Miscellaneous “Hot” Topics

Molecular Electronics

Photonic Crystals

Spintronics* *Sorry, there is no time for this!

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Molecular Electronics

Artist’s Depiction of a Long Molecule Between Metal Contacts

Molecular ElectronicsFrom Wikipedia:

“Molecular Electronics(sometimes called moletronics) involves the study & application of molecular building blocks for the fabrication of electronic components. This includes both passive & active electronic components. Molecular electronics is a branch of nanotechology.”

Wikipedia Continued“An interdisciplinary pursuit, molecular electronics spans physics, chemistry, and materials science. The unifying feature is the use of molecular building blocks for the fabrication of electronic components. This includes both passive (e.g. resistive wires) and active components such as transistors and molecular-scale switches. Due to the prospect of size reduction in electronics offered by molecular-level control of properties, molecular electronics has aroused much excitement both in science fiction and among scientists. Molecular electronics provides means to extend “Moore's Law” beyond the foreseen limits of small-scale conventional silicon integrated circuits.

• Molecular electronics is split into two related but separate subdisciplines:

1. Molecular Materials for Electronics:Utilizes the properties of the

molecules to affect the bulk properties of a material.

2. Molecular scale electronics:Focuses on single-molecule

applications.

Prophecies of the Future of Technology are Risky, Even if Made by Very Intelligent, Educated people!!

“Heavier-than-air flying machines are impossible.” (1895)

“I have not the smallest molecule of faith in aerial navigation other than ballooning...I do not care to be a member of the

Aeronautical Society.” (1896)“There is nothing new to be discovered in physics.

All that remains is more precise measurement.” (1900)

For example consider some “memorable quotes” from perhaps

The Greatest Scientistof the 19th Century:

Lord Kelvin(William Thompson)

Typical “Fortune Teller” or “Psychic"

Another 19th Century Example

“Everything that can be invented has been invented.”

Charles H. Duell, CommissionerU.S. Office of Patents, 1899

More Prophecies of the Future of Technology!

“I think there is a world market for maybe five computers.”T.J. Watson, President & CEO, IBM Corporation, 1941-1956

“640K of computer memory ought to be enough for everybody!”Bill Gates, co-Founder, Microsoft Corporation.

One of the wealthiest men in the world.

“There is no reason anyone would want a computer in their home.” Ken Olson, co-Founder, Digital Equipment Corporation (DEC)

“There is not the slightest indication that nuclear energy will ever be obtainable.”

Albert Einstein, Nobel Laureate.One of the greatest scientists who ever lived!

• More examples of the risk in predicting the future: Some quotes from the 20th Century:

More 20th Century Examples

“Computers in the future may weigh no more than 1.5 tons.”

The Magazine Popular Mechanics, 1949

“I have traveled the length and breadth of this country and talked with the best people, and I

can assure you that data processing is a fad that won't last out the year.”

Business book editor, Prentice Hall, 1957

More 20th Century Examples“I believe OS/2 is destined to be the most important operating system, and possibly

program, of all time”.Bill Gates, 1987

“.. and it probably never will support anything other than AT-hard disks, ..”

Linus Torvalds in his Linux release note from August 26, 1991

More 20th Century Examples“Windows NT addresses 2 Gigabytes of

RAM, which is more than any application will ever need. .”

Microsoft on the development of Windows NT, 1992

“.. and it probably never will support anything other than AT-hard disks, ..”

Linus Torvalds in his Linux release note from August 26, 1991

Moore’s “Law”

• The number of transistors that can be fabricated on a silicon integrated circuit--and therefore the computing speed of such a circuit--is doubling every 18 to 24 months.

• After 4 decades, solid-state microelectronics has advanced to the point at which more than 100 million transistors, with feature size around 120 nm can be put onto a few square centimeters of silicon.

Moore’s “Law” (1965)Every 1.5 years the number of transistors on a chip is doubled.Does this mean that there could be a transistor the size of a single-atom by 2020?

Smaller, Denser, Cheaper Electronics

Silicon & Moore’s Law: Practical Problems• Heat dissipation.

– At present, a state-of-the-art a 500 MHz microprocessor with 10 million transistors emits almost 100 watts--more heat than a stove-top cooking surface!

• Leakage from one device to another. – The band structure in silicon provides a wide range of allowable

electron energies. Some electrons can gain sufficient energy to hop from one device to another, especially when they are closely packed.

