Agilent Technologies E5500 Series User's Guide download pdf (Page 23)

Introduction to the Agilent 5500 1

Agilent 5500 SPM User’s Guide 23

described below, can be generally described by their function within

these three domains.

Figure 6 Zones of interaction as the tip approaches the sample

The tip-sample interaction is complicated by additional forces,

including strong capillary and adhesive forces that attract the tip and

sample. The capillary force arises when water, often present when

imaging in the ambient environment, wicks around the tip, holding the

tip in contact with the surface. As long as the tip is in contact with the

sample, the capillary force should be constant because the fluid between

the tip and the sample is virtually incompressible. The total force that

the tip exerts on the sample is the sum of the capillary, adhesive and van

der Waals forces.

The van der Waals force counters almost any force that attempts to push

the atoms closer together. When the cantilever pushes the tip against the

sample, the cantilever bends rather than forcing the tip closer to the

sample atoms. The deflection, therefore, can be used as a reliable

indicator of surface topography.

Contact Mode AFM

In Contact Mode AFM, the AFM tip is attached to the end of a

cantilever with a low spring constant (typically 0.001 - 5 nN/nm). The

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Agilent Technologies E5500 Series User's Guide Page 23