Secondary ion emission. Part II: Testing of the thermodynamic non-equilibrium model of surface ionization

Abstract

Using experimental values of the relative yields of positive and negative secondary ions for 31 pure elements and 9 compounds bombarded with 13.5 keV Cs⁺ ions temperatures of sputtering centers, T _sc , have been determined. Similarly, the degrees of ionization of sputtered atoms, α₊ and α₋, have been determined from M ₊ and M ₋ yields and as assumed secondary ion transmission efficiency of 1%. Two non-equilibrium equations of surface ionization (NESI) were used to determine T _sc . The calculated temperatures, as well as the degrees of ionization, have periodic dependence on the atomic number of the target, Z ₂. Most of the calculated temperatures are lower than the boiling temperatures, T _b , of bombarded targets and for refractory elements T _sc values are even lower than the melting temperatures, T _m . However, T _sc for most of the amphoteric and non-metallic elements are higher than T _b but lower than their critical temperatures, T _c .

Key Words:

• sputtering
• secondary ion yields
• surface ionization
• theory
• thermodynamics