The description of FFM - Force Modulation Microscopy

Force Modulation imaging is a secondary imaging mode derived from contact AFM that measures relative elasticity/stiffness of surface features, and is commonly used to map the distribution of materials of composite systems. As with LFM and MFM, Force Modulation imaging allows simultaneous acquisition of both topographic and material-property maps.

In Force Modulation imaging mode, the probe tip tracks the sample topography as in normal contact AFM. In addition, a periodic signal mechanically drives the cantilever (and tip) in the Z-direction. The amplitude of cantilever modulation that results from this applied signal varies according to the elastic properties of the sample.

The resulting force modulation image is a map of the sample's elastic response. The frequency of the applied signal is typically a few kilohertz, which is faster than the z feedback loop is set up to track. Thus, topographic information can be separated from local variations in the sample's elastic properties, and the two types of images can be collected simultaneously, as shown below.

 

Examples (click to enlarge)


Topography.

FMM response (amplitude).
Surface of the semiconductor substrate after performing electrochemical process. FMM picture reveals areas (darker spots) with lower stiffness. Scan size 12x12um.

Topography.

FMM response (amplitude).
Test sample (alumina layer on silicon substrate). Scan size 15x15um.

Topography.

FMM response (amplitude).
Test sample (metallic layer on silicon substrate). Scan size 20x20um.

Topography.

FMM response (amplitude).
Surface of the integrated circuit (metallic connection). Scan size 20x20um.

Topography.

FMM response (amplitude).

FMM response (phase).
Surface of the polymer. Scan size 4x4um.


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