Field ionization critical distance

The critical distance for field ionization is related to I and by16... 

The potential energy diagram for an ion formed right at the critical distance of field ionization, xc (i.e. the most energetic ion), in a retarding potential analyzer is shown in Fig. 2.4. From this diagram, one obtains... 

Ionization of the image gas by tunneling is most likely to occur where critical distances are small this corresponds to sites where the local field strength F is... 

Classical and quantum treatments of electromagnetic fields [7], near a plane dielectric interface, show that the probability of photo-ionization or photo-excitation of an atom exhibits a pronounced peak at the critical angle of incidence of a plane wave propagating in the dense medium. The probability of absorption or emission of a photon is proportional to the photometric intensity of the electromagnetic field. In particular, consider a plane wave propagating in the dense medium with refractive index /2i, at angle of incidence Ox. The intensity of the transmitted field at a distance dy from the interface is given by... 

The large electrical field at the tip of a field electron microscope can be used to ionize gas atoms that approach it or adsorb on it [13, 14, 19, 21, 30, 40, 42, 43]. If the tip is positively charged in order to repel the positive ions formed, field ionization of an approaching atom occurs at a critical distance X [about 4-8 A (0.4-0.8 nm)] from the tip, defined by X — )/E, where is the ionization... 

FIM A very high positive potential is applied to a tip of radius = 10 cm in the presence of a gas (usually helium, but hydrogen and neon are also used). The gas atoms are ionized in the high electric field at a critical distance... 

The term surface ionization is frequently used to describe the process in which ionization takes place within some critical distance from the surface. A number of surface-dependent ionization methods, such as field desorption, fast atom bombardment, and laser desorption, are described as surface ionization methods. Another use of this term is more restricted surface ionization (SI) is defined as the ionization process, which can be interpreted by use of the Saha-Langmuir equation. 

---