B - St. Cloud State University

Ryan’s MFP-3D Procedural Operation ‘Manualette’ Version 10 (v080501; Igor 6.04A); 11.14
A
1.0
0.5
1 nm relative trigger
B 14
12
10
15 nm relative trigger
0.0
8
nm
-0.5
-1.0
nm
6
4
2
-1.5
0
-50
nm
-100
-150
Figure 11.2.7.4: Two examples of low force relative Deflection triggers: A) a ~1 nm relative trigger- notice contact regime
of force curve is minimal- best used for functionalized tips in which some sort of dissociation event is being measured; B)
increasing the relative trigger to a few nm’s worth of deflection. Note there is some weird adhesion to the surface.
• With a calibrated spring constant, choosing force as the trigger parameters allows forces to be dialed
in, which is generally more intuitive than using cantilever deflections.
SURFACE CHARGE CAN ALSO AFFECT FORCE CURVE AQUISTION-
Occasionally, the substrate chosen can be subject to surface charges, causing some crazy nonlinear
deflections in the free air and near point of contact when using very low spring constant
cantilevers. The author has found this to be true of 0.03 N/m (and below) levers using clean glass,
or mica glued to a glass slide. Glass is notorious for having a surface charge. Figure 11.2.7.5A
shows an example of surface charging affecting the force distance curve: notice the non-linearity in the
approach and retract parts of the curve, caused by the long range forces of the surface charge pulling the tip
towards the surface, or an inherently deep water layer. Either way, it’s tough to get a proper virtual deflection
curve fit. To solve this, it’s a good idea to have an atomically flat material that doesn’t possess strong surface
charge- Figure 11.2.7.5B shows a piece of graphite adhered to a magnetic sample puck on an AR magnetic
puck holder, along with the Static Masters to help dissipate charges. All this said, sometimes you can’t get rid
of the charge. Good luck-
0
-2
0
-50
nm
-100
-150
A
B
Figure 11.2.7.5: Surface charge can affect cantilever deflection in force-distance curves: A) attractive forces pulling
cantilever towards surface in approach; B) Eliminating charge by removing any glass components in sample mounting.
Here, the sample (graphite) is fixed to sample puck via silver paint, and placed on an AR magnetic sample holder, and
the use of a Static Master.