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Nanotechnology: Hype or New Horizons?

Richard M. WhiteEECS Department

andBerkeley Sensor & Actuator CenterUniversity of California, Berkeley

Invited plenary talk presented 13 June 2006 at theIEEE International Microwave Symposium

San Francisco, CA

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Nanotechnology

One definition: Nanotechnology is the creation of useful functional materials, devices and systems through control of matter on the nanometer (10-9 m) length scale, and exploitation of novel phenomena and properties (physical, chemical, biological) at that length scale

The experience with MEMS (micro-electro-mechanical systems) products suggests that NEMS development might be similar

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Lucas Nova Sensor

Analog DevicesHoneywell

MicrobeamAccelerometer

DiaphragmPressure Sensors

Texas Instruments

DeformableMicromirror Array

Microsensors Microactuators

MEMS Examples

Lucent Rockwell

Nanogen

DNA Array

rf SwitchOptical Switch

RF Electronics

Microfluidics

Air Bag DeploymentAccelerometer

Gene Chip

Affymetrix

Analog Devices

Inertial NavigationUnit

(Slide courtesy of Dennis Polla, DARPA)

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Carbon Nanotube~2 nm diameter

Things Natural(Carbon Chemistry)

Things Manmade(Silicon Chemistry)

DNA~2-1/2 nm diameter

Fly ash~ 10-20 μm

Human hair~ 70-100 μm wide

Ant~ 5 mm

Quantum corral of 48 iron atoms on copper surface positioned one at a

time with an STM tipCorral diameter 14 nm

Atoms of siliconspacing ~tenths of nm

Head of a pin1-2 mm

Microworld

1 nanometer (nm) 1 micrometer (μm) 1 millimeter (mm)

10-2 m10-3 m10-4 m10-5 m10-6 m10-7 m10-8 m10-9 m10-10 m

Visible

Nanoworld

InfraredUltraviolet MicrowaveSoft x-ray

Dust mite200 μm

MicroElectroMechanical devices10 -100 μm wide

Macroworld

Transistor gate60 nm

The Macro to Nano World

(Slide courtesy of Dennis Polla, DARPA)

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What nanostructures have been made – and how?

NanowiresNanotubesMats of nanotubesQuantum dotsTransistorsOptical devicesSensors…..

Individual elements System applicationsMemoriesLogic circuitsBiosystemsSensor systemsCommunicationsField-emitter displaysOptical barcodes for biosensing…..

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Synthesis of Nanowires(Some Examples)

Wang et al.

Kamins et al.

Ag, Au, Zn, InP, ZnO, Si, Ge, Si-Ge, SiGeC, GaAs, ZnS, GaN, InGaAs, In2O3 and other materials ….

Yang et al.

Cao et al.

Busbee et al.

Gundiah et al.

Fukui et al.

2 μm Islam et al.

Samuelson et al.

Xia et al.

Lieber et al.Sunkara et al.

Meyyappan et al.

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Si

Electrode (Au)photons

p-GaAs

n-GaAs

Electronics Optoelectronics

Sensors

Nanowires

Sci. Am., 2001

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Nanowires

Nanowire Potential• High frequency electronics• Displays• Sensors with high surface-volume ratio• Nanoelectrodes• Vertical Interconnects• Digital computing• Waveguides

Conventional photolithographycompared to carbon nanotubes(Nanotube diameter ~1nm)

Nanowires around human hair

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Carbon Nanotubes (CNTs)

Single-walled (SWNT) Multi-walled (MWNT)

CNTs may behave as electrical conductors, semiconductors, or insulatorsdepending on their symmetry about the horizontal axis– think of them asformed by rolling a sheet of regularly spaced carbon atoms (called graphene)like chain-link fencing on itself at various angles and adding end caps.

CNTs are typically about 1 nm in diameter and may be microns long, so theyare essentially one-dimensional conductors. They are open structures – allsurface and no bulk volume – so they are chemically very reactive.

They have very high elastic constants in the axial direction, and may flextransversely

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What’s special about carbon nanotubes?Smalley – Discoverer of C60 “buckyballs”

Strongest fiber that will ever be made – C-C covalent bonding andseamless hexagonal network architecture

Maximum strain ~10%, much higher than any other materialElectrical conductivity of copper or siliconThermal conductivity of diamond – 3000W/mK in axial directionChemistry of carbonSize and perfection of DNA

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How do you make nanotubes and nanowires?

Initially done in electric discharges in a hydrocarbon vapor – then search for the product!

Can grow nanowires in more orderly fashion using chemical vapor deposition with a catalyst on a crystallographically oriented substrate (see following slides), or with an electric field in desired growth direction

Manufacturing uniform product where you want it is still a problem

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Simultaneous Growth of Nanowires and Connecting Electrodes

1. Metal deposition, metal-silicide formation

2. Growth of Nanowire 3. Nanowire Bridge

Metal on Si surfaceEvaporation at 45o angle

Si SiO2Si

Saif Islam et al., Nanotechnology 15 (2004) L5–L8

[111]

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M. Saif Islam, S. Sharma, T. I. Kamins, and R. StanleyWilliams, Nanotechnology 15, L5-L8 (May 2004)

