Published on January 24, 2008
A Brief Introduction to Nanotechnology: A Brief Introduction to Nanotechnology Christian A. Zorman Department of Electrical Engineering and Computer Science Case Western Reserve Univesity Cleveland, Ohio 44106 [email protected] Nanotechnology Defined: Nanotechnology Defined “The development and use of devices that have a size of only a few nanometres.” physics.about.com “Research and technology development at the atomic, molecular or macromolecular level in the length scale of approximately 1 - 100 nm range, to provide a fundamental understanding of phenomena and materials at the nanoscale and to create and use structures, devices and systems that have novel properties and functions because of their small and/or intermediate size.” www.nano.gov “Branch of engineering that deals with things smaller than 100 nm (especially with the manipulation of individual molecules).” www.hyperdictionary.com “Nanotechnology, or, as it is sometimes called, molecular manufacturing, is a branch of engineering that deals with the design and manufacture of extremely small electronic circuits and mechanical devices built at the molecular level of matter.” www.whatis.com “The art of manipulating materials on an atomic or molecular scale especially to build microscopic devices.” Miriam Webster Dictionary Perspective of Length Scale: Perspective of Length Scale Size of an atom 1 m 1 mm 1 mm 1 nm Humans Car Butterfly Gnat 1 km Boeing 747 Laptop Wavelength of Visible Light Micromachines Width of DNA Smallest feature in microelectronic chips Proteins Biological cell Nucleus of a cell Aircraft Carrier Size of a Microprocessor Nanostructures & Quantum Devices Top Down Bottom Up Resolving power of the eye ~ 0.2 mm http://www.dod.gov/news/Dec1997/n12301997_9712302.html Perspective of Size: Perspective of Size Water molecules – 3 atoms Protein molecules – thousands of atoms DNA molecules – millions of atoms Nanowires, carbon nanotubes – millions of atoms Carbon nanotube water molecule Protein molecule Molecule of DNA www.iacr.bbsrc.ac.uk/notebook/ courses/guide/dnast.htm www.phys.psu.edu/~crespi/research/_carbon.1d/public student.biology.arizona.edu/.../ group2/crystallography.htm How Small is a nm?: How Small is a nm? 1 µm = one millionth of a meter 1 nm = one billionth of a meter ≈ 1/50,000 thickness of a hair! ≈ a string of 3 atoms If we shrunk all distances by 110,000,000,000 X The sun and earth would be separated by 1 m A football field would be 1 nm Human hair thickness ~ 50 µm 110,000,000 km 110 m Surface vs. Volume: Surface vs. Volume Si has a diamond structure with a = 5.43 Å A Si nanocube 10 nm on a side is composed of: ~6250 unit cells ~50,000 atoms Each nanocube face is composed of: ~340 unit cells per face ~680 surface atoms per face Total surface area is: ~4080 atoms (~10% surface atoms) A bulk Si film 1 µm thick on a 10 cm square: ~6.3 X 1019 unit cells ~5 X 1020 atoms ~1.4 X 1017 surface atoms (~0.03% surface atoms) a Diamond unit cell Si nanocube Bulk Si film In a nanoscale material, the surface/boundary/interface plays an important role! More than just size…: More than just size… Chemical – take advantage of large surface to volume ratio, interfacial and surface chemistry important, systems too small for statistical analysis Electronic – quantum confinement, bandgap engineering, change in density of states, electron tunneling Magnetic – giant magnetoresistance by nanoscale multilayers, change in magnetic susceptibility Interesting phenomena: STM of dangling bonds on a Si:H surface http://pubweb.acns.nwu.edu/~mhe663/ More than just size …: More than just size … Interesting phenomena: Fluorescence of quantum dots of various sizes Phonon tunneling Mechanical – improved strength hardness in light-weight nanocomposites and nanomaterials, altered bending, compression properties, nanomechanics of molecular structures Optical – absorption and fluorescence of