nanotechnology - wayne state universityglawes/nano.pdf · q: what is nanotechnology? narrow...
TRANSCRIPT
Nanotechnology Gavin Lawes
Department of Physics and Astronomy
Length scales (Part I)
10-10 m 10-5 m 105 m 1010 m 1 m
Earth-Moon distance 4x108 m (courtesy NASA)
Michigan width 2x105 m (courtesy Google)
Red blood cell 1x10-5 m (courtesy PBS)
Magnetic nanoparticle 5x10-9 m
Person 2m
Length scales (Part II)
10-3 m
10-9 m
10-7 m
10-5 m
10-1 m
10-3 m=1 mm
10-6 m=1 µm=1 (micron)
10-9 m=1 nm (nanometer)
Courtesy CSU Hayward
Head of a pin 1,000,000 nm
Thickness of a human hair: 100,000 nm
Courtesy Intel
Transistors 65 nm
Visible light 400 to 700 nm
Distance between atoms in a solid ~0.3 nm
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.
10-3 m
10-9 m
10-7 m
10-5 m
10-1 m
Optical microscopy
Electron microscopy
Nanotechnology
How can we see things on the nanoscale?
• The development of scanning probe techniques (STM, AFM) in 1981 revolutionized the imaging of nanoscale systems.
Scanning Electron Microscope
Sandia National Laboratory
Mite on a chip Attogram (10-18 g) scale
Courtesy H. Craighead, Cornell University
• Uses reflected electrons to image small objects.
Transmission Electron Microscope
5 nm
γ-Fe2O3 nanoparticles
TEM Philips CM10
Liver Cell University of New England
• Uses electrons passing through sample to image small objects
Scanning Tunneling Microscope
Courtesy Kiel University
Courtesy J.C.S. Davis, Cornell
STM Tip
Quantum Corral
Courtesy IBM
BiO planes in BSCCO
Atomic Force Microscope
Pictures courtesy P. Hoffmann, WSU
Silicon atoms
4 nm
AFM tip
• Images small objects by the mechanical response of a cantilever.
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.
Computers Ultra-high density hard drives. Smaller transistors. New polishing methods using nanoparticle slurries.
Magnetic nanoparticle
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?
30 nm lines 90 nm lines Courtesy IBM research
Lithography
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.
Focused ion beam
Courtesy C. Kruse, Bremen
Expose resist to light using mask.
Chemically etch regions not protected by the resist.
Mask Resist Material
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
Courtesy NIH
Xenon atoms positioned using STM
Courtesy D. Eigler IBM
DNA Tweezers
Courtesy B. Yurke, Bell Labs Courtesy C. Mirkin, Northwestern
Gold-polymer nanorods
(Self-assembly)
How do things change on the nanoscale?
Mechanical properties change Silicon spur being broken
Courtesy J. Parpia, Cornell University
Courtesy UC Berkeley
Carbon nanotubes
Courtesy D. Ralph, Cornell University
Single electron transistor
Electronic properties change
Optical properties change
Courtesy Iowa State
CdSe Quantum (or Nano) Dots
Courtesy NYTimes
Medieval Stained Glass
Magnetic properties change
Courtesy Dataclinic.co.uk
20 nm
Iron oxide nanoparticles
• The magnetization direction of magnetic nanoparticles can change spontaneously at room temperature. This is bad for long-term magnetic storage.
Hard disk data sector
Dynamical properties change
Courtesy P. Keyes, WSU
Pollen grains in water
Courtesy P. Keyes, WSU
Simulation of Brownian Motion
• At small length scales, even individual collisions with water or air molecules can be important.
At R=1 mm, A/V=3x103 m-1
At R=10 nm, A/V=3x108 m-1
Why does surface area matter for nanotechnology?
Factor of 105 difference!
Air resistance
The relative importance of drag forces increase as the surface to volume ratio, which becomes very large in nanoscale systems.
alt.
v
% 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.
Courtesy H. Craighead, Cornell University
Cantilever • The dissipation in nanodevices can be reduced by over a factor of 10 by heating them to 1000 oC.
• This is important for removing molecules attached to the surface.
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).
200 um
Trailing clamp Leading clamp
Displacement gauge
Actuation Plate
Suspension spring
Courtesy A. Corwin, Sandia Labs
Inchworm actuator
A. Corwin et al, APL 84, 2451 (2004)
Interfacial adhesion changes frictional forces
Atomic scale friction
A. Socoliuc et al., Science 313, 207 (2006)
Commensurate surfaces higher friction
Incommensurate surfaces lower friction
Atomic scale 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.
End