nanotechnology - wayne state universityglawes/nano.pdf · q: what is nanotechnology? narrow...

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