nanocrystals, single photon phenomena, photonic bandgap engineering Fluidic – enhanced flow properties with nanoparticles, nanoscale adsorbed films important Thermal – increased thermoelectric performance of nanoscale materials, interfacial thermal resistance important. Development of Nanotechnology: Development of Nanotechnology Fundamental Understanding Characterization and Experimentation Synthesis and Integration Nano to Macro Inorganic and Organic Optical with Mechanical with Electrical with Magnetic with … Slide10: nanopedia.cwru.edu Nanotech – The next new thing? Slide11: Ohio’s Position in Nanotechnology James Murday, Naval Research Laboratory Nanofabrication: Nanofabrication Nanofabrication can generally be divided into two categories based on the approach: “Top-Down”: Fabrication of device structures via monolithic processing on the nanoscale. “Bottom-Up”: Fabrication of device structures via systematic assembly of atoms, molecules or other basic units of matter. Integrated Circuits and Nanotech: Integrated Circuits and Nanotech The IC industry is approaching a period where nanotech approaches will be required to sustain technology growth J.D. Plummer, M.D. Deal, and P.B. Griffin, “Silicon VLSI Technology – Fundamentals, Practice and Modeling” Prentice Hall, NJ Nanotech and Microfabrication: Nanotech and Microfabrication Microfabrication is a top-down technique utilizing the following processes in sequential fashion: Film Deposition CVD, PVD Photolithography Optical exposure, PR Etching Aqueous, plasma Many of these techniques are useful, directly or indirectly in nanofabrication Slide15: SEM showing one of the two doubly-clamped 3C-SiC beams in a device structure. The device was fabricated using top-down techniques. Length: 1.1 m Width: 120 nm Thickness: 75 nm Top - Down Nanofabrication What are Nanostructures?: What are Nanostructures? At least one dimension is between 1 - 100 nm 2-D structures (1-D confinement): Thin films Planar quantum wells Superlattices 1-D structures (2-D confinement): Nanowires Quantum wires Nanorods Nanotubes 0-D structures (3-D confinement): Nanoparticles Quantum dots Dimensionality, confinement depends on structure: Bulk nanocrystalline films Nanocomposites Si0.76Ge0.24 / Si0.84Ge0.16 superlattice 2 m Si Nanowire Array Multi-wall carbon nanotube http://www.aip.org/mgr/png/2003/186.htm Thin Films: Thin Films Nanoscale Thin Film Single “two dimensional” film, thickness < ~100 nm Electrons can be confined in one dimension; affects wavefunction, density of states Phonons can confined in one dimension; affects thermal transport Boundaries, interfaces affect transport Bulk crystal a Free standing thin film d Thin film Substrate http://scsx01.sc.ehu.es/waporcoj/charlas/cursodoctorado/12 Thin Film Applications: Thin Film Applications 100 nm sputtered YSZ film for solid oxide fuel cells Amorphous Si TFT on a SiNx passivated polyimide foil Solid Fuel Cells: (nanostructured) thin film solid electrolytes and electrodes with high conductance Thin Film Transistors for liquid crystal displays: requires high mobility and flexible substrates Gas sensing applications Thin layers in electronic devices http://www.bu.edu/mfg/pdf/Tuller.pdf Wagner et al, Thin Solid Films, Vol. 490, pp. 12 – 19 (2003). Nanowires: Nanowires Solid, “one dimensional” Can be conducting, semiconducting, insulating Can be crystalline, low defects Can exhibit quantum confinement effects (electron, phonon) Narrowing wire diameter results in increase in band gap Narrowing wire diameter can result in decrease in thermal conductivity New forms include core-shell and superlattice nanowires 2 m Si Nanowire Array Nanotube defined – a long cylinder with inner and outer nm-sized diameters Nanowire defined – a long, solid wire with nm diameter Si/SiGe Nanowires Abramson et al, JMEMS (2003) Wu et al, Nanoletters, Vol. 2, 83 – 86 (2002) Nanowires Applications: Nanowires Applications Field effect transistors