The name is absent

3. A line was fit to the contact region of the force curve to determine the cantilever
deflection sensitivity, s, so that the curve could be converted from tip deflection voltage
to relative tip deflection position in run.

4. The cantilever deflection was subtracted from the sample z position to convert the
force curve to a plot of tip deflection versus tip-sample separation, D, rather than sample
position.

5. The point of zero tip-sample separation was defined as the intersection of the lines that
fit the large tip-sample separation and the contact region of the force curve.

6. The cantilever deflections were converted to forces with the measured spring constant.

7. Hundreds of such force curves were averaged before carrying out the electrostatic
analysis described below.

2.2.3 Tip charge density measurement

Following the strategy described in previous works [1, 49], Silicon Nitride tips were
taken from a wafer (DNP, Veeco Probes), which provided silicon nitride reference
surfaces with an identical preparation, stoichiometry, and history as the tip. Force curves
were recorded over the identical silicon nitride reference surface and used to find the
surface charge density of the tip by the detailed analysis described below and
summarized in Figure 2.3.

17

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