Chapter 4
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FIGURE 4-35 Chemicals may be deposited from an AFM probe onto a sample’s
surface. At the right is an example DPNTM for creating an array of nanodots. |
4.6 Mechanical Measurements |
The probe in an AFM may interact with the hard forces at a surface. Such interactions allow making nano-mechanical measurements on a surface.The primary method for making mechanical measurements is the force/distance curve. When the probe is pressed firmly into a surface, it may cause a nano-indentation of the surface. |
4.6.1 Force / Distance Curves |
A force/distance (F/D) curve is a measure of the forces on the probe as a function of the distance of the probe from a sample's surface. Typically an F/D measurement is initiated with the probe in free space above the surface. Then the probe is lowered towards the surface until it interacts with the hard force in the repulsive regime. Then the probe is pulled away from the surface until it is in free space again. A force distance curve and
the corresponding positions of the probe are illustrated in Figure 4-36. |
As the probe begins to interact with the surface, it is pulled into the surface by capillary forces. This process is called jump to contact and often this step breaks the tip off the probe. The position of the jump to contact is dependent on the thickness of the contamination layer on the surface. When retracting as the probe is pulled from the surface, the adhesion causes the probe to "stick" to the surface, and then disengage
from the surface. |
Errors can occur in the F/D curve if a position sensor is not used to measure the motion in the Z axis. The error occurs because the Z ceramic |
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