Reactivity and Topography Imaging

The nanoscale topography and reactivity images of a heterogeneously reactive and non-flat substrate can be obtained separately and simultaneously by 

FIGURE 1.5 (a) Voltage-switching mode of SECM for (left) topography and (right) reac- 

FIGURE 1.6 (a) Setup of intermittent-contact SECM with a piezoelectric bender actuator, (b) Forward and (c) reverse scan images of the edge of a gold band on glass obtained with a 160-nm-radius recessed Pt tip in 1 mM FcTMA+. (Reprinted from Lazenby, R. et al., J. Solid State Electrochem., Vol. 17, 2013 pp. 2979-2987.) 

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SECM images contain information about both local reactivity and the topography of the sample surface. However, it is our opinion that the greatest utility of SECM in biological and biochemical investigations is its ability to map chemical species and reactivity (i.e., processes) rather than topography. Since the theoretical models of SECM are based on established electrochemical principles, the data can often be interpreted in a quantitative manner, and kinetic investigations at fixed lateral tip position are possible with a time resolution of ms or better. 

As we have seen in the previous chapter, the apparent topography and corrugation of thin oxide films as imaged by STM may vary drastically as a function of the sample bias. This will of course play an important role in the determination of cluster sizes with STM, which will be discussed in the following section. The determination of the size of the metallic nanoparticles on oxide films is a crucial issue in the investigation of model catalysts since the reactivity of the particles may be closely related to their size. Therefore, the investigation of reactions on model catalysts calls for a precise determination of the particle size. If the sizes of the metal particles on an oxidic support are measured by STM, two different effects, which distort the size measurement, have to be taken into account. 

When the tip is scanned laterally above the substrate, the obtained image reflects both the surface topography and the distribution of its chemical reactivity. This makes the data interpretation difficult if no a priori information... 

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