Positive secondary ion yields are strongly enhanced by the presence of reactive gas species. Oxygen primary ion beam or oxygen backfilling is commonly used for this purpose. However, for some metal elements that form a weak oxide bond such as Nb, Mo and Ag, depth profiling with an oxygen primary beam may not enhance the ion yields. This lead us to find an alternative way to study the yield enhancement on metal ion species by backfilling the sample surface with reactive gas species such as trichlorotrifluoroethane (C2Cl3F3) and tetrachloroethene (C2Cl4) while depth profiling with an argon primary ion beam. (C) 2004 Elsevier B.V. All rights reserved.