s silicon memory greater than today’s silicon memory chips” (HP press release) chips” (HP press release)

where are where are the sense the sense

amps?amps?

RDL RDL vsvs TTLTTL

HalfHalf--select select problemproblem

Si: 65nm node (25nm gate) 32aJ/device

demonstrated


Why should we care about devices anymore?Why should we care about devices anymore?Honestly compare your favorite Honestly compare your favorite nanonano--device (confined device (confined semiconductor, molecular, nanotube, spin, etc.) on the basis ofsemiconductor, molecular, nanotube, spin, etc.) on the basis of


Interesting?Interesting?


The First Electrical Computers: The ENIAC (Electronic Numerical Integrator and Computer)

Eckert & Eckert & MauchlyMauchly (U. Penn) 1946: 1st digital computer.(U. Penn) 1946: 1st digital computer.5K 5K ±±, 350 , 350 ××, 50 , 50 ÷÷ per sec. per sec. 18’ x 80’.18’ x 80’. 18K vacuum tubes.18K vacuum tubes.Cost: $0.5M, $1,800/month electrical bill (180 KW)Cost: $0.5M, $1,800/month electrical bill (180 KW)

Why integration?Speed? Power? Cost? Density?

Reliability


Generations of functionalityGenerations of functionality

mechanical

transistor

IC


We have a long way to go - can you recognize this?We have a long way to go - can you recognize this?

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A Decade of Molecular Scale Transport Mark Reed Yale ...admol/presentations/Mark_Reed.pdf · A Decade of Molecular Scale Transport Mark Reed Yale University ... Kushmerick et al,