Nanotechnology Gavin Lawes Department of Physics and Astronomy
Earth-Moon distance 4x10 8 m (courtesy NASA) Length scales (Part I) Person 2m Magnetic nanoparticle 5x10-9 m 10 10 m 10 5 m 1 m 10-5 m 10-10 m Michigan width 2x10 5 m (courtesy Google) Red blood cell 1x10-5 m (courtesy PBS)
Length scales (Part II) 10-1 m 10-3 m 10-5 m 10-3 m=1 mm 10-6 m=1 µm=1 (micron) Courtesy CSU Hayward Head of a pin 1,000,000 nm Thickness of a human hair: 100,000 nm Visible light 400 to 700 nm 10-7 m 10-9 m 10-9 m=1 nm (nanometer) Distance between atoms in a solid ~0.3 nm Transistors 65 nm Courtesy Intel
Q: What is Nanotechnology?
Q: What is Nanotechnology? A: Depends on who you ask.
Q: What is Nanotechnology? Narrow Nanotechnology is the engineering of functional systems at the molecular scale -Center for Responsible Nanotechnology Broad Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nm. -National Nanotechnology Initiative We will follow the broad definition for nanotechnology, since we need to understand the properties of small objects before we can build machines from them.
How can we see things on the nanoscale? 10-1 m The development of scanning probe techniques (STM, AFM) in 1981 revolutionized the imaging of nanoscale systems. 10-3 m 10-5 m Optical microscopy Nanotechnology 10-7 m 10-9 m Electron microscopy
Scanning Electron Microscope Uses reflected electrons to image small objects. Mite on a chip Attogram (10-18 g) scale Sandia National Laboratory Courtesy H. Craighead, Cornell University
Transmission Electron Microscope γ-fe2o3 nanoparticles Uses electrons passing through sample to image small objects 5 nm Liver Cell University of New England TEM Philips CM10
Scanning Tunneling Microscope STM Tip BiO planes in BSCCO Courtesy Kiel University Quantum Corral Courtesy J.C.S. Davis, Cornell Courtesy IBM
Atomic Force Microscope Images small objects by the mechanical response of a cantilever. Silicon atoms AFM tip 4 nm Pictures courtesy P. Hoffmann, WSU
What can nanotechnology do for us? Biomedical New drug delivery systems. New imaging techniques. Better sunscreens. Materials Science Stronger and lighter materials. Combining properties on the nanoscale. Stain resistant pants and better paints. Magnetic nanoparticle Computers Ultra-high density hard drives. Smaller transistors. New polishing methods using nanoparticle slurries.
Why do we need nanotechnology for these things? 1. Cells are a few microns in size, so nanometer sized objects can freely move through cell walls, into the cell nucleus. 2. Nanoparticles have a very large surface area, making them useful for applications relying on the interface between different materials. 3. Electronic components are already less than 100 nm; increasing their performance will rely on working at smaller length scales. 4. The physical properties of materials at small length scales is very different than in bulk.
How do you make nanotechnology?
Top-down approach Like making a statue of an elephant: start with a big block of marble, and chip away everything that doesn t look like an elephant. Lithography Focused ion beam 30 nm lines 90 nm lines Courtesy IBM research Courtesy C. Kruse, Bremen
Mask Resist Material Expose resist to light using mask. Chemically etch regions not protected by the resist. Remove portions of resist not exposed to light.
Bottom-up approach Like making a statue of an elephant from Lego, if the Lego blocks were 1 nm across. DNA Xenon atoms positioned using STM Courtesy NIH Courtesy D. Eigler IBM
(Self-assembly) DNA Tweezers Gold-polymer nanorods Courtesy B. Yurke, Bell Labs Courtesy C. Mirkin, Northwestern
How do things change on the nanoscale?
Mechanical properties change Silicon spur being broken Courtesy J. Parpia, Cornell University
Electronic properties change Carbon nanotubes Single electron transistor Courtesy UC Berkeley Courtesy D. Ralph, Cornell University
Optical properties change CdSe Quantum (or Nano) Dots Medieval Stained Glass Courtesy Iowa State Courtesy NYTimes
Magnetic properties change Iron oxide nanoparticles Hard disk data sector 20 nm Courtesy Dataclinic.co.uk The magnetization direction of magnetic nanoparticles can change spontaneously at room temperature. This is bad for long-term magnetic storage.
Dynamical properties change Pollen grains in water Simulation of Brownian Motion Courtesy P. Keyes, WSU Courtesy P. Keyes, WSU At small length scales, even individual collisions with water or air molecules can be important.
Why does surface area matter for nanotechnology? At R=1 mm, A/V=3x10 3 m -1 At R=10 nm, A/V=3x10 8 m -1 Factor of 10 5 difference!
Air resistance v alt. The relative importance of drag forces increase as the surface to volume ratio, which becomes very large in nanoscale systems.
% of Au atoms near surface Gold atoms are about 0.2 nm apart. What fraction of Au atoms are near the surface (2 layers away) in a 2 mm dia. gold ball? 20 nm dia. gold ball? at R=1 mm, 1.2x10-4 % of atoms are near the surface. at R=10 nm, 12 % of atoms are near the surface.
Surface loss mechanisms Dissipative losses in small devices can be strongly affected by the motion of atoms and molecules bonded to the surface. Cantilever The dissipation in nanodevices can be reduced by over a factor of 10 by heating them to 1000 o C. This is important for removing molecules attached to the surface. Courtesy H. Craighead, Cornell University
Nanoscale friction Laws of Friction 1. The force of friction is directly proportional to the applied load. 2. The force of friction is independent of the apparent area of contact. 3. Kinetic friction is independent of the sliding velocity. NB: Both of these have the same apparent area of contact, but the real area of contact is larger in the bottom case (under a larger normal load).
Interfacial adhesion changes frictional forces Trailing clamp Inchworm actuator Actuation Plate Leading clamp Displacement gauge 200 um Suspension spring Courtesy A. Corwin, Sandia Labs A. Corwin et al, APL 84, 2451 (2004)
Atomic scale friction Atomic scale friction Commensurate surfaces higher friction A. Socoliuc et al., Science 313, 207 (2006) Incommensurate surfaces lower friction
Summary Recent scientific developments have spurred nanotechnology research. Things on small length scales often act very differently from things at larger length scales. This can be used to develop new applications for nanotechnology, but also leads to new types of problems to be addressed.
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