Secondary ion mass spectrometry analysis of metal oxides using 70 keV argon, carbon dioxide, and water gas cluster ion beams

Manganese (II) oxide (MnO), manganese (IV) oxide (MnO₂), cobalt (II,III) oxide (Co₃O₄), and nickel (II) oxide (NiO) were analyzed with time-of-flight secondary ion mass spectrometry using 70 keV gas cluster ion beams. The obtained mass spectra are influenced by projectile chemistry and to a lesser extent velocity. Gas cluster ion beams containing CO₂ or H₂O enhanced the relative yield of metal oxide and metal hydroxide secondary ions compared to beams containing only Ar. For all gas cluster ion beams tested, steady-state ion ratios [M_xO_y]⁺/[M_x]⁺ were reached. For manganese oxides, the [Mn_xO_y]⁺/[Mn_x]⁺ ratio reflected the metal oxidation state whereas the [Mn_xO_yH_z]⁺/[Mn_x]⁺ ion ratios did not. This study demonstrates that secondary ion mass spectrometry using 70 keV gas cluster ion beams provides a novel approach to the quantitative analysis of the surface and subsurface regions of metal oxides related to energy-storage materials.