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THE GENESIS OF MOLETRONICS

Saurav Chandra Sarma

Introduction

Introduction

Molecular Rectifiers

Fabrication of molecular junction

Some common terms

Factors affecting Conductance

Research Highlights

Other molecular Devices

Conclusion

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Sketch of my talkMolecular Rectifiers Fabrication Research

HighlightsLogic Gates Molecular

SwitchesMolecular

WiresIntroduction Molecular Rectifiers Fabrication Common

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Moore’s Law

3The Wall Street Journal

The number of transistor that can be

placed on a single integrated circuit

double about every two year.

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Moore’s Law

4Google images

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• Term coined by Mark Ratner, in 1974.

• Can be defined as technology utilizing

Single molecules,

Small groups of molecules,

Carbon nanotubes, or

Nanoscale metallic or

Semiconductor wires to perform electronic functions.

Molecular Electronics

• This device must exchange information, or transfer states or must be able to

interface with components at the macroscopic level.

• Usually consist of organic molecules sandwiched between conducting

electrodes.

.

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1959 1971 1974 Late 1970s 1980s 1997 2000

R. Feynmann lecture

Kuhn and Mann

experiment

Aviram and Ratner first paper on moletronics

Conferences arranged by

F. Carter

Shirakawa, Heeger and MacDiarmid

awarded Nobel Prize in Chemistry

First attempt to measure single

molecule transport by Reed and Tour

Development of STM and AFM by

IBM

Pioneers of Moletronics

Bottom-Up ( Why molecules..??)

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Speed:Good molecular wires can reduce the transit time of typical transistors.

New functionalities: New property can easily be assigned to a molecule that are not possible to implement in conventional solid state physics.

Flexibility:Pi conjugation and therefore conduction can be switched on and off by changing molecular conformation providing potential control over electron flow.

Self-assembly:Can create large arrays of identical devices.

Size: Molecules are small that leads to higher packing density of devices.

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Molecular Rectifiers Molecular

Wires

Molecular Switches

Molecular Devices

Molecular Transistor

Molecular Sensors

Molecular Devices

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What is a Rectifier…???

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HALF-WAVE RECTIFIER

RECTIFIERS: It converts alternating waveform to direct waveform.

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First pioneering paper in Moletronics

10Aviram, A. et. al., Chem. Phys. Lett. 29, 277–283 (1974).

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Proposal of Molecular Rectifier

An organic molecule to have rectifier properties should have roughly the

properties of p-n junction.

11Aviram, A. et. al., Chem. Phys. Lett. 29, 277–283 (1974).

By the use of EDG/EWG substituents in the aromatic ring, we can

increase/decrease electron density in the aromatic ring and thus create p-

type and n-type molecular junctions.

Hemiquinone

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Mechanism of rectification by substitution group

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13Aviram, A. et. al., Chem. Phys. Lett. 29, 277–283 (1974)

Alligator group

Molecular bridgeLeft electrode

Right electrode

Potential Barrier

Energy Levels

D

A

Y

X

Zero Biased

14Aviram, A. et. al., Chem. Phys. Lett. 29, 277–283 (1974)

D

AX=EDGY= EWGD= Donor halfA= Acceptor half

Y

X

VI

Forward Biased

Current Flows

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X=EDGY= EWGD= Donor halfA= Acceptor half

Y

X

X=EDGY= EWGD= Donor halfA= Acceptor half

VI

Reverse Biased

No Current Flows

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D

A

Fabrication of molecular junction

DEPOSITION TECHNIQUE:

Self-assembled monolayer (SAM)

Langmuir-Blodgett (LB) Technique

SOPHISTICATED TECHNIQUES:

The size of the molecule is less than the resolution of the lithographic

method

Following sophisticated techniques are used:

• Electro-migration technique

• Scanning Probe technique

• Mechanically Controllable break-junctions (MCBJs)

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Langmuir- Blodgett film technique

• LANGMUIR-BLODGETT (LB) TECHNIQUE : A LB film consists of one or more monolayers of an organic material, deposited from the surface of a liquid onto a metal surface by immersing the the solid substrate into the liquid.

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Self-assembly monolayer technique

• SELF-ASSEMBLED MONOLAYERS (SAM): The substrate covered with the metal layer is

dipped into the molecular solution. Ampiphilic molecules equipped with one anchoring

group adsorbs chemically onto the metal surface.

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Mechanically Controllable Break Junction technique

20Reed et. al., Science, 278, 252-253 (1997)

Schematic of MCB junction a Bending beamb Counter supportc Notched gold-wired Glue contactse Piezo-elementf Glass tube containing solution

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• Changing the environment around the electrodes.

