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M. Meyyappan Center for Nanotechnology NASA Ames Research Center Moffett Field, CA 94035 email: mmeyyappan@mail.arc.nasa.gov Nanotechnology: Advantages and Applications

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What is Nanotechnology? Nanotechnology is the creation of USEFUL/FUNCTIONAL materials, devices and systems (of any size) through control/manipulation of matter on the nanometer length scale and exploitation of novel phenomena and properties which arise because of the nanometer length scale: Source: K.J. Klabunde, 2001 • Physical • Chemical • Electrical • Mechanical • Optical • Magnetic • •

Unique Properties of Nanoscale Materials : 

Quantum size effects result in unique mechanical, electronic, photonic, and magnetic properties of nanoscale materials Chemical reactivity of nanoscale materials greatly different from more macroscopic form, e.g., gold Vastly increased surface area per unit mass, e.g., upwards of 1000 m2 per gram New chemical forms of common chemical elements, e.g., fullerenes, nanotubes of carbon, titanium oxide, zinc oxide, other layered compounds Unique Properties of Nanoscale Materials Source: Clayton Teague, NNI

NNI Program Component Areas (PCAs) : 

• Fundamental Nanoscale Phenomena and Processes • Nanomaterials • Nanoscale Devices and Systems • Instrumentation Research, Metrology, and Standards for Nanotechnology • Nanomanufacturing • Major Research Facilities and Instrumentation Acquisition • Societal Dimensions NNI Program Component Areas (PCAs) Source: Clayton Teague, NNI

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Nanotechnology R & D Nanomaterials Applications and Related

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Various Nanomaterials and Nanotechnologies • Nanocrystalline materials • Nanoparticles • Nanocapsules • Nanoporous materials • Nanofibers • Nanowires • Fullerenes • Nanotubes • Nanosprings • Nanobelts • Dendrimers • • Molecular electronics • Quantum dots • NEMS, Nanofluidics • Nanophotonics, Nano-optics • Nanomagnetics • Nanofabrication • Nanolithography • Nanomanufacturing • Nanomedicine • Nano-bio • •

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Impact of Nanotechnology Nanotechnology is an enabling technology • Information Technology - Computing, Memory and Data Storage - Communication • Materials and Manufacturing • Health and Medicine • Energy • Environment • Transportation • National Security • Space exploration • •

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• Ability to synthesize nanoscale building blocks with control on size, composition etc. further assembling into larger structures with designed properties will revolutionize materials manufacturing - Manufacturing metals, ceramics, polymers, etc. at exact shapes without machining - Lighter, stronger and programmable materials - Lower failure rates and reduced life-cycle costs - Bio-inspired materials - Multifunctional, adaptive materials - Self-healing materials • Challenges ahead - Synthesis, large scale processing - Making useful, viable composites - Multiscale models with predictive capability - Analytical instrumentation

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• Carbon Nanotubes • Nanostructured Polymers • Optical fiber performs through sol-gel processing of nanoparticles • Nanoparticles in imaging systems • Nanostructured coatings • Ceramic Nanoparticles for netshapes Source: IWGN Report

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More Examples of Nanotech in Materials and Manufacturing • Nanostructured metals, ceramics at exact shapes without machining • Improved color printing through better inks and dyes with nanoparticles • Membranes and filters • Coatings and paints (nanoparticles) • Abrasives (using nanoparticles) • Lubricants • Composites (high strength, light weight) • Catalysts • Insulators

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Nanoelectronics and Computing Past Shared computing thousands of people sharing a mainframe computer Present Personal computing Future Ubiquitous computing thousands of computers sharing each and everyone of us; computers embedded in walls, chairs, clothing, light switches, cars….; characterized by the connection of things in the world with computation.

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“There is at least as far to go (on a logarithmic scale) from the present as we have come from ENIAC. The end of CMOS scaling represents both opportunity and danger.” -Stan Williams, HP • A few more CMOS generations left but cost of building fabs going up faster than sales. Physics has room for 109x current technology based on 1 Watt dissipation, 1018 ops/sec no clear ways to do it! - Molecular nanoelectronics ? - Quantum cellular automata ? - Chemically synthesized circuits ? • Self assembly to reduce manufacturing costs, defect tolerant architectures may be critical to future nanoelectronics

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• Quantum Computing - Takes advantage of quantum mechanics instead of being limited by it - Digital bit stores info. in the form of ‘0’ and ‘1’; qubit may be in a superposition state of ‘0’ and ‘1’ representing both values simultaneously until a measurement is made - A sequence of N digital bits can represent one number between 0 and 2N-1; N qubits can represent all 2N numbers simultaneously • Carbon nanotube transistors by several groups • Molecular electronics: Fabrication of logic gates from molecular switches using rotaxane molecules • Defect tolerant architecture, TERAMAC computer by HP architectural solution to the problem of defects in future molecular electronics - Stan Williams, HP

