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Appendix D: Noise Floor
To measure the noise floor, it is necessary to scan the sample with no voltage applied to the
X and Y piezoelectric ceramics. The AFM-View software can measure the structural noise of
the system when the tip is in feedback with the surface.
1.
Make sure the tip is a sizeable distance from the surface. Initiate the Tip Retract
function, if necessary.
2.
Under the System tab in XY Parameters, change the value of the XY HV Gain to
zero. This shuts off the voltage to both the X and Y ceramics.
3.
Under the Topo Scan tab, set the scan parameters for noise measurements:
•
Scan Size = 0.5 µm
•
Scan Rate = 1 Hz
•
Scan Lines = 512
•
X,Y Center = (2, 2)
•
Left, Right Image = Z-Drive, Z-Error
4.
Using the Manual Z Motor Control, move the probe toward the sample until the probe
begins to come into focus.
5.
Initiate Automated Tip Approach.
6.
Begin a scan. It is not necessary to complete a whole scans; 50 scan lines is plenty.
7.
To analyze the noise floor measurement, open the completed Z-Drive scan in
Gwyddion.
8.
Crop the data, if necessary.
9.
Level the image by pressing the "Level data by mean plane subtraction" button and
the "Correct lines by matching height median" button.
10.
Find the noise value with the "Statistical Quantities" button, under Ra (Sa) for sur-
face roughness.
V 1.1 / LS-AFM Users Guide
Appendix D-1
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