Surface step effects

Despite the above comments on the application of roughening to thin polymer crystals it is certainly possible that thermal effects could cause a significant number of surface steps, and that this is all that is required to lead to a breakdown of the nucleation argument. 

Surface chemistry then allows for the following two steps, effectively adding H and H across the alkene ... 

The (photo)electrochemical behavior of p-InSe single-crystal vdW surface was studied in 0.5 M H2SO4 and 1.0 M NaOH solutions, in relation to the effect of surface steps on the crystal [183]. The pH-potential diagram was constructed, in order to examine the thermodynamic stability of the InSe crystals (Fig. 5.12). The mechanism of photoelectrochemical hydrogen evolution in 0.5 M H2SO4 and the effect of Pt modification were discussed. A several hundred mV anodic shift of the photocurrent onset potential was observed by depositing Pt on the semiconductor electrode. 

Tamowski DJ, Korzeniewski C. 1997. Effects of surface step density on the electrochemical oxidation of ethanol to acetic acid. J Phys Chem B 101 253. 

In some cases, the step sites have different chemistry, i.e., they break chemical bonds, thereby producing new chemical species on the surface. This happens for example during NO adsorption on a stepped platinum surface l In this circumstance the step effect on ordering is through the new types of chemistry introduced by the presence of steps. Hydrocarbons for example dissociate readily at stepped surfaces of platinum or nickel while this occurs much more slowly on the low Miller-Index surfaces in the absence of a large concentration of steps As a result ordered hydrocarbon surface structures cannot be formed on the stepped surfaces of these metals while they can be produced on the low Miller-Index surfaces. 

It would be interesting to extend such studies to other light-atom substrates, such as the metals beryllium and aluminium, and to investigate step effects. Heavier-atom surfaces can also be analyzed in the form of thin films of mono-atomic thickness on a lighter substrate, as has recently been done ... 

As we will discuss later the step effects are found to be quite general, and the role of steps in dissociation reactions has also been observed directly for ethylene activation on Ni surfaces, see Figure 4.20 [69,70]. 

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