Download SOP for AFM Elmer Diaz

Standard Operating Procedure
June 6, 2012
Elmer Diaz
Atomic Force Microscopy
AFM
Instrument Model
Figure 1. AFM EasyScan 2 AFM model
Description:
AFM is a characterization tool that can be used by surface morphology including:
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Surface roughness
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Changes in surface height by using scratch test
Changes in nanoparticles (NPs) which are on surface
Operation:
Set up
Installing the tip
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Install the tip in the tip holder as well as mount the sample on the sample stage
Samples must be flat within approximately 500 nm, this is the limit in which the
microscope can measure
Once the tip is installed and sample is mounted, approach the sample by
rotating 3 screws, this will change tip to sample distance by mm at a time
Be careful not to contact tip with surface, when moving few mm distance
If approach the tip to the surface, the tip can break and need to re-installed a
new tip
You can see the tip of the AFM and the surface in the positioning window, you
can see the shadow (See Fig. 2)
Switch bottom, so you can see the top view of AFM tip surface
In side view – approach the tip to the surface by using the advance and retract
bottoms, this should move farther away from the tip when you hit the retract
bottom, the shadow moves closer (see Fig. 2)
The reason that the shadow moves and not the tip is because the camera is
fixed relative to the tip and not fixed relative to the substrate. Even though the
actual tip is moving up and down, what you see is the shadow moving up and
down
Click the advance bottom to activate the server model so that on the screen you
see approximately a cm between the shadow of the tip & actual tip if get too
close the tip will contact surface and the tip will break
If too far away, when start scanning there is not enough force between tip and
surface, so you need to go back and re-approach the surface
When tip and shadow are very close together tip is close to the surface. 1 cm is
a good distance (See Fig. 2)
Hit the approach bottom, this activates the piezo that is connected to the tip &
will move few hundred nms and the tip comes in close contact to the surface
Figure 3 shows top view of the tip and surface
Figure 2. Side view of screen capture of AFM in operating mode panel
Figure 3. Top view of screen capture of AFM in operating mode panel
Adjusting settings
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Once the AFM tip is scanning across the surface you will be able to see the
results in this topology window (see Fig. 4)
Figure 4. Scanning topography of AFM
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The topology is showing is the change in the Z height of the piezo compared to
the X, Y position of the tip relative to the surface, you see noise
To decrease noise, set the amplitude set point, corresponding to what type of
tip you have in the AFM
For example, we used the Sicona-n type (Si-N-type)
The features for this type of tip are as follows:
o length of cantilever is 400 µm, with 40 µm thickness 2.5 µm, tip
frequency is 11-18 kHz, tip spring constant k (k = 0.1-0.6 N/m),
o 0.01-0.025 (Ohm/cm)
o The spring constant of AFM cantilevers can vary from 0.001 to 100 N/m,
depending on the application, a typical value for contact mode is 0.1
N/m
Using F = kx to determine the amount of force needed for the amplitude (A) set
point, in this case the A is set up 7 nN. Set the A to 7 nN
Change image scan size, if scan in smaller image the tip will move across the
surface slower & increase resolution, for example to 5 microns.
Change the tip speed number of seconds takes per line, 0.2 /0.5 are good
speeds
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Change the number of points per line to 256, it takes more data points
Change the X, Y slope, the Z plane of the substrate compared to the Z plane of
the piezo, and thus de tip can be off by few hundreds nms, this results in
surface topology that looks like has an incredible high slope, when surface is flat
Set up the X and Y offset slope in degrees. It’s difficult to know what offset
degrees are used
Click on the offset bottoms & will automatically sets up this parameter for you
Change the gains (P-Gain and I-Gain), this will cause different changes in the
piezo Z height depending on how the amplitude is changing relative to the tip
point, or set point
If increase the P-Gain, values around 8 to 10 thousand are reasonable, this will
increase resolution but also increase the noise
Typically the I-Gain is a fifth of the P-Gain, this will further decrease noise
Tip Voltage is another parameter that can be changed, depending on scanning
mode will not make difference
It can be set as high as 1 – 2 Volts,
Increase image size to 20 microns,
Sample has 10 x 10 features, you should be able to see something
Allow the instrument to scan across, re-adjust settings if needed
Figure 5 shows a final topography scan after adjusting all these settings
Figure 5. Topography scans after adjusting settings