Thermoelectric materials Light emitting diodes Detectors Sensors Nanolasers Superlattice nanowires in applications requiring superlattices 5 nm Si nanowire FET Cui et al, Nanoletters, Vol. 3, 149 – 152 (2003). Nanolaser from 100 nm CdSe nanowire http://www.photonics.com/spectra/tech/XQ/ASP/techid.1525/QX/read.htm Carbon Nanotubes: Carbon Nanotubes Carbon nanotube properties: One dimensional sheets of hexagonal network of carbon rolled to form tubes Approximately 1 nm in diameter Can be microns long Essentially free of defects Ends can be “capped” with half a buckyball Varieties include single-wall and multi- wall nanotubes,ropes, bundles, arrays Structure (chirality, diameter) influences properties: Semiconducting vs. metallic Thermal, electrical conductance Mechanical strength, elasticity Multi-wall carbon nanotube http://www.aip.org/mgr/png/2003/186.htm Armchair Zigzag Chiral http://physicsweb.org/article/world/11/1/9/1 Other Nanotubes…: Other Nanotubes… Boron nitride nanotubes Resistance to oxidation, suited for high temperatures Young’s modulus of 1.22 TPa Semiconducting Predictable electronic properties independent of diameter and # of layers SiC nanotubes: Resistance to oxidation Suitable for harsh environments Can functionalize surface Si atoms Boron nitride nanotubes adopt various shapes (red=boron, blue=nitrogen): http://pubs.acs.org/cen/topstory/7912/7912notw1.html SiC nanotubes grown at NASA Glenn: http://www.grc.nasa.gov/WWW/RT2002/5000/5510lienhard.html Nanoparticles/Quantum Dots: Nanoparticles/Quantum Dots “Zero-dimensional” particle Surface effects/chemistry important Radius < 100 nm < 106 atoms per nanoparticle Size smaller than critical length scales (e.g. mean free path, wavelength) Nano/quantum physical phenomena present “Large” nanoparticles have same structure as bulk; “small” may be different Synthesis: RF plasma, chemical, thermolysis, pulsed laser “Old” examples Stained glass – small metal oxide clusters comparable in size to the wavelength of light Photography – small colloidal silver particles for image formation molecules nanoparticles Radius of particle or cluster bulk quantum dots Nanoparticles/Quantum Dots: Nanoparticles/Quantum Dots Metalic nanoparticles www.aveka.com Si nanoparticle; single-crystal; hexagonal shape Bapat et al, J Appl Phys, Vol. 94, 1969 – 1974 (2003) Gradient of gold nanoparticles on a silica surface http://www.bnl.gov/bnlweb/pubaf/pr/2002/bnlpr071802.htm Semiconductor Nanoparticles: Semiconductor Nanoparticles Nanoparticles comprised of “bulk semiconductor” elements exhibit unique optical properties Shift in optical absorption particle toward shorter wavelengths with reduced size For particle radius > exciton radius photon induced transitions in exciton energy levels produce series of discrete optical absorption levels For particle radius < exciton radius no exciton and individual electron and hole transitions of discrete optical absorption levels observed Fluorescence at different wavelengths from a single UV light due to quantum confinement in semiconductor quantum dots www.nanosysinc.com Nanoparticle Probes: Nanoparticle Probes Objective: To detect and “kill” individual cancer cells before they manifest as tumors using functionalized nanoparticles 5 to 10 nm particles (small enough to interact with intracellular markers) nanoparticles are coated and functionalized with antibodies, oligonucleotides, peptide ligands and drugs Introduced to body via bloodstream “Look” for markers inside cell by MRI or deliver agent or irradiate Nanostructured Bulk Materials: Nanostructured Bulk Materials Includes: Amorphous/glassy materials (atomic scale ordering) Any material with nanostructured grain sizes (nm ordering) Nanoporous materials (nm ordering) Multilayer nanoscale thin films (nm ordering – SL period) Characteristics (Å to nano to micro) affect chemical, physical, mechanical properties, which are usually enhanced Solid