• Capacitive coupling between components.• Fabrication methods (Photolithography).

– Device size is limited by diffraction to about one half the wavelength of the light used in the lithographic process.

• “Silicon Wall”– At 50 nm & smaller it’s not possible to dope silicon uniformly.

Conclusion: This is the end of the line for bulk behavior!!

Related to Moore’s “Law” is

Moore’s “Second Law.”Moore’s 2nd “Law” is a financial “law”!

Plant Cost Mask Cost

X 1

000$

Billions of Dollars!!

Silicon & Moore’s LawMoore’s “Second Law”

• Continued exponential decrease in silicon device size is achieved by a continuing exponential increase in financial investment. An estimated cost for a fabrication facility by 2015 is

$200 billion!!!!!

• In addition, transistor densities achievable under the present & foreseeable silicon format are not sufficient to allow microprocessors to do the things imagined for them.

Nearing the End of Moore's Law

So far, history has proved Gordon Moore more or less right. But transistor growth may soon slow for a number of reasons: Difficulties to contend with the heat produced and power consumed by transistor-crammed chips Photolithography as we know it is expected to reach its ultimate limits before 2020 Chip voltages cannot be reduced forever

The Limits of Silicon Technology

Still in 2002 Intel's chief technology officer Pat Gelsinger said, "We're on track, by 2010, for 30-gigahertz devices, 10 nanometers or less, delivering a tera-instruction of performance."

But Gelsinger was wrong. By 2010 Intel and its competitors were making processors that topped out at less than four gigahertz, and 22 nm had only reached the design lab.

Hope for Moore's Law in New Technologies?

Miniaturization of integrated circuits based on photolithography may soon come to an end. However, new technologies have emerged that may push miniaturization to the nanoscale. On the forefront are memristors and graphene. In 2011 the first quantum computer was announced and shortly after researchers at IBM presented the first graphene integrated circuit. The graphene IC has only one transistor (framed in the bottom picture) and two coils, but it operates at 10 GHz.

Image source: IBM

Single-Atom Transistor

Miniaturization reached its ultimate limit in February 2012, when scientists at University of New South Wales, Australia, reported having created a single-atom transistor – at least under the eye of a scanning tunneling microscope. It is a phosphorous atom that has replaced a silicon atom in a group of six, and which acts as a switch when a voltage is applied. Ok, it might take a while before this device finds its way to computer stores.

Image source: UNSW/Sydney Morning Herald

Death to Moore's Law!

Despite impressive progress in hardware technology, there are alternatives that should be considered. Steve Wozniak, the inventor of the Apple II, once said: "The repeal of Moore's Law would create a renaissance for software development. Only then will we finally be able to create software that will run on a stable and enduring platform."

Finally: An Accurate Statement

”Bill Gates is a very rich man today ... and do you want to know why? The

answer is one word: versions.”

Dave Barry

Welcome Windows 1, 2, 3, NT, 95, 98, 2000, ME, Xp, Vista, 7, 8. We’re so happy

to pay for all of you!

Electronics Development Strategies

Top-Down• Continued reduction in size of bulk semiconductor devices.

Bottom-UpMolecular Scale Electronics

• Design of molecules with specific electronic functions.• Design of molecules for self assembly into

supramolecular structures with specific electronic functions.

• Connecting molecules to the macroscopic world.

Bottom-Up: Why Molecules?• Molecules are small.

– With transistor size at 180 nm on a side, molecules are some 30,000 times smaller.

• Electrons are confined in molecules.– Whereas electrons moving in silicon have many possible energies that will

facilitate jumping from device to device, electron energies in molecules and atoms are quantized - there is a discrete number of allowable energies.

• Molecules have extended pi systems.– Provides thermodynamically favorable electron conduit - molecules

act as wires.• Molecules are flexible.

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

• Molecules are identical.– Can be fabricated defect-free in enormous numbers.

• Some molecules can self-assemble.– Can create large arrays of identical devices.

Molecules as Electronic DevicesHistorical Perspective

1950’s: Inorganic Semiconductors• To make p-doped material, one dopes Group IV (14) elements (Si, Ge) with

electron-poor Group III elements (Al, Ga, In)• To make n-doped material, one uses electron-rich dopants such as the Group V

elements N, P, As.