• Changing the alligator group attached to the metal electrode

• Inducing asymmetry in the molecular design.

Rectification Ratio

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• Rectification Ratio can be defined as the ratio of the current at conducting

voltage to the current at insulating voltage.

RR=

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Conductance Quantum

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• Conductance given by the Landauer expression

G=

G= Conductance

Ti=Transmission probabilities in the conductance channels.

• Monovalent metal single atom ( such as Au, Cu and Ag ) possess a single channel

for electron transmission. Therefore,

Conductance Quantum= 1 G0 =

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Conductance Trace

• It is the graph of conduction as a function of electrode separation.

23https://www.weizmann.ac.il/chemphys/orental/research.html

Conductance histogramConductance vs. Displacement graph

Repeated ‘n’ times

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Conductance Quantization at molecular level

24Tao et. al., Science, 301, 1221-1223 (2003)

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Electrode Separation

X

Alkanedithiols:SHHS

RC6=10.5 MW

HS SH

N=6:

N=8:

RC8=51 MW

SHHSN=10:

RC10=630 MW

Factor affecting molecular conductance- Chain Length

25Zhou et. al., J Chem. Phys., 128, 044704-907 (2008)

G(L) = Ae-βL

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Effect of Twist angle

26Venkataraman et. al., Nature, 442, 904-907 (2006)

G α cos2θ

Conductance for the series decreases with increasing twist angle

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Factor affecting molecular conductance- Aromaticity

27Chen et al, JACS 442, 918-920 (2014)

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The highest conductance is achieved by structure that can

easily acquire quinoid like structure and hence attain a

better coupling between gold electrodes and other cyclic

units.

28Ratner, A. et. al., Nano Lett., 15 (3), 1577–1584 (2015)

New design of molecular rectifierIntroduction Molecular

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Molecular Devices

Conclusion

Fermi-Level Pinning

29Ratner, A. et. al., Nano Lett., 15 (3), 1577–1584 (2015)

• Energy offset between the electrode fermi-level and the frontier orbital of the molecule is unchanged even when bias is applied.

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Transmission Window

30Ratner, A. et. al., Nano Lett., 15 (3), 1577–1584 (2015)

New design of molecular rectifierIntroduction Molecular

Rectifiers Fabrication Common Terms

Factors Research Highlights

Molecular Devices

Conclusion

Transmission Window

The environment does the trick

31Venkataraman, L. et al. Nat. Nanotechnol. 10, 522–527 (2015)

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The environment does the trick

Single-molecule junctions with high

rectification ratios can be realized by

exposing different electrode surface

areas to an ionic liquid.

32Venkataraman, L. et al. Nat. Nanotechnol. 10, 522–527 (2015)

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Polar Solvent Non-Polar Solvent

33Whitesides, G. et. al., J. Am. Chem. Soc., 133 (39), 15397–15411 (2011)

Molecular half-wave rectifierIntroduction Molecular

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Molecular Devices

Conclusion

S Fc2

34Whitesides, G. et. al., J. Am. Chem. Soc., 133 (39), 15397–15411 (2011)

Molecular half-wave rectifierIntroduction Molecular

Rectifiers Fabrication Common Terms

Factors Research Highlights

Molecular Devices

Conclusion

S Fc

35Whitesides, G. et. al., J. Am. Chem. Soc., 133 (39), 15397–15411 (2011)

Molecular half-wave rectifierIntroduction Molecular

Rectifiers Fabrication Common Terms

Factors Research Highlights

Molecular Devices

Conclusion

S CH3

36Whitesides, G. et. al., J. Am. Chem. Soc., 133 (39), 15397–15411 (2011)

Molecular half-wave rectifierIntroduction Molecular

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Molecular Devices

Conclusion

37Nijhuis, C. et. al., Nano Lett., 10, 3611—3619 (2010)

Mechanism of RectificationIntroduction Molecular

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Molecular Devices

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Other Molecular Devices

38Venkataraman, L. et. al., Nano Lett., 11 (4), 1575–1579 (2011)

A Single molecule potentiometer

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Higher conductance state:

Electrode Olefin SulfideElectrode

Low conductance state:

ElectrodeSulfide Olefin Sulfide

Electrode

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Other molecular devices

Molecular Wires

Molecular Switches

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Cuerva et. al., Nanoscale, 3, 4003-4014 (2011)

Challenges of moletronics

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Stability of molecules.

Reproducibility of results.

Controlled fabrication within specified tolerances.

Hard experimental verification.

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“The Next Big Thing is very, very small

Trillions of transistors

THz processors

Infinite storage capacity

High computation power

Concluding Remarks

It is the birth of a new technological revolutionAnd the death of silicon”

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