formations crystalline, amorphous, polycrystalline Polycrystalline materials can be nanostructured if grain sizes < 100 nm Nanostructured Bulk Materials Applications: Nanostructured Bulk Materials Applications Manufacturing – thermal barrier coatings ceramic films problem: require lower thermal conductivity/high strength solution: nanostructured films? Other applications: Catalysts Solar cells Stronger, long lasting materials applications Electronics Batteries Sensors Flat panel displays Nanocrystalline thermal barrier coating of YSZ http://www.msd.anl.gov/groups/im/highlights/thermal/thermalconductivity.html Nanocrystalline diamond coatings for field emission tips http://www.msd.anl.gov/groups/im/highlights/diamondemission/emission.html Nanocomposites: Nanocomposites Nanocomposite – consists of two or more synthesized materials of which at least one has nanoscale dimensions Can exhibit enhanced chemical, optical, physical, mechanical properties as compared with constituent bulk Multiple material possibilities Organic + organic Organic + inorganic Inorganic + inorganic Nanoparticle or nanowire or nanotube + matrix material Why nano and not micro? Micro also gives increase elastic modulus, but microparticles act as stress concentrators, decrease in strain to failure, decrease in strength and toughness Nanocomposite Applications: Nanocomposite Applications Luminescent nanocomposites for opto-electronics Electronics (e.g. dielectric layers) Intracellular manipulation Thermoelectric materials High-strength, toughness structural materials Electrolytes in batteries Insulation Coatings Gas separation Fire barriers Polymer containing 40 wt% silica particles for use as a gas separation membrane TiO2-oligonucleotide nanocomposites hybridized with DNA for cellular manipulation Paunesku et al, Nature Mats, Vol. 2, 343 – 346 (2003) Merkel et al, Science, Vol. 296, 519 – 522 (2002) What can we measure?: What can we measure? structure properties composition crystallinity strain defects mechanical electrical/optical magnetic thermal atomic species concentration diffusion segregation tensile strength hardness yield modulus of elasticity failure stiffness conductivity electron states carrier density band gap conductivity Seebeck coefficient specific heat susceptibility magneto-resistance dielectric constant surface roughness Atomic Force Microscopy: Atomic Force Microscopy The optical microscope – cannot see features smaller than ~half the wavelength of light Can we use something other than light and lenses? AFM basic components: Tip (<~10 nm diameter) on a cantilever Detector (generally position) Raster-scan (to drag tip) Force/height control Image processing software Lateral resolution 0.1 nm Vertical resolution 0.02 nm Image of graphite using an AFM AFM modes: AFM modes Tip angstroms from surface (repelled) Constant force Highest resolution May damage surface contact mode non-contact mode Tip hundreds of angstroms from surface (attracted) Variable force measured Lowest resolution Non-destructive tapping mode Intermittent tip contact Variable force measured Improved resolution Non-destructive Courtesy of F. Ernst AFM images: AFM images Cu Nanowires R. Adelung et al. Ge islands on Si K. Brunner et al. Courtesy of F. Ernst Scanning Electron Microscopy: Scanning Electron Microscopy Instead of light, the SEM uses electrons to see 3-D images SEM operation: Air pumped out (vacuum) e- gun emits beam of high energy electrons e- beam focused via lenses Scanning coils move beam across sample Secondary electrons are “knocked off” surface Detector counts electrons Image given by # e- Resolution ~5 nm Courtesy of F. Ernst SEM and AFM images: SEM and AFM images SEM: Cu Nanowires AFM: Cu Nanowires R. Adelung et al. Courtesy of F. Ernst Transmission Electron Microscopy: sample Transmission Electron Microscopy A TEM works like a slide projector but with e- instead of light TEM operation: Air pumped out (vacuum) e- gun emits beam of high energy e- e- beam focused via lenses Beam strikes sample and some e- are transmitted Transmitted e- are focused, amplified Image contrast enhanced by blocking out high-angle diffracted e- Image passed through lenses and enlarged When image hits phosphor screen, light is generated Resolution ~<1 nm Courtesy of F. Ernst lens TEM of Ge on Si: TEM of Ge on Si HRTEM Cross-Sectional View Courtesy of F. Ernst TEM comparison: TEM comparison Standard TEM High resolution TEM Courtesy of F. Ernst Slide40: Carbon Nanotube Applications G. Dusburg, Infineon Technologies, Munchen Germany Slide41: Carbon Nanotube Applications G. Dusburg, Infineon Technologies, Munchen Germany Slide42: Carbon Nanotube Applications G. Dusburg, Infineon Technologies, Munchen Germany Slide43: Carbon Nanotube Applications G. Dusburg, Infineon Technologies, Munchen Germany Slide44: Materials for Interconnects 1999 When? Aluminum Copper Carbon Nanotubes Very low electrical resistivity of CNTs Resistivity of Al = 2.6 μΩ-cm Resistivity of Cu = 1.7 μΩ-cm Slide45: Fabrication of CNT interconnects F. Kreupl et al., Microelectronic Engg., 64, 399 (2002). Energy Applications: Conversion, Generation and Storage: Energy Applications: Conversion, Generation and Storage Metal organic framework for hydrogen storage Replace conventional material with nanocomposite to enhance performance Abramson et al, JMEMS, in review. Rosi et al, Science, Vol. 300, pp. 1127 -1129 (2003). Energy Applications: Catalysis: Energy Applications: Catalysis Oil refinement: zeolites are nanoporous (pores 3 – 10 Å) crystalline solids with well-defined structures (“molecular sieves”) used in oil refinement – increases gasoline yield from each barrel of crude oil by 50% Porous zeolite structure 2 atomic layer thick Au nanoclusters on TiO2 http://www.bza.org/zeolites.html http://www.iaee.org/documents/p03eagan.pdf Energy Applications: LEDs: Energy Applications: LEDs Change the nanostructure of Si (a very cheap material) to become nanoporous and visible light is emitted! Use quantum dots (quantum confinement) for light emission Cross-hairs of p-type and n-type nanowires (to get a p-n junction) http://www.trnmag.com/Stories/2002/103002/Nanoscale_LED_debuts_103002.html Quantum dot layers Network of nanowires http://www.trnmag.com/Stories/011701/Crossed_nanowires_make_Lilliputian_LEDs_011701.html Energy Applications: LEDs: Energy Applications: LEDs Quantum dots/ nanocrystals are smaller than the wavelength of light, so they do not scatter light; scattering can reduce optical efficiency by up to 50%! Energy Applications: Batteries: Energy Applications: Batteries Change electrode materials by nanostructuring (texturing) to improved electrical performance; nanoscale particles boost energy storage and power delivery by reducing the distance Li ions travel during diffusion Nanobattery: Fill a nanoscale membrane with an electrolyte, cap with electrodes; contact with a probe tip Energy Applications: Solar: Energy Applications: Solar Solar cells integrated into roof shingles Nanoscale crystals of semiconductor coated with light-absorbing dye emit electrons Nanostructured diamond solar thermal cells capture light, which heats the lattice, which emits electrons; small tip gives high energy electrons Tetrapods (the light absorbing materials) double the efficiency of plastic solar cells because they always point in the right direction http://www.spacer.com/news/solarcell-01b.html Nanostructured diamond solar thermal cells Branched tetrapod Slide52: nanopedia.cwru.edu Web-based Resources Slide53: Acknowledgements Prof. Alexis Abramson: Department of Mechanical and Aerospace Engineering, Case Western Reserve University. [email protected] Dr. David Smith: Department of Electrical Engineering and Computer Science, Case Western Reserve University. [email protected] Prof. Michael Roukes: Condensed Matter Physics, California Institute of Technology.