Surface Physics and Chemistry in High Electric Fields

Abstract

To specify the term “high electric fields” in the title of this chapter, we mention typical static field strengths encountered in a variety of situations. To start with, we note that the maximum field strength that can be maintained between two conductors in air is limited to less than about 10⁴ V/cm above which dielectric breakthrough leads to the formation of an ionized plasma. In semiconductors, fields of the order of 10⁶ V/cm can be maintained, whereas fields within the double layer at the electrolyte-electrode interface can reach 10⁷ V/cm. Around localized charges in zeolite cavities, electric fields of the order of 10⁸V/cm = 1V/Å have been estimated on the basis of Coulomb’s law

$$F = \frac{{3.4}}{{r^2 }}\frac{q}{e}[V/{\AA}]$$

at a distance r, measured in Ångstroms, away from a charge of magnitude q/e, measured in units of the elementary charge e. Fields of this order can also be established within 10³ Å of a metal tip with a tip radius of less than 10³ Å, provided dielectric breakthrough is avoided by working in ultrahigh vacuum. The upper limit of electric field strength that can be maintained over macroscopic distances is dictated by the onset of field emission and field evaporation, and is of the order of 6 V/Å.