1960’s: Organic Equivalents• Inorganic semiconductors have their organic molecular counterparts. Molecules

can be designed so as to be electron-rich donors (D) or electron-poor acceptors (A).

• Joining micron-thick films of D and A yields an organic rectifier (unidirectional current) that is equivalent to an inorganic pn rectifier.

• Organic charge-transfer crystals and conducting polymers yielded organic equivalents of a variety of inorganic electronic systems: semiconductors, metals,

superconductors, batteries, etc. BUT: Organic semiconductors weren’t as good as the

inorganic standards (more expensive & less efficient)

1970’s: Single Molecule Devices

In the 1970’s organic synthetic techniques start to grow up prompting the idea that device function can be combined into a single molecule.Aviram and Ratner suggest a molecular scale rectifier. (Chem. Phys. Lett. 1974)

But, no consideration as to how this molecule would be incorporated into a circuit or device.

1980’s Single Molecule Detection.

How to image at the molecular level. How to manipulate at the molecular level.

Scanning Probe Microsopy. STM (IBM Switzerland, 1984)AFM

1990’s: Single Molecule Devices• New imaging and manipulation techniques • Advanced synthetic and characterization techniques

• Advances in Self-Assembly »» Macroscopic/Supramolecular ChemistryThese developments have finally allowed scientists to address the question:“How can molecules be synthesized and assembled into structures that function in the same way as solid state silicon electronic devices and how can these structures be integrated with the macroscopic regime?”

Mechanically-Controlled Break Junction

Resistance is a few megohms. (Schottky Barrier)

Molecular Junction

Alkyl Tunnel Barriers

Conduction between the two ends of the moleculedepends on pi orbital overlap which in turn relies on a planar arrangement of the phenyl rings.

Resonant Tunneling Diode

mNDR = molecular Negative Differential ResistanceMeasured using a conducting AFM tip

Negative Differential Resistance

One electron reduction provides a charge carrier. A second reduction blocks conduction. Therefore, conduction occurs only between the two reduction potentials.

Voltage-DrivenConductivity Switch

Applied perpendicular field favorszwitterionic structure which is planarBetter pi overlap, better conductivity.

Dynamic Random Access Memory

Voltage pulse yieldshigh conductivityState - data bit stored

Bit is read as highin low voltage region

Device is fabricated by sandwiching a layerof catenane between an polycrystalline layer of n-dopedsilicon electrode and a metal electrode. The switch isopened at +2 V, closed at -2 V and read at 0.1 V.

Voltage-Driven Conductivity Switch

High/Low Conductivity Switching DevicesRespond to I/V Changes

Voltage-Driven Conductivity Switch

n-type

Voltage-Driven Conductivity Switch

Molecular Wire Crossbar Interconnect(MWCB)

Nanotube conductivity is quantized.Nanotubes found to conduct current ballistically and do not dissipate heat. Nanotubes are typically 15 nanometers wide and 4 micrometers long.

Carbon Nanotubes

Gentle contact needed

Molecular Self-Assembly• Self-Assembly on Metals

– (e.g., organo-sulfur compounds on gold)

• Assembly Langmuir-Blodgett Films– Requires amphiphilic groups

for assembly

• Carbon Nanotubes– Controlling structure

Cyclic Peptide Nanotubes as Scaffolds for Conducting DevicesHydrogen-bonding interactions promote stacking of cyclic peptidesPi-systems stack face-to-face to allow conduction along the length of the tube

Cooper and McGimpsey - to be submittedCYCLIC BIOSYSTEMS

Spontaneous self-directed chemical growth allowing parallel fabrication of identical complex functional structures.

Molecular Electronics:Measuring single molecule conduction

Kushmerick et al. PRL 89 (2002) 086802

Cross-wire

Wang et al. PRB 68 (2003)

035416

Nanopore STM Break Junction

B. Xu & N. J. Tao Science (2003) 301, 1221

Electromigration

H. S. J. van der Zant et al. Faraday Discuss. (2006)

131, 347

Nanocluster

Dadosh et al. Nature 436 (2005) 677

Scanning Probe

Cui et al. Science

294 (2001) 571

Reichert et al. PRL 88 176804

Mechanical Break Junction

Single-Molecule ConductivityL

ELECTRODER

ELECTRODEMOLECULE

L ELECTRODE

R ELECTRODE

MOLECULE

Fermi energy

Molecular Orbitals

eV

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MOLECULE

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Molecular Orbitals

Elastic

InelasticV

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Finding a true molecular signature:Inelastic Electron Tunnelling Spectroscopy (IETS)