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Expected Nanotechnology Benefits in Electronics and Computing • Processors with declining energy use and cost per gate, thus increasing efficiency of computer by 106 • Higher transmission frequencies and more efficient utilization of optical spectrum to provide at least 10 times the bandwidth now • Small mass storage devices: multi-tera bit levels • Integrated nanosensors: collecting, processing and communicating massive amounts of data with minimal size, weight, and power consumption • Quantum computing • Display technologies

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• Expanding ability to characterize genetic makeup will revolutionize the specificity of diagnostics and therapeutics - Nanodevices can make gene sequencing more efficient • Effective and less expensive health care using remote and in-vivo devices • New formulations and routes for drug delivery, optimal drug usage • More durable, rejection-resistant artificial tissues and organs • Sensors for early detection and prevention Nanotube-based biosensor for cancer diagnostics

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• DNA microchip arrays using advances for IC industry • ‘Gene gun’ that uses nanoparticles to deliver genetic material to target cells • Semiconductor nanocrystals as fluorescent biological labels Source: IWGN Report

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• Energy Production - Clean, less expensive sources enabled by novel nanomaterials and processes - Improved solar cells • Energy Utilization - High efficiency and durable home and industrial lighting - Solid state lighting can reduce total electricity consumption by 10% and cut carbon emission by the equivalent of 28 million tons/year (Source: Al Romig, Sandia Lab) • Materials of construction sensing changing conditions and in response, altering their inner structure Energy Production and Utilization

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Benefits of Nano in the Environment Sector • Nanomaterials have a large surface area. For example, single-walled carbon nanotubes show ~ 1600 m2/g. This is equivalent to the size of a football field for only 4 gms of nanotubes. The large surface area enables: - Large adsorption rates of various gases/vapors - Separation of pollutants - Catalyst support for conversion reactions - Waste remediation • Filters and Membranes - Removal of contaminants from water - Desalination • Reducing auto emissions, NOx conversion - Rational design of catalysts

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Benefits of Nanotechnology in Transportation • More efficient catalytic converters • Thermal barrier and wear resistant coatings • Battery, fuel cell technology • Improved displays • Wear-resistant tires • High temperature sensors for ‘under the hood’; novel sensors for “all-electric” vehicles • High strength, light weight composites for increasing fuel efficiency

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• Improved collection, transmission, protection of information • Very high sensitivity, low power sensors for detecting chem/bio/nuclear threats • Light weight military platforms, without sacrificing functionality, safety and soldier security - Reduce fuel needs and logistical requirements • Reduce carry-on weight of soldier gear - Increased functionality per unit weight

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Why Nanotechnology at NASA? • Advanced miniaturization, a key thrust area to enable new science and exploration missions - Ultrasmall sensors, power sources, communication, navigation, and propulsion systems with very low mass, volume and power consumption are needed • Revolutions in electronics and computing will allow reconfigurable, autonomous, “thinking” spacecraft • Nanotechnology presents a whole new spectrum of opportunities to build device components and systems for entirely new space architectures - Networks of ultrasmall probes on planetary surfaces - Micro-rovers that drive, hop, fly, and burrow - Collection of microspacecraft making a variety of measurements Europa Submarine

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Carbon Nanotube CNT is a tubular form of carbon with diameter as small as 1 nm. Length: few nm to microns. CNT is configurationally equivalent to a two dimensional graphene sheet rolled into a tube (single wall vs. multiwalled). CNT exhibits extraordinary mechanical properties: Young’s modulus over 1 Tera Pascal, as stiff as diamond, and tensile strength ~ 200 GPa. CNT can be metallic or semiconducting, depending on (m-n)/3 is an integer (metallic) or not (semicon). See textbook on Carbon Nanotubes: Science and Applications, M. Meyyappan, CRC Press, 2004.

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CNT Properties • The strongest and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture • Strength to weight ratio ~500 times greater than Al, steel, titanium; one order of magnitude improvement over graphite/epoxy • Maximum strain ~10%; much higher than any material • Thermal conductivity ~ 3000 W/mK in the axial direction with small values in the radial direction • Very high current carrying capacity • Excellent field emitter; high aspect ratio and small tip radius of curvature are ideal for field emission • Other chemical groups can be attached to the tip or sidewall (called ‘functionalization’)

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CNT Applications Sensors, Bio, NEMS • CNT based microscopy: AFM, STM… • Nanotube sensors: bio, chemical… • Molecular gears, motors, actuators • Batteries (Li storage), Fuel Cells, H2 storage • Nanoscale reactors, ion channels • Biomedical - Nanoelectrodes for implantation - Lab on a chip - DNA sequencing through AFM imaging - Artificial muscles - Vision chip for macular degeneration, retinal cell transplantation Electronics • CNT quantum wire interconnects • Diodes and transistors for computing • Data Storage • Capacitors • Field emitters for instrumentation • Flat panel displays Challenges Challenges • Control of diameter, chirality • Doping, contacts • Novel architectures (not CMOS based!) • Development of inexpensive manufacturing processes • Controlled growth • Functionalization with probe molecules, robustness • Integration, signal processing • Fabrication techniques

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CNT Synthesis • CNT has been grown by laser ablation (pioneered at Rice University) and carbon arc process (NEC, Japan) - early 90s. - SWNT, high purity, purification methods • CVD is ideal for patterned growth (electronics, sensor applications) - Well known technique from microelectronics - Hydrocarbon feedstock - Growth needs catalyst (transition metal) - Numerous parameters influence CNT growth (temperature, choice of feedstock, H2 and other diluents, choice of catalyst and preparation)

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CNTs on Patterned Substrates L. Delzeit et al., Chem. Phys. Lett., Vol. 365, p. 368 (2001); J. Phys. Chem. B, Vol. 106, p. 5629 (2002).

