molecular electronics for fun and profit(?)simons.hec.utah.edu/tstcsite/hutchinsonlectures... ·...
TRANSCRIPT
Molecular ElectronicsFor Fun and Profit(?)
Prof. Geoffrey HutchisonDepartment of ChemistryUniversity of [email protected]
July 22, 2009
http://hutchison.chem.pitt.edu
Moore’s “Law:” Transistor Count Doubles Every 18 Months
From Intel Corp. circa 2007
Gordon Moore: Co-founder of Intel
Similar trends observed in chip performance,price per peformance, etc.
Moore-San’s Law
Image courtesy M. Ratner
Don’t Underestimate Silicon...
Actually, these are from 1997(!)
Current Intel Roadmap
45nm 32nm
International Technology Roadmap for Semiconductors (ITRS)
http://www.itrs.net/reports.html
Moore’s Second Law: Exponential Economics
0
1,200,000,000
2,400,000,000
3,600,000,000
4,800,000,000
6,000,000,000
1966 1985 1992 1995 2002 2007
2007:~$6 billion!
Cost of a building a new fabrication plant doubles every 3-4 years:
Advances in conventional lithography are quickly becoming cost-prohibitive!
Cost
(U
S$)
Molecular Electronics: Just Nanoscale?
M2+
M2+
M2+
M2+
M2+
3D: Bulk Films
2D: Monolayer
1D: Chains
0D: Individual Molecules
Why Organic Electronics?
Relative to Inorganic Materials:
Pros
Greater “tailorability” through synthetic chemistry
“Wet” deposition
Wide-area
Inexpensive
Flexible, lightweight
Synthesis = 6.02x1023
Cons
Lower electron mobility
Slower switching speeds
Hard to obtain complementary p/n logic
Integration into industry?
Broad Applications for Molecular Electronic Materials
Light-Emitting Diodes
Hole transport layers
Flexible anodes
Photovoltaic Devices
Thin-Film Transistors
Flexible circuits
“Smart” Windows
Fast color changes
Anti-Static Films
Device fabrication
Photographic film
Batteries: Not Just Inorganics...
Energy Density for Secondary Batteries
0 50 100 150 200 250Gravimetric Energy Density / Whkg-1
Volu
met
ric
Ener
gyD
ensi
ty /
WhL-1
0
100
200
300
400Sm
alle
r
LighterLead
Ni-CdNi-MH
Li-IonLi-Metal
PolymerLi-Ion
Reaction Mechanism for LIBs
ElectrolyteOrganic Solvent
plusSupportingElectrolyte
(ex. LiBF4/PC)
AnodeGraphite
(IntercalationLayer)
CathodeLithium
Metal Oxide(ex. LiCoO2)
AnodeCurrent
Collector
CathodeCurrent
Collector
: Li+: Doped Li+
Reaction Mechanism for LIBs
ElectrolyteOrganic Solvent
plusSupportingElectrolyte
(ex. LiBF4/PC)
AnodeGraphite
(IntercalationLayer)
CathodeLithium
Metal Oxide(ex. LiCoO2)
AnodeCurrent
Collector
CathodeCurrent
Collector
e-e-
: Li+: Doped Li+
Ink-Jet Printing of Organic Electronics
Sekitani et al. PNAS 2008 p. 4976
Konarka: Ink Jet Printing for Solar CellsMar. 4, 2008Ink-Jet Printing
Transistors
GE: Ink Jet Printing for DisplaysMar. 11, 2008
Organic Field-Effect Transistors
Dielectric
Gate Electrode
Source DrainSemiconductor
Vsd
Isd ~ 0.0 A “Off”
Isd = 10x A “On”VgateDielectric
Gate Elecrode
Source DrainSemiconductor
Applied Gate Potential
Vsd
Dielectric
Semiconductor
Organic Field-Effect Transistors
Dielectric
Gate Elecrode
Source DrainSemiconductor
Applied Gate Potential
Operation of an OrganicField-Effect Transistor
S
S S
S
n
N
N
O O
OO
X
X
S
S
R
R
n
S
S
n
OO
O ONH
HN
n
Example OrganicSemiconductor Materials
Dielectric
Gate Electrode
Source DrainSemiconductor
Dielectric
Semiconductor
Back to the Nanoscale...
M2+
M2+
M2+
M2+
M2+
3D: Bulk Films
2D: Monolayer
1D: Chains
0D: Individual Molecules
Si Substrate
SiO2
PbSe PbSe
Enough Bulk Conductivity:How Do You Wire Up a Molecule?
STM tip
Many, Many Methods...
Crossbars
Break Junctions
Example: Device Fabrication
Sixty 15 mm x 6 mm chips are fabricated on a thin (200 µm) Si wafer.
Bonding pads are defined by photolithography.
Critical features are defined by e-beam lithography.
A timed etch is used to suspend the junctions.
Ralph Group, Cornell
Electromigration: Making a 1-3nm Gap
Current
Voltage
Ralph Group, Cornell
Single Molecule Transistors
V
Drain(Pt)
N
N N
NN
NN
N N
NN
NN
N N
NN
N
RuRu
Source(Pt)
Gate (Al)
Vg
Gate Oxide (Al2O3)
Ralph Group, Cornell
Note: No Guarantee of 2 Connections
Metal / Molecule Interface
WARNING: PowerPoint Science!
