Topographic images

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 Bl.19.27. AFM topographic images (7x7 pm ) of 20 epitaxial Ag films on mica prepared at five substrate temperatures (75, 135, 200, 275, and 350 °C) and four film thicknesses (50, 110, 200, and 300 mn)...

STM and SFM are most commonly used for topographic imaging, three-dimensional profilometry and spectroscopy (STM only). 

Because modes of operation are different, obtained topographic images may not resemble each other if the sample deformation caused by frictional or adhesive interaction become dominant. 

FIGURE 21.12 Tapping-mode topographic image of uniaxially elongated NR vulcanizate. The elongation ratio was about 4. The scan size was 20 p,m. 

The amplitudes of the signals with frequencies 2co and Iw can easily be measured using lock-in amplifiers. The 2w signal is used as control signal in the feedback electronics so that its value is kept constant. The feedback output is then the topographic image [modulated by e(x,y)]. Since the term B-f(Rlz) in Eq. (17) is kept constant by the feedback, the 1 w signal obtained simultaneously with another lock-in amplifier provides a map of surface... 

FIGURE 6.2 Diagrams of different AFM operating modes. (A) Contact mode and (B) dynamic mode for topographic imaging. (C) Force spectroscopy mode for interaction probing. Reprinted with permission from Liu and Wang (2010). 

The scanning tunneling microscope (STM) is an excellent device to obtain topographic images of an electrode surface [1], The principal part of this apparatus is a metal tip with a very fine point (see Fig. 15.1), which can be moved in all three directions of space with the aid of piezoelectric crystals. All but the very end of the tip is insulated from the solution in order to avoid tip currents due to unwanted electrochemical reactions. The tip is brought very close, up to a few Angstroms, to the electrode surface. When a potential bias AF, usually of the order... 

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