Molecular level structure between electrodes

en erg y

LUMO

HOMO

“The resistance of a single octanedithiol molecule was 900 50 megaohms, based on measurements on more than 1000 single molecules. In contrast, nonbonded contacts to octanethiol monolayers were at least four orders of magnitude more resistive, less reproducible, and had a different voltage dependence, demonstrating that the measurement of intrinsic molecular properties requires chemically

bonded contacts”.

Cui et al (Lindsay), Science 294, 571 (2001)

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Dynamics of current voltage switching response of single bipyridyl-dinitro oligophenylene ethynylene dithiol (BPDN-DT) molecules between gold contacts. In A and B the voltage is changed relatively slowly and bistability give rise to telegraphic switching noise. When voltage changes more rapidly (C) bistability is manifested by hysteretic behavior

Lortscher et al (Riel), Small, 2, 973 (2006)

Chem. Commun., 2006, 3597 - 3599, DOI: 10.1039/b609119a

Uni- and bi-directional light-induced switching of diarylethenes on gold nanoparticles

Tibor Kudernac, Sense Jan van der Molen, Bart J. van Wees and Ben L. Feringa

“In conclusion, photochromic behavior of diarylethenesdirectly linked to gold nanoparticles via an aromatic spacer hasbeen investigated. Depending on the spacer, uni- (3) or bidirectionality(1,2) has been observed.”

Switching with light

Current–voltage data (open circles) for (a) openmolecules 1o and (b) closed molecules 1c

Nanotechnology 16 (2005) 695–702Switching of a photochromic molecule on gold electrodes: single-moleculemeasurementsJ. He, F. Chen, P. Liddell, J. Andr´easson, S D Straight, D. Gust, T. A. Moore,A. L. Moore, J. Li, O. F Sankey and S. M. Lindsay

Temperature and chain length dependence

Giese et al, 2002

Michel-Beyerle et al

Selzer et al 2004

Xue and Ratner 2003

Electron transfer in DNA

DNA-news-1

DNA-news-4

DNA-news-2

Conjugated vs. Saturated Molecules: Importance of Contact Bonding

Kushmerick et al., PRL

(2002)

2 -vs. 1-side Au-S bonded conjugated system gives at most 1 order of magnitude current increase compared to 3 orders

for C10 alkanes !

SS S/AuAu/S

10-4

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101

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SS S/AuAu//

Au//CH3(CH2)7S/Au

Au/S(CH2)8SAu

Positive bias

negative bias

Lindsay & Ratner 2007

Where does the potential bias falls, and how?

•Image effect

•Electron-electron interaction (on the Hartree level)Vacuu

mExcess electron density

Potential profile

Xue, Ratner (2003)

Galperin et al 2003

L

Galperin et al JCP 2003

Experiment Theoretical Model

Experimental i/V behavior

Experimental (Sek&Majda)

junction Ratio of current: i(-1.0 V)/i(+1.0 V)a

Hg-SC12/C12S-Au 0.98 0.13

Hg-SC12/C10S-Au 1.03 0.07

Hg-SC16/C12S-Au 1.22 0.16

Hg-SC12/C9S-Au 1.44 0.20

Hg-SC16/C10S-Au 1.34 0.19

Hg-SC16/C9S-Au 2.03 0.27

aCurrent at the negative bias refers to the measurement with the Hg side of the junction biased negative relative to the Au side.

Cui et al (Science 2001):

The sulfur atoms (red dots) ofoctanethiols bind to a sheet of gold atoms (yellow dots), and theoctyl chains (black dots) form a monolayer. The second sulfuratom of a 1,8-octanedithiol molecule inserted into themonolayer binds to a gold nanoparticle, which in turn is contacted by the gold tip of the conducting AFM.

J. G. Kushmerick et al., Nano Lett. 3, 897 (2003). A. S. Blum, J. G. Kushmerick, et al., The J. Phys. Chem. B 108, 18124 (2004).

