UNIMO Technology UDR-204 Manuel d'instructions télécharger pdf (Page 223)

Force Imaging

Force Calibration (TappingMode)

Rev. B MultiMode SPM Instruction Manual 203

11.5.3 High Contact Force

Figure 11.5c shows a curve produced when the tip pushes too far into the sample. The ﬂat portion

on the left side of the amplitude curve in Figure 11.5c occurs because the tip is so close to the

surface that it no longer vibrates. As the piezo extends the tip further, the amplitude of vibration

does not change because the tip is always in contact with the sample surface. The contact force is

very high due to the stiffness of the TappingMode cantilevers. The tip may shatter if deﬂection

continues.

Figure 11.5c Amplitude Force Plot with High Contact Force

You can avoid this situation by using triggers (see Section 11.3.5) or by reducing the value of Z

scan start until there is no ﬂat portion on the left side of the curve. Rapidly increasing the value of

Z scan start is dangerous because the total oscillation amplitude of the cantilever is small relative

to the total Z travel of the long-range scanner.

11.5.4 Tip Selection

You may use virtually any TappingMode tip to obtain TappingMode force plots; however, the

ultimate choice depends upon the delicacy of the sample and the magnitude of the forces to be

gauged. Longer cantilevers have lower spring constants (i.e., they are more pliant) and therefore

offer greater sensitivity for most samples. Shorter cantilevers afford better control when gauging

strong attractive forces and are less prone to entrapment by surface tension forces. Sharper tips are

more likely to plastically deform the sample and are less sensitive to adhesive forces than tips that

are more blunt. Experiment to determine the tip that best meets your needs.

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UNIMO Technology UDR-204 Manuel d'instructions Page 223