1 The Atomic Force Microscope
Jan 21, 2016
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The Atomic Force Microscope
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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