In recent years, gas cluster ion beams (GCIB) have become the cutting edge of ion beam technology to sputter etch organic materials in surface analysis. However, little is currently known on the ability of argon cluster ions (Ar-n(+)) to etch metal oxides and other technologically important inorganic compounds and no depth profiles have previously been reported. In this work, XPS depth profiles through a certified (European standard BCR-261T) 30 nm thick Ta2O5 layer grown on Ta foil using monatomic Ar+ and Ar-1000(+) cluster ions have been performed at different incident energies. The preferential sputtering of oxygen induced using 6 keV Ar-1000(+) ions is lower relative to 3 keV and 500 eV Ar+ ions. Ar+ ions exhibit a steady state O/Ta ratio through the bulk oxide but Ar-1000(+) ions show a gradual decrease in the O/Ta ratio as a function of depth. The depth resolution and etch rate is substantially better for the monatomic beam compared to the cluster beam. Higher 0 concentrations are observed when the underlying Ta bulk metal is sputtered for the Ar-1000(+) profiles compared to the Ar+ profiles. (C) 2017 The Authors. Published by Elsevier B.V.