Operating instructions

MEASUREMENT MODES
58
Force Modulation
The Force Modulation mode is an extension of the Static force mode. The
static force acting on the cantilever is still used to produce a topography
image of the sample. Simultaneously, the cantilever is excited and the
resulting vibration amplitude measured. The vibration amplitude depends
on the drive amplitude, the stiffness of the cantilever and, most impor-
tantly, the stiffness of the tip-sample contact. Thus, the force modulation
mode can be used to produce material contrast when there is a significant
difference in the stiffness of the tip-sample contact of these materials.
Proceed as follows to operate the easyScan 2 AFM in the Force Modulation
mode:
- Select a cantilever that has a spring constant that is suitable for the sample
stiffness that you expect.
Good results were obtained with LFMR-type cantilevers. The FMR type
cantilever, which is explicitly sold for Force Modulation mode measure-
ments, cannot be used due to its insufficient width.
- Install the cantilever as described in section Installing the cantilever (p.28).
- Select the Force Modulation mode in the Operating mode panel.
- If necessary, verify the force Set point in the Z-Controller panel.
- In the Operating mode panel, click to measure the frequency
characteristic of the cantilever.
- Note the cantilever resonance frequency from the sweep chart and set
‘Excitation frequency’ to this value.
- Set ‘Excitation amplitude’ to the desired modulation amplitude.
- Increase the excitation amplitude when no Force Modulation signal can
be measured.
To display the measurement results:
- Create a new chart in the Imaging window by clicking in the Chart
bar.