Schematic illustration for amplitude vs tip-sample distance of an oscillating cantilever in free space (far away from the sample surface) and in the working area where the oscillation amplitude is damped to 20%–80% of that in free space . The rest position of the cantilever is , which is the tip-sample distance. When becomes zero or less, the cantilever stops oscillating and mechanical contact is established, capable of manipulating contaminants if they are present on the tip apex.
Amplitude-distance curves obtained on a gold film by a clean gold-coated tip (a) and by the same tip after being immersed in the thiol for the first (b) and the second (c) cycle of measurements, respectively. The change of the amplitude with respect to tip-sample distance is represented by open circles and filled gray circles when the tip is brought to (indicated by the black arrow) and retracted from (indicated by the gray arrow) the sample surface, respectively. The speed of the tip approaching to and retracting from the sample surface was .
A dynamic force microscopy image (scan area: ) of a gold film obtained by the same tip that was (a) cleaned from thiol and (b) recontaminated by thiol. The set point for the two images was . Gray-scale range is for both images.
The amplitude-distance curve (a) obtained using the tip that had collected the image shown in Fig. 3(b). The tip is first brought in contact with the sample followed by retraction. The black and gray arrows indicate tip approach and tip retraction, respectively. The three main peaklike features in the first amplitude-distance curve (a) when the tip is retracted from (filled circle) the sample are marked 1, 2, and 3. Magnification of the approaching amplitude-distance curve within the range of to is shown in (b). Also shown in (b) is a gray line showing the counterpart from a cleaned tip [Fig. 2(c)] and a broken line showing the set point of for imaging. The speed of the tip approaching to and retracting from the sample surface was .
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