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• Certain applications such as nanoelectrodes, biosensors would ideally require individual, freestanding, vertical (as opposed to towers or spaghetti-like) nanostructures • The high electric field within the sheath near the substrate in a plasma reactor helps to grow such vertical structures • dc, rf, microwave, inductive plasmas (with a biased substrate) have been used in PECVD of such nanostructures Plasma Reactor for CNT Growth Cassell et al., Nanotechnology, 15 (1), 2004

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Simulated Mars dust CNT in Microscopy Atomic Force Microscopy is a powerful technique for imaging; also CD metrology, nanomanipulation, as platform for sensor work, nanolithography... Conventional silicon and other tips wear out quickly. CNT tip is robust, offers amazing resolution. Nguyen et al., Nanotechnology, 12, 363 (2001) 2 nm thick Au on Mica imaged with SWNT Written using multiwall tube

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MWNT Scanning Probe: Profilometry in Semiconductor Manufacturing

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CNT Based Biosensors • High specificity • Direct, fast response • High sensitivity • Single molecule and cell signal capture and detection • Probe molecules for a given target can be attached to CNT tips for biosensor development • Electrochemical approach: requires nanoelectrode development using PECVD grown vertical nanotubes • The signal can be amplified with metal ion mediator oxidation catalyzed by Guanine.

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30 dies on a 4” Si wafer Potential applications: Lab-on-a-chip applications Early cancer detection Infectious disease detection Environmental monitoring Pathogen detection Fabrication of Genechip

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Single Wall Carbon Nanotube •Every atom in a single-walled nanotube is on the surface and exposed to environment Charge transfer or small changes in the charge-environment of a nanotube can cause drastic changes to its electrical properties Monitoring the change in conductivity forms the basis for sensing Single-Walled Carbon Nanotubes For Chemical Sensors Applications •Industrial Toxic Chemicals, Safety •Explosive Detection •Earth Observation •Leak Detection 32-channel sensor chip

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Various Inorganic Nanowires Down to 0.4 eV • All these have been grown as 2-d thin films in the last three decades • Current focus is to grow 1-d nanowires (INWs)

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Vertically-Aligned Nanowires for Device Fabrication ZnO Nanowires Germanium Nanowires P. Nguyen et al., Advanced Materials, Vol. 17, p. 549 (2005). H.T. Ng et al., Science, Vol. 300, p. 2149 (2003).

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Low Thermal Energy for Programming Reduced melting point at 1-D Reduced programmable element volume Reduced activation energy at 1-D Device Scalability Ultra-low current / voltage / power operation Reduced thermal interference between neighboring memory cells Top electrode Bottom electrode 2-D Thin film PRAM 1-D Nanowire PRAM Why 1-D Phase-Change Nanowire?

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In-situ Tm measurement of GeTe nanowire under TEM image monitoring (a) The GeTe nanowire is under room temperature. (b) The GeTe nanowire is heated up to 400C when the nanowire is molten and its mass is gradually lost through evaporation. The remaining oxide shell can be seen from the image. Liquid GeTe GeTe Nanowires: Melting Experiment and In-Situ Monitoring by TEM

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Tm of bulk GeTe: 725oC Tm of GeTe nanowires: ~390oC 46% reduction! The melting temperature of the nanowire is identified as the point at which the electron diffraction pattern disappears and the nanowire starts to be evaporated. Lower Tm is translated into potentially much reduced thermal programming energy of data storage device. GeTe Nanowires: Melting Point

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Future Outlook for Inorganic Nanowires Nanowire-based Radiation-harden Central Processing Unit Nanowire-based Detector Sensory Systems Nanowire-based Hybrid Energy Conversion/Storage Unit Nanowire-based Ultra-high Density Data Storage Nanowire-based Peripheral Optical Interconnect/ Transmitter

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Summary • Nanotechnology is an enabling technology that will impact electronics, computing, data storage, communications, materials and manufacturing, health and medicine, energy, transportation, environment, national security… • Though commercial applications have started to emerge, it is still early and long way to go before realizing true potential. Lot more work needed on: - Novel synthesis techniques - Characterization and understanding of nanoscale properties - Large scale production of materials - Application and product development • Opportunities and rewards are great and hence, tremendous worldwide interest • Integration of this emerging field into engineering and science curriculum is important to prepare the future generation of scientists and engineers