Topographic mode

Two different operation modes are commonly used. In the topographic mode, images are created by scanning the tip in the xy plane and recording the position required to keep It constant. A three dimensional map z(x, y, It = const.) is recorded. In the constant height mode, the probe scans the surface while the signal at the z-scanner is kept constant, and a three-dimensional image It(x,p,z = const.) is created. 

The tip is scanned across the sample surface using a piezoelectric transducer in one of two modes, topographic mode or current mode. In the topographic mode a con-... 

Fig. 2. Scheme of the operation modes in STM a topographic mode b constant height mode. 

Other artifacts that have been mentioned arise from the sensitivity of STM to local electronic structure, and the sensitivity of SFM to the rigidity of the sample s surface. Regions of variable conductivity will be convolved with topographic features in STM, and soft surfaces can deform under the pressure of the SFM tip. The latter can be addressed by operating SFM in the attractive mode, at some sacrifice in the lateral resolution. A limitation of both techniques is their inability to distinguish among atomic species, except in a limited number of circumstances with STM microscopy. 

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. 

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). 

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