1-nitro-2,5-di(phenylethynyl-4’-mercapto)benzene

Y. Selzer et al., Nano Letters 5, 61 (2005).

Red – single molecule; black – molecular layer. Dashed black is molecular layer per molecule

Red – single molecule; black – molecular layer per molecule

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Resonant tunneling?

Carbon Nano Tubes (CNT)

Issues:•Production of Single Walled CNTs yield a mixture of types (dimensions to less than 1nm)

• Metallic• Semiconductive

•Separation of types is time consuming

Potential Solutions•Continue development efforts

Benefits:•Novel electronic devices•High temperature applications•Improved microscopy

Solar Cells (Organic)

Issues:•Efficiencies•Material development•Manufacturing processes

Potential Solutions•Development of organic plastics with improved efficiency•Development of adsorptive dyes•Flexible conductors•Enhanced property covering material

Benefits:•Low cost energy•Inexpensive to manufacture yielding to wide spread applications

Credit: Nicole Cappello and the Georgia Institute of Technology

New Material Properties

Issues:•Unanticipated properties are being found in nano materials – Example:

• Thirteen atoms of Silver have been shown theoretically to be magnetic

• Thirteen atoms of Platinum have been experimentally shown to be magnetic

Potential Solutions:•Quantify and classify the material properties in the range between bulk material properties and quantum phenomena•Establish a program to employ theoretical projections to verify experimental data

Benefits:•Improve the time to develop nano based devices, due to eliminating the duplication of research efforts•Creation of new products based on applying novel nano propertiesExample: The creation of new memory devices that are 100x more dense than current technology

Silver properties reported May 30, 2006 in NanoTechWebPlatinum experiments reported by University of Stuttgart

Metrology

Issues:•Imaging realm is at limits of resolution, in the 1nm range•Time per image is long >one hour•Effective imaging applications require multiple images in minutes or less

Potential Solutions:•New solutions for metrology•Enhancements to equipment•New technologies

Benefits:•Improved resolution of material properties•Capability to employ in manufacturing processes•If one can not measure something, it can not be manufactured

Aberration Corrected HR-TEM Korgel Group Si Nanowire

Au dot structure&

Nanowire Twinning

Metrology

Issues:•Imaging is slow and computations are time consuming•Unique structures can not be verified•No validation results•Dimensions extend to below 1nm

Potential Solutions•Development and execution of validation plan•Improved algorithms•Improved equipment for rapid imaging

Benefits:•Improved understanding of materials•Ability to identify unique nano structures•Ability to create and verify novel materials

Not corrected

Corrected

Sloan, et al., MRS Bulletin, April 2004

Aberration Corrected TEM ImagingAberration Corrected TEM Imaging

K & I in nanotube

Proposal for Molecular Computers

Nanotechnology+ cheap+ high-density+ low-power– unreliable

Computer architecture+ vast body of knowledge – expensive– high-power

Reconfigurable Computing+ defect tolerant+ high performance– low density

++++ +

+_

__

_

Reconfigurable Computing

• Back to ENIAC-style computing

• Synthesize one machine to solve one problem

Defect Tolerance

Despite having >70% of the chips defective, Teramac works flawlessly.

Compilation has two phases:• defect detection through self-testing• placement for defect-avoidance

Lattice of covalently bonded carbon atoms

Single-walled Carbon Nanotube d d = 0.4nm -

10nm

L

L = ?

Nano-wires

• carbon nanotubues, Si, metal• >2nm diameter, up to mm length• excellent electrical properties

A carbon nanotube: one molecule

Independent Claims 

1. A transistor that uses a carbon nanotube ring as a semiconductor material, the carbon nanotube ring having semiconductor characteristics.

12. A transistor that uses a carbon nanotube ring as an electrode material, the carbon nanotube ring having conductivity or semiconductor characteristics.

18. A carbon nanotube ring having p-type semiconductor characteristics.

19. A semiconductor device in which a carbon nanotube ring having p-type semiconductor characteristics is placed on an n-type semiconductor substrate thereof.

Alternatives for transistors Carbon nanotube transistors Single electron transistors (SET)

Memory devices MRAM (various different approaches Phase change RAM

PhotonicsNano-electromechanical system (NEMS)Fuel cellsThermo-photovoltaicsQuantum computersSoftware

Nanotechnology in Electronics

Nano-switch

Nano-switch Between Nano-wires

Self-assembly