Inverse velocities of sputtered monatomic ions: Systematics and quantification

The emission of secondary ions of about fifteen different elements, sputtered from Ti-base metal specimens, has been studied by SIMS. Both positive and negative ion yields have been measured at different exit energies up to ca 350 eV. It is found that when the logarithm of ionizability is plotted versus the inverse of the exit velocity, each element suggests a straight line behavior at energies above ca 20 eV. The gradient of the straight line is related to the respective 1st ionization potential (for positive ions) or electron affinity (negative ions). This behavior gives considerable support to the premises of modern theory of ionization in sputtering. Furthermore, the straight line plots for different elements are seen to converge as exit velocity increases; the intercepts at zero inverse velocity are found to be proportional to the respective element concentrations. This in principle offers a means of quantification in elemental analysis by SIMS, a method that does not require any external standards. The usefulness of the new method is demonstrated for ten elements sputtered from two specified titanium-base alloy standards from NIST.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday