X-ray photo-electron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS) along with MARLOWE and TRIM computer simulations were used to study the retention of Cs+ primary ions in Si substrates during sputtering. Cs concentrations were found to depend on (a) primary ion energy, (b) primary ion incidence angle, and (c) sputtering time (within the transient region). With the exception of the XPS and RBS data collected as a function of Cs+ impact energy, Cs concentration variations, Delta[Cs], appear to correlate with sputter yield variations, DeltaSY, via Delta[Cs] c proportional to 1/(DeltaSY + 1). Computer simulations reveal variations in Cs+ scattering with impact energy, etc. This and/or self sputtering may explain the inconsistencies noted with impact energy. (C) 2004 Elsevier B.V. All rights reserved.