One-Site
“Bridging”
Three-Site
Coordination
“Coulomb Blockade”
Source Drain
“Coulomb Blockade”
Source Drain
e-
“Coulomb Blockade”
Source Drain
e-
Source Drain
e- e-
“Coulomb Blockade”
Source Drain
e-
Source Drain
e- e-
SourceDrain
e- e-
Coulomb Blockade in [Ru2(tppz)3]+4
0.00 0.02 0.04
7.5
0.0
-7.5
Gate (V)
Bias (mV)
0 1250 2500
Conductance (nS)
4K Temp. Single-MoleculeCoulomb Blockade Transistor
DrainSource Drain
e-
Source
e-
Charge passes when source, drain and molecule bridge electronic
states are aligned
Charge does not pass when molecule bridge electronic states
are above or below
Vsd
Is it Really Single-Molecule?
few and eventually a single atomic chain.10 A conductance
histogram constructed from 1000 consecutive traces shows
clear peaks around 1, 2, and 3 ! G0 (Figure 1). When the
single atom chain is broken in the absence of molecules,
the conductance either decreases exponentially with the
electrode displacement due to tunneling across the gap
between the two Au electrodes or drops from G0 to below
our experimental detection limit possibly due to the broken
ends snapping back as the contacts relax (Figure 2a, yellow
traces).
The conductance histograms of three differently substituted
aromatics, 1,4-benzenedithiol, 1,4-benzenediisonitrile, and
1,4-benzenediamine, are compared in Figure 2b. For each
of the molecules, a large fraction of the individual traces
show additional steps at conductance levels below G0, as
shown in Figure 2a. Conductance histograms are constructed
from more than 3000 consecutively measured conductance
traces without any data selection or processing so as to
include all possible molecule/electrode conformations in the
statistical analysis.11 In comparison to the data for the dithiol
or the diisonitrile, the conductance histogram for 1,4-
benzenediamine is strikingly well-defined. Indeed, within our
experimental accuracy, the histogram differs from that of
Au only for conductance between 0.003 and 0.015 G0. This
implies that the additional steps occur only within this
conductance range. From a Gaussian fit to this peak (inset
Figure 2b), we deduce the most prevalent conductance value
for the molecule to be 0.0064 ( 0.0004 G0. A Gaussian
cannot be fit to the diisonitrile data although a broad peak
is visible in Figure 2b between 0.001 and 0.1 G0. The
conductance for the dithiol occurs over a wide range. The
resulting histogram is diffused showing no well-defined trend
in the conductance.12 (See the Supporting Information for
other control experiments.)
The broadening of the conductance histograms of the
diisonitriles and dithiols is not unexpected. Thiols are known
to bind to gold in a variety of motifs, for example, a-top
and threefold hollow sites. The binding of sulfur over a-top
and threefold hollow sites has been calculated to yield a
difference of up to a factor of 3 in the conductance.13
Moreover, the dithiols may contain oligomeric molecules
formed through oxidative disulfide formation. Isonitriles14
suffer from similar complications. They are known to
oligomerize easily15 and also have a variation in their binding
to the surface gold atoms.16
We have measured the conductance of a series of alkanes
with amine end groups that progresses from 1,2-ethylene-
diamine to 1,8-octanediamine. The conductance histogram
for each alkane (Figure 3a) displays a prominent primary
peak.17 We determined the conductance of these molecules
from the center position of a Gaussian fit to the primary
peaks.18 Figure 3b shows these conductance values plotted
against the number of methylene groups on a semilog scale
along with an exponential fit to the data. The clear
exponential dependence provides additional evidence that the
peak in the histograms corresponds to the conductance of a
Figure 1. Conductance histogram constructed from 1000 tracesmeasured while breaking Au point contacts in the absence ofmolecules on a linear scale. The bias is 25 mV, and bin size is10-4 G0. The inset shows five traces at arbitrary x axis offsets.
Figure 2. (a) Sample conductance traces measured without molecules (yellow) and with 1,4-benzenediamine (blue), 1,4-benzenedithiol(red), and 1,4-benzenediisonitrile (green) shown on a semilog plot. All data were measured at 25 mV bias, although no bias dependencewas found up to 250 mV. (b) Conductance histograms constructed from over 3000 traces measured in the presence of 1,4-benzenediamine(blue), 1,4-benzenedithiol (red), and 1,4-benzenediisonitrile (green) shown on a log-log plot. The control histogram of Au without moleculesis also shown (yellow). Histograms are normalized by the number of traces used to construct the histograms. Inset: same data on a linearplot showing a Gaussian fit to the peak (black curve). Bin size is 10-4 G0.
Nano Lett., Vol. 6, No. 3, 2006 459
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Venkataraman, L. et. al. Nano Letters 2006 v. 6, 458-462
You must do statistics....
You must do statistics...
Careful controls(“no molecules”)
Dilution Experiments
Is it Really A Molecule?
Is it a nanoparticle?
What are molecular “signatures?”
What are control experiments?
What are our statistics?
WARNING: Be Skeptical!We can do theory...
But what’s the real experiment?
Prospectus
Statistics, Statistics, Statistics!
Charge Transport Mechanisms
More Charge Transport
Ensembles & Dynamics
Solar Energy: Where things get (more?) complicated