Notre Dame extended Research Community

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The Atomic Force MicroscopeMichael CrockerValerie GossRebecca QuardokusNatalie Wasio

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The Braille Game!

Can you feel the surface and identify the features?

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Braille Game Braille cells with letters are “felt” to “see” the surface and identify the raised bumps as letters. The cells are made from ribbed card board box cut into rectangles and raised bumps are made by poking an impression on one side to the rectangles. (15 minutes) Phase I: Analyze individual cells Advise students that there is only one correct orientation for each cell, and when turned properly it will match a letter. Student may not look at cells to determine letters. Phase II: Collect responses Use the board to collect responses, determine word.

(NANO)

(a) (b) (c)

Shown above are three orientations for the letter ‘n’. There are no matches in the Braille key

(a) Not represented in the key (b) Not orientated with two columns (c) Not oriented with two columns

(STM)

Nano objects are smaller than the wavelength of light, and cannot be detected with a light microscope!

Braille Key

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target

sourceHow do we see an object?

detector…and often you’ll need a lens

When things are large enough…

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What is nano?

10-9 meters (one billionth of a meter)Objects between 1-100 nm

1 mm = 1000 μm

μm, micrometer, micron

1 μm = 1000 nm

Individual fibers are 18 ± 1 μm How many mm?How many nm?

Blue mouse pad 400X

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How can we visualize or “see” such small items?

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Invented and built in 1985 by Calvin F. Quate , Gerd

Binnig, and Christoph Gerber.

This is the first Atomic Force Microscope.

The AFM works by ‘touching’ objects with the

probe and reading the surface rather than looking

at them.

The first AFM

sciencemuseum.org.uk

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What is the AFM? An analog!

AFM Chip, Cantilever + Tip holder

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http://www.tedpella.com/probes_html/

budgetsensors.htm 7/13/11

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AFM cantilever and AFM tips

www.veeco.com, 7/13/11

The tip is roughly 20 µm long, the cantilever is 450 µm in length and 20-50 µm wide, and the thickness is usually 3-4 µm thick.

http://www.tedpella.com/probes_html/

budgetsensors.htm 7/13/11

Basic operation of the AFM

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AFMs monitors the forces of attraction and repulsion between a tip and a sample surface

The tip is attached to a cantilever which moves up and down in response to forces of attraction or repulsion with the sample surface

Movement of the cantilever is detected by a laser and photodetector

AFM Schematic

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Nanosurf AFM acquires an image by scanning a sharp probe across the surface

Let’s talk about

contact mode

Actuator contains a piezoelectic crystal that expands and

contacts as a voltage is applied across its crystal surfaces…a few

hundred volts can be applied to move the scanner tens of

microns

Two common AFM system designs

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Sample moves relative

to the tip Tip moves relative to the

sample

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The powerful, versatile AFM

~30 um scan

http://www.nanotech-now.com/Art_Gallery/antonio-siber.htm

Resolutions:

X and Y 2 -10 nm

Z 0.05 nm

Microstructure of solids:

CD, glass beads, circuits

Biological samples:

skin cross section, viruses, bacteria, blood, DNA and RNA

July 13, 2011

Feedback loop and gains

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To make a topographical image in contact mode, a feedback loop is implemented to keep the deflection of the cantilever constant as the Z height changes to bumps on the surface.

The topographical image is created by recording the Z output as a function of x and y position.

Borrowed image to illustrate scanning

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Limitations on the tip size

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Double effect – tip artifact

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Salt crystals imbedded in a polymer matrix

borrowed image

Gains control

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In which image are the gains too high, too low, or just about right?

borrowed image

Thank you!

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AFM Image Library

Dan Witt’s AFM images – calibration gridMishawaka High School Teacher, July 2010

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Silicon calibration grid, vgoss – AFM

Ram memory chip, vgoss - AFM

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Ram memory chip, vgoss - AFM

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CD, vgoss - AFM

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staphylococcus aureus bacteria on glass substrate, vgoss -AFM

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staphylococcus aureus bacteria, on glass substrate, vgoss - AFM

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2 nM DNA origami in air, vgoss -AFM

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2 nm DNA origami in liquid, vgoss - AFM

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2.36 nm

0.00 nm

1.0µm