INVERSE VELOCITIES OF SPUTTERED MONATOMIC IONS - SYSTEMATICS AND QUANTIFICATION

The emission of secondary ions of about fifteen different elements, sp uttered From Ti-base metal specimens, has been studied by SIMS. Both p ositive and negative ion yields have been measured at different exit e nergies up to ca 350 eV. It is found that when the logarithm of ioniza bility is plotted versus the inverse of the exit velocity, each elemen t suggests a straight line behavior at energies above ca 20 eV. The gr adient of the straight line is related to the respective Ist ionizatio n potential (for positive ions) or electron affinity (negative ions). This behavior gives considerable support to the premises of modern the ory 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 d oes not require any external standards. The usefulness of the new meth od is demonstrated for ten elements sputtered from two specified titan ium-base alloy standards from NIST.