Mass Fractionation and Energy Distribution of Sputtered Monatomic Positive Ions

Authors

U. Södervall, Chalmers University of Technology
H. Odelius, Chalmers University of Technology
A. Lodding, Chalmers University of Technology
E. U. Engström, Chalmers University of Technology

Abstract

Secondary ion yields in sputtering depend significantly on the mass of the emitted species. Ionization as observed by secondary ion mass spectrometry is characterized by isotope fractionation; the yield of an isotope ion of mass M_i being proportional to M^-𝝰, where a varies with the emitted species, its kinetic energy E_k, and the matrix.

By means of SIMS, isotope ratios have been measured for ions at energies up to ca 120 eV in different metallic matrices. For singly charged positive monatomic ions, a has been found to range between O and ca 4. While a may drop steeply at low or moderate E_k, at higher energies the gradient decreases and usually becomes positive. To some extent the trends of a are complementary to those of the energy dependence of elemental ion yields.

In the present work, the main tendencies are surveyed for pure element matrices as well as for several elements sputtered from a given metallic matrix. It is attempted to correlate a with the energy distributions of ionic yields. Isotope effects appear inherent in all three basic mechanisms of ion emission, i.e., in sputter yield, ionization, and charge survival.

Recommended Citation

Södervall, U.; Odelius, H.; Lodding, A.; and Engström, E. U. (1987) "Mass Fractionation and Energy Distribution of Sputtered Monatomic Positive Ions," Scanning Microscopy: Vol. 1: No. 2, Article 5.
Available at: https://digitalcommons.usu.edu/microscopy/vol1/iss2/5