Constant current topography

Leveraging on this positive outcome, we next explicitly consider the effect of the experimentally used W tips in the experiment. As in Refs [3, 4], the constant current topographies were simulated by integrating the states in the CB edge from its... 

FIGURE 1.10 Constant-current topography images of (a) differentiated PC12 eeUs, (b) eardiac myocyte, and (c) hippocampus neurons obtained with the earbon-based nanotips held at —500 mV versus Ag/AgCl in PBS containing 10 mM Ru(NH3)6Cl3. (Reprinted with permission from Takahashi, Y. et al., Proc. Natl. Acad. Sci. USA, Vol. 109, 2012 pp. 11540-11545.)... 

A peak area surface area of solid granular CCT constant current topography... 

Itaya and colleagues decided to employ STM to see if any correlation existed between the surface topography and the electrochemistry in Figures 2.27(a) and (b). The images were obtained at constant current with the tip and sample controlled independently. 

Figure , (a) STM constant current image of the nc-Si implanted with a dose of 10 cm (b) corresponding STM-REBIC image and (c) topography and REBIC profile of the line indicated in (a) and (b). 

At constant current STM-REBIC and CITS images were also acquired after thermal treatment of the nc-Si films. The topography shows the same features as in the as-implanted samples while the STM-REBIC images do not show any contrast. The contrast of the cell boundaries in the CITS images is also removed after the annealing of the films. These results indicate that the thermal treatment induces an enhancement in conductivity of the samples due to a recrystallization process and a change in the cell boundaries defect distribution and structure. 

This means that the tunnehng current is proportional to the local density of states (LDOS) of the sample at the center of the sphere (tip) and therefore, a constant current image reflects the LDOS of the sample. This demonstrates that an STM image does not display the mere topography of a sample surface. Instead, the electronic properties of the surface play an important role—which holds especially true for molecules adsorbed onto a surface. The electronic states of the molecules (HOMO, highest occupied molecular orbital and LUMO, lowest unoccupied molecular orbital) mix with those of the substrate surface, but modified by molecule-substrate interactions. Therefore, depending on the substrate site and material, an image of the molecules is obtained. 

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