Figures—continued scanning tips

Figure Bl.19.7. A series of time-lapse STM topographic images at room temperature showing a 40 mn x 40 mn area of Au(l 11). The time per frame is 8 mm, and each took about 5 min to scan. The steps shown are one atomic unit in height. The second frame shows craters left after tip-sample contact, which are two and three atoms deep. During a 2 h period the small craters have filled completely with diflhismg atoms, while the large craters continue to fill. (Taken from [29], figure 1.)...

Figure 4. Series of 1x1 fim topographic AFM images of blue PCD A showing the progressive growth of the tip-induced red domains. In the first scan, striations indicative of the polymer backbone direction are observed. By the fourth scan, a topographically distinct (i.c. lower) region, only 30 nm wide, appears. This region continues to grow in subsequent scans.

Figure 4.12 AFM topographic images and profiles corresponding to the white lines recorded after 1, 7,15 and 20 scans on a strontium soap film deposited on to alreshly cleaved mica surface. After the first scan the surface is already perturbed molecules have been displaced by the silicon tip and form small islands of 1 to 1.2 nm (length of the soap molecule). During the various scans molecule displacements continue and spherical, cylindrical and lamellar aggregates are successively obtained...

For the friction force between a silicon AFM tip and a NaCl(OOl) surface in UHV, such a transition was in fact observed [997] (Figure 9.16). At an applied normal load of 4.7 nN, stick-slip was observed with a clear hysteresis between forward and backward scan on the same line. By reducing the applied load to 3.3 nN, the stick-slip amplitude stays almost constant but the hysteresis, which is proportional to friction loss, is clearly reduced. When changing the applied force to —0.47 nN to compensate pardy the adhesion force of 0.7 nN, the stick-slip pattern changed into a continuous modulation with no detectable hysteresis between trace and retrace. This corresponds to a frictionless sliding at least within the force resolution of the experiment. This effect of vanishing friction due to very small loads is called static superlubricity. 

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