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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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 22
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 33
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 44
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 55
L.P. L.P. Kouwenhoven Kouwenhoven et al. (1998)et al. (1998)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 66
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 77
Excited states:
Coulomb diamondCoulomb diamond
A.K. Hüttel (2003)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 88
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 99
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1010
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1111
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1212
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1313
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1414
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1515
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).
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1616
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1717
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1818
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 1919
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2020
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2121
-2 0 2
Ratner group
Theory of MCB BDTTheory of MCB BDTTheory of MCB BDT
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2222
ComparisonComparison of of moleculesmolecules
Courtesy H. Weber
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2323
Molecular Measurements: which is best?Molecular Measurements: which is best?
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2424
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2525
- 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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2626
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2727
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2828
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 2929
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3030
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3131
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3232
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3333
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3434
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3535
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3636
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3737
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3838
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 3939
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4040
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4141
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4242
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).
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4343
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4444
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4545
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4646
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4747
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4848
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 4949
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5050
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5151
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5252
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5353
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5454
Conformational ChangeConformational ChangeJ. Gaudioso et al., Phys. Rev. Lett. 85, 1918 (2000);
P. Weiss et al., Science 292, 2303 (2001)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5555
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5656
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).
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5757
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)
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5858
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 5959
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
DensityDensityPower dissipationPower dissipationReliabilityReliabilityIntegrationIntegrationSpeedSpeedCostCost
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 6060
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
DensityDensityPower dissipationPower dissipationReliabilityReliabilityIntegrationIntegrationSpeedSpeedCostCost
Interesting?Interesting?
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 6161
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
MPI Dresden Colloquia February 2004 M. Reed (YaMPI Dresden Colloquia February 2004 M. Reed (Yale)le) slide slide 6262
Generations of functionalityGenerations of functionality
mechanical
transistor
IC
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