Form trench anddeposit catalyst

Nanowire grows perpendicularto (111)-oriented sidewall

Nanowire connectsto opposite sidewall

Connecting NanostructuresBridging Nanowires

2 µm

2 µm2 µm

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(a) Catalysts deposition

Catalysts

Doped epi-layer

Bottom electrode

Top electrode

Insu

latin

g la

yer

Insulating layer

Nanowire

(b) Nanowire growth

Insulating layer

Nano-colonnades

(c) Nanowire bridging

Metal contact

Metal contact

(d) With metal electrodes

Fabrication of Nano-Colonnades

(S. Islam et al., U. C. Davis)

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Natural Colonnades: Stalagmites

Bottom Electrode

Top Electrode

Colonnades form in both ways in mountain caves

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Observation, Manipulation and More

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IBM Millipede mass memory using1024 cantilevers with AFM-like tipsto emboss and read tiny pits in apolymer-coated surface (non-volatile;can read, write, and erase)

Scanning Tunneling Microscope (STM)

Quantum corral of 48 iron atoms on copper surface positioned one at a time with an STM tip Corral diameter 14 nm(IBM gallery)

Atomic Force Microscope (AFM)

IBM SEM image of

carbon nanotube

to study chirality(Delft U.)

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Making nanostructures byreplica molding with PDMS(bathtub caulking compound)

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Making structures withnanoscale featuresby soft lithography

Conventional ICs are made

by photolithographic process.

Nanoscale features can be

realized using “soft lithography”

using a “rubber stamp” to

transfer features from a master

pattern to a corresponding (thiol)

chemical layer on the part.

Features down to 50 nm are

possible

(Whitesides, Sci. Am. 2001)

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Nanomanufacturing

(Slide from D. Polla, DARPA)

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Two Underwhelming Commercial Nanotech Applications

Sunscreen madewith nanoparticlesof aluminum oxideis transparent, notwhite and obvious!

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Nanoelectronics

SiO2

Au Source

Drain

Nanotube

p-type transistor (no intentional doping) I(on)/I(off)~105

High contact resistanceLow transconductance

1.4 nm

R. Martel et al. Apple. Phys. Lett. 73, 2447 (1998)

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Nanotube inverter (IBM)

Flip-flops (cross-coupled inverters) and ring oscillators have also been demonstrated

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Getting rid of metallic nanotubes to make semiconductor devices

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Nanobattery using droplets of electrolytes on top of “nanograss” to generate power

Nanobattery Schematic utilizing membrane pores to maintain electrolytes

Representation of a bio-nanobattery using modified proteins for energy storage

MEMS field applications require novel sources of power.

Nanobatteries • Comparable energy densities to conventional batteries• Can be integrated into MEMS during the fabrication process • Variety of applications requiring minute power

(Slide from D. Polla, DARPA)

Nanobatteries

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Cal Fun

Alex Zettl’s nanomotor(Physics Dept., UC Berkeley)

500 μm min

C. Chang, L. Lin(ME and BSAC, UC Berkeley)

h

Collector

High Voltage

(600 V min)

Probe TipPolymer Solution

Liquid Jet (polyethylene oxide)makes 50 to 500 nm dia.

fibers

Holt, Park, et al. (LLNL andME Dept., UC Berkeley)

Measured gas and water flowrates through membranes with aligned <2nm diameter CNTsare extremely high, orders of magnitude higher than predicted by continuumhydrodynamics models.

Electrospinning

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Nanoparticle Hazards?

1. Grey goo?

Eric Drexler (in “Engines of Creation”) proposed replicationof “assemblers” – nanorobots under computer control thatwould create copies of themselves by assembling atomsto make more assemblers until a enough existed for trulymass production. But if hackers took over, or theintelligent assemblers organized themselves with evil intent,the Earth might be flooded with the product – a grey goo!.

Richard Smalley, professor who received 1996 Noble Prizein Chemistry for discovering C60 (buckyballs or fullerenes)said this will never happen for two reasons:

Fat finger problem: the assembler manipulator arms that have to put all the atoms in just the right places in a nanometer-sized region will be too big to fit

Sticky finger problem: the assemblers’ manipulator arms won’t be able to let loose of the atoms they’re trying toput in place

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Nanoparticle Hazards? (continued)

2. Tiny toxins?

German housecleaning spray product Magic Nano caused serious butnon-fatal respiratory problems. But apparently the product doesn’tactually contain nanoparticles (it does use a propellant)

However:

* Inhaled nanoparticles can get into the brains of rats via the olfactory nerve* Installing nanotubes in lungs of rats can cause adverse reactions* Nanoscale aluminum oxide stunts root growth in corn and soybeans* Fullerenes can damage microbes, and in human cells fullerenes can cause

damage like that seen in brain cells of fish* Modifying surfaces of nanoparticles can reduce their toxicity – but may

also negate the very properties that make them useful for some applications.

So: Keep studying and stay tuned

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Nanotechnology exciting new phenomenaApplications in electronics, sensors, photonics, biomedicine, …Some possible risks but these are being studied

Definitely, new horizons

SUMMARY

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References

“Nanotechnology: Science, Innovation, and Opportunity”, Lynn E. Foster(Prentice Hall, 2006)

“The Wondrous World of Carbon Nanotubes”, 96 pp., (Eindhoven University of Technology, Netherlands, 2003) -- check Google

“Scientific American, Special Issue on Nanotechnology”, 285(3),September, 2001